Gas and solution exchange

The movement of particles from an area of high concentration to an area of low concentration, through a semi-permeable membrane until equilibrium is reached.

The diffusion of water molecules, from an area of high water concentration to an area of low water concentration, through a semi-permeable membrane.

The movement of mineral ions and molecules from an area of low concentration to an area of high concentration, through a semi-permeable membrane, using energy

The stomata, found in the lower epidermis, controls the gas exchange. carbon dioxide diffuses into the cell and oxygen and water vapour diffuses out of the cell. The opening and closing of the stomata is controlled by guard cells.When the plant has lots of water the guard cells go turgid and makes the stomata open so gases are exchanged. When the plant has little water, the guard cells become flaccid and close the stomata. This minimises the amount of water vapour escaping.