Energy enters in a food chain, in form of solar energy through producers, i.e., green plants and photosynthetic bacteria. The green plants and photosynthetic bacteria synthesise their food (carbohydrate) through photosynthesis These organisms occupy the first trophic level in food chain. Primary consumers (e.g., rabbit, deer, squinels etc.), secondary consumers (carnivorous birds- snake, lizards etc.) and tertiary consumers (eagle, lion etc.) forms the successive trophic levels.