Organisms that are able to make their own food (in the form of sugars) by using the energy of the Sun are called autotrophs, meaning "self-feeders". Photosynthesis is the name of the process by which these autotrophs eat. Organisms which require food from sources outside themselves; other organic matter, or other chemical syn thesis of food, are called heterotrophs, meaning "other-feeders". Because the autotrophic bacteria were able to feed themselves by using the energy of the Sun, they were not dependent on the same limited food supply as their heterotrophic contemporaries and were able to flourish.
The appearance of these organisms capable of performing photosynthesis was of
monumental significance -- if it weren't for the photosynthetic activity of
these early bacteria, Earth's atmosphere would still be without oxygen
and the appearance of oxygen-dependent animals, including humans, would
never have occurred!
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