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 are called heterotrophs, meaning "other-feeders". Because autotrophic bacteria were able to feed themselves by using the energy of the Sun, they were not dependent on a limited food supply 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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