Question

What would have is plasma membrane has not been selectively permeable

Answer 1

If it were not permeable, the cell wouldn’t be able to get necessary nutrients, which would lead to its death.

On the other hand, if it were fully permeable, anything would be able to enter the cell, which would upset the balance between the cell’s contents and the outside of it.

Answer 2

Cell membranes are selectively permeable. Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all. A few lipophilic substances move freely across the cell membrane by passive diffusion.