Which term describes the tendency to maintain a balance, or optimal level, within a biological system? homeostasis melatonin rhythm insomnia?

Homeostasis.

Explanation:

Homeostasis my be defined as the mechanism of maintaining the proper life processes of the body. Almost all the living organisms has the tendency to perform homeostasis.

The main function of the homeostasis is to maintain the balance of the internal life in accordance with the change in the external and internal environment. The optimal level of the body is maintained by the process of the homeostasis.

Thus, the correct answer is option (1).

then that particular organisms become extinct.

yes it is weird but true