Let me put this way. Every creature lives by acquiring things from its environment to maintain and promote its own existence. Let me then provide a working definition.
An environmental acquisition system of a living organism is that system of an organism which must acquire something from the environment, process that which it has acquired, for a product that maintains and promotes the life of that organism.
1) The respiratory system.
2 The digestive system.
3) The vestibular system.
4 ) The ocular system.
5 ) The manipulative system.
6.) The procreative system.
7 ) The judgmental system.
One of the things that an intelligent person should know, What determines if one or more words may or may not be asserted of or denied of another word?
It is the reason why some, correctly claimed, that standards were independent of both gods and men. Therefore, those who ask for opinions are lost two-fold--or more.
Those are the sacred seven of scripture, and biology of man. Each of them exists so that we may have life and have it more abundantly. The failure of any of them means that system cannot contribute its share of life to the body whole.