This picture is an example of early autotrophs.
Click on image for full size
Image courtesy of Corel Photography
Over a very long time, gradual changes in the earliest cells gave rise to new life forms. These new cells were very different from the earlier heterotrophs because they were
able to get their energy from a new source -- the Sun.
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 use energy from the sun and eat.
Because the autotrophic bacteria were able to feed themselves by
using the energy of the Sun, they were no longer dependent on the same
limited food supply as their ancestors and were able to flourish. Over millions of years of
evolution, photosynthetic bacteria eventually gave rise
to modern day plants.
The appearance of organisms capable of performing photosynthesis was very significant -- 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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