Every cell is surrounded by a thin membrane. what is the main function of this cell membrane?

It controls what enters and leaves the cell.

The cell membrane is a thin flexible layer around the cells of all living things. It is sometimes called the plasma membrane or cytoplasmic membrane.

Basically, it:
 
1.) Protects the cell from changes in the chemical and physical environment surrounding it
 
2.) Controls which types of molecules can pass into and out of the cell
 
3.) Holds the cell together and restricts what goes in and out of the cell.

I hope this helped!!! Have a blessed day :)))

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