Organisms must be able to adapt to a changing external and internal environment. an organism's ability to maintain a stable internal environment is known as homeostasis. how does a cell's membrane an organism maintain homeostasis? a. cell membranes control the substances that enter or leave cells. b. cell membranes use a large portion of the cell's energy supply. c. cell membranes protect the cell organelles from large doses of radiation. d. cell membranes directly control the temperature of the cell. the answer is a.