Diffusion is the overall movement of substances from a high concentration towards a low concentration.
For osmosis, it helps to think about the concentration of the water. A dilute sugar solution has a high concentration of water, and a concentrated sugar solution has a low concentration of water. The water is diffusing from an area of high water concentration (the dilute sugar solution) to an area of low water concentration (the concentrated sugar solution).
1 Which are the water molecules and which are the sugar molecules?
2 Which side of the diagram shows:
a the most concentrated sugar solution
b the highest concentration of water?
3 a In which direction are water molecules likely to move most often: from A to B, or from B to A? Explain your answer.
b On which side of the diagram will the water level rise?
Osmosis is useful in plants. The diagram shows part of a plant root. The cell membrane is a partially permeable membrane.
4 a How do you think the mineral salts get into the root hair cells?
b Explain your answer.
5 How does the high concentration of mineral salts inside the root hair cell help the plant to absorb water from the soil?