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?