CAIE IGCSE Biology 3.2.5 Osmosis in Plant Tissues

Practise analysing changes in plant-tissue mass or length across solution concentrations, using percentage change, graph intercepts and water potential to explain results.

Exam points

predict whether potato tissue gains or loses mass or length in solutions of different concentrations
use a graph's zero-change point to identify the solution concentration where there is no net movement of water
explain changes in plant-tissue length or shape from water movement down a water-potential gradient by osmosis

[Maximum number: 1]

Some students investigated osmosis in raw potato sticks.

The students measured the mass of four of the potato sticks using an electronic balance.

Fig. 4.1 shows an electronic balance.

Fig. 4.1

The students left each potato stick in one of four different liquids for 5 hours:
- distilled water
- 0.1 mol per $\mathrm{dm}^{3}$ sodium chloride solution
- 0.5 mol per $\mathrm{dm}^{3}$ sodium chloride solution
- 1.0 mol per $\mathrm{dm}^{3}$ sodium chloride solution.

After 5 hours they measured the mass again and calculated the change in mass.

Predict which of the liquids would cause the largest decrease in mass of a potato stick.

1.0 (mol dm ${ }^{-3}$ sodium chloride solution) ;

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3.2.5—Effects on plant tissues of immersing question 1