INTRODUCTION

Molecules can be transported across the plasma membrane via passive or active transport. Active transport is characterized as requiring energy in the form of ATP, while passive transport does not require energy. During active transport pumps are often used to assist in moving a molecule against a concentration gradient.

Compare and contrast active vs. passive transport.

Passive transport, shown below, is the diffusion of particles through the proteins. The particles move from an area of high concentration to an area of low concentration. The cell does not need to use any energy to make this happen.

Active transport, shown below, is the movement of particles through proteins against the normal direction of diffusion. In other words, particles are moved from an area of low concentration to an area of high concentration. The cell must use energy to make this happen. This energy comes from the molecule ATP, which stores energy in a form that cells can use.