Passive transport involves the movement of materials across a cell membrane without using energy and is driven by concentration gradients. It can work in both directions to move substances in or out of the cell. The three main types of passive transport are diffusion, facilitated diffusion, and osmosis.

1. Passive transport
• The movement of materials across the cell membrane without using
energy
• Caused by concentration gradient (A region of space over which the
concentration of a substance changes)
• Works in both directions (when a substance enters or leaves the cell)
• Three types of passive transport:
• Diffusion
• Facilitated diffusion
• Osmosis