What is the difference between Photosynthetic Pigments and Chloroplasts? I know plants have both but Prokaryotes (Bacteria and Archeae) only have the former.


Photosynthetic pigments are the chemicals which take part in photosynthesis, in particular they are they ones which absorb photons and fluoresce (emit photons of a different wavelength) or emit electrons. Pigments are molecules, and chlorophyll is a key example. These pigments are required for photosynthesis to take place, as they generate the electrons which create the electrochemical gradients which power photosynthesis, thus all photosynthetic organisms will have photosynthetic pigments of some kind.

Chloroplasts are membrane-bound organelles in plant cells, made up of many hundreds of thousands of molecules including pigments. Plant photosynthesis takes place on their internal membrane, the thylakoid. Specifically, the thylakoid membrane of chloroplasts is the membrane across which the aforementioned electrochemical gradients are created in plants.

Chloroplasts originated from a free-living bacterium, probably a cyanobacterium, entering a eukaryotic cell. So prokaryotes don't have them because the chloroplast endosymbiosis event was one way in which plants diverged from their non-plant ancestors. So you can think of a cyanobacterium as a free-living chloroplast - they have their own internal membranes similar to the thylakoid across which electrochemical gradients are created for photosynthesis. Conversely, you can think of a chloroplast as a small cyanobacterium living symbiotically inside a plant cell.

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