AP BIOLOGY

Detailed explanation-1: -These molecules need special transport proteins to help them move across the membrane, a process known as facilitated diffusion. These special proteins are called channel proteins or carrier proteins (Figure below), and they are attached to the cell membrane.

Detailed explanation-2: -Processes of passive transport play important roles in homeostasis . By allowing the movement of substances into and out of the cell, they keep conditions within normal ranges inside the cell and the organism as a whole.

Detailed explanation-3: -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. Each transport protein is specific to a certian molecule (indicated by matching colors).