What is it?

Homeostasis is the self-regulation of the internal environment of organisms or cells. If the internal environment of cells fluctuate with every change in the external environment, cells would not be able to carry out essential reactions such as enzyme functions.

Give me an example!

Cellular homeostasis is similar to the way people regulate their environment at home. When winter comes, you probably do not leave all the windows and doors open. And in the summer you probably do not close those same doors and windows and crank up the heat. Generally, people try to regulate the temperature so the inside of the house is uniformly comfortable through out the year.

The membrane is essential for homeostasis. Due to the effects of diffusion and osmosis, cells must actively regulate the flow of water and salts in and out of the cells. This often involves the use of energy in the form of ATP. When ATP is used, this is termed active transport.