AP BIOLOGY

Detailed explanation-1: -Cell membranes enable organisms to maintain homeostasis by regulating the materials that may enter or leave a cell. Some materials easily cross the cell membrane without the input of energy; other materials require energy input in order to cross through the cell membrane.

Detailed explanation-2: -The cell membrane controls what goes in and out by having protein channels that act like funnels in some cases and pumps in other cases. Passive transport does not require energy molecules and happens when a funnel opens in the membrane, letting molecules flow through.

Detailed explanation-3: -Homeostasis is the maintenance of stable internal conditions in a changing environment. Individual cells, as well as organisms, must maintain homeostasis in order to live. One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane.

Detailed explanation-4: -Osmosis. Osmosis is a special type of diffusion-the diffusion of water molecules across a membrane. Like other molecules, water moves from an area of higher concentration to an area of lower concentration. Water moves in or out of a cell until its concentration is the same on both sides of the plasma membrane.