A student carried out an investigation to estimate the water potential of potato tissue. The main steps in the procedure and in the analysis of results are outlined in Fig. 6.1. [Figure 6.1]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [3] any three from
2. idea that water moves down a water potential gradient / from a high to low water potential / AW ;
3. sucrose solutions produce differences in water potential inside the cell and externally
4. or
5. different concentrations of external sucrose solution produces different gradients of water potential;
6. high concentration of, sucrose / solutes, is, lower / more negative, water potential; ora
7. loss of water by osmosis out of potato cells lowers mass of block; ora for gain of mass
8. no net gain or loss means water potential inside and out are equal;
9. [1] concentration where the, curve / line, crosses the x-axis (and use a reference table)
10. or
11. the concentration at which there is zero percentage change in mass (and use a reference table) ;