3.1 Diffusion and Osmosis

2026 Syllabus Objectives

By the end of this topic, you should be able to:

1. Describe the role of water as a solvent in organisms, with reference to digestion, excretion, and transport
2. Understand that the energy for diffusion and osmosis comes from the kinetic energy of the random movement of molecules and ions
3. Understand diffusion as the net movement of molecules or ions from a region of higher concentration to a region of lower concentration (down a concentration gradient), as a result of their random movement
4. Investigate the factors that influence diffusion: surface area, temperature, concentration gradient, and distance
5. Understand osmosis as the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
6. Understand that plants are supported by the pressure of water inside cells pressing outwards on the cell wall
7. Describe the effects of osmosis on plant and animal tissues and explain the importance of water potential gradient and osmosis in the uptake and loss of water
8. Investigate and explain the effects on plant tissues of immersing them in solutions of different concentrations, using the terms turgid, turgor pressure, plasmolysis, and flaccid
9. Investigate osmosis using materials such as dialysis tubing

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