Question

Compare cell membranes with the screen doors used on houses in summer.Explain why neither can be completely impermeable or completely permeable.

Answer 1

A Cell membrane holds the cell together and separates and protects the cell interior from the outside environment. It is selectively permeable. Similarly, the screen doors used in houses, protects the inside of the house from certain external disturbance like flies, mosquitoes, dust etc., while at the same time, allowing people to walk in and out by opening/shutting the screen door.

As it can be seen, both are selective in what it allows to enter or exit.

If either of these were to be completely impermeable, nothing would have been able to get inside or exit. Had they been completely permeable, it would not have given any protection from external factors or from what is inside to escape.