selective permeability
Probably the most important feature of a cells phospholipid membranes is that they are selectively permeable or semipermeable . A membrane that is selectively permeable has control over what molecules or ions can enter or leave the cell, as shown in Figure below . The permeability of a membrane is dependent on the organization and characteristics of the membrane lipids and proteins. In this way, cell membranes help maintain a state of homeostasis within cells and tissues, organs, and organ systems so that an organism can stay alive and healthy.