The cell membrane is ________________________, which means that some substances can pass through it, while others cannot.

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The cell membrane is semi-permeable. That is, it allows entry to only some molecules, while others cannot pass through.

A cell requires a lot of chemicals for its regular operation and it cannot produce all of them. Similarly, a cell generates a number of chemicals which are not useful and must be excreted. Thus, a cell has to constantly interact with its environment for the exchange of materials (entry of useful molecules and excretion of waste materials). There are a very large number of molecules in the environment, many of which may be harmful to the cell. Thus, the cell needs border control, something which can allow access only to certain molecules, while restricting the entry to others. The semi-permeable cell membrane carries out this important task for the cell.

The amphipathic phospholipids that make up the cell membrane cause it to be semi-permeable.

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