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Active Transport

Active transport is a process that happens in all cells. Molecules move through a membrane. They move from an area with a lot of molecules to an area with less. Cells need to do this all the time to meet their needs and keep balance.

In order for molecules to move, active transport uses energy it gets from the cell. When movement doesn’t need energy it is passive transport. There are two types of active transport – primary and secondary. 

On the right is active transport. Molecules use energy to move from one side of the cell to the other.

Concentration Gradient

Active transport goes against the concentration gradient. A concentration gradient is a place where a lot of molecules meets a place with fewer molecules. This is a change in concentration.

Molecules usually move to areas that have less molecules. In active transport, they go the other way. They move toward the area with more. Because of this, it requires energy. 

Primary and Secondary Transport

The difference between these kinds of transport is the energy that they use.  Primary transport is also called direct active transport. This uses chemical energy to move molecules. 

Usually, a cell uses chemical energy in the form of ATP to make the movement. The sodium-potassium pump is a type of primary transport. It pumps sodium out of the cell and potassium into the cell.

An image of a sodium potassium pump moving molecules into a cell.

sodium-potassium pump.

Secondary transport is also known as co-transport. To move molecules in or out of the cell, it uses electrochemical energy. First, one molecule moves in the normal way. It goes from high concentration to low. That movement makes energy that can be used. Then, another molecule can move the other way, against the gradient. 


There are proteins that do a lot of the work in active transport. Because of where they are, they can move molecules in and out of the cell. The proteins that do this are very specific. For example, a protein that can move glucose will not be able to move calcium. There are a lot of these special proteins in your body.

An image of proteins moving molecules through a cell membrane.

Proteins moving molecules through the membrane.

 Written by: Christina Kinslow