The autotrophs are the primary producer in the food chain and they are the ones who initiate the food chain. They produce food by using sunlight or sometimes chemical energy or reactions. They primarily use carbon dioxide, sunlight and water to form sugars or carbohydrates which become their energy source. They use the process of photosynthesis or chemosynthesis to generate food. Examples of autotrophs are green plants, green algae, bacteria.
Heterotrophs cannot make their food via sunlight or other inorganic sources and hence are dependent on the autotrophs or other animals. The heterotrophs have been ranked as secondary and tertiary consumers and cannot be producers. They consume the organic products made by autotrophs to obtain energy for various metabolic and biological activities. The heterotrophs can be herbivore, carnivore, fungi, parasitic plants.
Some are photo-hetrotrophs, who use light as energy but cannot use carbon dioxide as the carbon source since they cannot fix the carbon like autotrophs.
