Heterotroph

Based on Food Habits

Heterotrophs are primarily classified into four different types based on their food habit and presence in the food chain. They are herbivores, carnivores, omnivores, and detritivores.

1. Herbivores feed on autotrophs like plants and algae for food. Herbivores occupy the second trophic level of the food chain.

Examples: Deer, cow, and buffalo

2. Carnivores eat meat and feed on herbivores, thus called primary consumers. Carnivores inhabit the third trophic level of the food chain.

Examples: Tiger, wolf, and crocodile

3. Omnivores: They eat both plants (autotrophs) and meat (herbivores and carnivores) and are thus called secondary consumers. Similar to carnivores, omnivores also occupy the third trophic level of the food chain.

Examples: Humans, bears, and foxes

4. Detritivores (Decomposers) feed on the remains of plants and animals and fecal matter. Detritivores help to clean the ecosystem and keep them healthy.

Examples: Bacteria, fungi, worms, and insects

Based on Energy Source

Heterotrophs are also sometimes classified based on their energy source into two types. They are photoheterotrophs and chemoheterotrophs.

a. Photoheterotrophs get their energy from light. They, however, obtain carbon from other organisms as they cannot utilize carbon dioxide directly from the atmosphere.

Examples: Purple non-sulfur bacteria, green non-sulfur bacteria, and heliobacteria

b. Chemoheterotrophs get both light and carbon from other organisms. They cannot utilize light and carbon dioxide from the atmosphere.

Examples: Bacteria and archaebacteria in deep-sea vents and volcanoes

Autotrophs and heterotrophs have many differences with some similarities.

Differences

Basis	Autotroph	Heterotroph
1. Produce own food	Yes.	No.
2. Examples	Plant, algae, and autotrophic bacteria	All animals, including humans, parasitic plants, fungi, protists, and heterotrophic bacteria
3. Source of energy	Sunlight or chemical reactions	Autotrophs
4. Trophic level in the food chain	Exist in the first trophic level of the food chain.	Exist in the second and third trophic levels of the food chain.
5. Role in the food chain	Producer	Consumer
6. Photosynthesis	Perform photosynthesis to produce their food	Cannot perform photosynthesis
7. Carbon Source	Use inorganic carbon as the carbon source	Use organic carbon as the carbon source
8. Types	They are of two types: 1) photoautotrophs and 2) chemoautotrophs	They are also of two types: 1) phytotoheterotrophs and 2) chemoheterotrophs
9. Dependent	They are independent as they can produce their food and thus are also called ‘self-feeders’	They are dependent on autotrophs for food and thus are also called ‘other-eaters’

Similarities

Both are:

• Living things and thus need food and energy to survive
• Can reproduce
• Respond to the environment and maintain homeostasis
• In need of carbon source (inorganic  or organic)
• Made of cells
• Part of the ecosystem and food chain of the biosphere

The key differences and similarities between an autotroph and a heterotroph are shown using a Venn diagram.