Types of Heterotrophs based on the energy source

1. Photoheterotrophs

• Photoheterotrophs or heterotrophic phototrophs are a group of living beings that derive their energy from solar energy but depend on autotrophs for food.
• These heterotrophs cannot utilize carbon dioxide as a carbon source and require other organic compounds. These are also known as holozoic organisms.
• These photoheterotrophs utilize systems like electron transport chains or direct proton pumping in order to generate an electrochemical gradient to provide molecular energy.
• Photoheterotrophs can generate ATPs through phosphorylation, but they depend on organic compounds for growth and biomolecules.
• Photoheterotrophy is an important lifestyle for organisms living in areas where growth and survival are limited by the availability of energy-rich niches.
• Most commonly, photoheterotrophs occur in surface water with large populations of living beings. The ability to utilize solar energy to produce energy decreases their dependency on respiration.
• Some of the examples of photoheterotrophs include Heliorestis baculata, H. convulata, and Synechococcus elongatus.

2. Chemoheterotrophs

• Chemoheterotrophs are heterotrophs that obtain their energy from chemical compounds and consume food produced by autotrophs.
• Unlike phototrophs, chemotrophs cannot utilize solar energy and depend on energy obtained from reduced carbon compounds by the process of respiration.
• A particular group of chemoheterotrophs can derive energy from inorganic chemical substances; however, they still require organic compounds to build their biomass and form biomolecules.
• Chemoheterotrophs are the larger group of heterotrophs which includes organisms from all domains. 
• Chemoheterotrophs are essential for the normal functioning of an ecosystem as these organisms take up organic materials from plants and other autotrophs and cycle them through the food web.