Last Updated on July 17, 2020 by Sagar Aryal
An autotroph is a group of organisms capable of producing their own food by utilizing various substances like water, sunlight, air, and other chemicals.
- The autotroph is made up of two words; ‘auto’ meaning self and ‘troph’ meaning food.
- Autotrophs are thus, capable of producing their own food without any assistance from others.
- Autotrophs are also called ‘producers’ as they form the base of ecological food chains and are responsible for all other food for all other organisms.
- These organisms are extremely important as all other life forms depend directly or indirectly on these organisms for food and energy.
- The most commonly known autotrophs are plants; however, several other varieties of autotrophs are found in nature, ranging from algae, phytoplankton, and some bacteria.
- Most autotrophs use photosynthesis to convert solar energy to chemical energy, but various autotrophs also utilize other processes like phototrophy and chemotrophy.
- All green plants contain chlorophyll as the photosynthetic pigment for the process of photosynthesis. Other pigments like bacterial rhodopsin and carotenoids are also found in some bacteria, algae, and phytoplankton for photosynthesis.
- Some rare autotrophs generate food by the process of chemosynthesis which derives the energy from chemical reactions, rather than sunlight.
- Organisms performing chemosynthesis live in extreme environments where the toxic chemicals necessary for the reactions are found. Bacteria found in volcanoes use sulfur to produce their food.
- Autotrophs form the first trophic level in the food chain. These organisms are then eaten by herbivores which form the second trophic level and so on.
- An increase in the number of autotrophs eventually increases the number of consumers. Meanwhile, a decrease in the number of autotrophs causes starvation to all other trophic levels.
A heterotroph is a group of organisms that obtain their food from other organisms and are not capable of producing their own food.
- The term heterotroph is made up of two words; ‘hetero’ meaning others and ‘troph’ meaning food.
- Heterotrophs are also called consumers as they consume food prepared by autotrophs. These organisms form higher trophic levels in the food cycle.
- Heterotrophs are further divided into two types based on the source of their energy. Photoheterotrophs obtain their energy from light but depend on producers for their carbon source.
- Chemoheterotrophs, in turn, obtain both their energy and carbon from other producers.
- Some heterotrophs directly depend on autotrophs for their food like herbivores feeding on plants. Other heterotrophs indirectly depend on the producers by feeding on the first type of heterotrophs.
- Most heterotrophs depend on the process of photosynthesis in a number of different ways. In addition to providing the energy and food, photosynthesis also provides oxygen tot eh heterotrophs.
- The reduced carbon compounds formed by autotrophs are then oxidized by heterotrophs to produce energy for their growth and reproduction.
- Heterotrophic nutrition is further divided into three types; saprotrophic nutrition, parasitic nutrition, and holozoic nutrition.
- Saprotrophs are the type of heterotrophs that feed on the dead and decaying organic materials as a source of energy, carbon, and nutrients.
- Holozoic organisms are another group of heterotrophs that consume solid food from other organisms and break down the food into smaller particles before they are transported to different parts of the body.
- Parasites are heterotrophs that are entirely dependent on other organisms for all forms of nutrition. In this association, the parasite is benefitted, whereas the host is not.
Key Differences (Autotroph vs Heterotroph)
Basis for Comparison
|Definition||An autotroph is a group of organisms capable of producing their own food by utilizing various substances like water, sunlight, air, and other chemicals.||A heterotroph is a group of organisms that obtain their food from other organisms and are not capable of producing their own food.|
|Source of energy||The source of energy in autotrophs is either sunlight or chemical reactions.||Autotrophs are the direct or indirect source of energy in heterotrophs.|
|Dependency||Autotrophs are independent and can produce their own food.||Heterotrophs are directly or indirectly dependent on autotrophs.|
|Trophic level||Autotrophs form the lowest trophic level in the food chain.||Heterotrophs form the second or third trophic levels in the food chain.|
|Solar energy||Solar energy can be stored in some autotrophs.||Solar energy storage or utilization is not possible in heterotrophs.|
|Role||Autotrophs act as producers.||Heterotrophs act as consumers.|
|Types||Autotrophs are of two types; photoautotrophs and chemoautotrophs.||Heterotrophs are also of two types; phytotoheterotrophs and chemoheterotrophs.|
|Organisms||Autotrophs are mostly plants, algae, and some bacteria.||Heterotrophs are mostly animals, fungi, and some bacteria.|
|Photosynthesis||Photosynthesis acts as the major metabolic pathway for the production of energy.||Photosynthesis doesn’t occur in heterotrophs.|
|Photosynthetic pigments||Photosynthetic pigments are usually present.||Photosynthetic pigments are absent.|
|Carbon source||Autotrophs use inorganic carbon as the carbon source.||Heterotrophs use organic carbon as a carbon source.|
|External energy source||Autotrophs require an external source of energy like sunlight or chemical reactions.||Most heterotrophs do not require a separate energy source. Photoheterotrophs might use sunlight as a source of energy.|
|Availability||Autotrophs make food at a particular period of time. Plants make food in the day while chemoautotrophs depend on the chemical reaction.||Food is available to heterotrophs almost any time of the day.|
|Examples||Plants, algae, cyanobacteria, etc.||Humans, animals, fungi, heterotrophic bacteria.|
Examples of Autotrophs
- Green plants are the most important group of autotrophs that utilize solar energy for the assimilation of inorganic compounds to form organic compounds.
- Plants bear chlorophyll as a photosynthetic pigment that is capable of trapping solar energy, which is then converted into chemical energy via various metabolic pathways.
- Primary consumers like herbivores directly depend on plants for their food as well as energy, whereas secondary consumers like carnivores indirectly depend on green plants.
- Green plants occupy the primary trophic level in the food chain and provide the energy that is then distributed through the entire chain.
- Plants utilize carbon dioxide water and sunlight to prepare carbohydrates (glucose) and oxygen.
- Green algae are another group of organisms that can produce their own food via photosynthesis.
- These are photoautotrophs and are mostly found in ponds and wetlands.
- These organisms, like plants, bear chlorophyll as the photosynthetic pigment to trap the solar energy necessary for the process.
- Green algae forms green mats on the ground, which helps to add oxygen to the atmosphere.
- Nitrosomonas is a group of nitrogen-fixing bacteria that convert molecular nitrogen into an organic form that can be taken up by plants in the soil.
- These are chemoautotrophs that utilize the energy produced from the chemical reaction as a means for food preparation.
- These organisms take up nitrogen and reduce it to nitrate form that can then be incorporated into the plants in the form of amino acids.
- Thus, from the reaction involved in nitrogen fixation, they obtain the energy necessary for amino acid preparation.
Examples of Heterotrophs
- Animals make up most of the organisms in the consumers a trophic level of the food chain.
- All animals are heterotrophs, depending directly or indirectly on plants and plant products for food and energy.
- Herbivores are the primary consumers that directly feed on plants and obtain their source of carbon.
- Carnivores are the secondary consumers that feed on herbivores for their food.
- These animals obtain carbon in the organic form, which is then broken down to generate energy for growth and reproduction.
- Humans, as omnivores, feed both on plants and animals and thus are heterotrophs.
- Fungi are heterotrophs that do not feed on autotrophs but absorb their food.
- These are saprophytes that feed on nutrients rather than the organic matter.
- Most saprophytic fungi dwell in areas with the dead and decaying matter as it provides simpler forms of energy.
- They secrete digestive enzymes that help break down the food into smaller particles before consuming them.
- Some fungi, however, are parasitic and thus feed on the host, with or without harming the host.
- Fungi act as decomposers in the food chain that helps cycle the energy back to the atmosphere for the autotrophs to capture.
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