The scientists needed solutions of known water potential to generate their calibration curve.

Table 5 shows how to make a sodium chloride solution with a water potential of −1.95 MPa

Complete Table 5 by giving all headings, units and volumes required to make 20 cm3 of this sodium chloride solution.

Table 6 shows some of the concentrations of sodium chloride solution the scientists used and the water potential of each solution.

There is a linear relationship between the water potential and the concentration of sodium chloride solution.

Use the data in Table 6 to calculate the concentration of sodium chloride solution with a water potential of −3.41 MPa

Answer = ______________ mol dm–3

In addition to determining the water potential in the leaf cells, the scientists measured the growth of the leaves.

They recorded leaf growth as a percentage increase of the original leaf area.

Their results are shown in Figure 9.

One leaf with an original area of 60 cm2 gave a voltage reading of −7 µV

Use Figure 8 (on page 28) and Figure 9 to calculate by how much this leaf increased in area. Give your answer in cm2

Answer = ______________ cm2

Sunflowers are not xerophytic plants. The scientists repeated the experiment with xerophytic plants.

Suggest and explain one way the leaf growth of xerophytic plants would be different from the leaf growth of sunflowers in Figure 9.

Use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly.