Homeostasis is the state of maintaining a stable what?

A stable internal environment

Explanation:

This internal environment includes the tissue fluid that bathes the cells. Homeostasis allows this to happen by maintaining the exchange between your plasma in the blood capillaries and the tissue fluid (interstitium).

This will remove any waste products, like carbon dioxide, that'll affect the rate of chemical reactions (too much CO2 will lower ph of any fluid) and provide oxygen and glucose. By providing glucose to the cells, your blood will be maintaining a blood glucose level and it wouldn't rise too much.

atp is used for energy.