Plant Biology - Chloroplasts

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The green colour of algae, and of cabbages, pine trees and grasses, comes from small green bodies called chloroplasts within their cells. Chloroplasts are distant descendants of once free-living green bacteria. They still have their own DNA, and they still reproduce by asexual division, building up to a substantial population within each host cell. As far as a chloroplast is concerned, it is a member of a reproducing population of green bacteria. The world in which it lives and reproduces is the interior of a plant cell. From time to time its world suffers a minor upheaval when the plant cell divides into two daughter cells. Roughly half the chloroplasts find themselves in each daughter cell, and they soon resume their normal existence of reproducing to populate their new world with chloroplasts. All the while, the chloroplasts use their green pigment to trap photons from the sun and channel the sun's energy in the useful direction of synthesising organic compounds from carbon dioxide and water supplied by the host plant. The oxygen wastes are partly used by the plant and partly exhaled into the atmosphere through holes in the leaves called stomata (singular 'stoma'). The organic compounds synthesised by the chloroplasts are ultimately made available to the host plant cell. Interestingly reminiscent of the Mixotrich's Tale, some chloroplasts show evidence of having entered plant cells indirectly, by piggybacking inside other eukaryotic cells, which would presumably have ...

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