Autotrophs are organisms that produce their food by using light, carbon dioxide, water and other chemicals. Autotrophs use photosynthesis and chemosynthesis as a method of synthesising their food. They are the primary producers in any food chain. They are found on land as well as in oceans in the form of aquatic plants.

Types of Autotrophs

There are two types of autotrophs:

Photoautotrophs: 

• All photoautotrophs have chlorophyll in their leaves, which allows them to capture and absorb light for photosynthesis.
• They absorb light from the sun and convert it into energy that is used to produce food.
• They are eukaryotic organisms. 
• Many prokaryotes are also capable of photosynthesis
• Bacteria are examples of prokaryotes as they make their food and multiply in numbers by themselves.

Chemoautotrophs:

• They produce food by chemosynthesis. 
• Unlike photosynthesis, where light, water and carbon dioxide is used to produce food, in chemosynthesis, a combination of chemicals is used.
•  For example, methane and hydrogen sulphide are used with oxygen to make carbon dioxide and energy.

These are also divided into two groups:

1. Chemoorganotrophs: They use organic molecules as a source of their energy. 
2. Chemolithotrophs: They use inorganic molecules as a source of their energy.

• Chemotrophs are also known as lithotrophs. 
• Many bacteria come in this category, like bacteria in worms found in deep-sea and nitrifying bacteria.
• Lithotrophs live in environments that do not have access to sunlight.
• They undergo biosynthesis, which means oxidation of inorganic materials.
• During biosynthesis, the chemicals provide electrons, and so they are oxidised to produce energy.
• For example, when hydrogen sulphide is oxidised, the electrons are used in oxidative phosphorylation, which produces ATP.

Autotroph Examples

1. Algae – Algae are eukaryotic organisms with a very large and diverse biodiversity. They have a nucleus. They have no roots, stems or leaves.
2. Cyanobacteria ( or Cyanophyta): These are prokaryotic organisms. They have a combination of pigments and can perform oxygenic photosynthesis, where the final electron acceptor is water.
3. Maize plant (or Corn): It is a C4 plant that has a height of more than 1 metre and less than 4 metres. Maize is consumed by human beings and is used as cattle feed. It is also used as biofuel and as a raw material for several industries.
4. Grass: It is used as cattle feed, shelter for wildlife, food for humans, for furniture construction and many other purposes.
5. Wheat: It is used for making bread, pasta, tortillas and many other food items. Wheat plants have long leaves and hollow stems.
6. Seaweed: It is also known as microalgae, a species of multicellular marine algae. It grows in oceans, rivers, lakes and water bodies.
7. Phytoplankton:  It is also a microscopic marine algae containing chlorophyll and needs sunlight to reproduce as well as survive.
8. Euglena: It comes from the genus protist and is a single-celled organism. It has characteristics of both plants and animals. For example, it can manufacture food and can also move around to procure food.
9. Bacteria: They are prokaryotic single-celled organisms without a nucleus membrane. They are microscopic, but they are biodiverse. As such they exist in a huge number. 
10. Proteobacteria: Its common name is purple bacteria and it makes up one of the largest phyla in the bacteria domain. It contains many different types of bacteria including phototrophs and chemolithotrophs.
11. Heliobacteria: They are prokaryotic bacteria that process sunlight to produce energy. They are found in the soil, hot springs, soda lakes and waterlogged soils of fields.
12. Sulphur bacteria: They are microorganisms that use sulphur and the compounds of sulphur as a form of energy source. They also need light as energy. 
13. Chloroflexi: They are identified as green nonsulfur bacteria. They are mostly found in water bodies like oceans, rivers and lakes.

Conclusion 

Autotrophs are organisms that can produce their own food. They are phototrophs if they produce food with the help of sunlight, water and carbon dioxide. They are chemoautotrophs if they need chemicals to produce their food.

Most autotrophs make their food by the process of photosynthesis because they have cellulose and chlorophyll. As autotrophs produce their food, they are the producers in any food chain. They are in the top position of every food chain. Examples of decomposer autotrophs include bacteria, plants, algae and a few prokaryotic organisms.