cell membrane and cell transport vocabulary

Concentration gradient:

Sometimes you'll have a set of similar molecules concentrated in one spot. Let's say that there is a barrier placed and all of them are found in this one space - so it's pretty crowded. If you remove the barrier, the molecules will naturally want to spread apart - think of people in a subway and the doors of the subway open. The space in which the molecules occupy, therefore will go from an area of high concentration to an area of where they are spread apart, thus they are less concentrated (low concentration). That's what concentration gradient is.

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