3.3 Active Transport
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There are three ways in which substances can pass through membranes. They are diffusion, osmosis and active transport. Diffusion and osmosis have been explored in the previous two sections and in this section we are going to look at active transport.
Sometimes a cell needs to take in a substance when there is a low concentration of that substance outside of the cell. It can do this by active transport. Active transport moves in substances against a concentration gradient (which means that a substance moves from a place where there is a low concentration to a place where there is a higher concentration of that substance). The cells do this by using the energy that is created by respiration to take particles from one place to another. Scientists sometimes refer to this process as a cell pumping a substance in or out of a cell. The pumps are large protein molecules located in the cell membrane.
Sometimes a cell needs to take in a substance when there is a low concentration of that substance outside of the cell. It can do this by active transport. Active transport moves in substances against a concentration gradient (which means that a substance moves from a place where there is a low concentration to a place where there is a higher concentration of that substance). The cells do this by using the energy that is created by respiration to take particles from one place to another. Scientists sometimes refer to this process as a cell pumping a substance in or out of a cell. The pumps are large protein molecules located in the cell membrane.
Active transport occurs in the small intestine. Glucose in the gut is absorbed into the cells lining the intestine by active transport.