What is Chloroplast?
[[File:Plagiomnium affine laminazellen.jpeg|thumb|260px|Chloroplasts visible in the cells of ''Plagiomnium affine'']] [[Image:Chloroplast.svg|thumb|260px|right|'''Chloroplast''' ultrastructure:<br /> 1. outer membrane<br /> 2. intermembrane space<br /> 3. inner membrane (1+2+3: envelope)<br /> 4. '''stroma''' (fluid)<br /> 5. '''thylakoid''' lumen (inside of thylakoid)<br /> 6. thylakoid membrane<br /> 7. '''grana''' (stacks of thylakoids)<br /> 8. '''thylakoid''' (lamella)<br /> 9. starch<br /> 10. [[ribosome]]<br /> 11. plastidial DNA<br /> 12. plastoglobule (drop of lipids) ]] A '''chloroplast''' is a small [[organelle]] inside the [[Cell (biology)|cells]] of [[plants]] and [[algae]]. They absorb [[light]] to make [[sugar]] in a process called [[photosynthesis]]. The sugar can be stored in the form of [[starch]]. Chloroplasts contain the [[molecule]] [[chlorophyll]], which absorbs sunlight for photosynthesis. In addition to chlorophyll, a chloroplast uses [[carbon dioxide]] (CO<sub>2</sub>) and [[water]] (H<sub>2</sub>O) to form sugar and gives off [[oxygen]] (O<sub>2</sub>). Chlorophyll is what gives green plants their green colour. Chloroplasts also contain various yellow and orange [[pigment]]s to assist in [[photon]] capture for photosynthesis. [[File:Chloroplast-new.jpg|thumb|center|400px|Diagram of a chloroplast]] == Structure == Each chloroplast is surrounded by a double walled semi-permeable membrane. These are collectively known as peristromia. In the layered stacks are flat disk-shaped thylakoids. They contain light-absorbing pigments, including chlorophyll and [[carotenoid]]s, as well as [[protein]]s which bind the pigments. Like [[mitochondria]], chloroplasts also contain their own [[DNA]] and [[ribosome]]s. == Evolution == Chloroplasts are one of the many different types of organelles in the cell. They may have originated as [[endosymbiosis|endosymbiotic]] [[cyanobacteria]]. This was suggested by Konstantin Mereschkowski in 1905,<ref>{{cite journal | author= Mereschkowsky C | t