The sun is the ultimate source of energy for all living things. The energy flow occurs through food chain. A food chain is the simple model that shows how matter and energy moves through the ecosystem from one organism to another.
Green plants trap the sun’s energy by the process of photosynthesis and make food.
This food is eaten by herbivores like cow or deer etc.
Herbivores are then eaten by carnivores like tiger. This flow of food in the form of energy is called Food Chain.
A food web is also the good model that shows how matter and energy moves various organisms.