AP BIOLOGY

Detailed explanation-1: -Plasma membranes must allow certain substances to enter and leave a cell, while preventing harmful material from entering and essential material from leaving. In other words, plasma membranes are selectively permeable-they allow some substances through but not others.

Detailed explanation-2: -Cell Membrane (Plasma Membrane) The cell membrane consists of a lipid bilayer that is semipermeable. The cell membrane regulates the transport of materials entering and exiting the cell.

Detailed explanation-3: -In its role as gatekeeper, the cell membrane regulates molecular traffic into and out of the cell via specialized membrane proteins.

Detailed explanation-4: -A plasma membrane is permeable to specific molecules that a cell needs. Transport proteins in the cell membrane allow for selective passage of specific molecules from the external environment.