AP Bio Study Guide

Big Idea 2.B

What is active transport?

Active transport is the movement of molecules against a gradient, which requires energy, usually in the form of ATP.

Some types of active transport are:

Transport proteins use energy to transport materials across the membrane. For example, the sodium-potassium pump uses ATP to maintain Na+ and K+ concentrations on opposite sides of the plasma membrane.

Exocytosis is the process by which vesicles fuse with the plasma membrane and release their contents to the outside of the cell. This is common when the cell produces substances and exports them. Similarly, endocytosis is the process by which a substance outside of the cell is captured when the plasma membrane merges to engulf it. The substance is then released into the cytoplasm enclosed in a vesicle.