The biosphere can best be defined as

These are the regions of the earth that are occupied by living organisms.

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The biosphere can be defined as the place where life occurs. It is a place rich in variety of plants, animals and many other life forms.

Explanation:

Biosphere can be defined as the place where there is a interaction between the living and non living system. The living forms of life like plants and animals  interact with soil, air and water in order to survive.

So, a biosphere can be defined as a place which is full of life.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.