In particularly in the body but also plants. I'm doing GCSE Biology Unit 3 and just want to know when active transport is used and when diffusion is used. For example which is used in the small intestine, in the lungs, in the kidney ? Thanks
Active transport is used in the kidneys when useful substances, such as glucose, are reabsorbed. It also used in the small intestine. When the concentration of glucose is higher in the blood, diffusion can no longer be used. Energy must be used for the glucose to travel AGAINST the concentration gradient (ie from low to high concentration)
Diffusion is used in the lungs (alveoli) and small intestine (villi). I'm unsure if there are more. REMEMBER... water doesn't travel by diffusion = osmosis.
Diffusion in plants is used to absorb nutrients from the soil and for gaseous exchanges in the leaves.