Autotroph

An autotroph is an organism able to make its own food. Autotrophic organisms take inorganic substances into their bodies and transform them into organic nourishment. Autotrophs are essential to all life because they are the primary producers at the base of all food chains. There are two categories of autotrophs, distinguished by the energy each uses to synthesize food. Photoautotrophs use light energy; chemoautotrophs use chemical energy.

Photoautotrophs

Plants are the most abundant and recognizable autotrophs on Earth . If you have noticed a houseplant on a windowsill imperceptibly turn its leaves toward the sun , you have probably guessed that plants are photoautotrophs. Plant leaves soak up the energy in sunlight and use it to make food. Plants take in water through their roots and atmospheric carbon dioxide through their leaves. Plant cells absorb light energy to fuel the synthesis of inorganic hydrogen , oxygen , and carbon into a sugar that nourishes them. This process is known as photosynthesis .

Because plants, as autotrophs, make living tissue solely out of nonliving material, they form the foundation of all food chains. Can you think of one thing you eat that does not, ultimately, come from plants? Plants are called primary producers because they create themselves out of transformed inorganic matter and, thus, are the "original food" that sustains all living things.

Chemoautotrophs

Until recently, scientists believed there existed only a few kinds of bacteria that used chemical energy to create their own food. Some of these bacteria were found living near vents and active volcanos on the lightless ocean floor. The bacteria create their food using inorganic sulfur compounds gushing out of the vents from the hot interior of the planet .

In 1993, scientists found many new species of chemoautotrophic bacteria living in fissured rock far below the ocean floor. These bacteria take carbon dioxide and water into their bodies and use the chemical energy in sulfur compounds to create nourishing carbohydrates and sugars. A unique characteristic of these chemoautotrophic bacteria is that they thrive at temperatures high enough to kill other organisms. Some scientists believe these unique bacteria should be classified in their own new taxonomic kingdom.