what does it mean that biological membranes are selecrively permeable?

Question

please answer this question to me... it will help me to pass my test better.

Answer 1

Biological membranes are selective in allowing certain classes of molecules to pass through them. This depends upon whether the cell needs them or not. For this they have enzymes and carrier molecules that can bring the molecules in even though it requires energy to bring it in.

Answer 2

"Biological membranes are selectively permeable" means that they will let some things pass through them, but not others.