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It also conforms to current international trends inthe teaching of Biology. Biology is a practical subject which equips students withconcepts and skills that come in handy in solving the day to dayproblems in life. The study of Biology aims at providing the learnerwith the necessary knowledge with which to control or change theenvironment for the benefit of an individual, family or community. This book recognises these aspects and provides adequate practicalexercises to sharpen the students practical skills. In addition, it alsoprovides study questions and end of topic questions for selfevaluation. This book is written in a clear, concise language and ispart of the Secondary Biology series. I am grateful to the panel of writers and everybody who tookpart in the writing, editing and production of this third edition. THE MANAGING DIRECTORKenya Literature BureauCONTENTSPrologueAcknowledgements1.0 Transport in plants and animalsTransport in plantsInternal structure of rootsThe stemAbsorption of water and mineral saltsTranspiratonStructure and function of xylem tissueForces involved in water movements in plantsFactors affecting transpirationTranslocationTransport in animalsComparisons between open and closed circulatory systemsThe mammalian circulatory systemThe structure and function of the heartStructure and function of arteries, capillaries and veinsDiseases and defects of the circulatory systemStructure and function of blood cellsThe red blood cellsThe white blood cellsBlood clotting processBlood groupsThe lymphatic systemImmune responsesRevision Questions2.0 Gaseous ExchangeIntroductionGaseous exchange in plantsThe mechanism of opening and closing of stomataMechanisms of gaseous exchange in plantsGaseous exchange in animalsGaseous exchange in protozoaGaseous exchange in insectsGaseous exchange in fishGaseous exchange in amphibiansGaseous exchange in mammalsFactors affecting the rate of breathing in human beingsDisease of the respiratory systemRevision Questions3.0 RespirationIntroductionSignificance of respirationTypes of respirationAerobic respirationAnaerobic respiration in plants and animalsApplications of anaerobic respiration in industries and at homeRespiratory susbstratesFactors affecting rate of respirationRevision Questions4.0 Excretion and HomoestasisExcretion in plantsEconomic importance of plant excretory productsExcretion and homeostasis in unicellular organismsExcretion in animalsStructure and function of mammalian skinStructure and function of the kidneyRole of Nephron in excretionKidney diseases and disordersStructure of the liver and functionsPrinciples of homeostasisRole of hypothalamus in thermo-regulationSkin and thermo-regulationOsmoregulation water and salt balance Regulation of blood sugar levelRevision QuestionsIndexAcknowledgementsThe Managing Director, Kenya Literature Bureau, would like tothank the following writers who contributed in the production of thisthird edition:Basil Lihanda Shikoti Secondary School, KhayegaJames G.
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The study of Biology aims at providing the learnerwith the necessary knowledge with which to control or change theenvironment for the benefit of an individual, family or community. This book recognises these aspects and provides adequate practicalexercises to sharpen the students practical skills. In addition, it alsoprovides study questions and end of topic questions for selfevaluation. This book is written in a clear, concise language and ispart of the Secondary Biology series. I am grateful to the panel of writers and everybody who tookpart in the writing, editing and production of this third edition. THE MANAGING DIRECTORKenya Literature BureauCONTENTSPrologueAcknowledgements1.0 Transport in plants and animalsTransport in plantsInternal structure of rootsThe stemAbsorption of water and mineral saltsTranspiratonStructure and function of xylem tissueForces involved in water movements in plantsFactors affecting transpirationTranslocationTransport in animalsComparisons between open and closed circulatory systemsThe mammalian circulatory systemThe structure and function of the heartStructure and function of arteries, capillaries and veinsDiseases and defects of the circulatory systemStructure and function of blood cellsThe red blood cellsThe white blood cellsBlood clotting processBlood groupsThe lymphatic systemImmune responsesRevision Questions2.0 Gaseous ExchangeIntroductionGaseous exchange in plantsThe mechanism of opening and closing of stomataMechanisms of gaseous exchange in plantsGaseous exchange in animalsGaseous exchange in protozoaGaseous exchange in insectsGaseous exchange in fishGaseous exchange in amphibiansGaseous exchange in mammalsFactors affecting the rate of breathing in human beingsDisease of the respiratory systemRevision Questions3.0 RespirationIntroductionSignificance of respirationTypes of respirationAerobic respirationAnaerobic respiration in plants and animalsApplications of anaerobic respiration in industries and at homeRespiratory susbstratesFactors affecting rate of respirationRevision Questions4.0 Excretion and HomoestasisExcretion in plantsEconomic importance of plant excretory productsExcretion and homeostasis in unicellular organismsExcretion in animalsStructure and function of mammalian skinStructure and function of the kidneyRole of Nephron in excretionKidney diseases and disordersStructure of the liver and functionsPrinciples of homeostasisRole of hypothalamus in thermo-regulationSkin and thermo-regulationOsmoregulation water and salt balance Regulation of blood sugar levelRevision QuestionsIndexAcknowledgementsThe Managing Director, Kenya Literature Bureau, would like tothank the following writers who contributed in the production of thisthird edition:Basil Lihanda Shikoti Secondary School, KhayegaJames G. Kiura Kihuruini Secondary School, KahuroOnyango Tumbo Chulaimbo Secondary School, MasenoShadrack R.Mungania Teachers Service Commission H Q,NairobiRosebella Jerotich Umoja Secondary School, EldoretThe Managing Director, Kenya Literature Bureau, would like tothank Kikuyu Day Secondary School, Kenya Medical ResearchInstitute, East African Standard and C.
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In addition, it alsoprovides study questions and end of topic questions for selfevaluation. This book is written in a clear, concise language and ispart of the Secondary Biology series. I am grateful to the panel of writers and everybody who tookpart in the writing, editing and production of this third edition. THE MANAGING DIRECTORKenya Literature BureauCONTENTSPrologueAcknowledgements1.0 Transport in plants and animalsTransport in plantsInternal structure of rootsThe stemAbsorption of water and mineral saltsTranspiratonStructure and function of xylem tissueForces involved in water movements in plantsFactors affecting transpirationTranslocationTransport in animalsComparisons between open and closed circulatory systemsThe mammalian circulatory systemThe structure and function of the heartStructure and function of arteries, capillaries and veinsDiseases and defects of the circulatory systemStructure and function of blood cellsThe red blood cellsThe white blood cellsBlood clotting processBlood groupsThe lymphatic systemImmune responsesRevision Questions2.0 Gaseous ExchangeIntroductionGaseous exchange in plantsThe mechanism of opening and closing of stomataMechanisms of gaseous exchange in plantsGaseous exchange in animalsGaseous exchange in protozoaGaseous exchange in insectsGaseous exchange in fishGaseous exchange in amphibiansGaseous exchange in mammalsFactors affecting the rate of breathing in human beingsDisease of the respiratory systemRevision Questions3.0 RespirationIntroductionSignificance of respirationTypes of respirationAerobic respirationAnaerobic respiration in plants and animalsApplications of anaerobic respiration in industries and at homeRespiratory susbstratesFactors affecting rate of respirationRevision Questions4.0 Excretion and HomoestasisExcretion in plantsEconomic importance of plant excretory productsExcretion and homeostasis in unicellular organismsExcretion in animalsStructure and function of mammalian skinStructure and function of the kidneyRole of Nephron in excretionKidney diseases and disordersStructure of the liver and functionsPrinciples of homeostasisRole of hypothalamus in thermo-regulationSkin and thermo-regulationOsmoregulation water and salt balance Regulation of blood sugar levelRevision QuestionsIndexAcknowledgementsThe Managing Director, Kenya Literature Bureau, would like tothank the following writers who contributed in the production of thisthird edition:Basil Lihanda Shikoti Secondary School, KhayegaJames G. Kiura Kihuruini Secondary School, KahuroOnyango Tumbo Chulaimbo Secondary School, MasenoShadrack R.Mungania Teachers Service Commission H Q,NairobiRosebella Jerotich Umoja Secondary School, EldoretThe Managing Director, Kenya Literature Bureau, would like tothank Kikuyu Day Secondary School, Kenya Medical ResearchInstitute, East African Standard and C. M.
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This book is written in a clear, concise language and ispart of the Secondary Biology series. I am grateful to the panel of writers and everybody who tookpart in the writing, editing and production of this third edition. THE MANAGING DIRECTORKenya Literature BureauCONTENTSPrologueAcknowledgements1.0 Transport in plants and animalsTransport in plantsInternal structure of rootsThe stemAbsorption of water and mineral saltsTranspiratonStructure and function of xylem tissueForces involved in water movements in plantsFactors affecting transpirationTranslocationTransport in animalsComparisons between open and closed circulatory systemsThe mammalian circulatory systemThe structure and function of the heartStructure and function of arteries, capillaries and veinsDiseases and defects of the circulatory systemStructure and function of blood cellsThe red blood cellsThe white blood cellsBlood clotting processBlood groupsThe lymphatic systemImmune responsesRevision Questions2.0 Gaseous ExchangeIntroductionGaseous exchange in plantsThe mechanism of opening and closing of stomataMechanisms of gaseous exchange in plantsGaseous exchange in animalsGaseous exchange in protozoaGaseous exchange in insectsGaseous exchange in fishGaseous exchange in amphibiansGaseous exchange in mammalsFactors affecting the rate of breathing in human beingsDisease of the respiratory systemRevision Questions3.0 RespirationIntroductionSignificance of respirationTypes of respirationAerobic respirationAnaerobic respiration in plants and animalsApplications of anaerobic respiration in industries and at homeRespiratory susbstratesFactors affecting rate of respirationRevision Questions4.0 Excretion and HomoestasisExcretion in plantsEconomic importance of plant excretory productsExcretion and homeostasis in unicellular organismsExcretion in animalsStructure and function of mammalian skinStructure and function of the kidneyRole of Nephron in excretionKidney diseases and disordersStructure of the liver and functionsPrinciples of homeostasisRole of hypothalamus in thermo-regulationSkin and thermo-regulationOsmoregulation water and salt balance Regulation of blood sugar levelRevision QuestionsIndexAcknowledgementsThe Managing Director, Kenya Literature Bureau, would like tothank the following writers who contributed in the production of thisthird edition:Basil Lihanda Shikoti Secondary School, KhayegaJames G. Kiura Kihuruini Secondary School, KahuroOnyango Tumbo Chulaimbo Secondary School, MasenoShadrack R.Mungania Teachers Service Commission H Q,NairobiRosebella Jerotich Umoja Secondary School, EldoretThe Managing Director, Kenya Literature Bureau, would like tothank Kikuyu Day Secondary School, Kenya Medical ResearchInstitute, East African Standard and C. M. Muange for allowing us touse their photograph.
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| 1,750,415,787.359488 |
Kiura Kihuruini Secondary School, KahuroOnyango Tumbo Chulaimbo Secondary School, MasenoShadrack R.Mungania Teachers Service Commission H Q,NairobiRosebella Jerotich Umoja Secondary School, EldoretThe Managing Director, Kenya Literature Bureau, would like tothank Kikuyu Day Secondary School, Kenya Medical ResearchInstitute, East African Standard and C. M. Muange for allowing us touse their photograph. CHAPTER ONETransport in Plants and Animals1.1 IntroductionIn form one, we learnt that animals and plants require nutrients andoxygen for the various metabolic activities taking place in theirbodies. Nutrients and oxygen must be transported to all the livingcells of the body. Metabolic activities release by-products such ascarbon IV dioxide carbon dioxide and nitrogenous wastes thatmust be removed the moment they are formed. Otherwise ifallowed to accumulate, they will poison the cells. A means oftransport is essential for organisms to carry the required substancesto various parts of the body and to remove the waste products fromthe various parts of the body. The type of transport system dependson the size of organism. Lower organisms such as bacteria and simple multi-cellularorganisms have small bodies that make them to have large surfacearea to volume ratio. As a result of this, most of their body surfaceis in contact with the environment. Therefore, diffusion alone isenough to transport substances across their cell membranes andwithin the cells of organisms such as hydra and spirogyra. In higher organisms the surface area to volume ratio is smalldue to their large body size. Hence, the tissues and organs are farremoved from the site of supply of materials. In order for theinteriorly located tissues and organs to obtain adequate supply ofmaterials, and at the same time have rapid waste elimination, anelaborate transport system is essential. This would transportsubstances closer to the tissues from where diffusion can take placeefficiently.1.2 Transport in PlantsTransport is essential in plants. Study Questions1. State the substances absorbed by the roots and transported tothe rest of the plant body?2. What substance is transported from leaves to the rest of thebody?In simple plants such as mosses and liverworts, transport ofsubstances occur from cell to cell through the processes of diffusion,osmosis, and active transport. These plants lack specialisedtransport systems.
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State the substances absorbed by the roots and transported tothe rest of the plant body?2. What substance is transported from leaves to the rest of thebody?In simple plants such as mosses and liverworts, transport ofsubstances occur from cell to cell through the processes of diffusion,osmosis, and active transport. These plants lack specialisedtransport systems. In higher plants, the transport function is carriedout by a specialised transport system known as the vascularbundle. It comprises of the xylem and the phloem tissues. Thexylem transports water and mineral salts while the phloemtransports dissolved food substances such as sugars. To understand the mechanisms involved in the transport ofsubstances in higher plants it is necessary to study the anatomy ofroots and stems in relation to transport. Practical Activity 1To observe the external structure of the rootRequirementsPetri dishes, razor blade, ruler, slides and dissecting microscope,hand lens and seedlings of pea or bean. Procedure1. Uproot one of the seedlings and wash off the soil carefullywithout destroying the roots.2. Identify the radicle or tap root. Measure 3 cm length from theroot tip and cut off. Transfer the piece onto a glass slide. Add afew drops of water to avoid drying.3. Examine the piece using a hand lens or a dissecting microscope. Identify the root hairs and their region of growth. Make a fullylabelled drawing of your observations. Study Questions3. How are the root hairs adapted to their functions?4. Make a fully labelled drawing of your observation in practicalactivity 1.Internal Structure of Roots and Root HairsThe primary functions of roots are: i Anchorage holding the plant firmly in the soil . Ii Absorption uptake of mineral salts and water . Otherfunctions performed by certain specialised roots are storageand breathing gaseous exchange .A microscopic examination of internal structure of a young rootshows various structural features. See figure 1.1 a and 1.1 b . Fig. 1.1 a : Transverse section of a young dicotyledonous rootFig. 1.1 b : Longitudinal section through a dicotyledonous root tipThe root cap is at the terminal position of the root tip. It consistsof simple parenchyma cells that protect the apical meristem as theroot tip is pushed past soil particles.
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1.1 a : Transverse section of a young dicotyledonous rootFig. 1.1 b : Longitudinal section through a dicotyledonous root tipThe root cap is at the terminal position of the root tip. It consistsof simple parenchyma cells that protect the apical meristem as theroot tip is pushed past soil particles. The cells of the root cap arerelatively impermeable to water and solutes. As the outer cells wearout, die and disintegrate, new cells from the apical meristemreplace them. The apical meristem is made up of simple undifferentiated cellswhich are actively dividing. This gives rise to many new cells. Two to three millimetres from the tip, is a zone of cellelongation. The cells here lengthen and increase in size, pushingthe root tip through the soil. About 1 centimetre from the tip is another zone characterisedby a dense growth of hair-like structures known as root hairs. Seefigure 1.1 b . New root hairs continuously develop nearer the tip asold ones wither and disintegrate. Rapid and active absorption ofwater occurs in this zone. It is also the region where the varioustissues begin to form by the process of cell differentiation. Suchtissues include the piliferous layer, cortex, vascular bundles,endodermis and pericycle. Transverse sections through the root hairzone of monocotyledonous and dicotyledonous roots show thearrangement of these tissues at the primary stages of development. See photomicrograph in plates 1.1 and 1.2Plate 1.1: Monocotyledon rootPlate 1.2: Dicotyledon rootPiliferous LayerThis is a special epidermis of young roots whose cells give rise toroot hairs. The cells are thin-walled to allow passage of water andmineral salts. As the root tissues matures, a less permeablesuberised epidermis replaces the piliferous layer. CortexIt is made up of loosely packed, thin-walled parenchyma cells. Inyoung roots, it forms the extensive region between the epidermisand the vascular bundles. Water molecules pass through this tissueto reach the vascular bundles. The cortex also acts as a storagetissue. EndodermisIt is a single layer of cells surrounding the vascular bundles.
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Inyoung roots, it forms the extensive region between the epidermisand the vascular bundles. Water molecules pass through this tissueto reach the vascular bundles. The cortex also acts as a storagetissue. EndodermisIt is a single layer of cells surrounding the vascular bundles. It ischaracterised by possession of: Starch grains that stain blue-black with iodine solution. Casparian strip which has an impervious deposit on the radialand cross walls. The endodermis controls the amount of water and mineral saltsentering into the vascular bundles. PericycleIt is a single layer of cells immediately below the endodermis thatgives rise to lateral roots. Vascular BundlesIn both monocotyledonous and dicotyledonous roots the vascularbundles occupy the central position as shown in photomicrographs1.1 and 1.2. Each vascular bundle consists of xylem and phloem. Inmonocotyledons, xylem alternate in the arrangement with phloem. On the other hand, in dicotyledons the xylem is star-shaped and thephloem is located at the centre of the star. Root hairsThey are microscopic outgrowths of epidermal cells. Since they arenumerous and thin-walled, they provide a large surface area forwater and mineral salts absorption. They make, very close contactwith soil, bending round particles and penetrating into the crevices. Root hairs have short life span, but are continuously replaced bynew ones that develop nearer to the tip. Figure 1.2 shows thestructure of a typical root hair cell. Fig. 1.2: Structure of a root hair cellPractical Activity 2To observe the internal structure of the rootsRequirementsLight microscope, permanent slides of: i Monocotyledon roots. Ii Dicotyledon roots. Procedure1. Place the permanent slide of the monocot root on themicroscope.2. Observe under the low power and the medium power of themicroscope.3. Draw a labelled plan diagram of the section.4. Repeat the above procedure with other slide of the dicotyledon. Study Question5. How does the arrangement of vascular tissues in themonocotyledonous roots compare to those of the dicotyledonousroots?The StemThe primary functions of the stem are: i To support and expose the leaves and flowers to theenvironment.
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Draw a labelled plan diagram of the section.4. Repeat the above procedure with other slide of the dicotyledon. Study Question5. How does the arrangement of vascular tissues in themonocotyledonous roots compare to those of the dicotyledonousroots?The StemThe primary functions of the stem are: i To support and expose the leaves and flowers to theenvironment. Ii To conduct water and mineral salts from the roots to rest ofthe plant. Iii To conduct manufactured foods from the leaves to the otherplant cells and storage organs. Other functions performed by specialised stems include storage offood and water, gaseous exchange and perennation. Perennation isthe survival of biennial and perennial plants from one year to thenext by vegetative means. An examination of transverse sections ofyoung, herbaceous stems show various structural features relatedto water conduction. The Internal Structure of a StemThe primary structural organisation in stems consists of severaltissues, possessing different cell types. The following are the tissuesfound in young stems. See figure 1.3 a and b . Fig. 1.3 a : Transverse section of a monocotyledon stemFig. 1.3 b : Transverse section of a young dicotyledon stemThe EpidermisThe epidermis is a single layer of cells covering all other stemtissues. The epidermal cells are elongated in the direction of thestem length and flattened. They have no chloroplasts and theirouter walls are covered by a waxy cuticle that prevents excessiveloss of water through evaporation. The cuticle also protects theinner tissues from infection and mechanical injury. Young stems usually possess guard cells and therefore stomataon the stem epidermis through which air moves in and out of theunderlying stem tissues. The CortexThe cortex is a section of the stem beneath the epidermis. Itextends inwards to the vascular bundles. The following simpletissues may be found within it: parenchyma, collenchyma andsclerenchyma. CollenchymaThe cortex collenchyma tissue lies just beneath the epidermis. Itmay form a complete cylinder or it may occur in separate strands. From a longitudinal view, collenchyma cells are elongated and havea pointed oblique ends. The walls are thickened at the corners withcellulose and pectin deposits.
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The following simpletissues may be found within it: parenchyma, collenchyma andsclerenchyma. CollenchymaThe cortex collenchyma tissue lies just beneath the epidermis. Itmay form a complete cylinder or it may occur in separate strands. From a longitudinal view, collenchyma cells are elongated and havea pointed oblique ends. The walls are thickened at the corners withcellulose and pectin deposits. Due to this thickening, collenchymaserves as a strengthening tissue. ParenchymaParenchyma tissue constitutes the greater part of the cortex. Thecells are irregular in shape, thin walled and loosely packed, hencecreating intercellular spaces filled with air. The cells function in thestorage of water and food. Some cells contain chloroplasts andtherefore photosynthesise. These cells are known aschlorenchyma and make some stems green. SclerenchymaThe cortex sclerenchyma is found in close association with thevascular bundles. The walls of the sclerenchyma cells are thickenedby deposition of lignin in a process known as lignification. Likethe collenchyma, the sclerenchyma serves as a strengtheningtissue. The PithThe pith is the central region of the stem. It consists of parenchymacells that store water and food substances. In some stems, the pithmay be hollow. Vascular bundlesVascular bundles consist of highly specialised cells that arecontinuous from roots through the stem to the leaves. Theytransport water and dissolved minerals from the roots up the plantand the products of photosynthesis from the leaves to the rest ofthe plant body. Practical Activity 3To observe the internal structure of stemsRequirementsLight microscope, slides of transverse sections of: i the monocotyledon stem ii the dicotyledon stem. Procedure1. Place the permanent slide of the monocotyledon stem on themicrocsope.2. Observe under the low power and medium power of themicroscope.3. Draw a labelled plan diagram of the section.4. Repeat the above procedure with the other slide of the dicot. Study Questions6. What tissues make up the vascular bundles?7.
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Draw a labelled plan diagram of the section.4. Repeat the above procedure with the other slide of the dicot. Study Questions6. What tissues make up the vascular bundles?7. Draw plan diagrams to show the arrangement of vascularbundles in a named: i monocotyledon ii dicotyledon stem. Absorption of water and mineralsalts a Absorption of waterWater is drawn into the root hair cells by osmosis. Due to thepresence of dissolved substances in the cell sap of root hairs, theconcentration of the cell sap is greater than that of the surroundingsolution in the soil. A concentration gradient therefore, existsbetween the sap in the vacuole of the root hair cell and the soilwater. This exerts a higher osmotic pressure, thus drawing thewater molecules across the cell wall and cell membrane into theroot hair cells. The osmotic forces exerted by the absorbing cells, overcomethe water retaining powers of the soil thereby enabling water in thesoil to enter the root. More water drawn into the root hair cellsdilutes the cell sap making it less concentrated than that in theadjacent cortex cell of the root. Due to osmotic gradient, watermoves from the adjacent cells to the next by osmosis. Similarly,water passes through the successive cortex cells until it enters thexylem vessels located in the centre of the root. These xylem vesselsof the root then conduct the water up into the xylem vessels of thestem into the leaves as shown in figure 1.4 a , b and c . Fig. 1.4: Absorption of water by plants b Uptake of Mineral SaltsThe soil water contains dissolved mineral salts which plants requirefor their growth and proper functioning. They must therefore beabsorbed from the soil into the plant. Generally, the concentrationof the cell sap in the root hairs is greater than that in the soil. Themineral salts therefore enter the root hairs against theconcentration gradient. This suggests that salts can be drawn fromthe soil even when their concentration is lower than that in the rootcells. This process requires the use of energy and is thereforereferred to as active transport. Any substance that hindersrespiration inhibits active transport. Active transport is believed to involve substances known ascarriers.
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This suggests that salts can be drawn fromthe soil even when their concentration is lower than that in the rootcells. This process requires the use of energy and is thereforereferred to as active transport. Any substance that hindersrespiration inhibits active transport. Active transport is believed to involve substances known ascarriers. These carriers are believed to combine with the mineralions and then carry them across the plasma membrane into the cell. Thus the carriers move back and forth carrying the salt ions fromthe soil water to the root hair cells. Like water, the mineral salts after absorption move through theroot cells into the xylem vessels of the vascular tissue in the centreof the root. Once inside these vessels, the salts and water arecarried up the stem into the leaves by a combination of cellprocesses which include osmosis, diffusion, root pressure,transpiration stream, cohesive forces and capillary attraction. TranspirationTranspiration is the process by which plants loose water in the formof water vapour into the atmosphere. Water loss from the plantsoccurs from the following sites: stomata, cuticle and lenticels. I Stomatal TranspirationThis is the loss of water vapour through the stomata. It accounts for80-90 of the total transpiration in plants. Most of the stomata arefound on the leaves but may also occur on the epidermis of youngherbaceous stems. Ii Cuticular TranspirationThis is the loss of water in the form of water vapour through thecuticle. Up to 20 of the total transpiration may take place throughthin cuticles. In plants with thick cuticles, the loss is negligible. Iii Lenticular TranspirationThis is the loss of water in the form of water vapour through thelenticels. These are areas with loosely fitted cells on woody stems. The loss through the stem is negligible. The internal structure of a leaf in figure 1.5 shows that eachstoma opens into the substomatal air spaces that are lined withspongy mesophyll cells. As water vaporises from the spongymesophyll cells into the sub-stomatal air spaces their cell sapbecomes concentrated than the adjacent cells. This increasesosmotic pressure of the spongy mesophyll cells. As a result, waterflows into the cell from other surrounding cells which in turn take inwater from xylem vessels within the leaf veins. Fig.
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As water vaporises from the spongymesophyll cells into the sub-stomatal air spaces their cell sapbecomes concentrated than the adjacent cells. This increasesosmotic pressure of the spongy mesophyll cells. As a result, waterflows into the cell from other surrounding cells which in turn take inwater from xylem vessels within the leaf veins. Fig. 1.5: The internal structure of a leafYou therefore notice that the water lost through the leaf comesinto the leaf through the xylem in the leaf which is in continuousconnection with the xylem of the stem and that of the root. It istherefore necessary to study the structure and function of thexylem. Structure and function of xylem tissueXylem tissue is made up of two main types of cells namely vesselsand tracheids. In some plants both types of cells are present. Xylem VesselsThese are tubular and non-living tissues as shown in figure 1.6.During cell differentiation, the cross walls of the cells which formthe vessels and the cytoplasm disintegrate resulting into a longhollow tube running continuously from the roots through the stemto the leaves. The walls of the vessels are strengthened bydeposition of lignin material that prevents them from collapsing. The patterns of lignification are diverse as shown in figure 1.6. Thebordered pits on the xylem vessels permit the passage of water inand out of the lumen into the neighbouring cells. Xylem vessels arecharacteristic features in flowering plants angiosperms . Theefficient conduction of water and mineral salts through the floweringplant is the function of the xylem vessels. TracheidsLike the vessels, tracheids are modified xylem cells with lignifiedpitted walls and are non-living. Unlike the vessels, tracheids havetapering or chisel-shaped ends and the cross walls remainperforated. The pits on the sidewalls allow lateral water to cellssurrounding the xylem. See figure 1.7. Aaa ee Fig, 1.6: Xylem vessels - Sian Figure 1.7: TracheidThis makes them less efficient in conducting water than the vessels. Tracheids perform both functions of support and transportation ofwater in the pteridophytes, gymnosperms and angiosperms. Study Questions8.
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The pits on the sidewalls allow lateral water to cellssurrounding the xylem. See figure 1.7. Aaa ee Fig, 1.6: Xylem vessels - Sian Figure 1.7: TracheidThis makes them less efficient in conducting water than the vessels. Tracheids perform both functions of support and transportation ofwater in the pteridophytes, gymnosperms and angiosperms. Study Questions8. I Why are the xylem vessels more efficient in transportationof water than tracheids? Ii What is the significance of xylem vessels being dead?Forces involved in Transportation of Waterand Mineral saltsAs water evaporates from the plant, more is absorbed from the soil. This forms a continuous stream of water flowing from the roots, upthe stem to the evaporating surface. This continuous flow of wateris known as the transpiration stream. See figure 1.8. Thetranspiration stream carries water and salts in solution form, fromthe roots to the leaves. This flow takes place in the xylem tissues. The forces behind this continuous flow of water and mineral saltsthrough the plant include: transpiration pull, cohesion and adhesionforces, capillary and root pressure. These forces are discussed indetail below. I Transpiration pullAs water vaporises from the spongy mesophyll cells into the substomatal air spaces, their cell sap becomes concentrated than theadjacent cells. This change increases the osmotic pressure of thespongy mesophyll cells. As a result, water flows into the cell fromother surrounding cells which in turn take in water from xylemvessels within the leaf veins. These developments create a pull orsuction force that pulls a stream of water from the xylem vessels inthe stem and roots. It is this force that is referred to astranspiration pull, that partly maintains the continuous column ofwater from the roots to the leaves. This is important in thereplacement of water lost from the plant through transpiration. Fig. 1.8: Water loss and transpiration in plants ii Cohesion and Adhesion forcesWater molecules attract one another in such a way that they alwaysstick together. The forces that keep them together are referred toas cohesion force.
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Fig. 1.8: Water loss and transpiration in plants ii Cohesion and Adhesion forcesWater molecules attract one another in such a way that they alwaysstick together. The forces that keep them together are referred toas cohesion force. At the same time water molecules areattracted to the walls of the container in which the water iscontained by a force referred to as adhesive force. The cohesive and adhesive forces in very thin columns can bevery high and not easily broken. These forces are important in themaintenance of a continuous and an uninterrupted water column inthe xylem vessels up the trees. Iii CapillarityIf an open ended tube is placed vertically with one end immersed inwater, the liquid will rise in the tube until the weight of the watercolumn balances the attractive forces operating between the waterand the walls of the tube. The narrower the tube the higher liquidwill rise. In a glass tube of 0.01 mm diameter, water will ascend bycapillarity to a height of about three metres. In the xylem vessels,water would rise to some extent because the vessels are narrower,and there is a higher attractive force between the water moleculesand the cell walls. For effective capillarity there should be no airbubble in the water column. Iv Root PressureIf the stem of a plant is cut above the soil level, it is observed thatcell sap, continue to exude from the cut surface of the stump forsometime. This shows that, there is a force in the roots that pusheswater up the stem. This force is known as root pressure and canbe considerably high in some plants like the grape vines. Root pressure may be attributed to the active pumping of wateracross the endodermis to the xylem vessels. Energy is essential inthis process. Respiratory inhibitors such as cyanide, reduce rootpressure. Significance of TranspirationTranspiration makes the plant lose water if unchecked. However,transpiration has some beneficial effects on the plant as follows: i It serves to replace water lost through the leaves. Ii Through the process, mineral salts and water are transportedin the plant. Iii It serves to cool the plants, a significant factor especially inhot environments. Iv It helps in the removal of excess water especially in aquaticplants. V It is responsible for turgor in plants. Factors affecting Transpiration RateFactors that affect the rate of the transpiration can be grouped intostructural and environmental. These factors are discussedbelow.
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Respiratory inhibitors such as cyanide, reduce rootpressure. Significance of TranspirationTranspiration makes the plant lose water if unchecked. However,transpiration has some beneficial effects on the plant as follows: i It serves to replace water lost through the leaves. Ii Through the process, mineral salts and water are transportedin the plant. Iii It serves to cool the plants, a significant factor especially inhot environments. Iv It helps in the removal of excess water especially in aquaticplants. V It is responsible for turgor in plants. Factors affecting Transpiration RateFactors that affect the rate of the transpiration can be grouped intostructural and environmental. These factors are discussedbelow. I Structural factorsThese are factors related to the morphology of the leaf.1. CuticlePlants growing in arid or semi-arid habitats have their leavescovered with a thick layer of cuticle. The cuticle is a waxywaterproof material. The cuticle reduces rate of transpiration. This may be seen inplants such as sisal, cactus, and aloe. Plants growing in wet habitatshave the problem of containing too much water in their tissues. Such plants have a very thin layer of cuticle on their leaves. Thethin cuticle allows high rate of transpiration as a means of gettingrid of excess water.2. Leaf Size and ShapeThe rate of transpiration is high in plants with broad leaves. Thisexposes a large surface area for water loss as compared to theplants with small and sometimes needle-like leaves. Therefore,plants growing in habitats where water is scarce usually haveleaves with small surface area to minimise transpiration.3. StomataSince transpiration takes place mainly through the stomata inleaves, their position in the leaf, number and size of the apertureare very important as far as transpiration is concerned. Most landplants have few or no stomata on the upper leaf surfaces, but manyon the lower surface. In desert plants, the number of stomata onthe leaves is greatly reduced. Some have got their stomata sunkenbelow the epidermis forming pits. Water vapour tends toaccumulate in these pits thus reducing transpiration. Many plants close their stomata if the rate of transpiration ishigher than that of water uptake. Plants will close their stomata ona hot dry sunny day to lower the rate of transpiration. Thisphenomenon known as midday closure, protects the plant fromwilting.
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Water vapour tends toaccumulate in these pits thus reducing transpiration. Many plants close their stomata if the rate of transpiration ishigher than that of water uptake. Plants will close their stomata ona hot dry sunny day to lower the rate of transpiration. Thisphenomenon known as midday closure, protects the plant fromwilting. Some desert plants have reversed stomatal rhythm,closing their stomata during the day and opening them at nightwhen the atmosphere is cool. Such a mechanism helps them toconserve water in their tissues.4. Leaf FallDuring periods of drought, some plants such as the broad-leafeddeciduous trees shed their leaves to reduce the surface area forwater loss. In some species of grass, the aerial shoot dries up toground level.5. Hairy LeavesIn some plants leaves are covered with hairs or scales. These trap alayer of still moist air on the surface of the leaves, thus reducingtranspiration. Ii Environmental FactorsThese factors are related to environmental conditions.1. TemperatureHigh temperature increases the capacity of the atmospheric air tohold more water vapour. High temperature increases the internaltemperature of the leaf which in turn increases latent heat ofvaporisation and therefore enhances evaporation from the leaf cells. The rate of transpiration increases. The reverse takes place whentemperature is low.2. HumidityThe rate of transpiration is generally high in dry atmosphere due tohigh concentration of water vapour in the intracellular air spacesthan in the dry atmosphere. This causes water vapour to diffuse outof the leaf into the dry atmosphere. The humidity differencebetween the inside and outside of the leaf is known as thesaturation deficit and it determines the rate of water loss fromthe leaf. In dry atmosphere, saturation deficit is high. Consequently,the rate of transpiration in dry atmosphere is high. On the otherhand, in high humidity the saturation deficit is low therefore therate of transpiration is low. Under such conditions some plantssecrete droplets of water through specialised pores calledhydathodes. This process of water loss is called guttation and iscommon in hydrophytes plants growing in wet habitats .3. WindStudy the sketch graph below showing the relationship betweenwind and the rate of transpiration. Wind carries away water vapouras fast as it diffuses out of the leaves through the stomata. Thisprevents the air around the leaves from being saturated with watervapour.
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WindStudy the sketch graph below showing the relationship betweenwind and the rate of transpiration. Wind carries away water vapouras fast as it diffuses out of the leaves through the stomata. Thisprevents the air around the leaves from being saturated with watervapour. This helps to maintain a high diffusion gradient between theinside and outside of the leaf. On a windy day the rate transpirationis high. However, when the air is still the region around the leafsoon becomes saturated with water vapour. Diffusion of watervapour from the leaf surface is low leading to low transpiration rate. Fig. 1.9: Effects of wind on rate of transpiration4. Light IntensityLight intensity affects transpiration rate by influencing stomatalopening. The stomata of most plants open fully during daylighthours when light intensity is high. This brings the sub-stomatal airinto direct contact with the external environment. The water vapourtherefore diffuses out at a higher rate than in dim light whenstomata are partially closed. It is important to note that in a naturalsetting, these factors do not influence transpiration in isolation.5. Atmospheric PressureThe lower the atmospheric pressure the greater the rate ofevaporation. Plants found at high altitudes where atmosphericpressure is very low are likely to lose a lot of water due to high rateof transpiration. Most of them have adaptations to preventexcessive water loss.6. Availability of WaterTranspiration depends on walls of the mesophyl cells beingthoroughly wet. A plant must have adequate water supply from thesoil. Practical Activity 4To investigate the rate of transpiration from leaf surfacesRequirementsLeafy shoots, anhydrous cobalt II chloride paper, glass slides,elastic bands, stop watch or stop clock, cellotape and a pair offorceps. Procedure1. Select one broad healthy leaf on a potted plant or herbaceousplant growing outside the laboratory.2. Using a pair of forceps pick two large pieces of anhydrous cobalt II chloride paper and quickly place each piece on the twosurfaces of the leaf. Note the colour of anhydrous cobalt II chloride paper. 3. Quickly cover them with the dry glass slides and note the time.4. Secure the slides into position with elastic rubber bands asshown in figure 1.105.
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3. Quickly cover them with the dry glass slides and note the time.4. Secure the slides into position with elastic rubber bands asshown in figure 1.105. Separately note the time taken by each of the two cobalt II chloride papers to turn pink. Note the time as soon a pink spotappears and also when the whole paper turns pink.6. Hold a covered piece of anhydrous cobalt II chloride paper toact as a control. This can be held in the hand with a pair offorceps.7. Note the time it takes the piece of paper to turn pink in the air. Do not handle anhydrous cobalt II chloride paper directly withyour hands.8. Record your results in form of a table showing time taken byanhydrous cobalt II chloride paper to turn pink while in the airor above water, under leaf surface and above leaf surface. Study Questions9. What conclusion can be made from this experiment regardingrates of transpiration on leaf surfaces?10. A Explain the difference that is noticed between theanhydrous cobalt II chloride paper on the lower leafsurface and that on the upper surface of the leaf. B i Why was a control experiment necessary? Ii Why is it not advisable to hold the anhydrous cobalt II chloride paper using bare fingers? Fig. 1.10: Experimental set-up for investigation of the rate of transpiration fromthe leaf surfacePractical Activity 5To investigate the rate of transpiration by a leafy shootusing a potometerRequirementsLeafy shoots of herbaceous plants, sharp knife or blades,potometers, beakers, plastic rulers, retort stands, rubber bands,water, jelly, large water container like a basin and stop watches orwristwatches. Procedure1. Obtain suitable leafy shoots from herbaceous plants and keepthe stem under water in a trough, basin or sink.2. Assemble a potometer as shown in figure 1.10. Select a suitableleafy shoot and cut off the last few centimetres of the stalkunder water in the sink. 3. Stand the base of the shoot in the water to prevent blockage ofthe water channels with air. Fix a rubber bung over the cut endwhile it is still in water.4. Connect the end of shoot in the bung to the potometer alreadyfilled with water.
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Stand the base of the shoot in the water to prevent blockage ofthe water channels with air. Fix a rubber bung over the cut endwhile it is still in water.4. Connect the end of shoot in the bung to the potometer alreadyfilled with water. Apply jelly to the stem around the rubber bungto render the system airtight.5. Transfer the set-up to a bench near a window in the laboratory. The end of the capillary tubing should rest in a beaker of water. For a commercially made potometer that is already mounted,dipping of capillary in a beaker of water is not required. Open up the reservoir tap and run out the water to expel any air inthe capillary tube. When all the air has been expelled, introduceone air bubble into the capillary tube. This is done by lifting thecapillary tube from the beaker for a few seconds. Adjust its position using the reservoir tap. The bubble should bemoved to the end of the capillary tube. Place a plastic rubberbehind the capillary tube to measure rate of movement of the airbubble per unit time. Leave the set-up in this position and recordthe position of air bubble and time. When the bubble has travelledmost of the length of the ruler, note the position of the air bubbleand the time. From this, find the distance moved and time taken. Transfer the set-up to other areas such as next to a workingfan, bright light or shaded area. Tabulate the results and explainthem. Fig. 1.11 Set-up of a potometerTranslocation of Organic CompoundsThe transport of soluble organic products of photosynthesis withinthe plant is known as translocation. It occurs in the phloem of thevascular tissues. Like the xylem vessels, the phloem tubes run fromthe roots to the leaves. The organic products translocated aremainly food materials. These products of photosynthesis includesugar, amino acids and vitamins.
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Like the xylem vessels, the phloem tubes run fromthe roots to the leaves. The organic products translocated aremainly food materials. These products of photosynthesis includesugar, amino acids and vitamins. They are translocated to differentregions of the plant where they are required for various purposes. These regions include: a The growing and developing regions of the plants such asyoung shoots, leaves, flowers, fruits and roots. B The storage organs or tissues such as tubers, corms, bulbs,rhizomes and seeds. C The secretory organs such as nectar glands in some insectpollinated plants for example banana Musa spp. .Phloem StructurePhloem is a living tissue which consists of sieve tubes andcompanion cells. During cell differentiation and development ofsieve tubes, most of the cytoplasm is pushed towards the cell wallleaving a lumen filled with a slimy sap containing fine protein fibrils. The cross walls between adjacent sieve tubes are perforatedforming a sieve plate with pores . This allows continuous flow ofsubstances. The companion cell possesses a dense cytoplasm andprominent cell organelles. See figure 1.12. These cells havenumerous mitochondria which generate the energy required fortranslocation. The cytoplasmic filaments consists of fine proteinfibres. The filaments are continuous from one sieve tube to the nextvia the pores in the sieve plates. Materials are believed to bemoved either downwards or upwards along these filaments. Fig. 1.12: Phloem tissueStudy Question11. The rate of transpiration of maize plants was measured over a24-hour period in a farm in Kitale, Kenya and the following werethe results. Table 1.1Time of dayWater loss per hour cm3 7 am9 am11 am1 pm3 pm5 pm7 pm9 pm11 pm1 am3 am1323 a Plot the results on a graph. Place time on the x-axis. B Relate time of day to environmental factors. C Explain how the rate of transpiration varies within the 24hours.1.3 Transport in AnimalsThe Circulatory SystemLarge and complex animals have circulatory systems that consist oftubes, a transport fluid and some means of pumping the fluid or airwithin the tubes. A circulatory system transports the substances andmaintains a steep concentration gradient at the surfaces wherediffusion takes place.
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Table 1.1Time of dayWater loss per hour cm3 7 am9 am11 am1 pm3 pm5 pm7 pm9 pm11 pm1 am3 am1323 a Plot the results on a graph. Place time on the x-axis. B Relate time of day to environmental factors. C Explain how the rate of transpiration varies within the 24hours.1.3 Transport in AnimalsThe Circulatory SystemLarge and complex animals have circulatory systems that consist oftubes, a transport fluid and some means of pumping the fluid or airwithin the tubes. A circulatory system transports the substances andmaintains a steep concentration gradient at the surfaces wherediffusion takes place. Such surfaces include the lungs and gills. Two types of circulatory systems exist in animals: open andclosed. In an open circulatory system the transport fluid iscontained in the general body cavity or coelom. This type ofsystem is common in invertebrates especially arthropods. There is atransporting fluid in a body cavity. The cavity is known ashaemocoel. A closed circulatory system on the other hand, isfound in vertebrates and annelids where the transporting fluid blood is conveyed in special tubes referred to as blood vessels. Comparison between Open and ClosedCirculatory SystemIn closed circulatory system, blood is pumped into closed vessels,hence generation of high pressure which causes the blood to flowfaster. Tissues receive their requirements at a faster rate andremoval of metabolic waste, is also faster. As a result, organismswith closed circulatory system are more active than those with opencirculatory where blood is pumped into the haemocoel thus loosingits pressure. In a closed circulatory system, blood is not in directcontact with the tissues as is the case in an open circulatory bloodsystem. Transport in InsectsInsects have an open circulatory systems where blood is containedin haemocoel and within a dorsal tubular heart. See figure 1.13. Theblood contains suspended leucocytes white blood cells and somepigments but it is not largely involved in the transport of oxygenand carbon dioxide. Transport of gases in insects is principally bydiffusion in the tubes called tracheal system as will be discussedlater in chapter 2.In a cockroach a typical insect there is a tubular heart justabove the alimentary canal.
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See figure 1.13. Theblood contains suspended leucocytes white blood cells and somepigments but it is not largely involved in the transport of oxygenand carbon dioxide. Transport of gases in insects is principally bydiffusion in the tubes called tracheal system as will be discussedlater in chapter 2.In a cockroach a typical insect there is a tubular heart justabove the alimentary canal. The heart has thirteen chambers, threein the thorax and ten in the abdominal segments. The anteriorsegment is joined to the aorta that empties the blood into sinusesof the head. Each chamber contains a pair of valves at the anteriorpart, which prevent back flow of the blood. Each chamber has a pairof lateral openings called ostia which are closed by valves. Thevalves allow blood to flow into the heart through the ostia but notout of it. Fig. 1.13: Open circulatory system in a cockroachThe Mammalian Circulatory SystemA closed circulatory system is found in all vertebrates but is mostdeveloped in mammals where a powerful muscular heart pumpsblood into the arteries. The arteries divide into much smallervessels called arterioles which in turn divide into even much smallervessels called capillaries. Capillaries spread out in a networkfashion in the tissues. The capillaries eventually re-unite to formvenules that in turn form larger vessels called veins. The veins takeblood back to the heart. See figure 1.14 in page 20.Practical Activity 6 a In this activity you will use figure 1.14 in page 20.1. Trace the path followed by blood from any one point until itreturns to the same point e.g. i Kidneys ii Liver iii Right arm. From the above activity you notice that blood flows into the hearttwice for every complete circulation. This is called the doublecirculation. Blood from the body tissues is pumped to the lungs and thenback to the heart. This is called pulmonary circulation. From theheart, blood is then pumped to the rest of the body organs. This iscalled systemic circulation. Mammals and birds have a four-chambered heart. The righttwo chambers deal with deoxygenated blood while the left twochambers deal with oxygenated blood.
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From theheart, blood is then pumped to the rest of the body organs. This iscalled systemic circulation. Mammals and birds have a four-chambered heart. The righttwo chambers deal with deoxygenated blood while the left twochambers deal with oxygenated blood. Hence deoxygenated andoxygenated blood do not mix. Furthermore, blood is at a higher pressure since the heartpumps it twice. This enables the blood to flow faster to the tissues. These two advantages enable the birds and mammals to be moreactive. In some other animals e.g. fish, blood flows only once throughthe heart for every complete circuit. This is called single circulatorysystem. In such a circulatory, the heart has only one atrium andventricle. 2eSSES SOS cininionninge Nepal vinFig. 1.14: Mammalian circulationThe Structure and Function of the HeartExternal Structure of the HeartThe heart is a muscular organ located in the chest cavity inbetween the lungs. It pumps the blood to the whole body. Atranslucent membrane called pericardium encloses the heart. Thepericardial membrane secretes a fluid that acts as a lubricant whenthe heart is working. The outer part of the membrane is coveredwith a layer of fat that act as a shock absorber. This membrane alsohelps to keep the heart in position and check on over dilation of theheart. The heart is made up of special type of muscles calledcardiac muscles that contain interconnected muscle fibres. Thesemuscle fibres have their own blood supply through coronary artery. The coronary artery branches from the aorta just beyond the semilunar valves. It forms branches which run on the heart surface andinto the heart muscles before dividing into capillaries. Thecapillaries join up to form coronary vein which conveys blood to theright atrium. See figure 1.15. Fig. 1.15: External structure of the mammalian heartInternal Structure of the HeartThe mammalian heart is composed of four chambers. Two auricles atria form the upper chambers. They are thin-walled and smallerin volume than the lower chambers. The right auricle receive deoxygenated blood from the body organsexcept the lungs while left auricle receives oxygenated blood fromthe lungs through the pulmonary vein. The lower chambers are called ventricles and are composedof thick cardiac muscles.
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Two auricles atria form the upper chambers. They are thin-walled and smallerin volume than the lower chambers. The right auricle receive deoxygenated blood from the body organsexcept the lungs while left auricle receives oxygenated blood fromthe lungs through the pulmonary vein. The lower chambers are called ventricles and are composedof thick cardiac muscles. The left ventricle has thicker cardiacmuscles than the right ventricle. The volume of the left ventricle issmaller than that of the right ventricle. A thick muscular wall calledthe interventricular septum separates the two ventricles. Betweenthe atria and the ventricles are atrio-ventricular valves whichprevent the blood from flowing back into the auricles when ventriclemuscles contract. These are right atrio-ventricular valve ortricuspid valve and left atrio-ventricular valve or bicuspid valve. These valves are supported by tendons cordae tendinae which areattached to the wall of the ventricles on each side. The tendonsprevent the atrio-ventricular valves from turning inside out whenunder pressure as the ventricles contract. At the base of pulmonary artery and aorta are cup like valvescalled semilunar valves. The valves are opened by the force ofthe blood generated by contraction of the ventricles. The valvesprevent backward flow of blood when the ventricles relax. Seefigure 1.16.Circulation in the HeartDeoxygenated blood from the body tissues except the lungs entersthe right auricle through the vena cava. It then flows to rightventricle via the tricuspid valve. When the right ventricle contracts,blood from the right ventricle is forced via the semilunar valvesthrough the pulmonary artery into the lungs. Blood from the leftventricle is forced to flow via the semilunar valves through the aortato the body tissues. Oxygenated blood from the lungs flow throughthe pulmonary vein to the left auricle via the bicuspid valve to theleft auricle. Fig.
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Blood from the leftventricle is forced to flow via the semilunar valves through the aortato the body tissues. Oxygenated blood from the lungs flow throughthe pulmonary vein to the left auricle via the bicuspid valve to theleft auricle. Fig. 1.16: The internal structure of the mammalian heartPumping Mechanism of the HeartThe heart undergoes contraction systole and relaxation diastole rhythmically throughout the animal s life. Diastole Relaxation When ventricular muscles relax, the volume of each ventricleincreases, while pressure decreases. The atrio-ventricular valve orcuspid valve opens allowing deoxygenated blood from the bodytissues to flow into the right ventricle while oxygenated blood flowsfrom the left atrium into the left ventricle. The semilunar valvesclose preventing the blood from flowing back into the ventricles. The slight contractions of the auricles force the blood to flow intothe ventricles. Refer to figure 1.17 a which shows diastole on theleft side of heart. Fig. 1.17 a : Diastole ventricle relaxesSystole contraction When the ventricular muscles contract, the atrio-ventricular orcuspid valves close preventing the blood from flowing back into theauricles. The volume of the ventricles decreases while pressureincreases, to force blood out of the heart to the: i Lungs via the semilunar valve through the pulmonary artery. Ii Body tissues except the lungs via the semilunar valve throughthe aorta. The thick cardiac muscles of the left ventricle generate highpressure which forces the blood to the furthest tissue. A systole isalways followed by a diastole and the two make a complete heartbeat. See figure 1.17 b .The heart contracts at an average of about 60 to 70 times perminute. High temperature and emotions can result in an increasedrate of the heartbeat. The heartbeat is faster in a child than in anadult. Heartbeats may be felt as pulse by placing a finger on a fairlylarge artery, such as that at the wrist, against a bone. Fig.
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High temperature and emotions can result in an increasedrate of the heartbeat. The heartbeat is faster in a child than in anadult. Heartbeats may be felt as pulse by placing a finger on a fairlylarge artery, such as that at the wrist, against a bone. Fig. 1.17 b : Systole ventricle contractsHeartbeatThe heart is capable of contracting and relaxing rhythmicallywithout fatigue due to its special muscles called cardiac muscles. The cardiac muscle fibres are interconnected as shown in figure1.18 so that waves of contraction can travel throughout the mass ofthe muscle. Fig. 1.18: Structure of the cardiac muscleFig. 1.19: The electrical excitation that follows the contraction of the heartThe rhythmic contraction of the heart arise from within the heartmuscles without nervous stimulation. The contraction is thereforesaid to be myogenic. However, the heartbeat is initiated by the pacemaker or sinoartrio node SA . This is a small area of specialised cardiacmuscle fibres in the wall of right auricle. Its spontaneous rhythmicalelectrical activity initiates and maintains contractions of the heart heartbeat . However the rate of heartbeat is under nervouscontrol. The vagus nerve slows down the heartbeat where as thesympathetic nerve speeds up the heart beat. See figure 1.19.Structure and Function of Arteries, Capillariesand VeinsThe main blood vessels are arteries, veins and capillaries. ArteriesThey originate from the heart and carry blood away from the hearte.g. Aorta carry oxygenated blood from the heart to all parts of thebody except the lungs while pulmonary artery carry deoxygenatedblood to the lungs. Arteries carry blood at high pressure and have a thick muscularwall to resist the pressure of the blood inside them. The innermostlayer of the artery is called endothelium which is composed of asingle layer of cells. This layer is found in all blood vessels. Itprovides a smooth lining which offers the least possible frictionalresistance to blood flow. The middle layer is composed of elasticfibres and smooth muscles.
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This layer is found in all blood vessels. Itprovides a smooth lining which offers the least possible frictionalresistance to blood flow. The middle layer is composed of elasticfibres and smooth muscles. The outer layer is formed of elasticmuscular fibres collagen fibres as shown in figure 1.20 a .When ventricles contract systole , the muscular layer ofarteries relaxes stretching outwards to allow blood into the arteries. When ventricle muscles relax diastole , the muscular layercontracts, pressing inwards forcing the blood to flow forwards. Thisproduces the pulsating action in arteries. The muscular wall ofthe arteries is under the control of nerves and hormones which alterthe diameter of the arteries. This plays a major role in regulatingblood flow to the body organs. Fig.1.20 a : Structure of the arteryThe aorta forms branches which supply blood to major organsof the body. These branches divide to form small blood vesselscalled arterioles. The arterioles divide further to form the bloodcapillaries. CapillariesThey form one of the most important parts of the circulatorysystem. Capillaries are numerous and very close to the tissues insuch a way that each cell is near a blood capillary. Exchange ofsubstances between the tissues and the blood takes place acrossthe capillary wall. This is possible due to the fact that the walls ofcapillaries are made up of endothelial cells only that are only onecell thick. Thus provides the least distance for exchange ofsubstances within cells. Figure 1.20 b shows the structure of acapillary. Exchange of substances occurs by ultra filtration. The exchangeoccurs in capillary beds as shown in figure 1.20 c . Branching ofarterioles into capillaries increases the surface area of thecapillaries and pressure of blood in them. This forces smallmolecules out of the blood within the capillaries to form part of thetissue fluid. The tissue fluid formed is similar to plasma incomposition except it lacks protein, red blood cells and someleucocytes. Phagocytic leucocytes squeeze in between the cells ofthe capillary wall and pass into the tissue fluid. From the tissuefluid, cells extract substances such as glucose, oxygen, amino acids,vitamins, hormones and mineral ions. Fig.
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Phagocytic leucocytes squeeze in between the cells ofthe capillary wall and pass into the tissue fluid. From the tissuefluid, cells extract substances such as glucose, oxygen, amino acids,vitamins, hormones and mineral ions. Fig. 1.20 b : Portion of a capillary blood vesselUltra filtration results to a drop in pressure so that at thevenules and in the capillary bed, blood pressure is less than that ofthe tissue fluid. Substances from the tissue fluid pass back into thecapillaries by diffusion while water passes back by osmosis since theblood is more concentrated than the tissue fluid. Carbon IV oxidepasses into the blood through diffusion. More tissue fluid passes intolacteal of the lymphatic system as shown in figure 1.20 c . Fig. 1.20 c : Relationship between capillaries, cells and lymphaticsThe venules join up to form large vessels called veins. VeinsVeins carry blood from all parts of the body back to the heart. Bloodpressure in the veins is very low hence the blood flows smoothly. The veins have relatively larger lumen as compared to the arteries. This offers minimum resistance to blood flow. The walls of the veinsare made up of thin muscles as shown in figure 1.20 d .Fig. 1.20 d : VeinsVeins have valves as shown in figure 1.20 e throughout theirlength, which prevent back flow of blood thus ensuring that bloodflows only towards the heart. Forward flow of blood in veins is assisted by contraction of skeletalmuscles. Large veins are located in between the skeletal muscles. When the muscles contract they press the veins forcing the bloodflow towards the heart. This explains the need for physicalexercises. All veins carry deoxygenated blood with fewer nutrientsbut more nitrogenous waste and other metabolic wastes except: a Renal vein that carries blood from the kidney wherenitrogenous waste, some water and salts has been removed. B Hepatic portal vein that carries blood rich in dissolved foodsubstances from the gut to the liver. C Pulmonary vein that carries oxygenated blood from the lungsto the left auricle of the heart. Major Blood Vessels of the BodyFigure 1.21 illustrates major arteries which supply blood to someorgans of the body and major veins which collect blood from theorgans. Fig.1.20 e : Valves in veinsFig.
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This explains the need for physicalexercises. All veins carry deoxygenated blood with fewer nutrientsbut more nitrogenous waste and other metabolic wastes except: a Renal vein that carries blood from the kidney wherenitrogenous waste, some water and salts has been removed. B Hepatic portal vein that carries blood rich in dissolved foodsubstances from the gut to the liver. C Pulmonary vein that carries oxygenated blood from the lungsto the left auricle of the heart. Major Blood Vessels of the BodyFigure 1.21 illustrates major arteries which supply blood to someorgans of the body and major veins which collect blood from theorgans. Fig.1.20 e : Valves in veinsFig. 1.20: Major blood vessels of the human bodyTable 1.2: Differences between arteries and veinsArteriesVeins1. Walls are thick muscular andelastic.1. Walls thin less muscularand elastic .2. Have no valves except at thebase of large arteries leavingthe heart.2. Have valves at intervalsthroughout their length.3. Blood flows rapidly in pulses.3. Blood flows smoothly.4. Blood flows rapidly underpressure.4. Blood flows slowly underlow pressure.5. Tend to lie deeper in the body.5. Tend to lie near the bodysurface.6. Transport oxygenated bloodexcept pulmonary artery.6. Transport deoxygenatedblood except pulmonaryvein.7. Narrow lumen.7. Wider lumen. The photomicrograph 1.3 shows some of these differences. Practical Activity 6 b To display the circulatory system in a mammalRequirementsFreshly killed rats or rabbits , dissecting board or tray, dissectingpins, scissors, scalpels, forceps, hand lens, cotton wool and water. Procedure1. Dissect the mammal using the procedure in the dissecting guideand conduct the following: i Display the heart, lungs, liver, kidneys and the spleen. Ii Identify the coronary, carotids, jugular, renal, hepaticarteries and veins. Iii Trace the dorsal aorta and the posterior vena cava towardsand away from the heart. Similarly trace the anterior orinferior vena cava from the anterior region of the animalnoting its entry into the right atrium. Plate 1.3: T.S.
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Dissect the mammal using the procedure in the dissecting guideand conduct the following: i Display the heart, lungs, liver, kidneys and the spleen. Ii Identify the coronary, carotids, jugular, renal, hepaticarteries and veins. Iii Trace the dorsal aorta and the posterior vena cava towardsand away from the heart. Similarly trace the anterior orinferior vena cava from the anterior region of the animalnoting its entry into the right atrium. Plate 1.3: T.S. of an artery and vein of a human being2. Draw and label the transport system of the animal as displayedin the dissection. Study Questions12. Compare the physical appearances of the arteries and veinsgiving reasons for your observations.13. Name the blood vessels that convey blood to: i the brain ii the fore limb iii the lungs iv the liver v the kidneys vi the hind limb.14. What are the functions of the dorsal aorta and the vena cava? Practical Activity 7To investigate the external and internal structures of amammalian heartRequirementsFresh heart from a mammal such as cow, sheep, goat or pig,dissecting board or tray, dissecting pins, scissors, scalpel, forceps,hand lens and cotton wool. Procedure1. Examine the external features of the provided heart payingparticular attention to: i Its shape and thickness of its wall. Ii The remains of the blood vessels on its upper side. Iii Identify the atria and the ventricles. Iv Identify the coronary blood vessels on the outer walls ofthe heart.2. Dissect the heart to expose its internal structure. Carefullyexamine these structures to identify: i The chambers of the heart. Ii The muscular walls of the atria and ventricles. Iii The heart valves: bicuspid, tricuspid and semi-lunar valves. Iv The coronary blood vessels on the inner walls of the heart. V The remains of the vena cava, pulmonary vein and arteryand the aorta. Carefully note where these enter or leave theheart. Study Questions15. Draw and label the external structures of the heart.16. Draw and label the internal structures of the heart.
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Carefully note where these enter or leave theheart. Study Questions15. Draw and label the external structures of the heart.16. Draw and label the internal structures of the heart. Show witharrows the direction of blood flow through the heart. Practical Activity 8To investigate pulse rate at the wristRequirementsStop watches or clocks. Procedure1. Locate the radial, artery in the wrist at the base of the thumb ofa subject.2. Place the index and middle fingers on the radial pulse and notethe pulsating effect of blood flow in the artery.3. Start the stopwatch and count how many times the bloodpasses through the radial artery.4. Record the number of blood pulses for a one-minute time lapse.5. Repeat the count three times and enter the readings as in table1.3.6. Run round the laboratory block and return to the laboratory.7. Locate the pulse and record its rate after the exercise. Table 1.3: Pulse rateStudy Questions17. From the readings in the table above draw conclusions on thepulse rate of the subject.18. How does exercise affect the pulse rate?19. Suggest the origin of the pulse in the arteries and its effect ingeneral blood circulation. Practical Activity 9To investigate the direction of blood flow in the superficialveins of the armsRequirementsBandage or bandsProcedure1. Select volunteers with large visible veins in the arm.2. Firmly tie the bandage or a band around the upper arm abovethe elbow of the subject.3. Use the index and middle fingers to locate a suitable stretch ofa vein that is not branched such as the radial vein of the arm.4. Gently press the index finger on this vein or any prominent veinat a given point.5. Note any observable changes on the vein.6. Using the middle finger stroke the vein pushing the bloodupwards towards the elbow.7. Release the pressure on the vein and note what happens to theblood flow.8. Stroke the vein this time pushing the blood downwards towardsthe hand.9. Note any effects on the flow of blood when this is done. Study Questions20. What happens when a bandage or band is tied around the armof the subject?21. How is the blood flow affected after the first stroke in step 6?Give reasons for this. Diseases and Defects of Circulatory SystemThrombosisThis refers to formation of a clot in the blood vessels.
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Note any effects on the flow of blood when this is done. Study Questions20. What happens when a bandage or band is tied around the armof the subject?21. How is the blood flow affected after the first stroke in step 6?Give reasons for this. Diseases and Defects of Circulatory SystemThrombosisThis refers to formation of a clot in the blood vessels. The mostcommon of all is the coronary thrombosis that leads to blockageof coronary artery which supplies blood to the heart. The blockage may be due to arteries becoming increasinglyfibrous or accumulation of fatty materials on the artery walls. Thesubsequent narrowing of coronary artery results in less bloodflowing to the heart. Insufficient oxygen therefore, reaches theheavy oxygen dependent heart muscles. A serious blockage of theartery can result into fatal heart attack. Coronary thrombosis maybe caused by heavy intake of fat which results to high amount ofcholesterol in the blood. Cholesterol accumulates in the coronaryarteries blocking the associated blood vessels thus causing lessoxygen to reach the heart muscles. Other causes may be heavyintake of alcoholic drinks, smoking, overweight, psychological andemotional stress. Practising healthy lifestyles can control coronary thrombosis. ArteriosclerosisArteriosclerosis refers to the deposition of calcium in the walls ofthe blood vessels. It leads to hardening of the arteries which resultto permanent change in arterial wall. This leads to thickening andloss of elasticity of the vessel wall. The most common type ofarteriosclerosis is characterised by excessive growth of fibrousconnective tissue in the wall of the arteries. The cause of thedisease is not clearly known, however medical scientists haveestablished some relationship between the disease and overweight,lack of exercise and emotional stress. Taking drugs that reduce cholesterol in the blood can controlarteriosclerosis. Physical exercises can also reduce chances ofarteriosclerosis since the excess fat will be broken down while theheart is kept active and strong. Varicose VeinsIt is a condition in which the superficial veins especially at the backof the legs become swollen and flabby due to failure of some valvesto function properly. This results in the retention of tissue fluid. Thedisease can be controlled by regular physical exercises of the body. Hypertension or High Blood PressureNormal blood pressure varies between 90 60 and 140 90 mm ofmercury.
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Physical exercises can also reduce chances ofarteriosclerosis since the excess fat will be broken down while theheart is kept active and strong. Varicose VeinsIt is a condition in which the superficial veins especially at the backof the legs become swollen and flabby due to failure of some valvesto function properly. This results in the retention of tissue fluid. Thedisease can be controlled by regular physical exercises of the body. Hypertension or High Blood PressureNormal blood pressure varies between 90 60 and 140 90 mm ofmercury. The numerator refers to systolic pressure duringcontraction and the denominator refers to diastolic pressure duringrelaxation. High blood pressure is a disorder that is associated withheavy drinking, smoking, taking of large quantities of salt in thefood and general body stress. High blood pressure may also becaused by arteriosclerosis which causes the heart to generate highpressure that force the blood through the less elastic vessels. The heart of a hypertensive person is therefore overworked andthe person is prone to heart failure. Hypertension may lead tobursting of arteries and capillaries. If the blood vessels in the brainbursts, a stroke results and the brain cells die in the affected areas. Paralysis at least for some parts of the body, usually accompanies astroke. Some strokes are fatal. This disorder is more common in individuals aged above 40 years. Hypertension can be controlled by: i Having regular exercises. Ii Intake of less salt. Iii Avoiding excessive drinking of alcoholic beverages. Iv Not smoking cigarettes and other related drugs. V Avoiding general body stress by practicing healthy life stylesthat give individuals peace of the mind. The Structure and Functions of BloodComposition of BloodThe mammalian blood consists of fluid medium called plasma withcellular components suspended in it. These cellular components areerythrocytes red blood cells , leucocytes white blood cells andnon-nucleated thrombocytes platelets .The PlasmaPlasma is a pale yellow fluid consisting mainly of 90 per cent waterin which a variety of substances are suspended and othersdissolved. Substances in plasma include glucose, mineral salts,hormones, some enzymes, amino acids and lipids. Also found in theplasma are plasma proteins such as anti-bodies, albumin, fibrinogenand waste products of metabolism such as carbon IV oxide andurea.
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These cellular components areerythrocytes red blood cells , leucocytes white blood cells andnon-nucleated thrombocytes platelets .The PlasmaPlasma is a pale yellow fluid consisting mainly of 90 per cent waterin which a variety of substances are suspended and othersdissolved. Substances in plasma include glucose, mineral salts,hormones, some enzymes, amino acids and lipids. Also found in theplasma are plasma proteins such as anti-bodies, albumin, fibrinogenand waste products of metabolism such as carbon IV oxide andurea. Blood plasma from which fibrinogen and cells have beenremoved is called serum. The main functions of plasma are: i Transports red blood cells which contain oxyhaemoglobin tothe tissues hence facilitate transport of oxygen. Ii Forms the main medium in which dissolved food substancesare transported to the liver and then to the other body tissues. Iii Transports metabolic wastes such as urea carbon IV oxideand other nitrogenous wastes to the excretory organs wherethey are eliminated from the body such organs include kidneys,lungs and the skin. Iv Transportation of hormones. V Oxygen and carbon IV oxide are slightly soluble in water. Hence the plasma transports small amount of these gases. Vi Regulation of pH of the body fluids. Vii Distributes heat around the body hence regulate bodytemperature. Red Blood Cells Erythrocytes In an adult the red blood cells are made in the bone marrow of theshort bones such as the sternum, ribs and the vertebrate. In theembryo they are made in the liver and spleen. Mature red bloodcells have no nuclei but have a sunken centre that makes the cellresemble a biconcave disc as shown in figure 1.22 a and b . Theabsence of a nucleus leaves room for more haemoglobin to bepacked in the cell to enable it to carry more oxygen. Haemoglobin isa protein which contains iron and readily combines with oxygen toform an unstable compound known as oxyhaemoglobin. Red bloodcells carry oxygen in the form of oxyhaemoglobin. The haemoglobin has high affinity for oxygen. It readily picksup oxygen in the lungs where the concentration is high and easilyreleases oxygen in the tissues where the concentration is low. In the tissues, oxyhaemoglobin readily breaks down dissociates into haemoglobin and oxygen.
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Red bloodcells carry oxygen in the form of oxyhaemoglobin. The haemoglobin has high affinity for oxygen. It readily picksup oxygen in the lungs where the concentration is high and easilyreleases oxygen in the tissues where the concentration is low. In the tissues, oxyhaemoglobin readily breaks down dissociates into haemoglobin and oxygen. The oxygen diffuses outof the red blood cells and through the capillary walls into thetissues. The haemoglobin is then free to pick up more oxygenmolecules from the lungs. Fig.1.22: Red blood cellsRed blood cells are about five million per cubic millimetre ofblood. Due to their ability to change their shape, they are capableof squeezing through the narrow capillaries. Their large numbersand shape make them suitable for their function. The biconcaveshape increases their surface area over which gaseous exchangecan take place. Red blood cells have a life span of about four months afterwhich they break down and disintegrate in the liver and the spleen. The iron released from the breakdown of the old red blood cells isused in the manufacture of new cells. Although one per cent of allthe red blood cells is used in the manufacture of new ones daily,their number per cubic millimetre remains fairly constant in theblood of a healthy person. In the case of people living in high altitudes, the body respondsto the low oxygen concentration by increasing the total number ofred blood cells and the haemoglobin content in them. This responseincreases the oxygen carrying capacity of the red blood cells. Besides oxygen, haemoglobin can readily combine with carbon II oxide carbon monoxide to form carboxyhaemoglobin. Thiscompound does not readily dissociate and therefore reduces thecapacity of haemoglobin to transport oxygen to the tissues. Carbon II oxide is therefore a respiratory poison which can be fatal ifbreathed in for a considerable length of time. Burning charcoalstoves, jikos in a poorly ventilated room produces carbon II oxide. Exhaust fumes from vehicles also contain carbon II oxide. Itis important therefore that charcoal stoves are not allowed to burnin poorly ventilated rooms because carbon II oxide canaccumulate to levels dangerous to life. In addition to transport of oxygen red blood cells also transportabout 95 percent of carbon IV oxide.
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Burning charcoalstoves, jikos in a poorly ventilated room produces carbon II oxide. Exhaust fumes from vehicles also contain carbon II oxide. Itis important therefore that charcoal stoves are not allowed to burnin poorly ventilated rooms because carbon II oxide canaccumulate to levels dangerous to life. In addition to transport of oxygen red blood cells also transportabout 95 percent of carbon IV oxide. Here the enzyme carbonicanhydrase speeds up the conversion of carbon IV oxide to weakcarbonic acid. The carbonic acid dissociates into hydrogencarbonate and hydrogen ions. The hydrogen carbonate ions diffuseout of the red blood cells into the plasma in which it is thentransported to the lungs. The remaining 5 percent of carbon IV oxide is transported as dissolved carbon IV oxide in the plasma. White Blood cells Leucocytes Unlike red blood cells, white blood cells are nucleated, they lackhaemoglobin and hence their cytoplasm is colourless. They arefewer in number than the red blood cells. There are about 7,000leucocytes per cubic millimetre of blood. In an average healthyman, there are about 600 red blood cells to every leucocyte cell. However their number increases greatly during infection. They areformed in the bone marrow of long bones and lymph nodes. Theirfunction is to protect the body against pathogenic micro-organismssuch as bacteria, protozoa, viruses and their secretions. Leucocytes are of two main types: granulocytes andagranulocytes. Granulocytes are also called phagocytes orpolymorphs. They have lobed nuclei and granulated cytoplasm. See figure 1.23.Granulocytes use amoeboid movement to pass through thewalls of the capillaries into the affected tissues. In the tissues andblood, the granulocytes engulf pathogenic micro-organisms by aprocess called phagocytosis hence the name phagocyte. Onceingested, the micro-organism are digested. Some white blood cellsmay die in the course of phagocytosis.
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In the tissues andblood, the granulocytes engulf pathogenic micro-organisms by aprocess called phagocytosis hence the name phagocyte. Onceingested, the micro-organism are digested. Some white blood cellsmay die in the course of phagocytosis. The dead phagocytestogether with dead micro-organisms and damaged tissues form pus. The agranulocytes assist the phagocytes to destroy the pathogenicmicro-organisms. Agranulocytes on the other hand have rounded or bean-shapednuclei and lack granules in their cytoplast. They consist ofmonocytes and lymphocytes. The lymphocytes are formed in the lymph nodes and produceantibodies that protect the body from infection in the followingways: i Antibodies which are antitoxins neutralise the toxins antigens produced by pathogenic micro-organisms. Fig 1.23: Types of Leucocytes ii Some antibodies such as agglutinins cause clumping togetherof micro-organisms. This stops the microorganisms frommultiplying and eventually they die. In this way they areingested by the phagocytes. Iii Lysins destroy micro-organisms by digesting their cellmembranes or walls. Iv Opsonins are antibodies which adhere to the outer surface ofmicro-organisms thus making it easier for phagocytes to ingestthem. The antibodies are produced when micro-organismsinvade the body. After recovery from infection the level ofantibodies decreases gradually as they disintegrate. Seeimmune response .Platelets Thrombocytes Platelets are fragments from large cells in the bone marrow. Theyare discoid in shape and assume a star-shaped appearance inextracted blood. Their number is approximately 2.5 million per mm3of blood. They have no nucleus and play an important role in bloodclotting when blood vessels are injured. See figure 1.24.Fig. 1.24: PlateletsA blood smear observed under a microscope reveals the variouscomponents of blood. See photomicrograph in plate 1.4.Plate 1.4: Human blood smear courtesy of KEMRI Blood Clotting ProcessThe process of clotting involves a series of complex reactions wheresoluble blood protein is converted into a mass of tangled threads ofinsoluble protein.
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See figure 1.24.Fig. 1.24: PlateletsA blood smear observed under a microscope reveals the variouscomponents of blood. See photomicrograph in plate 1.4.Plate 1.4: Human blood smear courtesy of KEMRI Blood Clotting ProcessThe process of clotting involves a series of complex reactions wheresoluble blood protein is converted into a mass of tangled threads ofinsoluble protein. This process begins when blood vessels aredamaged. When blood vessels are injured, platelets exposed to airrupture on damaged tissues to release thromboplastin enzymethrombokinase which initiates the clotting process. Thromboplastinneutralises heparin an anti-clotting factor and activatesprothrombin to thrombin. This process requires calcium ions. Thrombin activates conversion of fibrinogen to fibrin which forms ameshwork of fibres, on the cut surface to trap red blood cells toform a clot. The clot dries up to form a scab that stops the bleedingand protects the damaged tissues from infection. Figure 1.25 showssimplified flow chart summarising the process of blood clotting. Thus blood clotting reduces loss of blood when blood vesselsare injured. Excessive loss of blood especially more than 2 litres canlead to severe anaemia unless corrected immediately by bloodtransfusion. Fig. 1.25: Simplified flow diagram showing the process of blood clottingIt is important to note that fibrinogen is only changed to fibrinwhen blood vessels are injured. Otherwise if this happens in vesselsthat are not injured, it would block up the blood vessels leading todeath. However, this does not happen because fibrinogen is notchanged to fibrin by the enzyme called thrombin. In undamagedvessels, blood does not contain thrombin but its inactive form calledprothrombin. Formation of prothrombin requires vitamin K.Undamaged vessels contain heparin which prevents conversion ofprothrombin to thrombin and neutralises any thrombin which maybe formed accidentally. Blood GroupsRed blood cells have certain proteins called antigens on theirplasma membrane. There are two of these antigens, designated Aand B. Blood groups are determined by the type of antigen presentin an individual s red blood cell. Thus an individual whose red bloodcells have antigen A is grouped as A.
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There are two of these antigens, designated Aand B. Blood groups are determined by the type of antigen presentin an individual s red blood cell. Thus an individual whose red bloodcells have antigen A is grouped as A. Antigen B is grouped as B.Antigen A and B is grouped as AB while that without antigens isgrouped as O type. The plasma too has proteins called antibodies. There are twotypes of antibodies designated a and b. If an individual has antigenA blood group A on his her red blood cells, he she cannot haveantibody a in his her plasma, but will have antibody b . Similarly anindividual with antigen B blood group B has antibody a in his herplasma. This is due to the fact that agglutination or clumping of redblood cells takes place if antibodies corresponding to the antigencome into contact. See table 1.4.Table 1.4: Blood groups, antigens and antibodiesBlood groupAntigen in red blood cellsAntibody in plasmaAAbBBaABA and BNoneONone neither A nor B Both a and bBlood transfusionBlood transfusion is the transfer of blood from a donor to thecirculatory system of the recipient. A recipient will receive bloodfrom a donor if the recipient cannot produce antibodiescorresponding to the donor s antigens. Otherwise agglutination clumping together of the recipient s red blood cells will take place. Table 1.5 gives a summary of blood types and reactions of the bloodtypes. Table 1.5: Reactions of blood typesKey:Capital letter: Antigens blood groups Small letter: Antibodies Compatible no agglutination X Not compatible agglutination Note: Blood group AB has neither antibody a nor b. Indviduals withblood group AB can receive blood from all others. They aretherefore refered to as universal recipient. On the other hand,individuals with blood group O can donate blood to all others. Thischaracteristic leads to individuals with this blood group being calleduniversal donor. Study Questions22. From the above table identify the universal donor and theuniversal recipient. 23. Why is it important to screen blood before transfusion?A doctor must ensure that before one donates blood he she ishealthy and is between 18 and 65 years of age.
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From the above table identify the universal donor and theuniversal recipient. 23. Why is it important to screen blood before transfusion?A doctor must ensure that before one donates blood he she ishealthy and is between 18 and 65 years of age. A drop of thedonor s blood is first tested to find out what group he she belongsto. Half a litre of the donor s blood is taken from a vein in the armand drained into a clean plastic bag to which an anti-coagulant hasbeen added, to stop clotting. The donor is given a drink to help topup blood volume and is advised to eat a balanced diet thereafter. The donated blood is kept in a blood bank at a temperature justabove freezing point for not more than one month. Donating bloodis good because it helps save lives. Healthy people should feel freeto donate blood regularly. The blood is normally not used for transfusion after one monthbecause most of the red blood cells will have died. Before bloodtransfusion is carried out, it is important that the blood is screenedfor pathogens such as Human Immunodeficiency Virus AcquiredImmuno-Deficiency Syndrome HIV AIDS and compatibility. In addition to the A and B antigens, there is another antigen onthe red blood cells known as the Rhesus factor. People whoseblood contains this antigen are described as rhesus positive Rh ve while those who lack it are referred to as rhesus negative Rh ve . If Rh ve blood is given Rh ve recipient, the latter responds byproducing the corresponding rhesus antibodies and nothing furtherhappens. But if the same recipient is given another dose of Rh veblood in a period of less than two weeks agglutination of red bloodcells occurs. In a case where a Rh ve mother bears a Rh ve baby,fragments of the foetus red blood cells containing the rhesusantigen pass across the placenta and get into the mother s bloodstream. The mother s red blood cells respond by producing rhesusantibodies that in turn pass across the placenta into the blood ofthe foetus red blood cells before the foetus birth. This reaction iscommon after the first born and affects the foetus of thesubsequent pregnancies. This is as a result of the antigen-antibodyreaction taking place on the surface of the red blood cells.
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The mother s red blood cells respond by producing rhesusantibodies that in turn pass across the placenta into the blood ofthe foetus red blood cells before the foetus birth. This reaction iscommon after the first born and affects the foetus of thesubsequent pregnancies. This is as a result of the antigen-antibodyreaction taking place on the surface of the red blood cells. Thiscondition is referred to as haemolytic disease of the new-born Erythroblastosis foetalis . The new born baby can be saved byreplacing its blood with Rh ve blood. With every successivepregnancy the antibody level increases in the blood stream of themother and subsequent foetuses, if the baby is also Rh ve he shewill suffer from serious haemolytic disease of the new born. Withthe advancement in technology, it is possible to transfuse blood tothe foetus when still in the mother s womb and save the child. In recent years, it has also been found that the haemolyticdisease of the new-born can be prevented by treating the motherwith an anti-rhesus globulin which coats the surfaces of red bloodcells thus preventing the antigen-antibody reactions. Practical Activity 10Complete the table below by collecting the necessary datafrom your classmatesTable 1.6: Blood groupsStudy Question24. Name the dreaded disease associated with blood transfusion. Lymphatic SystemAnimals particularly vertebrates have an additional transport systembesides the blood system. This is known as lymphatic system andit supplies all the regions of the body just like blood system. Thelymphatic system is made of narrow, thin walled tubes known aslymph vessels which branch to form lymph capillaries in which afluid known as lymph is transported. See figure 1.26.Fig.1.26: Lymphatic SystemLymphThis is a fluid similar to blood plasma except that it contains lessproteins. It is formed as a result of ultra-filtration of blood from thenarrow blood capillaries. As blood circulates it reaches the bodytissues through the blood capillaries that form a network throughoutthe tissues. The pumping force from the heart together with thenarrow lumens of the capillaries exert a high pressure that forcesthe fluid part of the blood to filter out of the capillary walls into thesurrounding tissues.
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It is formed as a result of ultra-filtration of blood from thenarrow blood capillaries. As blood circulates it reaches the bodytissues through the blood capillaries that form a network throughoutthe tissues. The pumping force from the heart together with thenarrow lumens of the capillaries exert a high pressure that forcesthe fluid part of the blood to filter out of the capillary walls into thesurrounding tissues. This filtrate consists of all the constituents ofblood plasma except the blood cells and the proteins. This isbecause the blood cells and proteins are too large to filter out of thecapillary walls. The fluid is known as tissue fluid or intercellularfluid. Once formed the tissue fluid bathes the cells of the tissuessupplying them with oxygen, food and other useful substances. The cells absorb these substances and pass out carbon IV oxide and other waste products in exchange. Most of the tissue fluidthen returns to the blood system through the venule end of thecapillaries. This is due to the lower hydrostatic pressure of the bloodat the venule and compared to that at the arteriole end of thecapillary. The excess tissue fluid, however, drains into the lymphvessels where it is known as lymph. The lymph glands produce antibodies and lymphocytes. Immune responsesImmune responses are reactions of the body that are as a result ofintroduction of antigens. They involve the production of antibodiesor leucocytes which combine with antigens. An antibody is achemical substance, usually a protein, which is formed in the bloodwhen an antigen is introduced into the tissue of a human being orany other animal. An antibody has a chemical composition which iscomplimentary to the antigen against which it reacts. This meansthat a particular antibody combines with or responds only to aparticular antigen to make it harmless. Antibodies are produced by the lymphocytes. When harmfulorganisms or proteins invade the body, some lymphocytes startproducing antibodies which are complimentary to them. The bonemarrow and the thymus gland also begin to produce morepolymorphs phagocytes and lymphocytes respectively. Types of ImmunityNatural Immunity Innate Immunity Natural immunity is inherited and controlled.
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This meansthat a particular antibody combines with or responds only to aparticular antigen to make it harmless. Antibodies are produced by the lymphocytes. When harmfulorganisms or proteins invade the body, some lymphocytes startproducing antibodies which are complimentary to them. The bonemarrow and the thymus gland also begin to produce morepolymorphs phagocytes and lymphocytes respectively. Types of ImmunityNatural Immunity Innate Immunity Natural immunity is inherited and controlled. This trait can betransmitted from parent to offsprings. Acquired Immunity or Artificial ImmunityAcquired immunity can either be naturally or artificially induced. When attacked by diseases like small pox, chicken pox, measles,poliomyelitis, and mumps the people who recover completely fromthese diseases develop resistance to any subsequent infectionsfrom the same diseases. If these people become infected again by the same disease causingorganisms pathogens , they do not become seriously ill. This isknown as acquired immunity. In some instances people who havebeen exposed to milder forms of a disease develop a resistance tothe acute forms of the disease, e.g. those who have been exposedto the tuberculosis bacteria may not be affected by the moreharmful forms of the same disease although they had neversuffered from the acute disease before. On the other hand, a personwho has never been exposed to the tuberculosis bacteria is likely toget seriously ill with the disease. Artificial acquired immunity occurs when a mild form of adisease-causing organism is injected into the body of a healthyperson. The infection stimulates the production of the correspondingantibody which then destroys the pathogens. The body thereafterretains the memory of the structure of this antigen in itslymphocytes. When the body is attacked by the same disease, itproduces the specific antibodies which destroy the disease causingorganisms. This type of immunity is called artificial acquiredimmunity. What happens is that, on coming into contact withspecific antigens a group of B lymphocytes called committed cells in the lymph nodes undergo cell division to produce a group oflarge plasma cells. The plasma cells synthesise the antibodies whichare released into the lymph and eventually reach the blood. In theblood the antibodies destroy the invading organisms. A smallnumber of plasma cells remain in the lymph nodes for years, evenafter the antibodies have eliminated the original infection and areremoved from the blood.
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The plasma cells synthesise the antibodies whichare released into the lymph and eventually reach the blood. In theblood the antibodies destroy the invading organisms. A smallnumber of plasma cells remain in the lymph nodes for years, evenafter the antibodies have eliminated the original infection and areremoved from the blood. This system provides a very rapidresponse to any subsequent infection by similar antigens. These methods of artificially inducing immunity has now beenadopted in many countries and many lives are saved from variousdiseases like smallpox, measles, poliomyelitis and tuberculosis. Thefirst work on immunisation was by a British doctor called EdwardJenner in 1797 who used a vaccine to prevent a smallpox attack. Hehad observed that most milkmaids did not suffer from smallpoxafter they had suffered from cowpox. He carried out an experimentby first making some scratches on a healthy boy and introducingsome pus from a pox vesicle of a woman suffering from cowpox. Later he introduced some pus taken from a woman suffering fromsmallpox into the boy s body. Doctor Jenner observed that the boy did not contract smallpox,though he only developed mild symptoms of the disease. Thus theboy had been immunised against the deadly disease because a mildantigen cowpox virus produced antibodies against the smallpox. Currently, the method of producing vaccines involves thetreatment of the disease causing organisms so that they areweakened. This treatment of pathogens is called attenuation. Theattenuated bacteria or viruses are then introduced into the body ofa healthy person or animal by either vaccination or inoculation. Theattenuated bacteria or viruses stimulate the production of specificantibodies by the body such that next time the body gets infectedby the pathogens, there will be no serious illness caused. Vaccinesgenerally contain attenuated disease causing organisms. Thesevaccines are currently produced commercially. The reaction of thebody to cowpox vaccine is an example of active immunisation. Similarly, the body actively makes its own antibodies against someantigens e.g. measles, whooping cough and poliomyelitis. In somecases the artificially acquired immunity is permanent andimmunisation is done only once in a lifetime. In some cases a booster vaccination is required to maintain immunity e.g. againstcholera, since the immunity lasts for a short time.
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In somecases the artificially acquired immunity is permanent andimmunisation is done only once in a lifetime. In some cases a booster vaccination is required to maintain immunity e.g. againstcholera, since the immunity lasts for a short time. Artificial passive acquired immunity is achieved whenantibodies from another source e.g. serum, are directly introducedinto the body of a person. The serum containing the antibodies iscalled antiserum, and it may be effective for only a few weeks. This type of immunity is called passive because the body is notactivated to produce its own antibodies. In newly born babiesantibodies pass from milk produced by the mother, so providing thebabies with passive immunity to some diseases for a period of time. Study Questions25. Explain how immunity is achieved in human beings.26. Name two types of immunity you know.27. List three diseases that are effectively controlled throughvaccination. The Role of VaccinationVaccination protects individuals from infections of many diseasessuch as smallpox, tuberculosis and poliomyelitis and it prevents thespread of the diseases. Diseases like smallpox, tuberculosis andtetanus used to be killer diseases but now, due to the developmentof vaccines, individuals can be protected from them. It is nowbelieved that smallpox has been eliminated from the world since1977. Pregnant mothers should be immunised against tetanus atleast once before giving birth. Table 1.7: Immunisation for childrenPlate 1.5: Vaccination against various diseases is done when need arise Courtesyof EA Standard In children, vaccination against certain diseases is done at differenttimes. Immediately after birth, the baby should be immunisedagainst tuberculosis and polio. The baby should then receive acompound vaccine against whooping cough and tetanus. Thecompound vaccination should be repeated after 10-14 weeks. At theage of nine months, the child should be vaccinated against measles. Measles is a major child-killer disease. Vaccinations should be given at regular intervals see table1.7 . For example, booster injections of vaccines against polio inbabies have to be given regularly after every four weeks, for thefirst 16 weeks. It is also recommended that healthy children shouldbe exposed to chickenpox when young for the attack is severe whenthe children mature. Immunisation against other diseases should be done as advisedby the health officers.
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Vaccinations should be given at regular intervals see table1.7 . For example, booster injections of vaccines against polio inbabies have to be given regularly after every four weeks, for thefirst 16 weeks. It is also recommended that healthy children shouldbe exposed to chickenpox when young for the attack is severe whenthe children mature. Immunisation against other diseases should be done as advisedby the health officers. Usually, people of all ages are vaccinated ifthere is an outbreak of diseases like cholera, see plate 1.5.Apart from immunisation the control of diseases can also bedone by restricting movement of people into and out of infectedareas. This method is called quarantine. It can be done atinternational, national or local levels. Facilities like water wells, should not be shared as long as thequarantine is in force. Internationally, before one enters anothercountry, one must be vaccinated against various diseases, andcertificates of vaccination obtained. In schools and homes, peoplesuffering from infectious diseases should be isolated to avoidinfection of healthy people. This minimises the spread of disease. Allergic reactionsAn allergy is a hypersensitive reaction to an antigen by the body. This occurs when the combination of an antibody with an antigenproduces a violent reaction or severe damage to the body. Allergicpeople are hypersensitive to materials like dust, pollen grains, somefoods, some drugs and certain air pollutants. The allergy manifests itself in various ways. In some people, oneating certain foods, rashes appear on the skin. Some drugs e.g.penicillin, chloroquine and aspirin can also cause rashes on the skin. Other allergic reactions are itching, sneezing, vomiting or difficultiesin breathing. The allergic conditions are brought about when the body reactsby overproducing antibodies against harmless antigens. Theantibody-antigen reaction takes place on the surface of cells thatburst open, releasing a chemical substance called histamine,Histamine increases the permeability of the epithelial cells thusmaking them take in fluid and swell up. The intercellular spaces toobecome filled with fluid, and swell. Histamine also causesinflammation and pain. A severe condition called anaphylaxissometimes occurs, in which blood vessels get dilated and thislowers the blood pressure to the extent of causing death. This ishow bee stings can cause death.
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Histamine also causesinflammation and pain. A severe condition called anaphylaxissometimes occurs, in which blood vessels get dilated and thislowers the blood pressure to the extent of causing death. This ishow bee stings can cause death. Avoiding the allergens allergycausing substances or administration of the antihistamine drugscan control this. Organ TransplantsCurrently, a lot research is being done on organ and tissueregeneration and human immune system. Surgeons can replacedamaged tissues of organs using similar organs from other personsor animals e.g. the pig, in transplant operations. It has also beenpossible to transplant kidneys, liver, spleen, reproduction organs,parts of skin and limbs. Parts of organs or tissues transplanted on tolarger parts of recipient are called grafts. It is known that although two organisms belong to the samespecies, their immune systems may be so different that grafts maybe rejected by the recipient. In most cases grafts involving identicaltwins or those from same individual are not rejected. The grafts may be rejected because the body of the hostrecognises the new tissue or organ as foreign to it. The donor tissuehas antigens to which the host s leucocytes produce antibodies andthe tissue may be rejected; if not, the graft will take or beaccepted. Some transplants of hearts, kidneys, cornea of the eye,lungs and bone marrow have been carried out by using drugs thatsuppress the immune response of the host. A substance calledinterferon is also used to suppress rejection of grafts. In organtransplants, sophisticated machines are used to keep the organs tobe transplanted and the patient alive. Other suggested activities1. Stem ringing experiment on translocation. 2. Visit to a health clinic to collect data information on: i Allergies ii Blood groups iii High blood pressure iv HIV AIDS in the school locality. Revision Questions1. Figure 1.27 is a longitudinal section of the root apex. I Label the parts A to E. ii State the function of parts labelled C, D and E. iii Label zones 1-2. Iv What are the differences between zone 2 and 3?Figure 1.272. Figure 1.28 is a plan diagram from a cross-section ofdicotyledonous plant stem.
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What were theblood groups of the two samples?15. People can die when they inhale gases from burning charcoal inpoorly ventilated rooms. Explain how this death comes about.16. A State two proteins in the blood which are responsible fordetermining the blood group of a person. B Give two reasons why a transport system is necessary inhigher animals.17. State any two adaptations of red cells to their functions. 18. What do you understand by the term double circulation?19. A Explain the differences between: i blood plasma and serum. Ii blood and lymph. Iii tissue fluid and blood plasma. B State the functions of the plasma.20. A Draw a large labelled diagram of internal structure of amammalian heart. B Describe the circulation in the heart. C Describe the working of the heart.21. A Describe two diseases and two disorders of blood vessels. Identify the causes of the disorders in a above and listtheir symptoms and treatment. B In a certain person, blood took a long time to clot after acut. What vitamin deficiency was the person likely to havebeen suffering from?22. A What do you understand by the term immunity? B State and discuss the two types of immunity. C What is a vaccination? State the role of vaccination inproviding immunity. D What causes allergies? CHAPTER TWOGaseous Exchange2.1 IntroductionThe process by which the respiratory gases oxygen and carbon IV oxide are passed across the respiratory surface is known asgaseous exchange. This is brought about by a concentrationgradient that exists between the body of living organisms and thesurrounding medium. In simple organisms, oxygen is absorbed bythe exposed surface of the body by simple diffusion. In morecomplex organisms, there are special organs such as lungs or gillswhich absorb oxygen and remove carbon IV oxide from the body. The importance of gaseous exchange in the living organisms isto promote oxygen intake for respiration and facilitate carbon IV oxide removal from the body as a wasted product of metabolism.2.2 Gaseous Exchange in PlantsGaseous exchange in plants involves two main respiratory gases:carbon IV oxide and oxygen. During daytime green plants take incarbon IV oxide and oxygen. The carbon IV oxide taken in isused for photosynthesis and oxygen produced as a by-product ofphotosynthesis is released into the atmosphere.
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In morecomplex organisms, there are special organs such as lungs or gillswhich absorb oxygen and remove carbon IV oxide from the body. The importance of gaseous exchange in the living organisms isto promote oxygen intake for respiration and facilitate carbon IV oxide removal from the body as a wasted product of metabolism.2.2 Gaseous Exchange in PlantsGaseous exchange in plants involves two main respiratory gases:carbon IV oxide and oxygen. During daytime green plants take incarbon IV oxide and oxygen. The carbon IV oxide taken in isused for photosynthesis and oxygen produced as a by-product ofphotosynthesis is released into the atmosphere. However some ofthe oxygen produced is used in the same plant for respiration. Butsince the rate of photosynthesis proceeds faster than respiration atdaytime, excess oxygen produced is removed. However, respirationcannot provide enough carbon IV oxide for photosynthesis atdaytime hence more carbon IV oxide diffuses into the leaves. Atnight respiration proceeds in absence of photosynthesis in greenplants, hence plants take in oxygen for respiration but give outcarbon IV oxide. Plants do vary in their size and thus influence thesurface area to volume ratio for gaseous exchange. Whether insimple or complex plants, gaseous exchange takes place bydiffusion across the respiratory surface. In plants such as the flowering plants, stomata in the leavesand lenticels in the woody stems and roots provide surfaces forgaseous exchange. Practical Activity 1 a To investigate the release of carbon IV oxide by plantsRequirementsFreshly plucked leaves from a plant one boiled and another keptfresh , boiling tubes 2 , bicarbonate indicator solution red incolour and aluminium foil. Procedure1. Obtain a freshly plucked leaf of a plant.2. Put a litre of diluted bicarbonate indicator in the boiling tubethat has been covered with aluminium foil and label A.3. Using a piece of thread, suspend the leaf above the indicator inthe boiling tube.4. Place a cork to cover the mouth of the boiling tube as shown infigure 2.1.5. Set up a control with a boiled leaf and label B.6. Keep the apparatus on the side bench for at least one hour. Note: Bicarbonate indicator is red at the beginning of theexperiment. Study Questions1.
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Place a cork to cover the mouth of the boiling tube as shown infigure 2.1.5. Set up a control with a boiled leaf and label B.6. Keep the apparatus on the side bench for at least one hour. Note: Bicarbonate indicator is red at the beginning of theexperiment. Study Questions1. Note the colour change of the bicarbonate indicator in practicalactivity 1 a above.2. Explain the colour change. Fig. 2.1: Release of carbon IV oxide by plants3. Why are boiling tubes covered with aluminium foil?Practical Activity 1 b To investigate the release of oxygen by plantsRequirementsWater plants, glass funnel, beaker, boiling tube, wooden block,wooden splints, sodium hydrogen carbonate and source of heat. Procedure1. Set up the experiment as shown in figure 2.2.2. Place the set-up in the sunlight to allow photosynthesis to takeplace. Fig. 2.2: Release of oxygen by plants3. Leave the set-up in the sunlight until sufficient gas has collectedin the boiling tube.4. Test the gas collected using a glowing splint. Study Questions4. What happens when the gas collected is brought near a glowingsplint?5. Identify the gas produced above and explain how plantsproduce it. Structure and function of the stomataStomata are tiny openings on the leaf surface bordered by sausageshaped guard cells. The guard cells are the only green cells of theepidermis. The inner sides of the guard cell are not attached to thewalls of the adjacent epidermal cells. Stomata occur mainly on thelower side of the leaf but less frequently on the upper side of theleaf surface that receive direct sunlight. Stomata open mostly atdaytime but close at night. However, their distribution on the leafsurface is related to the habitat. The stomata allow gaseousexchange to take place in the plants. Guard cells also control theopening and closing of the stomata. The guard cells are adapted totheir function by having differentially thicker inner cell walls. Seefigure 2.3 a and b .Fig. 2.3: a Stoma closedThe Mechanisms of Opening and Closing ofStomataThis process of opening and closing of stomata has been explainedby various theories.
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The guard cells are adapted totheir function by having differentially thicker inner cell walls. Seefigure 2.3 a and b .Fig. 2.3: a Stoma closedThe Mechanisms of Opening and Closing ofStomataThis process of opening and closing of stomata has been explainedby various theories. One such theory is the photosynthetic theorybased on the sugar formation by chloroplast in the guard cells tobring about cell turgor. During the daytime the chloroplast of guardcells produces sugar through the process of photosynthesis. Thissugar accumulates in the guard cells causing the osmotic pressureof the sap vacuoles of the cells to increase. This leads to drawing ofwater from the neighbouring cells by osmosis. The guard cells thusbecome turgid and bulge outwards making the stomata to open. Atnight, however, sugar is converted to starch which accumulates inthe guard cells. The osmotic pressure of the guard cells then falls asthe cells lose turgidity due to water loss to the adjacent epidermalcells. This condition results in the guard cells becoming flaccid anddraw towards one another leading to the closure of the stomata. The above theory has been found unsatisfactory, as there are someplants whose stomata open at night and close at daytime. Another possible explanation of stomatal closing and opening isin the conversion of sugar to starch and vice versa in the guardcells. The starch sugar interconversion theory is under the influenceof pH through enzyme action. For example, during the dayphotosynthesis takes place in guard cells using carbon IV oxide. The pH in the guard cells tends to rise as the conditions becomeless acidic as carbon IV oxide is continuously used up. Theincreasing pH favours the conversion of starch into glucose. Theglucose being osmotically active, brings about an osmotic effectthat result in water being drawn into the guard cells. Consequently,the guard cells become turgid and bulge outwards making thestomata to open. At night carbon IV oxide is hardly used up asphotosynthesis does not take place. Carbon IV oxide, thereforeaccumulates in the guard cells resulting in the lowering of pH. Thisfavours the conservation of glucose into starch. Fig. 2.3 b Stoma openThe latter is osmotically inactive and therefore the guard cells donot gain water.
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Carbon IV oxide, thereforeaccumulates in the guard cells resulting in the lowering of pH. Thisfavours the conservation of glucose into starch. Fig. 2.3 b Stoma openThe latter is osmotically inactive and therefore the guard cells donot gain water. Due to the resulting flaccid state of the guard cells,the stomata close. The closure may not be complete and somegaseous exchange may still take place at night. Mechanism of Gaseous Exchange in PlantsThe process of gaseous exchange in aerial roots, stems and leavesof both aquatic and terrestrial plants is the same. For gaseousexchange to take place, a concentration gradient must existbetween the atmospheric air outside and that in the interior of theroot, stem or leaf. This will permit oxygen to diffuse from theatmospheric air outside where its concentration is high, into theplant where its concentration is kept low due to utilisation inrespiration. Similarly, carbon IV oxide will diffuse out as ametabolic waste product along a concentration gradient into theatmosphere. Fig.2.4: A transverse section of a water lily showing the large airspacescharacteristic to hydrophytesStomata and Habitats of PlantsStomata are also modified in a number of ways depending on thehabitat in which the plant is growing. For example, xerophytes plants adapted to living in dry areas often have fewer stomatathat are smaller in size than those of hydrophytes plants in wetareas . These stomata are found mainly on the lower surface of theleaves. In some xerophytes the stomata are sunken and in othersthey open during the night and tend to close during daytime. Thepartial opening during the daytime allows for gaseous exchange. The modifications mentioned above, help in water conservation inthe tissues of the plant and at the same time reduce water lossfrom the plants by evaporation and transpiration. Hydrophytes are aquatic plants or plants growing in water. Some of these aquatic plants, are not completely submerged, forexample nymphea. They have many stomata that are large in size. Their stomata are mainly found on the upper surface of leaves. These stomata allow the hydrophytes to release excess water tothe atmosphere.
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Thepartial opening during the daytime allows for gaseous exchange. The modifications mentioned above, help in water conservation inthe tissues of the plant and at the same time reduce water lossfrom the plants by evaporation and transpiration. Hydrophytes are aquatic plants or plants growing in water. Some of these aquatic plants, are not completely submerged, forexample nymphea. They have many stomata that are large in size. Their stomata are mainly found on the upper surface of leaves. These stomata allow the hydrophytes to release excess water tothe atmosphere. The hydrophytes also have aerenchyma tissuewith large air spaces to store air for gaseous exchange as shown infigure 2.4.The mesophytes terrestrial plants growing in moist areas orareas with adequate water supply have a fairly large number ofstomata of medium size found on both surfaces of the leaves inmore or less equal numbers. Structure and Function of LenticelsLenticels are openings found on the stems and roots of some woodyplants and usually are formed by loosely packed corky cells. Theseopenings permit gaseous exchange to take place between theinterior of the plant and the outside by diffusion. The actualgaseous exchange takes place on the moist surfaces of cells underthe lenticels. However, in some aquatic plants such as themangrooves, plants that grow in muddy salty waters on beaches lenticels in specialised breathing aerial roots called pneumatophoresallow gaseous exchange to take place. See figure 2.5 and plate 2.1. Fig. 2.5: The structure of the lenticelPlate 2.1: Pneumatophores of the mangroovesPractical Activity 2To observe permanent slides of transverse sections ofleaves and stemsRequirementsPermanent slides of mesophyte, zerophyte and hydrophyte leaves,stems and light microscope. Procedure1. Place each slide in turn on the stage of the microscope andobserve.2. Draw a labelled plan diagram of each specimen observed. Study Question6.
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2.5: The structure of the lenticelPlate 2.1: Pneumatophores of the mangroovesPractical Activity 2To observe permanent slides of transverse sections ofleaves and stemsRequirementsPermanent slides of mesophyte, zerophyte and hydrophyte leaves,stems and light microscope. Procedure1. Place each slide in turn on the stage of the microscope andobserve.2. Draw a labelled plan diagram of each specimen observed. Study Question6. How are the structures observed related to gaseous exchange,for the mesophyte, xerophyte and hydrophyte?2.3 Gaseous Exchange in AnimalsTypes and Characteristics of RespiratorySurfaces in AnimalsVarious types of respiratory surfaces have been developed bydifferent animals to facilitate gaseous exchange depending on theanimal s size, activity and the environment in which it operates. Table 2.1: Types of respiratory surfaces in animalsType of respiratorysurfaceEnvironment or mediumof operationExample oforganism i Cell membraneWaterAmoeba ii Gill filaentsWaterFish iii TracheolesAirInsects iv Alveoli lungsAir Mammals Birds Frogs Reptiles v Skin vi Buccal cavityWaterAirFrogEarthwormAirFrogThe respiratory surface is the basic unit of any breathing systemupon which gaseous exchange takes place by diffusion. However,the respiratory surface must meet the conditions listed below toallow gaseous exchange to take place effectively. These are: i It must have a large surface area. Ii It must always be a moist surface. Iii It should possess a rich capillary network. Iv It must be a thin membrane. The above-mentioned conditions constitute characteristics of mostrespiratory surfaces. Gaseous Exchange in ProtozoaThe example of the amoeba, a member of the kingdom protoctistais used to represent protozoa. The amoeba is a single-celled aquaticorganism whose entire body surface is always in contact with thesurrounding water. The organism is small and has a large surfacearea exposed to its aquatic environment. It therefore does not needan elaborate gaseous exchange system since its gaseous exchangecan be adequately met by diffusion across its cell membrane. Oxygen dissolved in the surrounding water, diffuses across themembrane into the cytoplasm.
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The amoeba is a single-celled aquaticorganism whose entire body surface is always in contact with thesurrounding water. The organism is small and has a large surfacearea exposed to its aquatic environment. It therefore does not needan elaborate gaseous exchange system since its gaseous exchangecan be adequately met by diffusion across its cell membrane. Oxygen dissolved in the surrounding water, diffuses across themembrane into the cytoplasm. In a similar manner, carbon IV oxide and other soluble wastes diffuses out through themembrane into the surrounding water along a concentrationgradient as illustrated in figure 2.6. Fig. 2.6: Gaseous exchange in an amoebaGaseous Exchange in InsectsInsects are generally small animals. The small size is quiteadvantageous to the animal in terms of gaseous exchange sincesurface area to volume ratio remains large. However, being largerthan amoeba, there is need for the development of a breathingsystem. This system is made up of a large network of air tubes thatform a tracheal system. The system penetrates into all parts of thebody to improve on the efficiency of gaseous exchange. Figure 2.7shows the tracheal system of a grasshopper. Fig. 2.7: The tracheal system of an insectThe tracheal system of an insect which forms its breathing systemconsists of spiracles and tracheolesSpiracles are external openings present on either side of theabdomen and thorax of an insect through which air from theatmosphere enters the body. Each spiracle is supplied with amuscular valve, that controls its opening and closing, and also withhairs to prevent excessive loss of water from the body tissues byevaporation. The spiracles then open into large tracheal tubes called tracheawhich are arranged in definite pattern and penetrate the wholebody space of an insect. These air tubes are reinforced with spiralbands of chitin to keep them open. The trachea then subdivide intofiner air tubes called tracheoles, which ramify the body tissue of theanimal for direct supply of individual cells with oxygen. Since thetracheoles lack the spiral bands of chitin, they permit gaseousexchange across their thin moist walls. See figure 2.8.Fig.
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The trachea then subdivide into finer air tubes called tracheoles, which ramify the body tissue of theanimal for direct supply of individual cells with oxygen. Since thetracheoles lack the spiral bands of chitin, they permit gaseousexchange across their thin moist walls. See figure 2.8.Fig. 2.8: The branching of the tracheaMechanism of Gaseous Exchange in theTracheal System of an InsectAir is drawn into and out of the tracheal system by muscularmovement of the abdominal wall. In wasps and bees, abdominalsegments are moved in and out length-wise, while in locusts andcockroaches the segments are moved laterally. When spiracle valves are open, air is drawn into the trachealsystem. After that the valves close and air is forced along thesystem by the muscle movements. Oxygen diffuses into the tissuefluid and into the cells due to a higher oxygen diffusion gradient. Likewise carbon IV oxide diffuses out of tissue cells and into fluidsthen into the tracheal system due to a carbon IV oxide diffusiongradient as shown in figure 2.8.The thoracic spiracle valves close as the abdominal spiraclevalves open and the gas is released through the spiracle openingsin the abdomen of the insect. Insects which live in water also carry out gaseous exchange inwater. Insects such as the dragon fly or may fly larvae nymphs usetracheal gills that are seen as paired plates on either side of theabdomen as shown in figure 2.9.Fig.2.9: Position of may fly nymph tracheal gills However, most of the aquatic insects have an elaboratetracheal system and are not truly aquatic because they need tocome to the surface to breathe. For example, mosquito larvae havetheir spiracles near the rectum carried on a tube called respiratorysiphon. This siphon is opened when the larva comes to the surfaceof the water to take in air and is closed by valves when the larvasubmerges. Larvae come to the surface of water periodically tobreathe and position themselves as seen in figure 2.10 a .
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For example, mosquito larvae havetheir spiracles near the rectum carried on a tube called respiratorysiphon. This siphon is opened when the larva comes to the surfaceof the water to take in air and is closed by valves when the larvasubmerges. Larvae come to the surface of water periodically tobreathe and position themselves as seen in figure 2.10 a . In thepupa stage, a pair of siphons open just behind the head piercethrough the water surface to allow for gaseous exchange as shownin figure 2.10 b .Fig.2.10 a : The breathing structures of a mosquito larvaSome adult insects like water beetles and water bugs use bubblesof air trapped by hairs or other structures on their body surfaces. The air bubbles give these insects a silvery appearance. But likemost other aquatic animals, they first come to the surface toreplenish their stock of air. However, others still use the respiratorydevice, plastron for gaseous exchange. The plastron is a pile ofvery fine non-washable hairs which cover the cuticle for somedistance around the spiracle to hold off water and also to maintaina film of air over the body surface. Fig.2.10 b : The breathing structures of a mosquito pupaPractical Activity 3Observation of breathing movements of an insectRequirementsLive specimens of grasshopper locust cockroach, boiling tube andhand lens. Procedure1. Place the insect in a boiling tube and close.2. Using a hand lens observe the insect in the boiling tube. Recordthe observation and variations of the abdominal movements andspiracles of the insect.3. Remove the insect, hold it by the head and using the hand lensobserve the abdominal side. Study Questions7. Count and record the number of spiracles on the abdomen ofthe insect used in practical activity 3.8. Draw the abdomen and show the position and shape of thespiracles. Gaseous Exchange in a fishFish live in water in that contains oxygen and other gases aredissolved in it. The breathing system of a bony fish consists of themouth or buccal cavity, gills, opercular cavity and the operculum. See figure 2.11 a . Fig.
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Draw the abdomen and show the position and shape of thespiracles. Gaseous Exchange in a fishFish live in water in that contains oxygen and other gases aredissolved in it. The breathing system of a bony fish consists of themouth or buccal cavity, gills, opercular cavity and the operculum. See figure 2.11 a . Fig. 2.11 a : The position of the gills in a bony fishThe gills of a fish consist of a long curved bony structure calledgill bar. It is from the gill bar that most gill filaments arise. The gillfilaments trail in water to provide a large surface area for gaseousexchange. When a fish is lifted out of water, the surface tensioncauses the gill filaments to clump together thus reducing theeffective area of the respiratory surface. Arising from the other sideof the gill bar facing the mouth are the gill rakers. These appearas teeth-like structures whose function is to prevent food and anysolids present in water from reaching the delicate gill filaments. Theblood vessels from the body enter into the gill bar and branch intothe gill filaments as blood capillaries. These delicate structures areprotected in the bony fish by a larger bony plate on either side ofthe body near the head known as the operculum. See figure2.11 b .Fig. 2.11 b : A gill of a fishMechanism of Gaseous Exchange in the Gillsof Bony FishThe floor of the mouth cavity is lowered by muscular contractionsduring inhalation. Lowering of the floor of the mouth increases thevolume of the mouth cavity but reduces the pressure. As a resultwater flows into the mouth through the open cavity. Meanwhileeach closed operculum on either side of the mouth bulges outwardsto cause reduction of pressure in the gill cavity so that watercontaining dissolved oxygen then flows from the mouth cavity to thegill chamber over the gills. See figure 2.12.Fig. 2.12: Movement of water over gillsWhen all this is happening, the higher external pressurepresses the flexible free edge of each operculum against the side ofthe mouth of the fish. Each operculum in this case acts as a valve toensure that water enters only through the mouth. The mouth thencloses and muscles raise the floor of the mouth cavity.
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2.12: Movement of water over gillsWhen all this is happening, the higher external pressurepresses the flexible free edge of each operculum against the side ofthe mouth of the fish. Each operculum in this case acts as a valve toensure that water enters only through the mouth. The mouth thencloses and muscles raise the floor of the mouth cavity. This forcesthe remaining water in the mouth to flow towards the gill chamber. Water entering the mouth has a higher concentration of oxygenthan in the gill filaments. Due to this difference, oxygen diffusesfrom water flowing over the gills into the blood through the thinwalls of the blood capillaries. The oxygen absorbed then combineswith haemoglobin in the blood of the fish and is then transported toall parts of the body. On the other hand the carbon IV oxideconcentration in the blood capillaries of the gill filaments is higherthan that in water. This difference causes carbon IV oxide todiffuse out of the blood into the flowing water through the walls ofthe blood capillaries. To facilitate maximum gaseous exchange between the waterflowing over the gills and the blood in the gills, a steepconcentration gradient must be maintained across the respiratorysurface. For this reason, water and blood flow in opposite directionswithin the respiratory surface. This is the counter-current flowsystem. As the movement of blood and water continues in oppositedirections within the respiratory surface, oxygen diffuses out of thewater into the blood and carbon IV oxide from blood into water. By the time the blood leaves the respiratory surface, it has as muchoxygen as the water. This is so because as water moves along, lessand less oxygen diffuses out of it as blood becomes more and moreconcentrated with oxygen. See figure 2.13.Fig. 2.14. The counter current flow system across the gillsPractical Activity 4To examine the structure of a gillRequirementsFresh fish, scissors or scalpel, water in a beaker and handlens microscope. Procedure1. With a pair of scissors or scalpel cut out the operculum at thebase where it is attached to the body wall.2. Using the same pair of scissors or scalpel cut out a complete gillfrom the gill chamber.3. Put the gill in water.4. Observe and draw a complete gill. 5.
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Put the gill in water.4. Observe and draw a complete gill. 5. Examine a gill filament using a hand lens or under the lowpower of a microscope. Study Questions9. Draw the structure of the gill filament from the observations youmade in practical activity 4.10. Suggest how the total surface area of the gills in a fish can beestimated. State the significance of a large surface area of thegills to the fish.11. How is the gill of a fish adapted to its function?Mechanisms of Gaseous Exchange inAmphibiansAmphibians by nature live on both land and in water. This doublehabitation calls for special adaptation in gaseous exchange. Theyachieve this by employing the listed methods of gaseous exchange. These are:1. Gaseous exchange through lining of the buccal cavity.2. Gaseous exchange through the lungs.3. Gaseous exchange through the skin. Since the amphibians have neither ribs nor diaphragm, themechanisms which causes ventilation cannot be the same as thosein mammals. Air is therefore forced into and out of the lungs by theaction of the mouth. The example of frog is used in this section as arepresentative of the amphibians. Buccal Mouth CavityAir is taken or expelled from the mouth cavity by raising andlowering the floor of the mouth. The lining of the mouth cavity ismoist and oxygen from the air dissolves in it. Under the linings ofthe mouth, there is a rich supply of blood capillaries and oxygendiffuses into the blood and is carried by haemoglobin to all parts ofthe body. Carbon IV oxide from the tissues is brought by the bloodto the mouth cavity where it diffuses out. The LungsThe lungs lie in the body cavity of the amphibian. When the nostrilsare closed, the air can be forced into the lungs by the pumpingaction of the floor of the mouth. The air reaches the alveoli sacs ofthe lungs that are well supplied with blood through a large networkof blood capillaries. The oxygen in the air dissolves into the moistinner lining of the alveoli. It then diffuses into the blood across thewall of the capillaries, combines with haemoglobin in the red bloodcells and is transported to all parts of the body.
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The air reaches the alveoli sacs ofthe lungs that are well supplied with blood through a large networkof blood capillaries. The oxygen in the air dissolves into the moistinner lining of the alveoli. It then diffuses into the blood across thewall of the capillaries, combines with haemoglobin in the red bloodcells and is transported to all parts of the body. The carbon IV oxide from the tissues is carried by the blood and diffuses into thealveoli, then pumped out by the pumping action of the mouthcavity. The SkinFrogs have a thinner and moist skin than the toads. Beneath theskin is a large network of blood capillaries. Oxygen from the air andfrom the water diffuses through the skin into the blood stream. Onthe other hand carbon IV oxide in the blood diffuses out of theblood capillaries through the moist skin into the surrounding waterand air. Toads do not use the skin surface for gaseous exchangenormally except when they are hibernating. See figure 2.15.Fig.2.15: The surfaces of gasesous exchange in frogMechanisms of Gaseous Exchange inMammalsBreathing system in mammals consists of the following structures:lungs, trachea, chest cavity made of ribs and intercostal muscles,diaphragm and nostrils or nose as shown in figure 2.16 on page 60.The human being is used as a representative of mammals. NoseThe nose has two openings called nostrils which let in air into theair passages. As air moves in the passages, it is warmed andmoistened. The lining of nasal cavity of the nose also houses thesense organs for smell. The LarynxThe larynx is also the voice box. It is located on top of the trachea. Its muscle fibres and the vocal cords control the pitch of the voice. TracheaThe trachea is a tube made up of rings of cartilage which ensurethat it does not collapse during breathing. The lumens of thetrachea are lined with ciliated epithelium. The cilia beat in wavesand move the mucus and foreign particles towards the pharynxaway from the lungs. As the trachea enters the lungs, it divides intotwo branches called bronchi singular bronchus .LungsLungs are found in the chest cavity.
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The lumens of thetrachea are lined with ciliated epithelium. The cilia beat in wavesand move the mucus and foreign particles towards the pharynxaway from the lungs. As the trachea enters the lungs, it divides intotwo branches called bronchi singular bronchus .LungsLungs are found in the chest cavity. They are enclosed in a doublemembrane known as pleural membrane. One part of the membraneadheres tightly to the lungs and the other covers the inside of thethoracic cavity. The space between these membranes is known asthe pleural cavity. It is filled with pleural fluid which reduces frictionand therefore make the lungs move freely in the chest cavity duringbreathing. Fig. 2.16: The structure of the lung of a human beingWithin the lungs, each bronchus divides into small tubes calledbronchioles. The bronchioles branch and terminate in groups of tinyair sacs called alveoli singular alveolus hence the spongy nature ofthe lungs. The alveolus is covered by a fine network of bloodcapillaries as shown in figure 2.16 c on page 60.Practical Activity 5To display the respiratory system of a mammalRequirementsFreshly killed rats or rabbits , dissecting board or tray, dissectingpins, scissors, scalpels, forceps, hand lens, cotton wool, water anddrinking straw. Procedure1. Dissect the mammal using the procedure in the dissecting guideand display the following: i trachea ii rib cage iii the bronchi iv the lungs v diaphragm. Study Questions12. Connect the straw to the trachea of the animal in practicalactivity 5 and carefully blow air into the trachea, notice whathappens to the lungs. Count the number of lobes on the lungs and note the number inyour note book.13. Draw and label the respiratory system of the animal in thedissection. The Mechanism of BreathingBreathing is accomplished by changes in volume and air pressure ofthe thoracic cavity. The thoracic cavity is enclosed by ribs which areattached to the vertebral column at the back and sternum in front. The ribs are covered by intercostal muscles, and below the cavity isthe diaphragm.
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Connect the straw to the trachea of the animal in practicalactivity 5 and carefully blow air into the trachea, notice whathappens to the lungs. Count the number of lobes on the lungs and note the number inyour note book.13. Draw and label the respiratory system of the animal in thedissection. The Mechanism of BreathingBreathing is accomplished by changes in volume and air pressure ofthe thoracic cavity. The thoracic cavity is enclosed by ribs which areattached to the vertebral column at the back and sternum in front. The ribs are covered by intercostal muscles, and below the cavity isthe diaphragm. The diaphragm is a muscular sheet of tissueextending across the floor of the cavity between the thoracic cavityand abdomen. It curves upwards to form a dome shape. Breathing mechanism involves two processes: inspiration inhalation , and expiration exhalation . Inspiration is breathing in,and expiration is breathing out. These two processes are broughtabout by movement of the ribs and diaphragm. See figure 2.17 onpage 62.Inspiration InhalationThis process occurs when the thoracic cavity increases in volumeand therefore decreases in pressure. A number of movements areinvolved during the enlargement of the thoracic cavity. Duringinspiration the external intercostal muscles contract while theinternal intercostal muscles relax. This movement pulls the ribsupwards and outwards. The diaphragm, which is domeshapedflattens by the contraction of its muscles. The flattening of thediaphragm together with the outward movement of the ribsincreases the volume of the thoracic cavity and decreases thepressure inside it. Atmospheric pressure being higher than pressureinside the thoracic cavity, forces air to rush into the lungs throughthe nose and trachea hence inflating the lungs. Figure 2.17 a summarises these movements. Expiration ExhalationThis process occurs when the volume of the thoracic cavitydecreases and the pressure inside it increases. This is broughtabout by the following: the external intercostal muscles relax whilethe internal intercostal muscles contract bringing the ribs down totheir original position. At the same time the muscles of thediaphragm relax and it regains its original shape. These movementsdecrease the volume of the thoracic cavity and increase thepressure inside it. Thus air is forced out of the lungs through the airpassages into the atmosphere.
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At the same time the muscles of thediaphragm relax and it regains its original shape. These movementsdecrease the volume of the thoracic cavity and increase thepressure inside it. Thus air is forced out of the lungs through the airpassages into the atmosphere. See figure 2.17 b for the summary. Epee, tomes nt nee Diopeagmrcine ondrenrs to donehapa dacs lame of orsDiaplesgnflaened crease line of raeFig. 2.17: Movement of ribs during breathingPractical Activity 6 a To investigate the movement of the lungs and diaphragm ina model thoracic cavityRequirementsTwo balloons, bell jar, rubber stopper with a hole, y-shapedconnector and rubber sheet. Procedure1. Set up the apparatus as shown in figure 2.18.Fig. 2.18: To investigate the rib action during breathing using a model2. Pull down the rubber sheet at the base of the bell jar.3. Observe what happens to the balloons.4. Release the rubber sheet slowly and observe what happens tothe balloons. Study Question14. In what ways is this model similar or dissimilar to the working ofthe thorax of a living mammal?Practical Activity 6 b To investigate the rib action during breathing using a modelRequirementsPieces of timber hardboard, nails and a string. Procedure1. Loosely join up the pieces of timber as in figure 2.19. Ensurethat there is free movement where the timbers are joined. Fig. 2.19: Model illustrating the action intercostals muscle in moving ribs2. Tie pieces of string A and B at points X and X1 respectively.3. Make corresponding holes Y and Y1 on the cross timbers ribs so that the string can move at Y or Y1 when moved.4. Pull down string A at O1.5. Notice what happens to the ribs and the sternum.6. Now pull up string B at O1.7. Notice what happens to the ribs and the sternum.8. Record and explain the above observation. Exchange of Gases in the AlveolusThe alveoli and the blood capillaries are made of very thin walls. The wall of the alveolus is covered by a film of moisture whichdissolves oxygen in the inhaled air.
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Notice what happens to the ribs and the sternum.8. Record and explain the above observation. Exchange of Gases in the AlveolusThe alveoli and the blood capillaries are made of very thin walls. The wall of the alveolus is covered by a film of moisture whichdissolves oxygen in the inhaled air. Since oxygen concentration inthe blood is lower than in the alveolus, it diffuses through theepithelium, the capillary wall, the plasma and into the red bloodcells where it combines with haemoglobin. Carbon IV oxide in thecapillaries surrounding the alveoli is at a higher concentration thaninside the alveoli. Hence it diffuses into the alveoli. See figure 2.20.Water vapour passes out of the blood by the same process. Table2.2 shows the estimated percentage of different gases in inhaledand exhaled air. Table 2.2: Percentage composition of gases in inhaled andexhaled airGas in inhaled air in exhaled airOxygen2016.9Carbon IV dioxide0.034.0Nitrogen and other gases79.9779.97Regulation of BreathingBreathing movements normally take place unconsciously. In thebrain there is a region called medulla oblongata which controlsbreathing movements. As the carbon IV oxide in the bloodreaches this region it triggers this part of the brain to send impulsesto the rib muscles and the diaphragm, which in turn respondappropriately. This makes breathing to continue on and on. Fig. 2.20: Gaseous exchange in the alveolusDuring vigorous activity the concentration of carbon IV oxideincreases in the body tissues. As a result of this, more carbon IV oxide diffuses into the blood and reaches the medulla oblongata. The high concentration of carbon IV oxide in blood triggers themedulla oblongata to increase the rate of breathing. Increased rateof breathing helps to increase the amount of oxygen in the bloodthereby meeting the demands of the increased tissue respiration. Factors affecting the rate of breathing inhumans1. ExerciseDuring vigorous physical activity the rate of breathing increases soas to meet the increased oxygen demand. Faster breathing alsoeliminates the extra carbon IV oxide produced by increasedrespiration.2. AgeYounger people have a higher demand for oxygen.
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ExerciseDuring vigorous physical activity the rate of breathing increases soas to meet the increased oxygen demand. Faster breathing alsoeliminates the extra carbon IV oxide produced by increasedrespiration.2. AgeYounger people have a higher demand for oxygen. They thereforehave faster breathing rate.3. EmotionsGenerally the body emotions affect the production of hormoneadrenaline which increases the general metabolism and henceincreased rate of breathing. Examples include fear, anxiety andfright.4. TemperatureGenerally when the temperature is high there is a tendency in therate of gaseous exchange to increase. However, if the temperatureis too high the breathing rate will reduce.5. HealthOne effect of illness is fever. The temperature of the body tends toincrease hence increased metabolic rate, which leads to higher rateof breathing. Some respiratory diseases block the respiratory tractmaking breathing difficult. Study Question15. Suggest how altitude may affect the rate of breathing. Lung volumesLungs of an adult can hold approximately 5 500 cm3 of air whencompletely filled. This volume is known as lung capacity. Howeverthis volume is not reached normally. During normal breathing, asmall volume of air about 500 cm3 is taken in and out of the lungs. This volume of air is referred to as the tidal volume. A person is capable of having a forced inhalation in addition tothe tidal volume. This additional volume is called inspiratoryreserve volume and reaches about 2 000 cm3. The tidal volumeplus inspiratory reserve volume forms what is referred to asinspiratory capacity. After normal exhalation, it is possible toforce out extra volume of air. This volume is referred to asexpiratory reserve volume and can be up to 1 300 cm3. It is alsopossible to have the deepest possible exhalation. Such a volume ofair, which can only be forcibly pushed out of the lungs, is called thevital capacity. However, it is not possible to force all air out of the lungs evenafter the deepest exhalation. The air that normally remains in lungsis referred to as the residual volume and is about 1 500 cm3. Seefigure 2.21 for a graphical representation. Fig. 2.21: Lung volumes in a human beingPractical Activity 7Effect of exercise on the rate of breathingRequirementsStop watch wrist watch. Procedure1.
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The air that normally remains in lungsis referred to as the residual volume and is about 1 500 cm3. Seefigure 2.21 for a graphical representation. Fig. 2.21: Lung volumes in a human beingPractical Activity 7Effect of exercise on the rate of breathingRequirementsStop watch wrist watch. Procedure1. Pair up, one of you to be the subject and the other to record.2. When the subject is relaxed and breathing normally, the partnerwill count the number of inhalations per minute.3. Repeat this for a period of three minutes and record in table2.3.4. The subject should run around the laboratory and come back tothe laboratory. Count the number of inhalations as before. Table 2.3: Effect of exercise on breathing InhalationsTime min Before exercise 1After exercise 2 3Study Question16. From your results explain the effect of exercise on the rate ofbreathing. Practical Activity 8To compare the amount of carbon IV oxide in the inhaledand the exhaled airRequirementsTest-tubes, glass tubing, rubber tubing, corks, a T-shaped connectorand calcium hydroxide solution. Procedure1. Set up the apparatus as shown in figure 2.22.2. Controlling the breath, slowly breathe out through the mouthinto the mouth piece several times.3. Notice what happens to the solution in test-tubes A and B.4. Now breathe in slowly through the mouth by sucking in from thetest-tubes A and B.5. Notice what happens to the solution in test-tubes A and B.Study Question17. Explain the changes in calcium hydroxide solution in the testtubes in practical activity 8.Diseases of the Respiratory SystemRespiratory diseases are those which affect the breathing structuresand make gaseous exchange in animals difficult. They include:1. AsthmaAsthma is a common respiratory disease caused by: i Allergy to the respiratory structure due to pollen grains,atmospheric dust, animal s fur, scents from certain drugs, foodsand flowers. Fig. 2.22: Set-up for comparing amounts of carbon dioxide taken in and out ii Lung or bronchial infections by bacteria or viruses.
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AsthmaAsthma is a common respiratory disease caused by: i Allergy to the respiratory structure due to pollen grains,atmospheric dust, animal s fur, scents from certain drugs, foodsand flowers. Fig. 2.22: Set-up for comparing amounts of carbon dioxide taken in and out ii Lung or bronchial infections by bacteria or viruses. Therespiratory problem comes in form of attacks which are mild orsevere. When the weather is cloudy and chilly, or exposure to the causativeagents listed in i above, the attacks are more frequent. Thepatient may have difficulty in breathing because of the constrictionof air channels caused by muscular contractions. The patient,therefore, produces a characteristic wheezing sound accompaniedby the feeling of suffocation. Treatment and ControlTreatment and control of asthma consist of: i The spraying of a muscle-relaxant directly into the bronchialtubes. Ii Injection of drugs or oral application of pills prescribed by ahealth physician. Iii Avoiding the causative agents.2. BronchitisThis is an inflamation of the bronchial tubes. There are two types ofbronchitis, namely; acute bronchitis and chronic bronchitis. A Acute bronchitisThis is widespread illness in children and frail adults. It is causedby: i A complication of the common cold when one is exposed tolow temperatures especially in high attitudes. It results into thechilling of the body, giving way to bacterial infection. Ii A complication resulting from a previous disease attack forexample measles, dengue, whooping cough and influenza. Theclinical symptoms include: headache, mild fever and coughingthat are accompanied by uncomfortable feelings behind thesternum. The illness may clear in a few days or may persist forseveral months. B Chronic BronchitisChronic bronchitis develops after several repeated attacks of acutebronchitis. It is a fatal condition which makes the sufferer disabledand unfit to work. Its symptoms are: i Production of phlegm thick sputum that is greenish oryellow in colour due to pus from respiratory surface. Ii The patient has difficulty in breathing and finds it difficult towalk or sleep unless propped up in bed to ensure that thebronchial tubes are not clogged. Treatment and ControlPatients should seek early medical assistance when the illness isstill in its early stage.3.
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Theclinical symptoms include: headache, mild fever and coughingthat are accompanied by uncomfortable feelings behind thesternum. The illness may clear in a few days or may persist forseveral months. B Chronic BronchitisChronic bronchitis develops after several repeated attacks of acutebronchitis. It is a fatal condition which makes the sufferer disabledand unfit to work. Its symptoms are: i Production of phlegm thick sputum that is greenish oryellow in colour due to pus from respiratory surface. Ii The patient has difficulty in breathing and finds it difficult towalk or sleep unless propped up in bed to ensure that thebronchial tubes are not clogged. Treatment and ControlPatients should seek early medical assistance when the illness isstill in its early stage.3. Whooping CoughWhooping cough results from acute infection of the respiratory tractby a bacterium called Bordetella pertussis. The disease is endemicin Kenya. The symptoms are: i Prolonged coughing and vomiting. Ii Conjunctival haemorrhage accompanied by peri-orbitaloedema. Iii Severe bronchopneumonia. Iv Convulsions and coma. V Ulcers and cardiac failure or complications. Vi Malnutrition signs for protein and energy deficiency due torepeated vomiting with difficulty in feeding. Treatment i Complicated cases should be admitted to hospital forspecialised care and administration of antibiotics. Ii Patients should be fed on a balanced diet. Control: Children should be immunised at an early age.4. PneumoniaPneumonia is an inflammation of the lungs by micro-organisms. There are several types of pneumonia caused by different bacteria. Common ones include: i Lobar pneumonia caused by attacks of Streptococcuspneumoniae. Symptoms of attack of pneumonia occur after a short incubationperiod followed by: a coughing b fevers c chest pains and d deposits of fluid in the lungs. The invasion proceeds from the throat spreading to other parts ofthe body. This sets on when the patient s body is completelyweakened. TreatmentThe patient should use antibiotics which include penicillin andsulphonamides. Control i Avoid overcrowded places. Ii Provide good ventilation in living premises.5. Pulmonary TuberculosisTuberculosis is a respiratory disease caused by a bacterium calledMycobacterium tuberculosis.
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This sets on when the patient s body is completelyweakened. TreatmentThe patient should use antibiotics which include penicillin andsulphonamides. Control i Avoid overcrowded places. Ii Provide good ventilation in living premises.5. Pulmonary TuberculosisTuberculosis is a respiratory disease caused by a bacterium calledMycobacterium tuberculosis. It is airborne, but occasionally it isspread through infected cow s milk or other fluids taken as a meal. The symptoms include: i General weight loss. Ii Coughing, sometimes with sputum containing blood. Iii Slight afternoon fever. The bacterium destroys lung tissues making it hard for the patientto breathe. It may eventually result into death. Treatment involves use of antibiotics especially, streptomycin. Control i Detection of the disease in its early stages by radiographicalmethod. Ii Pasteurisation of milk. Iii Vaccination of the population using BCG Bacille CalmetteGuerin .6. Lung CancerCancer is an uncontrolled cell growth in the body resulting intotissue tumour or enlargement. The tumour can be benign whichaffects cells at a single point or malignant when affected cellsbreak away and spread to other parts of the body .There are no specific causes for lung cancer but it may resultfrom: i Smoking, in which the mucal walls of the bronchial tubes areblocked with deposits of tar from the cigarette smoke. Tarcontains cancer-causing carcinogenic substances that cantrigger uncontrollable growth of the lung cells. Ii Inhalation of cancer-causing substances such as asbestos dustsor exposure to: a radiation e.g. X-ray, gamma rays, cosmic rays. B Radio-active substances e.g.
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The tumour can be benign whichaffects cells at a single point or malignant when affected cellsbreak away and spread to other parts of the body .There are no specific causes for lung cancer but it may resultfrom: i Smoking, in which the mucal walls of the bronchial tubes areblocked with deposits of tar from the cigarette smoke. Tarcontains cancer-causing carcinogenic substances that cantrigger uncontrollable growth of the lung cells. Ii Inhalation of cancer-causing substances such as asbestos dustsor exposure to: a radiation e.g. X-ray, gamma rays, cosmic rays. B Radio-active substances e.g. uranium. C Substances that alter the genetic composition of a cell e.g.mustard gas, sulphur dioxide used as a preservative infoodstuff. Lung cancer destroys the lung cells and tissues and as a result thisinterferes with free exchange of respiratory gases, which mayeventually lead to death. TreatmentThis involves: i Surgery to remove the tumour. Ii Radiotherapy to destroy cancerous cells. Iii Chemotherapy to relieve the patient of pain and to destroy thecancer cells. Iv The combination of several drugs each toxic to cancer cellsenhances the treatment programme i and ii above. V By not smoking actively and passively and in foodpreservatives. Study Question18. Suggest how too much dust particles may affect therespiratory system. Revision Questions1. What is meant by the term gaseous exchange? Name the gasesexchanged. 2. Explain why the respiratory surface has to be: a thin, b moist.3. Explain how the following are adapted to their functions. A Guard cell. B Aerenchyma tissue.4. List the environmental factors influencing the opening andclosing of stomata.5. State the advantages and disadvantages of having stomata oneither side of the leaves.6.
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Explain how the following are adapted to their functions. A Guard cell. B Aerenchyma tissue.4. List the environmental factors influencing the opening andclosing of stomata.5. State the advantages and disadvantages of having stomata oneither side of the leaves.6. Samples of atmosphere and exhaled air were analysed by fourgroups of students for oxygen and carbon IV oxide content. The following are the results, expressed in volumes perthousand. I Amount of oxygen in atmosphere 200. Ii Amount of oxygen in exhaled air 160. Iii Amount of carbon IV oxide in atmosphere 300. Iv Amount of carbon IV oxide in exhaled air 41.Explain the difference in volume of each gas between theatmosphere and the exhaled air.7. For each of the following animals, name the structures whichare the sites of gaseous exchange during breathing in: a Mammals, amphibians, and insects. B Explain the significance of branching of the tracheal systeminto fine tubes in an insect.8. A Compare the mechanism of gaseous exchange in an insectand a mammal. B Explain why a fish has to pass large amounts of watercontinuously over its gills during gaseous exchange.9. In an experiment to analyse a sample of air, a J-tube was usedto find out the amount of carbon IV oxide and oxygen in thesample. The length of the sample air in the J-tube was 8 cm andafter mixing it with some sodium hydroxide solution for someminutes, the length was reduced to 7.6 cm. When pyrogallic acidwas also made to mix with the sample of air for some minutes,the length reduced further to 6.6 cm. A What was the percentage of: i Oxygen? Ii Carbon IV oxide in the air sample? Show yourworking. B Explain the role of sodium hydroxide solution and pyrogallicacid in the experiment.10. In insects, a rare disease has been found to attack therespiratory system. Name the parts of an insect which are mostlikely to be damaged by the disease. Give a reason for youranswer.11.
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In insects, a rare disease has been found to attack therespiratory system. Name the parts of an insect which are mostlikely to be damaged by the disease. Give a reason for youranswer.11. The following are events which take place during expiration in amammal. I The diaphragm and intercostal muscles relax. Ii The diaphragm returns to its original dome-shape. Iii The rib cage moves inwards. Iv The pressure in the thoracic cavity increases. A List the correct sequence of events which take place duringexpiration. B Explain what would happen to breathing in a mammal ifthe intercostal muscles were damaged by a disease.12. Figure 2.23 is intended to show a respiratory surface forgaseous exchange in a mammal. Suggest the corrections thatshould be made to the diagram before gaseous exchange cantake place. Fig. 2.2313. Figure 2.24 is an experiment set up to investigate gaseousexchange in living organisms. After every ten minutes each test-tube was gently shaken. A Name the test-tubes in which there will be a colour change. B Suggest the test-tube in which the indicator would changecolour fastest. Give reasons for your answer.14. A student divided a small air tight box into two chambers with awire mesh. In one chamber he kept a number of rats and in theother a number of potted plants. What was likely to happen ifthe box was placed in the dark for two hours? Explain youranswer.15. The apparatus in figure 2.25 can be used to demonstrate themechanism of breathing in a mammal. Fig. 2.24 a What structures in a mammal are represented by thefollowing: i The rubber balloon? Ii The syringe barrel? Iii The plunger? B If the plunger is pulled away from the balloon, what willhappen to the rubber balloon?Fig. 2.2516. In an experiment, the rate of gaseous exchange wasdetermined and recorded as shown in the table below. Usingthese figures, suggest which plant gaseous exchange structureswere responsible for these observed figures. Table 2.24StructureGaseous exchange in AApproximately 97BApproximately 2.5CApproximately 0.517.
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2.2516. In an experiment, the rate of gaseous exchange wasdetermined and recorded as shown in the table below. Usingthese figures, suggest which plant gaseous exchange structureswere responsible for these observed figures. Table 2.24StructureGaseous exchange in AApproximately 97BApproximately 2.5CApproximately 0.517. In the year 2003 a new disease called Severe Acute RespiratorySyndrome SARS emerged in China and within a short period oftime, it had killed people in Europe, America, Canada and Africa. It is mainly transmitted through air. I Name the organs that are likely to be infected. Ii What would be the easiest way of preventing the spread ofthe disease from one person to the other or country tocountry? CHAPTER THREERespiration3.1 IntroductionRespiration is the process by which food substances are chemicallybroken down in all living cells to release energy, carbon IV oxide,water or alcohol. Respiration takes place slowly and is controlled bymany different types of respiratory enzymes so that energy isproduced continuously and in small amounts. Respiration should not be confused with gaseous exchange. Notethat whereas respiration is a chemical process taking place insidetissue cells, gaseous exchange is a purely physical process whichtakes place at respiration surfaces. The term respiration asdescribed in this chapter is sometimes referred to as tissuerespiration or internal respiration. Practical Activity 1To investigate what gas is given off when food is burntRequirementsAny of the following foods starch powder, crushed beans, maizeflour, milk powder .Test-tubes, calcium hydroxide solution, rubber stopper, anhydrouscobalt chloride paper, source of heat, delivery tube and retort stand. Procedure1. Place some food sample in a dry test-tube and insert a oneholed rubber stopper into the mouth of the test-tube.2. Hold the test-tube containing the food sample horizontally. 3. Pour a little calcium hydroxide solution into another test-tubeand support it.4. Using a delivery tube connect the two test-tubes ensuring thatthe free end of the delivery tube into the calcium hydroxide asillustrated in figure 3.1.Fig. 3.1: Set-up for investigating the gas given off when food is burnt5.
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Pour a little calcium hydroxide solution into another test-tubeand support it.4. Using a delivery tube connect the two test-tubes ensuring thatthe free end of the delivery tube into the calcium hydroxide asillustrated in figure 3.1.Fig. 3.1: Set-up for investigating the gas given off when food is burnt5. Heat the test-tube containing the food sample strongly.6. Observe and record what happens to the food sample, calciumhydroxide solution and the upper sides of the test-tube with thefood sample.7. Disconnect the apparatus and rub anhydrous cobalt II chloridepaper on the inner upper side of the test-tube containing thefood sample.8. Record the colour change observed on the cobalt II chloridepaper. Study Question1. What conclusion can you draw from the above results ofpractical activity 1?Significance of RespirationAll living organisms require energy all the time. The energy isobtained from food substances which are either taken in ormanufactured during photosynthesis. Examples of foods which canprovide large amounts of energy are carbohydrates like starch andglucose and fats. The energy derived from these food substancesas a result of respiration is used for such activities as muscularcontraction, conduction of nerve impulses, secretion of enzymes,growth, repair of worn out tissues, functioning of body organs suchas kidneys, heart and brain. However, some of the energy is alsolost in form of heat. Tissue respiration takes place mainly in cell organelles calledmitochondria. Structure and Function of a mitochondrionFig. 3.2: The structure of the mitochondrionMitochondria are small round or rod shaped cell organelles found incells and provide sites for respiratory activity. Living cells such asthe kidney cells, the flight muscle of insects and birds, the spermcells and muscle cells have high energy requirements andconsequently possess large numbers of mitochondria. The structure of mitochondria is shown in figure 3.2. It has twomembranes, the outer and inner membranes that are separated byfluid filled spaces. The inner membrane folds into projections insidethe matrix called cristae. The cristae provide a large surface areafor respiratory activities.
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It has twomembranes, the outer and inner membranes that are separated byfluid filled spaces. The inner membrane folds into projections insidethe matrix called cristae. The cristae provide a large surface areafor respiratory activities. Enzymes are bound to the cristae. Types of RespirationThere are two types of respiration namely aerobic and anaerobic. Aerobic RespirationAerobic respiration is the process in which food substances such asglucose are broken down in the presence of oxygen in tissue cells torelease energy, water and carbon IV oxide. The total energyreleased at the end of respiration oxidation is very high. If all theenergy were released at once in the form of heat, it would burn thebody cells. To protect the cells from burning the heat energy isreleased in small quantities in stages. This energy is used to bring about a chemical reaction in whicha compound in the cell called adenosine diphosphate ADP combines with an inorganic phosphate molecule to form anothercompound called adenosine triphosphate ATP . This reaction issummarised as follows:The following equation summarises the process of aerobicrespiration in plants and animals. Molecules of adenosine trisphosphate ATP store the energyreleased in respiration in their bonds and avails it to cells readilywhen required. The chemical equation as represented above gives the falseimpression that respiration involves only one chemical reaction. Thewhole process in fact involves a series of many reactions. A specificenzyme catalyses each of these reactions. In broad terms,respiration takes place in two major phases and each phase consistof a series of reactions. First phaseThe earliest stages of respiration take place without using oxygen. These stages involves a series of chemical reactions which occur inthe cytoplasm of the cell. A compound with a three-carbon moleculecalled pyruvic acid is formed from glucose. The breakdown ofglucose is called glycolysis. What happens after pyruvic acid isformed depends on whether oxygen is available for use or not. Ifoxygen is not supplied to the cell, then pyruvic acid is then partiallybroken down to lactic acid in animals or to ethyl alcohol ethanol and carbon IV oxide in plants. See chart below. In glycolysis, one molecule of glucose yields two molecules of ATP.Alcohol production occurs in plant tissues and duringfermentation by yeasts and many bacteria.
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What happens after pyruvic acid isformed depends on whether oxygen is available for use or not. Ifoxygen is not supplied to the cell, then pyruvic acid is then partiallybroken down to lactic acid in animals or to ethyl alcohol ethanol and carbon IV oxide in plants. See chart below. In glycolysis, one molecule of glucose yields two molecules of ATP.Alcohol production occurs in plant tissues and duringfermentation by yeasts and many bacteria. The alcohol accumulatesin these organisms provided oxygen is excluded. Second phaseThis phase takes place in the matrix of the mitochondria. It involvesa series of enzymecontrolled reactions that require oxygen. Thepyruvic acid formed in the first phase is further oxidised by oxygenin a series of enzymatic reactions Kreb s cycle into carbon IV oxide, energy and water as the end products. In this reaction shown above, one molecule of glucose yields 38molecules of ATP.For the above process to be maintained in the living cells, thefollowing conditions are necessary: The cells must be provided with glucose or food. Oxygen must be taken in and react with the glucose. There must be respiratory enzymes to catalyse the reaction. Favourable temperature should be maintained for efficientenzyme functioning. The end products of the reaction i.e. carbon IV oxide, waterand energy must be constantly removed from the mitochondrion. Practical Activity 2To investigate production of heat by germinating seedsRequirementsBoiled bean seeds, soaked bean seeds, vacuum flasks, cotton wooland two thermometers, 10 formalin methanol and retort stand. Procedure1. Soak the seeds for 24 hours and then divide them into twoequal portions.2. Boil one portion of seeds for ten minutes, let them cool andwash them in 10 per cent formalin.3. Fill one vacuum flask with fresh not boiled seeds and the otherone with boiled seeds.4. Place a thermometer in each flask such that the bulb issurrounded by seeds. 5. Hold each thermometer with cotton wool as shown in figure 3.3and record the initial temperature.6. Record the temperature every morning and evening for a week. Fig. 3.3: Set-up for investigating production of heat by germinating seedsStudy Questions2. What does production of heat in the germinating beans imply?3.
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Record the temperature every morning and evening for a week. Fig. 3.3: Set-up for investigating production of heat by germinating seedsStudy Questions2. What does production of heat in the germinating beans imply?3. Explain by what process the heat in i above is produced. Anaerobic Respiration in Plants and AnimalsAnaerobic respiration is the process by which food substances suchas glucose are broken down without using oxygen. It takes place inthe cytoplasm. The glucose is not broken down completely intocarbon IV oxide and water to release energy, as is the case ofaerobic respiration. Instead, an intermediate compound, alcohol inplants and lactic acid in animals, is produced. The incompletebreakdown of glucose result into production of less energy than incase of aerobic respiration breakdown of glucose is complete. Theprocess of anaerobic respiration is summarised as shown below. In the absence of oxygen, most plant and animal tissues can respireanaerobically for a limited period. It is essential, however, that theyget rid of the end products lactic acid in animals and in plantsethanol and carbon IV oxide immediately. This is because theseend products become toxic to the organism if they are left toaccumulate within the cells. Anaerobic respiration that results in the accumulation of alcoholis referred to as fermentation. Fermentation occurs when bacteriaor yeast break down simple sugars into energy, carbon IV oxideand alcohol. Some bacteria break down alcohol into ethanoic acidthrough anaerobic respiration. Similarly the break down of sugar inmilk by bacteria results in the production of energy and lactic acidwhich causes milk to become sour. Oxygen Debt This is the oxygen required to get rid of the lactic acid thataccumulates in the body tissues when the supply of oxygen is lessthan the demand. Under these conditions, the animal tissues respirethrough anaerobic respiration and this causes lactic acid toaccumulate in the muscles. The lactic acid might cause fatigue andresult in muscle crumps. Another example of anaerobic respirationin animals is when a short distance runner or diver holds his or herbreath while running or diving. The oxygen debt incurred here is paid back by the person breathing more quickly and more deeplyin order to increase the supply of oxygen during the recovery periodafter the race. Figure 3.4 shows a panting athelete.
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Another example of anaerobic respirationin animals is when a short distance runner or diver holds his or herbreath while running or diving. The oxygen debt incurred here is paid back by the person breathing more quickly and more deeplyin order to increase the supply of oxygen during the recovery periodafter the race. Figure 3.4 shows a panting athelete. Fig. 3.4: Oxygen debt in a panting athleteDuring the process of paying back the oxygen debt, the lacticacid is oxidised to carbon IV oxide, water and energy whenoxygen is available or it is taken to the liver and converted intoglycogen. Application of Anaerobic Respiration inIndustries and at homeMan has applied the knowledge of anaerobic respiration in hiseveryday life for a long time with limited understanding of thephysiology of the process. Products of fermentation such as alcohol,wines, yoghurt and cheese are some of the examples. In Kenya,bread baking industry uses yeast and so is the beer brewing anddistillery industry. Power alcohol used as a substitute for petrol isproduced through fermentation. The production of vinegar ethanoicacid citric acid, oxalic acid, butyric acids and some drugs alsodepends on fermentation. These chemicals are of great commercialvalue. The type of alcoholic drink produced by fermentationdepends largely on the nature of the sugar solution used. Forexample, fermentation of apple juice produces cider, grape juiceproduces wine, and malt extract from germinating barley producesbeer. Distillation of some of the products of fermentation gives riseto stronger alcoholic drinks called spirits. For example, distillingwine makes brandy. Other applications of anaerobic respiration include biogasproduction for cooking, lighting and making of compost manure. Practical Activity 3To investigate the gas produced during fermentationRequirementsBoiling tube, measuring cylinder, test-tubes, thermometer, deliverytube, rubber stopper, 10 glucose solution, yeast, kerosene oil,retort stand and means of heating. Procedure1. Boil about 20 cm3 of glucose in a tube, cool to 40 OC add someyeast.2. Pour onto the glucose and yeast suspension some kerosene oil.3. Leave this for about one hour.4.
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Boil about 20 cm3 of glucose in a tube, cool to 40 OC add someyeast.2. Pour onto the glucose and yeast suspension some kerosene oil.3. Leave this for about one hour.4. Put some calcium hydroxide in test-tube connect this test-tubeto the boiling tube using the delivery tube and rubber stopper. See figure 3.5. Fig. 3.5: FermentationStudy Questions4. Record the changes that occur in the calcium hydroxide and inthe boiling tube.5. What gas is produced?Aerobic and anaerobic respiration are similar because they bothproduce energy. However, they have various differences as shown intable 2.1.Comparison Between Aerobic and AnaerobicAerobic RespirationAnaerobic Respiration i Oxygen is necessary forthe process to take place. The use of oxygen ensuresa complete combustion oroxidation of the substrate. I Oxygen is not requiredhence the substrate is notbroken down completely. Ii High amounts of energyare released hence anefficient way of obtainingenergy. The amount ofenergy released from onemolecule of sugar is 2880KJ. 38 ATP molecules . Ii Low amounts of energyare released hence it is aninefficient method ofobtaining energy. Theamount of energyreleased from onemolecule of sugar is 210KJ. 2ATP molecules . Iii The substrate iscompletely broken down tocarbon IV oxide andwater. Iii The substrate is notcompletely broken downand as a result lactic acidor alcohol is produced. Iv The end products arewater and carbon IV oxide which diffuses out ofthe cells and is excretedbefore it accumulates inthe body to toxic levels. Iv The end products arealcohol in plants and lacticacid in animals. Both ofthese end-products aretoxic to cells accumulatein the body. V Water molecules areproduced. V Water molecules are notproduced. Vi Over a short period oftime, energy is notreleased faster. Vi Over a short period oftime, energy is releasedfaster. Respiratory SubstratesRespiratory substrates are energy-rich food substances which whenoxidised release energy e.g.
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Theamount of energyreleased from onemolecule of sugar is 210KJ. 2ATP molecules . Iii The substrate iscompletely broken down tocarbon IV oxide andwater. Iii The substrate is notcompletely broken downand as a result lactic acidor alcohol is produced. Iv The end products arewater and carbon IV oxide which diffuses out ofthe cells and is excretedbefore it accumulates inthe body to toxic levels. Iv The end products arealcohol in plants and lacticacid in animals. Both ofthese end-products aretoxic to cells accumulatein the body. V Water molecules areproduced. V Water molecules are notproduced. Vi Over a short period oftime, energy is notreleased faster. Vi Over a short period oftime, energy is releasedfaster. Respiratory SubstratesRespiratory substrates are energy-rich food substances which whenoxidised release energy e.g. carbohydrates, fats and proteins. Carbohydrates are the main source of energy in respiration. These are mainly in the form of simple sugars such as glucose,fructose and galactose. They provide about 17 KJ per gram or 2 898KJ Mole when completely oxidised. Whereas plants synthesise their own food substances cellulose, starch and sugars , animals obtain most of these foodsubstances by feeding on plants. Some of the plant organs rich inthese food substances include maize, cassava, rice, fruits, yams,bananas, sweet potatoes, sugar cane and sorghum. Fats produce more energy than carbohydrates or proteins. When one gram of fat is completely oxidised it produces about 38KJ of energy. Plants synthesise fats and oils and store them inseeds, leaves and fruits. Some animals obtain them by feeding onother animals or animal products. Plants that are rich in fats andoils include sesame, groundnuts, sunflower, coconut, cashew nutsand castor oil seeds. Some of the animal products rich in fatsinclude fatty meat, milk, ghee, cheese and butter. Fats are not themain substrates of respiration because they are not very solubleand therefore are not easily transported to the sites of respiration. It will also require more oxygen to oxidise one gram of fat than onegram of glucose. Proteins are not normally used in respiration.
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Plants that are rich in fats andoils include sesame, groundnuts, sunflower, coconut, cashew nutsand castor oil seeds. Some of the animal products rich in fatsinclude fatty meat, milk, ghee, cheese and butter. Fats are not themain substrates of respiration because they are not very solubleand therefore are not easily transported to the sites of respiration. It will also require more oxygen to oxidise one gram of fat than onegram of glucose. Proteins are not normally used in respiration. However, inextreme cases of starvation the cells may use proteins to obtainenergy. Proteins are first broken into amino acids. Amino acids arethen deaminated broken down further and oxidised. One gram ofprotein produces 22 KJ when completely oxidised. Proteins aremainly found in plant leaves, seeds and fruits. Some of the plantsrich in proteins are beans, peas, sunflower, groundnuts, sesame andcashew nuts. Animals obtain proteins by feeding on plants rich inproteins or on other animals or animal products such as lean meat,milk, eggs and cheese. Respiratory Quotient and its SignificanceRespiratory quotient RQ is a ratio showing the relationshipbetween the amount of carbon IV oxide used against the amountof oxygen used in respiration. Where carbohydrates such as sucrose and glucose are completelybroken down to carbon IV oxide, water and energy, the amount ofcarbon IV oxide produced almost balances the amount of oxygenconsumed. In this case of complete aerobic respiration of sugars,the RQ ratio is 1.0.The value of RQ varies with the type of substrates andconditions under which they are respired. RQ can therefore rangefrom less than one to more than one. The respiratory quotients givean indication of the type of substrate oxidised and whether aerobicrespiration, anaerobic respiration or both are taking place. For example, in respiration of fat the RQ is about 0.7. Thiswould mean that the amount of carbon IV oxide produced is lessthan the amount of oxygen used. RQ values for carbohydrates andproteins are 1.0 and 0.9 respectively. A value of less than oneindicates higher consumption of oxygen and lower production ofcarbon IV oxide. This would represent anaerobic respiration inwhich alcohol and carbon IV oxide are produced.
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RQ values for carbohydrates andproteins are 1.0 and 0.9 respectively. A value of less than oneindicates higher consumption of oxygen and lower production ofcarbon IV oxide. This would represent anaerobic respiration inwhich alcohol and carbon IV oxide are produced. Respirationquotient also depends on age, temperature of the surrounding andstate of health of the organism. Factors affecting the rate of respirationFactors that affect the rate of respiration also affect the energyrequirements in organisms. Refer to chapter five of students bookone .Study Question6. State five factors that affect energy requirements in organisms. Other factors include:1. Oxygen ConcentrationRespiration is affected by the amount of oxygen available in thetissues. When the amount of oxygen is low the rate of respirationslows down. When the amount of oxygen is high, the rate ofrespiration increases. In diving animals the oxygen concentration intheir environment is low. Hence, soon after they dive, the cardiacfrequency drastically decreases bradycardia and the arterioles ofall the vital body organs constrict so that oxygen can be deliveredto the vital organs that cannot endure oxygen deprivation e.g. thebrain and the heart. As a result of this, less oxygen reaches other body tissues andorgans hence their respiration rate reduces.2. Substrate concentrationThe primary respiratory substrate in the tissues is sugar. Whensugar concentration increases the rate of respiration also increases. The reverse is also true.3. HormonesCertain hormones in the body such as adrenaline and thyroxine areknown to increase respiratory activities.4. Surface area: Volume ratio Body size The surface area to volume ratio affects the rate of respiration. Ifthe surface area to volume ratio is high, the organism would losemore heat energy. As more energy is lost to the surrounding morewill be required to replace the lost energy hence higher rate ofrespiration. Revision Questions1. A Define the term respiration. B Distinguish between gaseous exchange respiration.2. Explain the significance of respiration in living organisms.3. A What is the role of mitochondrion in respiration? B State how the mitochondrion is structurally adapted to itsfunction.4. Explain the meaning of the following terms: i Respiration Quotient RQ . Ii Oxygen debt. Iii Basal metabolic rate BMR . 5.
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A What is the role of mitochondrion in respiration? B State how the mitochondrion is structurally adapted to itsfunction.4. Explain the meaning of the following terms: i Respiration Quotient RQ . Ii Oxygen debt. Iii Basal metabolic rate BMR . 5. Describe what happens in the two phases of aerobic andrespiration.6. What is the economic importance of anaerobic respiration inindustry?7. A List the differences between aerobic and anaerobicrespiration. B What is the significance of anaerobic respiration? C Give examples of food in your community which provide uswith a lot of energy.8. Figure 3.6 illustrate an experiment on germinating peas. Fig. 3.6 a i What changes are observable at the end of theexperiment in figure 3.6 b ? Explain the change. Ii What chemical change is taking place in thegerminating peas? B If water had been used instead of potassium hydroxidesolution in the experiments, what would be observed?9. A student set up an experiment using soaked and dry seeds asshown in figure 3.7. Fig. 3.7 a State the objective of this experiment and the observationsmade after 24 hours. B Account for the observations made in a above. C Suggest why vacuum flasks were used in the experiment. D What alteration would you make in the set-up to make theresults more reliable?10. In an experiment on respiration, the rate of carbon IV oxideproduction in pea seedlings was recorded under differenttemperature, as shown in the table below. A Using the same axes, plot graphs to show carbon IV oxide production at each temperature against time. Let timebe on the horizontal axis. B What is the optimum respiration temperature for thisexperiment? Explain how the answer is arrived at. C Suggest reasons for the shape of the graph whentemperature was maintained at 40OC. CHAPTER FOURExcretion and Homeostasis4.1 IntroductionExcretion is a process by which living organisms separate andeliminate waste products formed during metabolic processes, fromtheir bodies. These waste products include carbon IV oxide,nitrogenous wastes, excess water, mineral salts, tannins, quinineand resins.
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C Suggest reasons for the shape of the graph whentemperature was maintained at 40OC. CHAPTER FOURExcretion and Homeostasis4.1 IntroductionExcretion is a process by which living organisms separate andeliminate waste products formed during metabolic processes, fromtheir bodies. These waste products include carbon IV oxide,nitrogenous wastes, excess water, mineral salts, tannins, quinineand resins. If these substances were left to accumulate in the cellsor in the tissue fluid surrounding the cells, they would becomepoisonous or toxic to the cells. This would also alter the conditionsunder which cells function efficiently, leading to their death. It istherefore necessary to remove these waste products as quickly asthey are formed in order to provide a suitable working environmentfor the cells. A suitable working environment for cells can be established ifthe waste products and excess substances are kept at very low andnarrow ranges within and around the cells. Metabolic processesapart from producing these substances, release energy some ofwhich is in form of heat and therefore alter body temperature. Others, such as acidic and alkaline substances alter the pH of bodyfluids. All these factors have adverse effects on the metabolism ofthe body. Organisms therefore, have a self-adjusting mechanismcalled homeostasis that functions to maintain a steady state in theinternal environment of living organisms in order to provideoptimum conditions for body metabolism. Excretion, egestion and secretion are terms that denoteprocesses of releasing substances in or from the bodies of livingorganisms and therefore require to be understood. Egestion is aprocess that results in the removal of undigested materials fromfood vacuoles or alimentary canals of animals. The undigested foodmaterials which may not have entered into cells, to take part inmetabolism may be released as solid remains from the body. However, the digested food materials which enter the body tissuesare broken down. The waste products formed are removed from thebody by excretion. On the other hand, secretion is the release ofcertain useful substances produced by cells. Such substancesinclude hormones, enzymes, oxalates, sebum and mucus. Plants and animals have various methods of disposing of wasteproducts and those methods involve diffusion and evaporation fromthe body. Excretion in PlantsPlants have not evolved complex organs for direct elimination oftheir wastes mainly because there is very little accumulation oftoxic wastes, for example, nitrogenous wastes.
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The waste products formed are removed from thebody by excretion. On the other hand, secretion is the release ofcertain useful substances produced by cells. Such substancesinclude hormones, enzymes, oxalates, sebum and mucus. Plants and animals have various methods of disposing of wasteproducts and those methods involve diffusion and evaporation fromthe body. Excretion in PlantsPlants have not evolved complex organs for direct elimination oftheir wastes mainly because there is very little accumulation oftoxic wastes, for example, nitrogenous wastes. Secondly, the mainwaste products are formed slowly from breakdown ofcarbohydrates. Often these wastes are reutilised by the plant. These waste products include carbon IV oxide, oxygen and water. The gases are removed from the plant by rapid diffusion throughthe stomata and lenticels. Some plants may store other wastes in their tissues, but in anon-toxic form. Some of these tissues or organs age and drop offfrom the plants for example leaves, flowers, fruits, and the bark. The substances stored include tannins, resins, calcium oxalate,calcium carbonate and alkaloids. Caffeine, nicotine, quinine andmorphine are examples of alkaloids stored in these tissues. Economic Importance of Plant ExcretoryProductsTannins are deposited in dead tissues of wood and barks of treesfor example, acacia, mangrove and wattle tree. Commercially,tannin is used in treatment of leather. It combines with animalproteins to form a complex compound that is not easily brokendown by animal proteases. Extracts of tannin are also sprinkled onred-hot pots to give them their characteristic attractive colourpatterns. Caffeine is stored in coffee berries and tea leaves. It is takenas a mild stimulant that increases mental activity and reducesfatigue. Quinine is a waste product stored in the bark of cinchona treeand aloe leaves. Human beings use it for the treatment of malaria. Cocaine is obtained from leaves of coca plant. It is used as alocal anaesthetic. If taken in large quantities it causes greatphysical and mental defects and addiction. Cannabis is stored in fruits, flowers and leaves of Cannabissativa bhang . It is extracted and used in the manufacture ofdrugs. Nicotine is found in leaves of tobacco plants and is used inmanufacture of insecticides and narcotic drugs.
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If taken in large quantities it causes greatphysical and mental defects and addiction. Cannabis is stored in fruits, flowers and leaves of Cannabissativa bhang . It is extracted and used in the manufacture ofdrugs. Nicotine is found in leaves of tobacco plants and is used inmanufacture of insecticides and narcotic drugs. Human beingssmoke it through cigarettes. Rubber is made from latex of rubber plant. It is used in shoeindustry. Sapodilla tree produces the type of latex that is used in themanufacture of chewing gum. Colchicine is an alkaloid derived from a plant that is used ingenetics in plant and animal breeding research and in cancertherapy. Gum arabica is an exudate from some varieties of acaciatrees, used in food processing and printing industry. Papain is obtained from raw pawpaw fruit skins. It contains aproteolytic substance used in food industry as a meat tenderiser. Khat from Khat edulis Miraa is chewed to act as a mildstimulant and used for medicinal purposes. CAUTION: Most of these plant products are many times misused inwhat is nowadays called drug abuse. In this, some of theseproducts such as khat, cocaine and cannabis are used without adoctors approval as stimulants. This behaviour is destructive toones health and is ill advised. Use of most of these substances inthe above mentioned manner is illegal in many countries. The samecase applies in trading in them. Practical Activity 11. From the school surrounding locality find out those plants thatare of medicinal value.2. List any other economic importance of such plants. Excretion and Homeostasis in UnicellularOrganismsMost simple organisms such as protozoa live in aquaticenvironment. Their waste products include carbon IV oxide andnitrogenous wastes. Protozoa such as amoeba and paramecium depend on diffusionas a means of excretion. Their bodies have high surface area tovolume ratio that provide large surface area for gaseous exchangeand excretion to take place by simple diffusion.
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| 1,750,415,789.007635 |
List any other economic importance of such plants. Excretion and Homeostasis in UnicellularOrganismsMost simple organisms such as protozoa live in aquaticenvironment. Their waste products include carbon IV oxide andnitrogenous wastes. Protozoa such as amoeba and paramecium depend on diffusionas a means of excretion. Their bodies have high surface area tovolume ratio that provide large surface area for gaseous exchangeand excretion to take place by simple diffusion. These wastesubstances diffuse from cytoplasm, where they are at a highconcentration, across the cell membrane into the surrounding waterwhere their concentration is low. Another method of excretion is by use of contractile vacuole. Amoeba and paramecium live in an aquatic environment that ishypotonic to their body fluid, hence there is excess inflow of waterby osmosis. Excess water and dissolved chemicals accumulate inthe contractile vacuole. On reaching maximum size, a contractilevacuole moves to cell surface and bursts releasing the contents tothe surrounding. Soon afterwards, other contractile vacuoles form inthe cytoplasm accumulate more waste contents and the processcontinues. See figure 4.1 a , b and c . Fig. 4.1: Excretion in AmoebaExcretion in AnimalsExcretion in animals is carried out by elaborate systems made up ofspecialised tissues and organs. This is because their bodies arecomplex and have greater number of cells, such that simplediffusion would not suffice as a method of excretion. The excretorytissues and organs include flame cells of platyhelminthes,nephridia of annelida, malpighian tubules of insects, gills,lungs, liver and kidneys of vertebrates. These organs are specialised to function in different environmentssuch as aquatic marine and fresh water and terrestrial. Excretion in MammalsThe main excretory organs in mammals such as human beings arelungs, kidneys, skin and liver. These organs are discussed in greaterdetail in the sub-topics that follow this. Structure and function of mammalian skinThis is the largest body organ as it covers the whole body surfaceand even continues into many body openings like nostrils, mouthand ears.
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| 1,750,415,789.045029 |
This is because their bodies arecomplex and have greater number of cells, such that simplediffusion would not suffice as a method of excretion. The excretorytissues and organs include flame cells of platyhelminthes,nephridia of annelida, malpighian tubules of insects, gills,lungs, liver and kidneys of vertebrates. These organs are specialised to function in different environmentssuch as aquatic marine and fresh water and terrestrial. Excretion in MammalsThe main excretory organs in mammals such as human beings arelungs, kidneys, skin and liver. These organs are discussed in greaterdetail in the sub-topics that follow this. Structure and function of mammalian skinThis is the largest body organ as it covers the whole body surfaceand even continues into many body openings like nostrils, mouthand ears. The main functions of the skin are: a Protection of the underlying tissues from entry of microorganisms, physical damage and ultra violet rays from the sun. B Regulation of body temperature. C Excretion of salts, excess water and traces of urea. D Reception of stimuli of heat, cold, pain, touch and pressure. E Synthesis of vitamin D. f Storage of fat. The skin is composed of two main layers. These are the upper layercalled the epidermis and the inner layer called the dermis. Seefigure 4.2. The epidermis is made up of three other layers that arediscussed later. Fig. 4.2: Structure of mammalian skin1. The malpighian layer: It is the innermost of the epidermallayers and is made up of actively dividing cells that give rise to anew epidermis. The cells have pigment granules called melaninthat gives colour to skin and also give protection against harmfulultraviolet rays from the sun.2. Granular layer is the middle layer of epidermis and consists ofliving cells that have granules. It gives rise to the cornified layer.3. Cornified layer is the outermost layer. It is made up offlattened dead cells that become filled with a tough flexiblesubstance called keratin. This layer is very important because itprovides protection against mechanical damage and invasion ofbacteria. It also reduces loss of water by evaporation. Cells ofthis layer are continuously lost through friction and replacedfrom beneath by granular layer.
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| 1,750,415,789.056319 |
This layer is very important because itprovides protection against mechanical damage and invasion ofbacteria. It also reduces loss of water by evaporation. Cells ofthis layer are continuously lost through friction and replacedfrom beneath by granular layer. Its thickness varies in the body,for example, it is thickest in areas of high friction like palms ofhands and soles of feet but thinnest on lips and eyeballs. The dermis is comparatively thicker than the epidermis. Manystructures such as blood vessels, nerve endings, lymphaticvessels, sweat glands and hair follicle are found in the dermis.4. Blood vessels and lymphatic vessels: Blood vessels containblood that supplies nutrients and oxygen to skin tissues andremove waste products and carbon IV oxide. Blood also helpsin temperature regulation. Lymphatic vessels drain excess tissuefluid.5. Nerve endings: The nerve cells which detect changes from theexternal environment thus creating awareness within the bodyof changes in temperature cold and heat , pressure and touch.6. Sweat glands are made up of a coiled tubule of secretory cellswhich extend into long tubules that opens on the surface of theskins as sweat pores. The secretory cells in the coiled tubuleabsorb excess water, mineral salts, traces of urea, lactic acid andcarbon IV oxide from the surrounding blood vessels andtissues. These substances are secreted into the tubule lumen toform sweat, which flow through the sweat duct to the skinsurface. Sweat glands are involved in body temperatureregulation through loss of excess heat by evaporation of water.7. Hair originates from a deep infolding of the epidermis thatforms hair follicle. The hair follicle is lined with granular andmalpighian layers of epidermis. At the base of the hair is adermal or hair papilla from which hair root develops. The hairfollicle is supplied with sensory nerve to increase sensitivity ofthe skin and blood vessels for supply of nutrients and removal ofwaste products. Each hair is made up of a base called hair rootand hair shaft which protrudes outwards. Growth of the hair isdue to continuous addition of new dead cells at the base of thehair. Erector pili muscles are attached to the follicle at one endand on the other end to the epidermis.
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| 1,750,415,789.070185 |
Each hair is made up of a base called hair rootand hair shaft which protrudes outwards. Growth of the hair isdue to continuous addition of new dead cells at the base of thehair. Erector pili muscles are attached to the follicle at one endand on the other end to the epidermis. These muscles undergocontraction and relaxation to alter the angle between the hairshaft and skin and therefore vary the amount of air trappedbetween the hair and skin, a phenomenon that is important intemperature regulation.8. Sebaceous glands are attached to the follicle. The glandsopen into the follicle. They secrete sebum which keeps the hairand epidermis flexible and waterproof. Sebum containsantiseptic substances for protection against bacteria.9. Subcutaneous layer: This is a layer of fat beneath the dermisand binds the skin to muscles and other organs deep in thebody. It acts as a storage region for fats and an insulation layeragainst heat loss. Practical Activity 2To observe the structure of the mammalian skinRequirementsPermanent slides of mammalian skin longitudinal section andmicroscopes. ProcedureObserve the slides provided under a microscope using low powerand medium power of the microscope. Study Questions1. Draw and label the structures observed.2. For the structures identified, state their functions. The LungsIn mammals, birds, reptiles and amphibians, carbon IV oxideformed during tissue respiration is removed from the body by thelungs. In all these groups of animals, the lungs are made up of manysmall air sacs called alveoli. The alveoli have a thin, elastic, singlelayer of epithelium. Below this layer is a dense network ofcapillaries. Blood capillaries around the alveoli have a higherconcentration of carbon IV oxide than that in the alveoli space. This creates a concentration gradient that causes carbon IV oxideto diffuse out of the blood into the alveoli. The carbon IV oxide isthen expelled from the lungs through a process of exhalation. Forthe lung structure refer to chapter 2 of this book .Structure and Function of the KidneyThe kidneys are important organs in the body whose functions areexcretion, osmoregulation, ionic balance and regulation of pH. Amammal has a pair of kidneys located in the lumbar region of thedorsal part of the abdominal cavity.
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| 1,750,415,789.08842 |
The carbon IV oxide isthen expelled from the lungs through a process of exhalation. Forthe lung structure refer to chapter 2 of this book .Structure and Function of the KidneyThe kidneys are important organs in the body whose functions areexcretion, osmoregulation, ionic balance and regulation of pH. Amammal has a pair of kidneys located in the lumbar region of thedorsal part of the abdominal cavity. They are beanshaped and darkred in colour. The right kidney is more anterior than the left. Aboveeach Kidney are the adrenal glands that secrete hormones. A kidneyis convex on one side and concave on the other side. The concaveside has a depression called hilum through which enters a renalartery to supply blood and renal vein to remove blood. From thehilum also leaves a large thick walled tube called ureter that linksthe kidney to an elastic thin-walled urinary bladder. The uretertransports urine from the kidney to the bladder, which temporarilystores the urine. When the urinary bladder is full, sphincter muscleslocated at the base of the bladder relax and urine is released viathe urethra. In males the urethra is long and is joined to thereproduction system unlike in females. See figure 4.3. Fig. 4.3: A generalised urinary system of a mammalA longitudinal section of mammalian kidney shows three distinctregions which include cortex, medulla and pelvis. The cortex whichis dark red in colour is placed to the inner convex surface. Themedulla which is red in colour, lies towards the centre of the kidneyand extends, in form of conical structures called pyramids. Thesepyramids open into swollen cavity called pelvis. The pelvis, which iswhitish in colour, narrows to form the ureter. The human kidneycontains urinary tubules known as nephrons. A human kidneycontains about five million nephrons. See figure 4.4 a and b . Fig. 4.4 a : Longitudinal cross-section of a mammalian kidneyFig. 4.4 b : Section through cortex and medullaPractical Activity 3To observe the structure of a mammalian kidneyRequirementsA mammalian kidney e.g. goats or any other available ones and ascalpelProcedure1. Observe the kidney provided.2. Draw and label the kidney showing external features.3.
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This blood is rich in nitrogenous wastes e.g. urea. It alsocontains dissolved food substances, plasma, proteins, mineral ions,hormones and oxygen. The afferent arteriole entering the glomerulus is wider than theefferent arteriole leaving it. The narrowness of the efferent arterioleproduces both resistance to blood flow and back pressure whichcreate extremely high pressure in the glomerulus. Secondly therenal artery branches directly from the dorsal aorta whose bloodflow is at high pressure. These builds up high pressure within theglomerulus. Due to this pressure the liquid part of the blood anddissolved substances of low molecular sizes including urea, glucose,salts and amino acids are forced out of the glomerulus into thecavity of the Bowman s capsule. Large sized molecules in theplasma such as proteins and blood cells are not filtered out becausethe walls of capillaries of glomerulus and Bowman s capsule havevery small pores. Hence the blood which remains is rich in plasmaproteins and has little water. This process is known asultrafiltration and the filtrate formed is called glomerularfiltrate. The filtrate then flows from the capsular space into theproximal convoluted tubule of the nephron. As the filtrate flowsalong the renal tubules, most of the filtered substances in theglomerular filtrate, useful to the body are selectively reabsorbedback into the blood. In the proximal convoluted tubule, all theglucose, amino acids, some water and mineral salts are activelyreabsorbed against a concentration gradient a process thatrequires energy. For efficient reabsorption the proximal convolutedtubule is adapted in the following ways:Fig. 4.6: The structure of the kidney nephron i Cells lining the tubule have numerous mitochondria whichprovide the necessary energy in form of ATP. Ii Cells of the tubule have microcilli which increases the surfacearea. Iii The tubule is long and highly coiled to provide a large surface. Iv The coiling of the tubule reduces the speed of the flow of thefiltrate thereby giving more time for efficient reabsorption. V The tubule is well supplied with blood capillaries. The loop of Henle forms an area where salts especially sodiumchloride are reabsorbed into the blood.
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For efficient reabsorption the proximal convolutedtubule is adapted in the following ways:Fig. 4.6: The structure of the kidney nephron i Cells lining the tubule have numerous mitochondria whichprovide the necessary energy in form of ATP. Ii Cells of the tubule have microcilli which increases the surfacearea. Iii The tubule is long and highly coiled to provide a large surface. Iv The coiling of the tubule reduces the speed of the flow of thefiltrate thereby giving more time for efficient reabsorption. V The tubule is well supplied with blood capillaries. The loop of Henle forms an area where salts especially sodiumchloride are reabsorbed into the blood. The U-shaped loop isgenerally longer and has a counter current flow establishedbetween the flow of filtrate and the large supply of blood in vessels. Active transport is involved in the reabsorption of sodium salts. Toregulate the intake of sodium salt, a hormone called aldosteroneis secreted by adrenal glands. Low content of salt in bloodstimulates adrenal glands to secrete more aldosterone hormoneand therefore more salt is reabsorbed from the filtrate and viceversa. When the filtrate reaches the distal convoluted tubule, acontrolled amount of water is reabsorbed into the blood by osmosis. This process is enhanced in two ways, first being due to the activeintake of sodium salt into the blood at the loop of Henle whichincreases the osmotic pressure of the blood. The second factorinvolves a hormone known as antidiuretic hormone ADH . Thishormone is secreted by the pituitary glands. Antidiuretic hormoneincreases the permeability of the tubule and blood capillaries towater. When there is excess water in the body for example, as aresult of excessive intake of fluids, the osmotic pressure of theblood falls causing the pituitary gland to reduce its secretion of ADHinto the blood. Water reabsorption in the tubule is thereby reducedand results in the production of large amounts of dilute urine. If, forexample, the body has lost excessive water through sweating,thereby raising the blood pressure, the pituitary gland will releasemore ADH which results in increased water reabsorption from thetubule into the blood.
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| 1,750,415,789.161547 |
When there is excess water in the body for example, as aresult of excessive intake of fluids, the osmotic pressure of theblood falls causing the pituitary gland to reduce its secretion of ADHinto the blood. Water reabsorption in the tubule is thereby reducedand results in the production of large amounts of dilute urine. If, forexample, the body has lost excessive water through sweating,thereby raising the blood pressure, the pituitary gland will releasemore ADH which results in increased water reabsorption from thetubule into the blood. This results in the production of little amountsof concentrated urine. It should also be noted that the distal convoluted tubule hassome modifications similar to those found in the proximalconvoluted tubule, that is, a large surface area, being surroundedby many blood capillaries and having a wall one cell thick. The filtrate in the collecting tubule becomes urine and tricklesdown into the collecting duct where it joins urine from the collectingtubules of other nephrons. The urine then flows into the pelvis viathe pyramid and is finally emptied into the urinary bladder throughthe ureter. About 1 to 2 litres of urine trickles into the urinarybladder in a day. In the urinary bladder, about 250 millilitres of urinewill initiate the urge to urinate. The sphincter muscles relax and theurine is passed out. The resultant urine composition of a healthyperson may be as follows:Water 95 Urea 2 Uric acid0.030 Creatinine 0.1 Salts of Na , K , Cl PO4 3 1.4 Ammonia 0.04 Proteins 0.0 Glucose 0.0 The quantity and concentration of urine in animals is affected byterrestrial, aquatic, desert conditions, the physiological and thestructural adaptations of the animals. For instance, in a desert rat,water reabsorption is maximised by the development of a long loopof Henle. Study Questions1. Explain why glucose and proteins are absent in urine.2. Describe how to test for the presence of glucose and proteins inurine.3.
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It is fatal if not treated. Kidney FailureIn situations where a kidney fails to function, the person can stilllead a normal life using the other kidney. However, if both kidneysmalfunction the individual will still survive if treated promptly. Suchtreatment can be administered in two forms. These are: a Kidney dialysis. B Kidney transplant. The Liver and its StructureThe liver is the second largest organ after the skin and is a specialorgan of excretion because many excretory products are producedby it. It lies immediately beneath the diaphragm and is made up ofseveral lobes. It receives more blood per unit time than any otherpart of the body other than the heart. It receives blood from twoblood vessels, namely the hepatic portal vein and the hepaticartery. Blood flows out of the liver through the hepatic vein. The liver consists of a large number of lobules. Each lobule ismade up of many liver cells. The cells are arranged radially arounda central blood vessel which is a branch of the hepatic vein. Theblood supply to each lobule is from two sources, the hepaticartery and the hepatic portal vein. These vessels branchbetween the liver lobules. Between the plates of liver cells are channels called canaliculiwhich receive bile. The bile moves outwards to the periphery of thelobules where it collects into bile duct. See figure 4.7 a and b . Fig. 4.7 a : Structure of the LiverFig. 4.7 b : The liver lobulesThe Functions of the LiverThe liver performs many functions that contribute a lot tohomeostasis. There are:DeaminationAmino acids one absorbed from the gut, they are used in synthesisof proteins of the body. Excess amino acids or proteins cannot bestored in the body since the body does not have a mechanism forsuch storage. Excess amino acids not used, are broken down in aprocess of deamination. In this process the amino group NH2 ofthe amino acid is removed and used to form ammonia. Theammonia is taken into the ornithine cycle which is a series ofreactions resulting to the formation of urea, a less toxic substancethan ammonia.
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| 1,750,415,789.198799 |
Excess amino acids not used, are broken down in aprocess of deamination. In this process the amino group NH2 ofthe amino acid is removed and used to form ammonia. Theammonia is taken into the ornithine cycle which is a series ofreactions resulting to the formation of urea, a less toxic substancethan ammonia. The process is summarised as shown in theequation at the bottom of the page: The urea formed is releasedinto the blood stream and is eventually passed out in the urinethrough the kidney. DetoxificationSome of the metabolic activities of the liver result into theproduction of toxic substances which if left to accumulate, woulddestroy or harm the tissues of the body. The liver also receivesharmful substances by way of drugs, food or drinks. It thereforemakes these substances harmless and eliminate the substances inharmless forms in a process called detoxification. The liver cellsthrough oxidation, reduction, and combination with othersubstances carry out this process of detoxification. For example,hydrogen peroxide produced by actively respiring cells is brokendown by enzyme catalase to form water and oxygen which areharmless. This enzyme is found in the liver. You will investigate thisaspect in Practical Activity 4 .ThermoregulationThe liver carries out many metabolic reactions some beingendothermic while others are exothermic. Under conditions of lowtemperature the hypothalamus sends impulses to liver to increaseexothermic reactions producing more heat that is distributedthroughout the body by the blood. Haemoglobin EliminationHaemoglobin from worn out red blood cells is also broken down inthe liver and the residual pigments urochrome which give urine ayellow tinge is eliminated by the kidney, bilirubin excreted via bilejuice into alimentary canal. Regulation of Plasma ProteinsPlasma protein are important components of the body. Majority ofthem are synthesised from amino acids in the liver. These includealbumin, fibrinogen, prothrombin and antibodies. Many of these areinvolved in regulatory mechanism of homeostasis. Digesting anddeaminating excess proteins also regulate their quantities. Erythrocytes have a life span of about 120 days after which they aretaken to the liver where they are broken down. Haemoglobin isbroken into a haem group and globin.
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| 1,750,415,789.203834 |
Many of these areinvolved in regulatory mechanism of homeostasis. Digesting anddeaminating excess proteins also regulate their quantities. Erythrocytes have a life span of about 120 days after which they aretaken to the liver where they are broken down. Haemoglobin isbroken into a haem group and globin. Globin is digested into aminoacids and enters the amino acid pool while the haem group ischanged in biliverdin and bilirubin and taken to gall bladder. Theseare later released into the gut as bile and then passed out throughfaeces. These two substances give faeces its characteristic browncolour. Other functions of the liver include the manufacture of redblood cells during the foetus stage, formation and elimination ofexcess cholesterol which is an important component cell membrane,regulation of fat metabolism, storage of blood, storage of vitaminsB, C, E, K and minerals. The other major function of the liver is blood sugar regulation. This will be discussed under homeostasis. Practical Activity 4To investigate the effect of enzyme catalase on hydrogenperoxideCatalase is an enzyme present in living tissues of plants andanimals. Its role in living tissues is to break down hydrogenperoxide H2O2 produced during cellular respiration. Hydrogenperoxide is a highly toxic chemical substance which should not beallowed to accumulate in the tissues. RequirementsFresh piece of liver, 20 hydrogen peroxide, boiling tube, woodensplint, source of heat, scalpel and measuring cylinder. Procedure1. Measure 2 cm3 of the 20 hydrogen peroxide and put this inthe boiling tube.2. Cut a small piece of liver and put it into the boiling tube.3. Immediately test for the gas being produced using a glowingsplint.4. Record your observations.5. Write an equation for the reaction that occurs.6. What do you conclude from the experiment?Liver Diseases and DisordersLiver CirrhosisThis is the contraction and hardening of the liver due to death ofliver cells. A fibrous tissue replaces the dead cells. The disease iscaused by ingestion of toxic chemicals such as alcohol, attack byeither bacteria or virus and liver parasites. Symptoms are slow in development and are normally seenwhen the disease is at advanced stages.
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| 1,750,415,789.218538 |
What do you conclude from the experiment?Liver Diseases and DisordersLiver CirrhosisThis is the contraction and hardening of the liver due to death ofliver cells. A fibrous tissue replaces the dead cells. The disease iscaused by ingestion of toxic chemicals such as alcohol, attack byeither bacteria or virus and liver parasites. Symptoms are slow in development and are normally seenwhen the disease is at advanced stages. These symptoms includebody weakness, loss of weight, indigestion, poor appetite, pain inthe upper right quarter of the abdomen and occasional vomiting ofbloody material. If a large portion of liver is damaged, death mayresult. Control and Treatment a Avoid excess alcohol intake. B Avoid fatty diet. C Take adequate diet and varied easily digestible food. D Have bed rest most of the time. E Low salt intake. F Consult a doctor. HepatitisThis is the inflammation of the liver. It is a viral disease and twotypes are known namely: Hepatitis A and B. Hepatitis A is morecommon among children and young adults. It is infectious and is passed from one person to anotherthrough contact of body fluids, contaminated food, milk and water. The symptoms appear between two to six weeks. These includeloss of appetite, nausea, fatigue, jaundice yellow of skin andabdominal pain. Hepatitis B is common in adults. It is transmittedthrough contaminated injections, instruments and other implementsthat pierce the skin and lead to exchange of fluids such as blood,semen and saliva. Symptoms appear between three to four months. Hepatitis B is more serious than A because it is difficult to cure andcause more deaths. ControlProper disposal of sewage, vaccination, bed rest, and prescribeddiet. JaundiceThis is characterised by yellowing of the membranes and skin. Itresults from failure of the liver to excrete all the bile pigments fromred blood cell haemoglobin breakdown. The bile pigmentaccumulates in blood and hence the yellowing of the skin. Thishappens due to blockage of bile duct or destruction of the liver as incirrhosis and hepatitis or mass destruction of red blood cells incirculation as in erythroblastosis foetalis. HomeostasisAn organism lives in an environment that keeps on changing inmany of its factors, for example temperature, availability of water,food and fresh air.
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| 1,750,415,789.253681 |
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