When a lucky bacterium developed the first successful photosystem about a half billion years after the first cells arose, the organisms of the world were split into two distinct classes: providers and consumers. Until that time, all were consumers, fueling their metabolic processes with the geochemically formed organic and inorganic compounds then commonly found in the ocean. (These natural foods, provided by the earth, were used up in the early history of life. Today only a handful of organisms, such as the bacteria that utilize the hydrogen sulfide in hot springs and deep-sea hydrothermal vents, rely on them as a source of energy.) The perfection of a photosystem— a protein complex containing a series of light-absorbing chlorophyll molecules — allowed these new bacteria to create their own source of chemical energy from the inexhaustible source of the sun. The sharp division between provider and consumer has lasted to this day. Plants and photosynthetic bacteria create food out of thin air (and light). All other organisms eat plants, directly or a few steps removed.
KeywordsHydrogen Sulfide Photosynthetic Bacterium Ribulose Bisphosphate Dark Reaction Capture Carbon Dioxide
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