Diffusion:
Diffusion is the process by which particles move from an area of higher concentration to an area of lower concentration. It occurs in both liquids and gases. Diffusion is driven by the random movement of particles and does not require any external energy input. The rate of diffusion is influenced by several factors, including temperature, concentration gradient, and the size and nature of the particles involved.

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 the concentration of solute molecules on either side of the membrane. The water molecules move from an area of lower solute concentration (higher water concentration) to an area of higher solute concentration (lower water concentration).

Key Differences:

1. Definition: Diffusion refers to the movement of particles from higher concentration to lower concentration, while osmosis specifically refers to the movement of water molecules across a membrane.

2. Substances Involved: Diffusion can occur with any type of particle, whether it is a gas, liquid, or solid, whereas osmosis specifically involves the movement of water molecules.

3. Membrane Requirement: Diffusion does not require a selectively permeable membrane, as it can occur in any medium. In contrast, osmosis occurs only when a selectively permeable membrane is present.

4. Direction of Movement: In diffusion, particles move in both directions until equilibrium is reached, whereas in osmosis, water molecules move in one direction, from an area of lower solute concentration to an area of higher solute concentration, until equilibrium is achieved.

5. Energy Requirement: Diffusion does not require any external energy input, as it is driven by the random movement of particles. On the other hand, osmosis also does not require additional energy, as it is a passive process.

6. Role in Biological Systems: Diffusion plays a crucial role in various biological processes, such as the exchange of gases in the lungs and the movement of nutrients and waste products across cell membranes. Osmosis is essential for maintaining the water balance within cells and across cell membranes.

7. Rate of Movement: The rate of diffusion depends on factors like temperature, concentration gradient, and particle size. In osmosis, the rate of movement of water molecules depends on the concentration gradient of solute molecules and the permeability of the membrane to water.

In conclusion, diffusion and osmosis are similar in that they involve the movement of particles, but they differ in terms of the substances involved, the requirement of a membrane, the direction of movement, and their roles in biological systems. Understanding these differences is crucial for comprehending various processes occurring in both living and non-living systems.