Using Waves at the Beach to Describe Concentration Gradients

Written by Jennifer A. Metzler, Ball State University

When discussing passive versus active transport and the difference between an input of cellular energy, I ask students to imagine they are at the beach or at a wave pool. Since passive transport is going down a concentration gradient, I tell them to liken it to having the waves at their back and moving into shore. It is not a problem for them at all and they do not need to expend any energy as they are going with the flow. With active transport going against the concentration gradient, I tell them to imagine turning around and having the waves hit their chest and try to move away from shore. In this case they must expend energy as they are going against the flow of the waves.

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