The movement of materials across the cell membrane without using cellular energy is called passive transport. On the other hand the energy-requiring movement of molecules across a membrane from a region of lower concentration to a region of higher concentration is called the active transport.
It includes processes such as osmosis. diffusion and facilitated diffusion.
Diffusion is the movement of dissolved molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.
Osmosis is the diffusion of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration.
Facilitated diffusion is a type of diffusion of molecules assisted by protein channels that pierce a cell membrane.
