PART - 1 - Unit III : CH - 8 Cell: The Unit of Life — BIOLOGY STD 11 Science — Question

The important function of the plasma membrane is the transport of molecules through it. This membrane is selectively permeable. Neutral solute molecules move through the membrane by simple diffusion from higher concentration to lower concentration by normal or passive transport. There is no energy expenditure in this.
Polar molecules cannot move through it by normal diffusion. They require carrier proteins for transportation, they are also called ion carriers. Their transport generally occurs by active diffusion. Energy is spent in this. Energy is obtained from ATP Transport of ions or molecules from lower concentration to higher concentration also occurs by expending energy.