Fusicoccin is a chemical that increases the sucrose concentration in phloem at the source. In this investigation you will be provided with a sample, U, which has been taken from the phloem of a plant. You will need to: • prepare proportional dilutions of a 10% sucrose solution • carry out the test for non-reducing sugars on each concentration of sucrose solution • carry out the test for non-reducing sugars on the unknown concentration of sucrose, U • estimate the concentration of sucrose in U. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume/cm³ S 10% sucrose solution none 50 Benedict's Benedict's solution harmful 30 W distilled water none 50 H dilute hydrochloric acid irritant 20 A 10g sodium hydrogencarbonate powder none – U solution of unknown sucrose concentration none 10 If any of the materials come into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection.

1. (a)(i)You will need to: • make a proportional dilution of 10% sucrose solution, S, which reduces the concentration by 2% between each successive dilution • prepare 5 cm³ of each concentration of sucrose solution. Complete Table 1.2 to show how you will prepare these concentrations. Table 1.2 percentage concentration of volume of S/cm³ volume of W/cm³ sucrose solution 10.0 5.0 0.0 [2]
2. (a)(ii)Record your results in an appropriate table for the known concentrations of sucrose solution.[5]
3. (a)(iii)State the result for U.[1]
4. (a)(iv)State whether U is taken from the phloem of a plant treated with fusicoccin. Give a reason for your answer. answer. reason[1]
5. (a)(v)Suggest how you could change the independent variable to have more confidence in your answer to (iv).[2]
6. (a)(vi)State why plant G was treated with 10 cm³ of water.[1]
7. (b)(i)A scientist investigated the effect of treating a plant with fusicoccin. Samples were taken from the phloem every 35 minutes for a total of 175 minutes. The concentration of sucrose in each sample was measured. These raw results were then used to calculate the rate of mass flow. The results are shown in Table 1.3. Table 1.3 time/min rate of mass flow /cm³min⁻¹ 35 6.00 70 10.25 105 15.00 140 19.50 175 23.75 Plot a graph of the data in Table 1.3 on the grid in [Figure 1.1]. Use a sharp pencil for drawing graphs.[4]
8. (b)(ii)Use your graph to find the time when the rate of mass flow was 20cm³min⁻¹. Show on the graph how you determined your answer. time = [2]
9. (b)(iii)Before treating the plant with fusicoccin, the scientist had obtained a rate of mass flow of 1.5 cm³min⁻¹. Describe the effect of fusicoccin on the rate of mass flow shown in Fig. 1.1.[1]
10. (b)(iv)Suggest how fusicoccin increases the loading of sucrose into phloem sieve tubes.[2]

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