The cells of plants and some protists possess chloroplasts, whose green chlorophyll gives plant leaves their characteristic color. Embedded in an internal membrane, chlorophyll absorbs sunlight and funnels it to a complex set of proteins nearby. Light energy is used to split water into oxygen (released as a waste product) and hydrogen, which is attached to nucleotide carriers. The hydrogen is then reacted with CO2 from the air to form sugars, the essential high-energy product that powers all of life. Like the mitochondrion, the chloroplast is a relic of a former free-living bacterium, and has its own DNA on its own chromosome.

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