An autotroph is an organism able to make its own food. Autotrophic organisms convert inorganic molecules into organic compounds. Autotrophs are referred to as primary producers, and they occupy the ecological niche at the base of all food chains. There are two categories of autotrophs, distinguished by the type of energy each uses to synthesize organic products. Photoautotrophs use light energy and chemoautotrophs use chemical energy.
Photoautotrophs are the most common autotrophs. Plants and some photosynthetic bacteria comprise the majority of photoautotrophs. Photoautotrophs contain organelles called chloroplasts, which have the ability to convert the energy from photons into chemical energy stored in sugars and other energy-containing molecules. This process is known as photosynthesis. Photosynthesis also requires water, which plants usually acquire through their roots and atmospheric carbon dioxide, which plants acquire through their leaves. In addition, photosynthesis results in the production of inorganic oxygen.
Plants and other photoautotrophs play an important ecological role in nearly all terrestrial ecosystems. Because photoautotrophs convert light energy into energy that is stored in energy-rich molecules, animals depend on them as a source of both energy and nutrients. Photosynthesizers form the base of common ecological food webs. For example, the base of the forest food chain may be trees; the base of a savannah food chain may be grasses; and the base of a desert food chain may be cacti.
Chemoautotrophs are bacteria that use chemical energy in inorganic compounds as a source of energy. They synthesize sugars from the inorganic molecule carbon dioxide.
Sulfur reducers are chemoautotrophs that use the energy in inorganic sulfur compounds as a source of energy. Sulfur reducers can be found living near vents and active volcanoes on the ocean floor, where inorganic sulfur from within the Earth’s core is released into the ocean water. These bacteria may live as symbionts with tube worms and clams found near the vents, providing them with a source of nutrition as well. These chemoautotrophic bacteria thrive at extremely high temperatures. Many of these bacteria, called extremophiles, are classified in the Domain Achaea.
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.
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.
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.
An organism that derives its carbon for building body tissues from carbon dioxide (CO2) or carbonates and obtains its energy for bodily functions from radiant sources, such as sunlight, or from the oxidation of certain inorganic substances. The leaves of green plants and the bacteria that oxidize sulfur, iron, ammonium, and nitrite are examples of autotrophs. The oxidation of ammonium to nitrite, and of nitrite to nitrate, a process called nitrification , is a critical part of the nitrogen cycle . Moreover, the creation of food by photosynthetic organisms is largely an autotrophic process.