Two methods of estimating the water potential of plant tissue are described. Method 1: Pieces of tissue are left in sucrose solutions of different concentrations. The percentage change in mass of the tissue is determined. Method 2: Pieces of tissue are left in sucrose solutions of different concentrations. The change in the density of the solutions in which the pieces of tissue have been left is estimated. A student compared the use of method 1 with method 2 to estimate the water potential of tissue in the fruit wall of red pepper, Capsicum annum. Fig. 1.1 shows a red pepper fruit and a labelled longitudinal section of the same fruit. [Figure 1.1] The student first used method 1. • Pieces of the red pepper fruit wall tissue of known mass were prepared. • These pieces of tissue were placed in solutions of different sucrose concentration. • The change in mass of the tissue after a period of time was calculated.

1. (a)(i)State the independent variable and the dependent variable in this investigation. independent dependent[2]
2. (a)(ii)The student was given a 1.0moldm¯³ stock solution of sucrose. The student decided to use the stock solution to make a range of sucrose solutions. The student made 50 cm³ of each solution. Suggest a suitable range of solutions the student could use and describe how these solutions could be made by proportional dilution of the 1.0moldm¯³ stock solution of sucrose.[3]
3. (b)Using the different sucrose solutions from (a)(ii), describe a method the student could use to collect the data needed to estimate the water potential of the tissue in the fruit wall of the red pepper. Do not include details of how to make the different sucrose solutions. Your method should be set out in a logical way and be detailed enough to let another person follow it.[6]
4. (c)(i)The student calculated the percentage change in mass of the tissue. Describe how the student could have calculated the percentage change in mass of the tissue and explain why the percentage change should be used.[2]
5. (c)(ii)Sketch a graph of the expected results on Fig. 1.2. Include axes labels and units. Indicate how this graph could be used to estimate the sucrose concentration equivalent to the water potential of the tissue in the red pepper fruit wall. [Figure 1.2][3]
6. (d)(i)Using the results of the experiment in Fig. 1.4 and the data in Table 1.1, state the water potential of the red pepper tissue. [Figure 1.4, Table 1.1][1]
7. (d)(ii)Suggest why the student thought that method 1 would give a better estimate of water potential than method 2.[3]

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