Diffusion and osmosis are both passive processes that involve the movement of molecules across a selectively permeable membrane, but they differ in the nature of the substances being transported and the driving forces behind the movement. Here's the key difference between diffusion and osmosis:

Diffusion:

- Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. It occurs due to the random motion of molecules, with no energy input required.

- It involves the movement of individual molecules, such as gases, solutes, or small molecules, across a concentration gradient.

- The driving force behind diffusion is the difference in concentration between the two regions, and the molecules move down the concentration gradient until equilibrium is reached.

Osmosis:

- Osmosis is a specific type of diffusion that involves the movement of water molecules across a selectively permeable membrane.

- It occurs when there is a difference in water concentration on either side of the membrane. Water molecules move from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration).

- The driving force behind osmosis is the difference in water concentration or osmotic pressure between the two compartments. Water moves down the water concentration gradient to equalize the osmotic pressure on both sides of the membrane.

In essence, diffusion involves the movement of molecules of any substance, whereas osmosis specifically refers to the movement of water molecules across a membrane due to differences in water concentration.