Resource Library

ENCYCLOPEDIC ENTRY

ENCYCLOPEDIC ENTRY

autotroph

autotroph

Encyclopedic entry. An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers.

Grades

6 - 12+

Subjects

Biology, Ecology

Powered by
Morgan Stanley

An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers.

Plants are the most familiar type of autotroph, but there are many different kinds of autotrophic organisms. Algae, which live in water and whose larger forms are known as seaweed, is autotrophic. Phytoplankton, tiny organisms that live in the ocean, are autotrophs. Some types of bacteria are autotrophs.

Most autotrophs use a process called photosynthesis to make their food. In photosynthesis, autotrophs use energy from the sun to convert water from the soil and carbon dioxide from the air into a nutrient called glucose. Glucose is a type of sugar. The glucose gives plants energy. Plants also use glucose to make cellulose, a substance they use to grow and build cell walls.

All plants with green leaves, from the tiniest mosses to towering fir trees, synthesize, or create, their own food through photosynthesis. Algae, phytoplankton, and some bacteria also perform photosynthesis.

Some rare autotrophs produce food through a process called chemosynthesis, rather than through photosynthesis. Autotrophs that perform chemosynthesis do not use energy from the sun to produce food. Instead, they make food using energy from chemical reactions, often combining hydrogen sulfide or methane with oxygen.

Organisms that use chemosynthesis live in extreme environments, where the toxic chemicals needed for oxidation are found. For example, bacteria living in active volcanoes oxidize sulfur to produce their own food. At Yellowstone National Park in the U.S. states of Wyoming, Idaho, and Montana, bacteria capable of chemosynthesis have been found in hot springs.

Bacteria that live in the deep ocean, near hydrothermal vents, also produce food through chemosynthesis. A hydrothermal vent is a narrow crack in the seafloor. Seawater seeps down through the crack into hot, partly melted rock below. The boiling-hot water then circulates back up into the ocean, loaded with minerals from the hot rock. These minerals include hydrogen sulfide, which the bacteria use in chemosynthesis.

Autotrophic bacteria that produce food through chemosynthesis have also been found at places on the seafloor called cold seeps. At cold seeps, hydrogen sulfide and methane seep up from beneath the seafloor and mix with the ocean water and dissolved carbon dioxide. The autotrophic bacteria oxidize these chemicals to produce energy.


Autotrophs in the Food Chain

To explain a food chain—a description of which organisms eat which other organisms in the wild—scientists group organisms into trophic, or nutritional, levels. There are three trophic levels. Because autotrophs do not consume other organisms, they are the first trophic level.

Autotrophs are eaten by herbivores, organisms that consume plants. Herbivores are the second trophic level. Carnivores, creatures that eat meat, and omnivores, creatures that eat all types of organisms, are the third trophic level.

Herbivores, carnivores, and omnivores are all consumers—they consume nutrients rather than making their own. Herbivores are primary consumers. Carnivores and omnivores are secondary consumers.

All food chains start with some type of autotroph (producer). For example, autotrophs such as grasses grow in the Rocky Mountains. Mule deer are herbivores (primary consumers), which feed on the autotrophic grasses. Carnivores (secondary consumers) such as mountain lions hunt and consume the deer.

In hydrothermal vents, the food chain’s producer is autotrophic bacteria. Primary consumers such as snails and mussels consume the autotrophs. Carnivores such as octopus consume the snails and mussels.

An increase in the number of autotrophs will usually lead to an increase in the number of animals that eat them. However, a decrease in the number and variety of autotrophs in an area can devastate the entire food chain. If a wooded area burns in a forest fire or is cleared to build a shopping mall, herbivores such as rabbits can no longer find food. Some of the rabbits may move to a better habitat, and some may die. Without the rabbits, foxes and other meat-eaters that feed on them also lose their food source. They, too, must move to survive.

Fast Fact

Photoheterotrophs
Some varieties of bacteria use light to create their own food, just like organisms that use photosynthesis. However, these bacteria are not autotrophs, because they must rely on chemicals besides carbon dioxide for carbon. These strange bacteria are called photoheterotrophs.

Fast Fact

Radiotrophs
Some fungi use gamma radiation and a natural pigment called melanin to create energy for growth. Gamma radiation is a high-frequency band of light that is invisible to people and can cause damage to human tissues when encountered in large doses. These strange, rare fungi are called radiotrophs. They are found inside and around the abandoned Chernobyl Nuclear Power Plant in Ukraine.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writers
Kim Rutledge, Kim Rutledge
Melissa McDaniel, Melissa McDaniel
Santani Teng, Santani Teng
Hilary Hall, Hilary Hall
Tara Ramroop, Tara Ramroop
Erin Sprout, Erin Sprout
Jeff Hunt, Jeff Hunt
Diane Boudreau, Diane Boudreau
Hilary Costa, Hilary Costa
Illustrators
Mary Crooks, National Geographic Society,
Tim Gunther, Tim Gunther
Editors
Jeannie Evers, Emdash Editing, Emdash Editing
Kara West, Kara West
Educator Reviewer
Nancy Wynne,
Producer
National Geographic Society, National Geographic Society
other
Last Updated

May 20, 2022

For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

Media

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources