Autotroph
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Green (from chlorophyll) fronds of a maidenhair fern: a photoautotroph |
An
autotroph (from the
Greek autos = self and
trophe = nutrition) is an
organism that produces
organic compounds from carbon dioxide as a carbon source, using either
light or reactions of inorganic chemical compounds, as a source of
energy. An autotroph is known as a
producer in a
food chain.
Plants and other organisms that carry out
photosynthesis are
phototrophs (or
photoautotrophs).
Bacteria that utilize the oxidation of inorganic compounds such as
hydrogen sulfide or ferrous iron as an energy source are
chemoautotrophs.
Autotrophs are a vital part of the food chains of all
ecosystems. They take energy from the sun (or from inorganic sources) and convert it into a form (carbon-based or organic molecules) that is used to carry out various biological functions such as cell growth, and that other organisms, called
heterotrophs, utilize as
food to carry out these same functions. Thus, heterotrophs—
animals,
fungi, as well as most
bacteria and
protozoa—depend on autotrophs for both energy and raw materials to make complex organic molecules. Heterotrophs obtain energy by breaking down organic molecules obtained in food.
Carnivorous animals as well rely on autotrophs because the energy and organic building blocks obtained from their prey comes from autotrophs they preyed upon.
There are some species of organisms that require
organic compounds as a source of
carbon, but are able to use light or inorganic compounds as a source of energy. Such organisms are not defined as autotrophic, but rather as heterotrophic. An organism that obtains carbon from organic compounds but obtains energy from light is called a
photoheterotroph, while an organism that obtains carbon from organic compounds but obtains energy from the oxidation of inorganic compounds is termed a
chemoheterotroph.
*
Mixotrophic*
Primary nutritional groups
