Primary, Secondary, and Bulk Transport

Active transport is the movement of molecules from an area of low concentration to a higher concentration across the plasma membrane. The movement of substances against the concentration gradient is non-spontaneous and requires energy and a protein. This process explains how signal molecules are transported across the cell membrane. As you watch, pay attention to the definitions of the types of proteins and energy used in active transport. You should be able to describe the process of cotransport.

There are three videos in this series.

Source: Wendy Riggs,,,
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Last modified: Thursday, January 11, 2024, 4:59 PM