What are two important passive processes for membrane transport?

Diffusion is a method of natural movement of gas molecules from a region of higher concentration to a region of lower concentration. The difference in concentration is called a concentration gradient.

Osmosis is the diffusion of water through a biological membrane. Water molecules move along the concentration gradient from the area of higher water concentration to lower concentration.

Facilitated diffusion is when proteins within the cell carry or escort certain materials or substances in or out of the cell.