Diffusion, Osmosis, and Active Transport

IGCSE Edexcel Biology
2.15 Movement of Substances
Key Concept: Diffusion and osmosis are passive processes, while active transport uses energy to move substances against a gradient.

Section A: Definitions

1. Define diffusion. [2]
2. Define osmosis. [2]
3. Define active transport. [2]

Section B: Comparison and Examples

4. State two differences between diffusion and active transport. [2]
5. Give one example of each process in living organisms. [3]
6. Explain why active transport requires energy from respiration. [2]
Total marks: 13

Mark Scheme

1. Net movement of particles from high to low concentration down a concentration gradient [2]
2. Diffusion of water through a partially permeable membrane from high water potential to low water potential [2]
3. Movement of substances against a concentration gradient using energy and carrier proteins [2]
4. Diffusion is passive and down the gradient; active transport uses energy and can move against the gradient [2]
5. Examples: diffusion of oxygen, osmosis in root hair cells, active transport of mineral ions (any one each) [3]
6. Energy (ATP) is needed to change carrier proteins and move substances against the gradient [2]