As rod cells detect light (not colour), they play no role in colour blindness so those who are colour-blind can usually see. The most common type of colour blindness is red-green (people with the condition perceive red and green as the same colour), where the cones most receptive to red light and green light are missing. Colour blindness is more frequent in than females because it is a sex-linked characteristic; the gene for the red and green cones is located in the X chromosome. Females have two X chromosomes (XX) and males only have one (XY) which means that females need both chromosomes carrying the defective gene to express it while males only need one. Process and analyse information from secondary sources to compare and describe the nature and functioning of photoreceptor cells in mammals, insects and in one other animal Mammal: Human Insect: Dragonfly Flatworm: Planarian Worm Type of Rods and cones Reticular/retinal cells in Eye cups photoreceptor separate ommatidia Type of image Image on retina is inverted Mosaic image of large (if formed) is unclear and and diminished visual field, can see in not inverted gives information – colour about light intensity and direction Similarity in Detects - rhodopsin Detects light - rhodopsin Detects light - rhodopsin photoreceptors Difference in Has higher resolving power Is made up of many Has photoreceptor cells photoreceptor and greater visual acuity called ommatidia (each has than insect or mammals and has its own cornea and poor visual acuity and no colour transparent crystalline vision. Two eye spots (Ocelli) cone which acts as lens) are used to detect light and pointing in different move away from it. direction. Can be more efficient detecting colour than mammals and fast movement. Structure that Cornea, aqueous humour, Cornea, lens (fixed, cannot No refraction refracts light lens (changes curvature), accommodate) vitreous humour Sensitivity to Rhodopsin is a photosensitive Greater detects light, UV Highly sensitive – pigment as well as visible light Visual acuity High visual acuity Lower visual acuity than Poor visual acuity mammals but more efficient in detecting movement Mammals have a similar eye structure to humans; the major difference within mammal eyes is the presence or absence of cone cells (nocturnal mammals have no cones, so they cannot see colour).
As rod cells detect light (not colour), they play no role in colour blindness so those who are colour-blind can usually see. The most common type of colour blindness is red-green (people with the condition perceive red and green as the same colour), where the cones most receptive to red light and green light are missing. Colour blindness is more frequent in than females because it is a sex-linked characteristic; the gene for the red and green cones is located in the X chromosome. Females have two X chromosomes (XX) and males only have one (XY) which means that females need both chromosomes carrying the defective gene to express it while males only need one. Process and analyse information from secondary sources to compare and describe the nature and functioning of photoreceptor cells in mammals, insects and in one other animal Mammal: Human Insect: Dragonfly Flatworm: Planarian Worm Type of photoreceptor Rods and cones Reticular/retinal cells in separate ommatidia Eye cups Type of image Image on retina is inverted and diminished Mosaic image of large visual field, can see in colour (if formed) is unclear and not inverted – gives information about light intensity and direction Similarity in photoreceptors Detects - rhodopsin Detects light - rhodopsin Detects light - rhodopsin Difference in photoreceptor Has higher resolving power and greater visual acuity Is made up of many called ommatidia (each has its own cornea and transparent crystalline cone which acts as lens) pointing in different direction. Can be more efficient detecting colour than mammals and fast movement. Has photoreceptor cells than insect or mammals and has poor visual acuity and no colour vision. Two eye spots (Ocelli) are used to detect light and move away from it. Structure that refracts light Cornea, aqueous humour, lens (changes curvature), vitreous humour Cornea, lens (fixed, cannot accommodate) No refraction Sensitivity to Rhodopsin is a photosensitive pigment Greater – detects light, UV as well as visible light Highly sensitive Visual acuity High visual acuity Lower visual acuity than mammals but more efficient in detecting movement Poor visual acuity Mammals have a similar eye structure to humans; the major difference within mammal eyes is the presence or absence of cone cells (nocturnal mammals have no cones, so they cannot see colour).
Biology_Notes_-_Communication_by_Arthur_Huang.docx