The biosphere refers to the entire mass of living species on the earth. The biological processes depend on sunlight for their energy. Each organism has certain limiting physical conditions for its survival and growth. It implies that the types of plants and animals in a particular region depend on the prevailing physical environment. Each organism prefers a certain habitat. The organisms not only act and react with each other, but also with the environment around them, thus creating an ever-dynamic system of actions and interactions, the subject-area of ecology.