Definition of Heterotrophs and Autotrophs, Types Examples,

Definition of Heterotrophs 

Definition of Heterotrophs are organisms that do not make their food and depend on other organisms for their food and energy.

  1. Heterotrophs are a group of organisms other than autotrophs that prepare their food and provide food for the heterotrophs.
  2. The word heterotrophic consists of two words; “Hetero” means other and “trophy” means food, indicating that these organisms are dependent on organisms other than food.
  3. Heterotrophs are also known as consumers in the ecosystem because they consume food prepared by autotrophs and form the highest trophic level in the food chain.
  4. Unlike autotrophs, heterotrophs do not have systems for reducing carbon sources. These organisms take complex biomolecules from producers and break them down into simpler components with the help of various enzymes.
  5. Heterotrophs remove reduced organic compounds from autotrophs and oxidize them to produce energy.
  6. Although most heterotrophs depend on autotrophs for energy and food, some heterotrophs obtain energy from solar energy or chemical reactions.
  7. Heterotrophs are important in ecosystems because they make up a large proportion of biomass and are responsible for the transport of energy and biomass through the food chain.
  8. Heterotrophs can be divided into different consumer groups as primary, secondary, and tertiary consumers. Heterotrophs also form decomposers in the food chain that feeds on dead and decaying biomass from the environment.
  9. Different groups of heterotrophs have different complexities and systems that allow them to extract energy and food from autotrophs.

What are the Types of heterotrophs based on the energy source?

Types of heterotrophs based on the energy


  1. Photoheterotrophs or heterotrophic phototrophs are a group of living things that obtain their energy from solar energy but depend on autotrophs for food.
  2. These heterotrophs cannot use carbon dioxide as a carbon source and require other organic compounds. These are also called holozoic organisms.
  3. These photoheterotrophs use systems such as the electron transport chain or direct proton pumping to create an electrochemical gradient to provide molecular energy.
  4. Photoheterotrophs can produce ATP through phosphorylation, but they rely on organic compounds for their growth and biomolecules.
  5. Photoheterotropy is an important lifestyle for organisms living in areas where growth and survival are limited by the availability of high-energy niches.
  6. Photoheterotrophs are most common in surface waters containing large populations of living things. The ability to use solar energy to generate energy reduces their reliance on breathing.
  7. Some examples of photoheterotrophs are Heliorestis bacula, H. Konsulat, and Synechococcus elongatus.


  1. Chemoheterotrophs are heterotrophs that obtain their energy from chemical compounds and consume food produced by autotrophs.
  2. Unlike phototrophs, chemotrophs cannot use solar energy and rely on energy that is obtained from low-carbon compounds through the process of respiration.
  3. A certain group of chemoheterotrophs can obtain energy from inorganic chemical substances; however, they still require organic compounds to build their biomass and form biomolecules.
  4. Chemoheterotrophs are a large group of heterotrophs that includes organisms from all domains.
  5. Chemoheterotrophs are essential for the normal functioning of an ecosystem because these organisms ingest organic materials from plants and other autotrophs and transmit them through the food web.

What are the types of heterotrophs based on electron source


  1. Organotrophs are heterotrophs that use organic compounds for both energy and food.
  2. These organisms obtain energy from the oxidation of organic compounds through internal respiration.
  3. In organotropes, the organic compound serves as the source of an electron, which then travels down the electron transport chain to produce ATP.
  4. Organotrophs include all animals and some bacteria. Organotrophic bacteria can be aerobic or anaerobic.


  1. Lithotrophs are heterotrophs that use inorganic compounds or geological processes as a source of electrons.
  2. The most common inorganic compounds used as electron sources include elemental sulfur and elemental gases.
  3. Most lithotrophs are small bacteria because inorganic compounds do not produce enough energy, as is the case with larger organic sugars.
  4. These can oxidize electron donors to produce electrons that are directed into electron respiration channels to form ATP.
  5. The only known lithotropic organisms are unicellular organisms; However, multicellular organisms can obtain energy from symbiosis with unicellular organisms.
  6. Most lithotrophs are found in areas such as the ocean floor or underground water sources where chemical food sources are found.

What are the Examples of heterotrophs?

1. Fungi

  1. Fungi are a group of eukaryotes that depend on dead and decaying matter for both food and energy.
  2. Fungi are organo-heterotrophic organisms that use complex organic compounds as a source of electrons.
  3. Fungi are decomposers in the food chain, where they consume dead and decaying organisms and release simple molecules so that these can be used by autotrophs.
  4. These mainly occur in arid and arid environments and occur in soil, where most of the dead and decaying components occur.
  5. There are a large number of fungi, which can be aerobic or anaerobic, and produce varying amounts of energy from organic compounds depending on the availability of oxygen.

Photoheterotrophic Cyanobacteria

  1. Photoheterotrophic cyanobacteria are a group of microorganisms with superior photosynthetic efficiency and minimal growth requirements.
  2. These bacteria cannot use carbon dioxide as a carbon source, but they can use solar energy for electron transfer in the electron transport chain.
  3. Bacteria are found in aquatic or humid environments where they feed on organic compounds produced by autotrophic aquatic organisms.
  4. These are increasingly being studied for their ability to produce large amounts of energy in the presence of sunlight.

Iron Reducing Bacteria

  1. Iron-reducing bacteria are bacteria that metabolize reduced iron into oxidized iron compounds to produce energy.
  2. The energy obtained from this process is used for the absorption and metabolism of the carbon source.
  3. These bacteria have been proposed to be used to purify metal or metal-contaminated environments.
  4. Even though iron-reducing organisms are associated with extreme environmental conditions, they can occur in other regions as well.
  5. The presence of these bacteria in extreme environments is due to the presence of inorganic compounds in such environments.


  1. Animals form the most important group of heterotrophs in the environment as they occupy the maximum number of trophic levels in the food chain.
  2. All animals are heterotrophs, but their dependence on autotrophs may vary, as some are autotrophs while others are indirectly dependent.
  3. Herbivorous animals feed on autotrophic organisms such as plants and phytoplankton for both energy and food.
  4. Carnivores, in turn, eat herbivores, which indicates an indirect dependence on autotrophs.
  5. Organic compounds are absorbed by organisms, which are then broken down into simpler molecules according to various mechanisms.

Heterotrophs in the food chain

  1. Heterotrophs are the largest group of living organisms in the food chain and occupy multiple trophic levels.
  2. The second trophic level is occupied by consumers who feed directly on autotrophs to initiate energy transfer in the system.
  3. At the third trophic level, heterotrophs are secondary consumers that feed on primary consumers. These are more complex groups of organisms that feed on organic compounds.
  4. Decomposers are another important group of organisms that live at higher trophic levels of the ecosystem. These are an essential group of heterotrophs that feed on the dead and decaying matter to release inorganic compounds back into the environment.
  5. Each trophic level transfers 10% of the energy, while the rest of the trophic level is stored as biomass.

Definition of Autotrophs

Autotrophs are organisms that are capable of making their own food using various inorganic components such as water, sunlight, air and other chemical substances.

Autotrophs are the source of all organic compounds on the planet that are used by organisms that cannot prepare their own food.

The word autotrophic is made up of two words; “Auto” means self and “troph” means food, which indicates that these organisms can prepare their own food.

They are also called producers in ecology, as they produce organic compounds from inorganic compounds, which then pass through different trophic levels of the food chain.

Autotrophs are one of the most important living organisms on the planet as all other living organisms depend on them for food and energy.

Depending on the type of autotrophs, they either use solar energy as the primary energy source or energy from chemical reactions.

All autotrophs use an inorganic carbon source, which is then converted into organic compounds in the presence of energy.

Green plants are the best-known group of autotrophs, as they are responsible for practically all organic components of the environment.

There are also other autotrophs such as green algae, phytoplankton, and bacteria that produce organic compounds in land and water environments.

Autotrophs occur in the first trophic level of most food chains, which are then consumed by heterotrophs to maintain the flow of energy in the chain.

The number of autotrophs in an ecosystem is important because it affects the population of all other groups of living organisms.

An increase in the number of autotrophs in an area leads to an increase in the number of heterotrophs, while a decrease in the number leads to a decrease in the number of other organisms.

The term autotrophy is often used interchangeably with autotrophs, which refers to the eating habits of these organisms.

What are the Types of Autotrophs?

Autotrophs can be divided into two categories based on the energy source they use to make their food.


  1. Photoautotrophs are autotrophs that use solar energy and carbon dioxide to prepare their own food through the process of photosynthesis.
  2. Photoautotrophs have a photosynthetic reaction center, which contains chlorophyll. Chlorophyll pigment is responsible for the transmission of radiation in the cells.
  3. Photoautotrophs can be divided into two groups based on the number of reaction centers in the photosynthetic system and their ability to use water; Oxygenic photoautotrophs and anoxygenic photoautotrophs.
  4. Oxygen photoautotrophs use water as a reducing force to produce oxygen. Anoxygenic photoautotrophs rely on the reducing power of the environment to assimilate carbon dioxide.
  5. Photoautotrophs were thought to be solely responsible for life on Earth; However, this idea was challenged by the discovery of chemolithoautotrophs.
  6. Photoautotrophs are green plants and algae that contain chlorophyll. Chlorophyll is involved in capturing energy from sunlight, which is used to convert carbon dioxide into glucose.
  7. Green plants are producers of terrestrial and aquatic ecosystems that are consumed by heterotrophs, the so-called consumers.
  8. The energy collected by green plants is transferred to other animals through the food chain which forms the basis of the ecosystem.
  9. Apart from green plants, many photosynthetic bacteria contain other photosynthetic pigments like rhodopsin, carotenoids, etc.
  10. Photoautotrophs are also important in the carbon cycle, as they use up the carbon dioxide released by heterotrophs during respiration.
  11. 2. Chemoautotrophs
  12. Chemoautotrophs are autotrophs that use energy from a chemical reaction with oxidation to prepare their food.
  13. They differ from photoautotrophs in that they do not rely on sunlight as an energy source.
  14. In the case of chemoautotrophs, the source of carbon is an oxidized form of carbon such as carbon dioxide.
  15. The best-known group of chemoautotrophs includes chemolithoautotrophs, which are found in rocks and use inorganic sources such as iron ions, hydrogen, and hydrogen sulfide.
  16. These autotrophs are found in extreme habitats such as deep-sea holes, acidic environments, and deep estuaries.
  17. All chemoautotrophs are microorganisms belonging to the Archaea and Bacteria domains. These have been studied extensively over the years to discover their role in the evolution of living things on the planet.
  18. Chemoautotrophs are also being studied for their role in astrobiology due to their ability to survive in extreme conditions.
  19. The energy consumed by these microorganisms is derived from chemical reactions taking place in the environment. The energy is then converted into cellular energy by the microorganisms.

What are the Examples of Autotrophs?

Given below are some examples of autotrophs;

Green plants

Green plants are prime examples of autotrophs as they are responsible for almost all the biomass on the planet.

Green plants are photoautotrophic plants that capture solar energy to reduce carbon dioxide to glucose.

Green plant cells contain chlorophyll, which is the photosynthesis center of these organisms. Chlorophyll captures rays of different wavelengths and uses the energy to transfer electrons to the water molecule.

These plants are called producers, and they provide food for other plants as well as for heterotrophs. These come from the primary trophic level in the food chain.

Food is prepared in the green parts of the plant, which is then transferred to other parts through the plant’s tissues.

Green plants are found in most ecosystems, where they are the main source of food and energy for all other living organisms.

Green sulfur bacteria

Green sulfur bacteria are strictly anaerobic, photoautotrophic microorganisms that form carbon compounds using sulfur compounds as electron donors.

The photosynthesis center of these bacteria is similar in structure and function to the photosystems of plants and cyanobacteria.

The light-induced electron transfer in green sulfur bacteria is not cyclic, leading to the formation of NADPH.

Green sulfur bacteria live in sulfur-rich environments with low light intensity. To receive enough light, they have an extensive antenna system to capture all the available photons.

Unlike photosynthesis in green plants, photosynthesis in green sulfur bacteria does not produce oxygen.


Methanogens are a group of bacteria that produce methane and other organic compounds using electrons contained in hydrogen gas.

These bacteria are found in underground areas such as the ocean floor, deep ocean trenches and vents, where they produce large bubbles of methane gas.

Most methanogens use acetate as the primary carbon source, which leads to the production of acetyl-CoA during autotrophic CO2 fixation.

The process of methane production by these bacteria is known as methanogenesis and is driven by energy obtained through various chemical reactions.

The biological production of methane is not as efficient as industrial processes; However, the methane produced by these organisms has a greater tolerance to contaminants.

Some examples of methanogenic bacteria are Methanococcal, Methanobacteria, Methanosarcina, etc.

D. Nitrogen-fixing bacteria

Nitrogen-fixing bacteria are a group of bacteria involved in the conversion of molecular nitrogen to its organic form. The organic form of nitrogen can be absorbed by plants as a nutrient.

These bacteria are chemoautotrophic bacteria that use the energy obtained in a chemical reaction to transfer electrons from donor to recipient.

Molecular nitrogen in the environment is converted by these bacteria into nitrate, which is then ingested by plants to produce amino acids.

Nitrogen fixation is an important process in the nitrogen cycle as well as in plants, as plants depend on the process for their nitrogen needs.

Some of these bacteria exist in a symbiotic relationship with various plants, which enables the conversion of unusable inorganic nitrogen into a usable organic form.

Some examples of nitrogen-fixing bacteria are Azotobacterium, Azospirillum, Rhizobium, etc.

Autotrophs in the Food Chain

  1. Autotrophs form the first trophic level of the ecological food chain. Autotrophs are called producers because they produce food and energy which are then transferred to organisms in the upper trophic levels.
  2. Autotrophs are the primary energy source in all food chains that provide energy to consumers and decomposers.
  3. About 10% of the energy produced by autotrophs is carried to the next trophic level, while the rest is stored in the ecosystem.
  4. Autotrophs form the largest trophic level in the ecological pyramid in terms of both biomass and energy.
  5. Autotrophs are directly consumed by primary consumers, thereby transferring energy. The energy then slowly moves up the chain, eventually reaching the apex predators.

What is the Difference between Autotrophic and Heterotrophic modes of nutrition?

Autotrophic NutritionHeterotrophic Nutrition
In autotrophic nutrition, organisms prepare their own foodIn heterotrophic nutrition, organisms do not prepare their own food
Autotrophs are the producers in the food chainHeterotrophs are the consumers in the food chain
Autotrophs use simple substances from surroundings to produce foodHeterotrophs consume organic compounds produced by the autotrophs
Example: Plants and some algaeExample: Animals and some plants

Autotrophic vs Heterotrophic 

  1. Autotrophs are members of the plant kingdom and some unicellular organisms such as cyanobacteria. On the other hand, heterotrophs are all members of the animal kingdom.
  2. The diet of autotrophs is that they are producers and prepare their own food in the presence of sunlight using the process of photosynthesis. Whereas the diet of heterotrophs is that they are consumers who depend on others for their food.
  3. Autotrophs can be divided into photoautotrophs and chemoautotrophs. And heterotrophs can be divided into photoheterotrophs and chemoheterotrophs.
  4. Autotrophs form the lowest trophic level in the food chain, while heterotrophs form the second or third trophic level.
  5.  Autotrophs act as producers and heterotrophs as consumers.
  6.  Solar energy can be stored in some autotrophs, whereas it is not possible to store or use solar energy in heterotrophs.
  7. In autotrophs, chloroplast helps in food preparation, whereas heterotrophs do not have chloroplasts and hence cannot make their food.
  8. Autotrophs draw energy from inorganic sources by converting light energy into chemical energy, whereas heterotrophs draw energy directly or indirectly from other organisms.
  9. Autotrophs cannot move from one place to another, whereas heterotrophs can move from one place to another in search of food and shelter.
  10.  Examples of autotrophs are green plants, algae, and some photosynthetic bacteria. Examples of heterotrophs are cows, buffaloes, tigers, humans, etc.
  11. Therefore, the main difference between autotrophs and heterotrophs is that the former can use photosynthesis to produce their food, whereas the latter cannot.
Definition of Heterotrophs and Autotrophs, Types Examples,

Definition of Heterotrophs and Autotrophs, Types Examples,

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