Unit 3

• Diffusion is the result of molecules of liquid, gas or dissolved solid moving about. 

• The molecules of a substance diffuse from a region where they are very concentrated to a region where they are less concentrated.
• Substances may enter cells by simple diffusion, controlled diffusion or active transport.
• Osmosis is the diffusion of water through a partially permeable membrane, from a dilute solution of salt or sugar to a concentrated solution because the concentrated solution contains fewer free water molecules.
• Cell membranes are partially permeable and cytoplasm and cell sap contain many substances in solution.
• Cells take up water from dilute solutions but lose water to concentrated solutions because of osmosis.
• Osmosis maintains turgor in plant cells.
• Active transport involves the movement of substances against their concentration gradient. • Active transport requires energy.
• Kinetic energy of molecules and ions results in their diffusion.
• Osmosis involves the diffusion of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
• The meanings of the terms turgid, turgor pressure, plasmolysis and flaccid.
• The importance of water potential and osmosis to animal and plant cells.
• Turgor pressure in cells provides support in plants.
• Active transport is important as it allows movement of substances across membranes against a concentration gradient.