Passive Transport

Passive transport is defined as the movement of ions and other atomic or molecular substances from an area of high concentration to an area of low concentration without any energy input.

The main function of passive transport is to control the entry and exit of substances to and from the cell by means of a selectively permeable membrane. Also, it helps the system to attain a state of equilibrium by equalizing the concentration of substances in both regions.

1) Diffusion

It is the movement of substances from an area of high concentration to an area of low concentration until the concentration becomes equal in both regions. The two common types of diffusion are:

a) Simple Diffusion: It occurs without the help of any protein molecule. Examples: The movement of water, oxygen, carbon dioxide, ethanol, and urea.

b) Facilitated Diffusion: It is a selective process that occurs with the help of a transmembrane protein molecule. Facilitated diffusion can occur either through a channel protein or through a carrier protein. Examples: Transport of glucose, sodium ions, and potassium ions.

2) Osmosis

The spontaneous movement of water molecules from a region of low solute concentration to a region of high solute concentration through a semipermeable membrane. It is a selective process that allows only solvent molecules to pass while restricting the solutes. Examples: Taking of nutrients and minerals inside the cell and getting rid of its waste products.