Describe diffusion as the movement of substances into and out of cells across the cell membranes.
Define diffusion as the spreading out of particles in a solution or a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration.
Identify key substances transported by diffusion, including oxygen and carbon dioxide during gas exchange, and urea moving from cells into the blood plasma for excretion by the kidney.
Explain how factors such as the concentration gradient, temperature, and membrane surface area affect the rate of diffusion.
Calculate and compare surface area to volume ratios for different organisms.
Understand that single-celled organisms possess a relatively large surface area to volume ratio, allowing sufficient molecular transport to meet their biological needs.
Explain the necessity for specialised exchange surfaces and transport systems in multicellular organisms due to their comparatively smaller surface area to volume ratios.
Describe how various biological structures, such as mammalian small intestines and lungs, fish gills, and plant roots and leaves, are structurally adapted for efficient material exchange.
Explain how the effectiveness of an exchange surface is increased by having a large surface area, a thin membrane (providing a short diffusion path), an efficient blood supply (in animals), and adequate ventilation (for gaseous exchange in animals).
