Life is Maintained
Cells are very picky, and constancy is key to proper functioning for these little guys. When thinking about the need for constancy, consider what might happen if you stopped brushing your teeth or showering every day. Your life would probably be thrown into chaos. You'd lose friends (yeah, as much as you'd like to believe that it's your personality that keeps 'em coming back, personal hygiene is pretty important), you'd get cavities and weird diseases…you might even be unlucky enough to develop what we call "Pig-Pen-itis," a disorder that curses you with perpetually orbiting dust clouds and stink lines. Nobody wants that, so our bodies try really hard to keep us in homeostasis.
The chemical processes that take place inside cells are highly sensitive to surrounding conditions. This is because variations in temperature, pH, and concentrations of various substances, like salt, can affect the function of enzymes. Enzymes are the VIPs, or Very Important Proteins, of the protein world. They catalyze, or set in motion, chemical reactions, or processes where one set of chemicals becomes a different set of chemicals. Enzymes can alter the rates at which all those reactions occur. In rare circumstances, enzymes may stop working, which is majorly bad news for the cell that they live in.
As important as constancy is, the reality is that a cell’s environment can change quickly. Just think about the changes your body encounters when you plunge into the cold ocean after basking in the hot sun, or when you wipe out on your surfboard and accidentally swallow a mouthful of salty water. If your cells didn’t have a way to cope with these situations, you’d be toast. Soggy, salty toast. Fortunately, living organisms have all kinds of strategies up their figurative sleeves to maintain homeostasis.
Temperature regulation is a great example. Endothermic organisms, or those who can generate heat internally, use their metabolisms to keep body temperatures constant. Most mammals and birds are endothermic. When the ambient (environmental) temperature is a little too cold, endotherms increase their metabolism, which produces more heat. On the other hand, when the ambient temperature becomes too hot, many animals release sweat to help cool themselves. Under most environmental conditions, the body temperature in these animals remains almost perfectly constant. Nice work, endotherms.