(a) You will investigate the effect of different temperatures on the permeability of the cell surface membrane of beetroot cells. Beetroot is a vegetable that contains a red pigment in its cells. When beetroot tissue is put into water, the red pigment can move out of the cells through the cell surface membrane, changing the water to a red colour. You are provided with the materials shown in Table 1.1. Table 1.1 labelled | contents | hazard | volume/cm³ --- | --- | --- | --- B | 2 pieces of beetroot | none | – W | distilled water | none | 100 The red pigment in beetroot cells can stain clothing and skin. Use blunt forceps to handle beetroot tissue and, if any pigment comes into contact with your skin, wash it off immediately under cold water. It is recommended that you wear suitable eye protection. You will need to: • put beetroot tissue in water at different temperatures • leave the beetroot tissue in the water for a period of time • record the intensity of colour in the water at each temperature. (b) A scientist investigated changes in the mean width of stomata in the leaves of a plant growing in hot, dry conditions. The scientist measured the widths of stomata at different times of day, from 02:00 hours to 22:00 hours. [Figure 1.1] shows where the scientist measured the width of each stoma. width of stoma [Figure 1.1] guard cell The scientist calculated the mean width of stomata for each time of day. The results are shown in Table 1.4. Table 1.4 time of day /hours | mean width of stomata /arbitrary units (au) --- | --- 02:00 | 86 04:00 | 36 07:00 | 4 15:00 | 2 22:00 | 95

1. (a)(i)The temperature range that you will use must include a minimum temperature of 25°C and a maximum temperature of 65°C. State three other temperatures that you will use in your investigation. 25°C, ............................ °C, ............................ °C, ............................ °C and 65°C[1]
2. (a)(ii)Record your results in an appropriate table, using only the symbols shown in Table 1.2. You may use the same symbol for more than one test-tube.[5]
3. (a)(iii)State the independent variable in this experiment.[1]
4. (a)(iv)Use your knowledge of cell surface membranes to explain the results that you recorded in (a)(ii).[3]
5. (a)(v)Step 2 to step 4 improve the validity of the results by removing the pigment that was released when the beetroot tissue was cut. State how you could confirm that all the pigment released when the beetroot tissue was cut has been removed.[1]
6. (a)(vi)Two significant sources of error in this investigation are shown in Table 1.3. Complete Table 1.3 to suggest how to make an improvement to reduce each of the sources of error identified. significant source of error | how to make an improvement --- | --- difficult to judge the intensity of colour | difficult to maintain the temperature of the water-bath |[2]
7. (b)(i)Plot a graph of the data shown in Table 1.4 on the grid in [Figure 1.2]. Use a sharp pencil.[4]
8. (b)(ii)Use your graph to estimate the mean width of stomata at 03:00 hours. Show on your graph how you estimated your answer. mean width = .................................................... arbitrary units[2]
9. (b)(iii)With reference to Table 1.4 and [Figure 1.2], describe the change in mean width of stomata between 02:00 hours and 22:00 hours.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.