Ecology and Environment. A Source Book for High School Students (en Inglés) - Chandan Sukumar Sengupta

Interdependence of plant and animal is also regulated by some of the factors of exchange mechanism through which they utilize resources and caste off waste materials. Everything moves in a definite pattern of interaction for maintaining balance in nature. Organisms inhabit the surrounding at respective trophic level define their role in particular for enabling the entire system to move in a balanced way. It is a self-regulating mechanism through which living and nonliving components of nature interact with each other. 

Even living organisms interact with each other for fulfilling their basic needs. Some organisms, like green plants, are capable of making their own food with the help of sunlight. They utilize water and carbon-di-oxide in this process and liberate oxygen. Such organisms are called autotrophs. Some organisms, like non-green plants and animals, depend upon green plants for their food.