Autotroph facts for kids

Overview of cycle between autotrophs and heterotrophs. Photosynthesis is the main way plants, algae, and many bacteria create food and oxygen from carbon dioxide and water (green arrow).

An autotroph is a living thing that can make its own food. They use energy from non-living sources, like sunlight or chemicals, to create complex food molecules. These molecules include sugars, fats, and proteins. Autotrophs get their carbon from simple things like carbon dioxide. They don't need to eat other living things for energy or carbon. Because they produce their own food, autotrophs are called the "producers" in a food chain. Plants on land and algae in water are common examples. Autotrophs can change carbon dioxide into organic compounds. These compounds are used to build their bodies and store chemical energy. Most autotrophs use water in this process, but some can use other hydrogen compounds.

These primary producers can turn light energy (like phototrophs) or energy from inorganic chemicals (like chemotrophs) into organic molecules. These molecules are stored as biomass. Other organisms, like heterotrophs, then use this biomass for food and energy. Photoautotrophs are the main primary producers. They use photosynthesis to turn light energy into chemical energy. They build organic molecules from carbon dioxide, which is an inorganic carbon source. Some chemolithotrophs are certain archaea and bacteria. These tiny organisms create biomass by using energy from inorganic chemical compounds. They are often found near hydrothermal vents deep in the ocean. Primary producers are at the very bottom of the trophic levels. They are essential for life on Earth.

Autotrophs use some of the energy they make to create special energy packets. These packets help them form organic compounds. Most chemoautotrophs use inorganic substances as their energy source. These can include hydrogen sulfide, hydrogen gas, sulfur, ammonium, and iron. Chemolithoautotrophs are tiny living things that make energy by changing inorganic compounds. They can live entirely on carbon dioxide from the air and inorganic chemicals. They don't need light or organic food. They use chemical reactions with minerals to create energy. These minerals often include hydrogen, iron, nitrogen, and sulfur. These organisms often live in extreme places. Examples include deep-sea hydrothermal vents, layered sediments, and hot, acidic springs.

A Look Back: The History of Autotrophs

The word autotroph was created by a German botanist named Albert Bernhard Frank in 1892. It comes from ancient Greek words meaning "nourishment" or "food." The first autotrophic organisms likely appeared very early in Earth's history. They became much more common during the Great Oxidation Event. This was a time when oxygen levels in Earth's atmosphere increased. This increase was due to more oxygenic photosynthesis by cyanobacteria. Photoautotrophs likely developed from other types of bacteria. These early photosynthetic bacteria used hydrogen sulfide. Because hydrogen sulfide was not always available, some photosynthetic bacteria evolved to use water for photosynthesis. This led to the development of cyanobacteria.

Different Kinds of Autotrophs

There are many different kinds of autotrophs in Earth's ecosystems. Lichens, found in cold tundra areas, are a great example. They are a partnership between algae (which do photosynthesis) and a fungus (which provides protection). This partnership allows them to thrive. Other important primary producers include coral (which host algae inside them) and many types of brown algae, like kelp.

Flowchart to determine if a species is autotroph, heterotroph, or a subtype

Special Autotrophs: Mixotrophs

Some organisms are a bit of both. They use organic compounds for carbon, but they can get energy from light or inorganic chemicals. These are called mixotrophs. For example, a photoheterotroph gets carbon from organic compounds but uses light for energy. A chemolithoheterotroph gets carbon from organic compounds but uses inorganic chemicals for energy.

Scientists have even found some fungi that might get energy from ionizing radiation. These radiotrophic fungi were discovered growing inside a reactor at the Chernobyl nuclear power plant. This shows how diverse life can be!

How Autotrophs Make Their Own Food

The main way primary producers get energy is through photosynthesis. This process makes energy available to almost all other life forms. Plants, many corals (with their internal algae), some bacteria (like cyanobacteria), and algae all perform photosynthesis. During photosynthesis, primary producers capture energy from the sun. They use this energy to create sugar and oxygen.

Chemosynthesis: Using Chemicals

Another way autotrophs make food is through chemosynthesis. Instead of sunlight, they use energy from chemical reactions. This is common in places where sunlight doesn't reach, like deep-sea hydrothermal vents. Certain bacteria and archaea use chemicals like hydrogen sulfide to create their food.

Why Autotrophs are So Important

Green fronds of a maidenhair fern, a photoautotroph

Without primary producers, Earth's living systems could not survive. Plants and other autotrophs create the energy that other living things eat. They also produce the oxygen that we breathe. Scientists believe the first organisms on Earth were primary producers living on the ocean floor.

Autotrophs are the foundation of all food chains in every ecosystem. They take energy from their surroundings, like sunlight or inorganic chemicals. Then, they use this energy to create fuel molecules, such as carbohydrates. This process is called primary production. Other organisms, called heterotrophs, eat autotrophs for food. This gives them the energy they need to live. All animals, most fungi, and many bacteria and protozoa are heterotrophs. They depend on autotrophs for their raw materials and energy. Heterotrophs get energy by breaking down the carbohydrates, fats, and proteins they eat. Even carnivorous animals rely on autotrophs indirectly. The nutrients their prey provides originally came from the autotrophs the prey consumed.

Most ecosystems rely on the primary production of plants and cyanobacteria. These organisms capture light energy from the sun. Plants use a small part of this energy for photosynthesis. During photosynthesis, a water molecule (H₂O) is split. This releases oxygen (O₂) into the atmosphere. It also changes carbon dioxide (CO₂) to release hydrogen atoms. These atoms power the process of primary production. Plants convert and store the sun's energy in the chemical bonds of simple sugars. These plant sugars are then linked together to form long-chain carbohydrates, like starch and cellulose. Glucose, a simple sugar, is also used to make fats and proteins. When autotrophs are eaten by heterotrophs (consumers like animals), the carbohydrates, fats, and proteins become energy sources for the heterotrophs. Proteins can be made using substances like nitrates, sulfates, and phosphates from the soil.

Where Did Autotrophs Come From?

Scientists think that the very first living cells were autotrophs. They believe these early autotrophs might have been heat-loving and oxygen-free organisms. They likely lived near deep-sea alkaline hydrothermal vents. These vents release hot, chemical-rich water from the Earth's crust. This idea is supported by studies of how life evolved. It suggests that the earliest life forms were able to make their own food using chemicals.

See also

In Spanish: Autótrofo para niños

• Electrolithoautotroph
• Electrotroph
• Heterotrophic nutrition
• Organotroph
• Primary nutritional groups