Question

What is the main function of a selectively permeable cell membrane?

Answer 1

The main purpose is protection. The lipid bilayer protects the cell from viruses and other threats to the cell. It also maintains homeostasis within the cell by monitoring the amount of substances the enter or exit the cell. 

Answer 2

Answer: it regulates what material enter and leave the cell.

Explanation: Membrane proteins open and close, allowing material in cells to enter and leave.