This PowerPoint relates to the SUBSTANCES ENTER AND LEAVE CELLS THROUGH THE CELL MEMBRANE

of the Biology 2 specification. Students learn:

(a) diffusion is the movement of substances down a concentration gradient. The process does not require energy and only certain substances pass through the cell membrane in this way.

HIGHER TIER

(b) osmosis is the diffusion of water through a selectively permeable membrane, from a region of high-water concentration to region of low-water concentration.

(c) how to carry out experimental work using living plant material and visking tubing as non-living material and be able to interpret experimental results in terms of membrane pore and particle size: the pore size is large enough to allow water molecules through but restricts the movement of solute molecules.

(d) active transport is an energy requiring process whereby substances can enter cells against a concentration gradient.