Question

How do diffusion and osmosis relate to the function of a cell membrane?

Answer 1

Cell membrane is a selectively permeable membrane which helps in transport of selected and low molecular weight substances from inside to outside or outside to inside. They have special phenomena for transport of substances namely osmosis and diffusion.

Complete answer:
Cell membrane or plasma membrane is a selectively permeable membrane which allows only selected molecules to pass across the barrier.
The transport of smaller molecules takes place by passive transport either by osmosis and diffusion. Since these processes take place across a specific concentration gradient they do not require energy in the form of ATP.
Diffusion – The diffusion is a process in which smaller molecules, ions and water molecules pass across the membrane from high concentration to lower concentration. Substances constantly move from regions of higher concentration to lower concentration until equilibrium is reached.
Osmosis- It is also a transport mechanism wherein substances move from lower solute concentration to higher solute concentration. But unlike diffusion it allows the transport of only water molecules or only fluids across the membrane. Osmosis has a wide variety of applications too in day-to-day life.

Note: Diffusion and osmosis both are passive transport mechanisms. They do not require ATP to transport material across the membrane.
While diffusion is utilised to transport all substances liquid, small molecules and gases across the membrane, osmosis transports only liquids or fluids across the membrane.
Osmosis takes place only in liquid medium whereas diffusion takes place in the entire three medium (namely solid, liquid and gases). Osmosis is utilised in animals for transportation of nutrients and excretion of waste metabolites. In plants it is used in absorption of nutrients and transport of molecules.