what is the importance of ion pumps in the cell, and why do molecules not enter without these pumps?

Answer 1

Ion pumps help regulate what goes in/out of a cell. Many molecules can't enter without these pumps because they're either too big. Also, sometimes a pump forces molecules to go against the gradient---without the pump, they would not be able to move against the gradient.

Answer 2

Importance is to maintain ion or electrolyte balance. Without the pumps (sodium-potassium pump, calcium channels, etc), normal body physiology would become disrupted. For example, cyanide shuts down the sodium-potassium pump which is why cyanide can kill you. Also, without these pumps molecules may not be able to enter into or leave a cell. For example, glucose is a large molecule that needs to be "carried" across the cell membrane, which is what a pump does.