What are the three types of diffusion?
The three types of diffusion are - simple diffusion, osmosis and facilitated diffusion.
$$(i)$$ Simple diffusion is when ions or molecules diffuse from an area of high concentration to an area of low concentration.
Examples of simple diffusion are the gaseous exchange that occurs during photosynthesis, and the evaporation of water in plants during transpiration.
$$(ii)$$ In osmosis, the particles moving are water molecules. They move from a region of low solute concentration to a region of high solute concentration, across a semi-permeable membrane.
For example - If water and salt solution are separated by a semi-permeable membrane, then water molecules flow to the region of salt solution as it has a higher solute (salt) content.
$$(iii)$$ Facilitated diffusion is the movement of hydrophilic molecules or ions across the plasma membrane. The difference is, the diffusion is facilitated by transport proteins (i.e. carrier proteins or pore proteins).
All three types of diffusion are forms of passive transport, and therefore don't require energy.