Biology 9700/34 May/June 2019: question paper and mark scheme

Question

Onion cells in sodium chloride solutions may show plasmolysis, where the cell surface membrane pulls away from the cell wall. Fig. 1.1 shows onion cells in different states of plasmolysis. • Cell A is showing no plasmolysis. • Cells B, C and D are all showing plasmolysis. no plasmolysis slight plasmolysis more plasmolysis complete plasmolysis A B C D Fig. 1.1 Different concentrations of sodium chloride solutions have different water potentials. When onion cells are put into a sodium chloride solution with a lower water potential than the cells, water leaves the vacuoles and the cells show plasmolysis. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 S1 0.50 mol dm–3 sodium chloride none 50 solution + onion tissue S2 sodium chloride solution none 50 + onion tissue S3 sodium chloride solution none 50 + onion tissue S4 sodium chloride solution none 50 + onion tissue If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. S1 is 0.50 mol dm–3 sodium chloride solution. S2, S3 and S4 are 1.00 mol dm–3, 0.25 mol dm–3 and 0.00 mol dm–3, but not necessarily in that order. You will need to: • observe a sample of onion cells from S1, S2, S3 and S4 • decide how many cells you will observe to record the states of plasmolysis • record the number of cells that show the different states of plasmolysis, A, B, C and D, as shown in Fig. 1.1 • use your results to identify the concentration of the sodium chloride solutions, S2, S3 and S4. Carry out step 1 to step 7 to prepare a slide of onion tissue. 1. Label one dry and clean microscope slide, S1. Put the slide on a paper towel. 2. Put a few drops of sodium chloride solution, S1, onto the microscope slide. 3. Remove a piece of the onion tissue from S1. Peel off the inner epidermis as shown in Fig. 1.2. The inner epidermis may start to separate or have become separated from the rest of the onion tissue, so the epidermis may be floating in the sodium chloride solution. Fig. 1.2 4. Cut one piece of the epidermis so that it will fit under a coverslip. Put the remaining epidermis into S1. 5. Put the piece of epidermis on the labelled microscope slide as shown in Fig. 1.3. If the piece of epidermis is folded, you may need to add more drops of S1 so that it floats and can be unfolded. piece of epidermis microscope slide sodium chloride solution paper towel Fig. 1.3 6. Put a coverslip over the piece of epidermis on the microscope slide. Use a paper towel to remove any excess solution that is outside the coverslip. 7. Observe the cells of the epidermis using the microscope. You may need to reduce the amount of light entering the microscope to observe the cells clearly. (a) You need to decide which objective lens you will use and decide the number of cells you will need to observe to give you confidence in your results. (i) State the objective lens you will use and the number of cells you will observe. Explain how this will give you confidence in your results. objective lens …… number of cells …… explanation …… [2] 8. Using the objective lens and the number of cells you decided in (a)(i), count the number of cells for S1 that are in each state of plasmolysis, A, B, C and D (as shown in Fig. 1.1). Record your results in (a)(ii). 9. Repeat step 1 to step 8 for each of S2, S3 and S4. Record your results in (a)(ii). (ii) Record your results in an appropriate table. [5] (iii) Solution S1 is 0.50 mol dm–3. S2, S3 and S4 are 1.00 mol dm–3, 0.25 mol dm–3 and 0.00 mol dm–3, but not necessarily in that order. Using your results in (a)(ii), identify the concentration of sodium chloride solution in S2, S3 and S4. S2 …… S3 …… S4 …… [1] Use a sharp pencil for drawings. You are expected to draw the correct shape and proportions of the different cells. (b) Observe the onion cells on the microscope slide you labelled S4. Select four adjacent, touching cells, with at least two cells showing plasmolysis. Make a large drawing of these four cells. Use one ruled label line and label to identify the cell surface membrane of one cell. [4] (c) A student investigated the effect of different concentrations of sucrose solutions on pieces of potato tissue. • Each piece of potato tissue was cut to exactly 50 mm in length and had a cross‑sectional area of exactly 10 mm × 10 mm. • Each piece of potato tissue was put into a different concentration of sucrose solution. • After 1 hour the length of each piece of potato was measured. The results of the student’s investigation are shown in Table 1.2. Table 1.2 sucrose change concentration in length / mol dm–3 / mm 0.0 +2.5 0.2 +1.5 0.4 0.0 0.6 –0.5 1.0 –1.5 (i) Describe the pattern of water movement shown in Table 1.2. …… [2] (ii) Using your knowledge of water potential, explain the result at 0.2 mol dm–3. …… [2] (iii) The student decided to compare the effect of different concentrations of sucrose solution using a different type of potato. Complete Table 1.3 to suggest how three variables would need to be standardised. Table 1.3 variable how variable may be standardised [3] [Total: 19]

Question

(a) A student investigated the effect of different factors on transpiration. In the investigation, three identical plants were put in flasks containing 70 cm3 of water as shown in Fig. 2.1. plant layer of oil flask 70 cm3 water Fig. 2.1 The plants were each kept in different conditions: • 20 °C + still air + high humidity • 20 °C + windy + low humidity • 30 °C + still air + low humidity. All other variables were kept constant. After 4 hours the water remaining in each flask was put into beakers labelled P1, P2 and P3. (i) Suggest a suitable control for this investigation. …… [1] (ii) Describe how the student could have decreased the humidity. …… [1] You have been given the beakers, labelled P1, P2 and P3, containing the water that was collected from each flask after the 4 hours. You will need to determine the volume of water lost by transpiration from each plant. (iii) Using the apparatus provided, measure the volume of water in P1, P2 and P3. Calculate the volume of water lost through transpiration by each plant. Record your results in an appropriate table. [2] (iv) State which plant was grown in high humidity. Give a reason for your answer. plant …… reason …… [1] (b) Plants lose water through stomata by transpiration. A scientist investigated the effect of carbon dioxide concentration in the air on the number of stomata present per mm2 of leaf area, in five plants. The carbon dioxide concentration was measured in parts per million (ppm). Table 2.1 carbon dioxide number of stomata / mm2 concentration / ppm plant 1 plant 2 plant 3 plant 4 plant 5 mean 288 294 307 286 301 292 296 306 271 285 266 278 270 274 328 254 241 265 263 242 253 357 242 237 297 235 246 383 234 227 231 234 219 229 (i) Complete Table 2.1 by calculating the mean number of stomata / mm2 at a carbon dioxide concentration of 357 ppm. Show all the steps in your working and use appropriate units. [2] (ii) Plot a graph of the mean results shown in Table 2.1 on the grid in Fig. 2.2. The first values for the x‑axis and the y‑axis are shown on the grid in Fig. 2.2. Use a sharp pencil for drawing graphs. 220 280 Fig. 2.2 [4] (iii) Describe the trend shown by your graph in Fig. 2.2. …… [1] (iv) A plant has 302 stomata / mm2. Use your graph in Fig. 2.2 to determine the carbon dioxide concentration in the air where this plant is growing. carbon dioxide concentration = …… ppm [1] (c) Fig. 2.3 is a photomicrograph of a stained transverse section through a leaf. You are not expected to be familiar with this specimen. Fig. 2.3 Use a sharp pencil for drawings. You are expected to draw the correct shape and proportions of the different tissues. Draw a large plan diagram of the whole leaf shown in Fig. 2.3. Use one ruled label line and label to identify the epidermis. [5] (d) Fig. 2.4 shows the same photomicrograph as in Fig. 2.3, with an eyepiece graticule scale added. The calibration of the eyepiece graticule scale is: 1 eyepiece graticule division = 39.7 µm. 30 X 20 10 Y 0 Fig. 2.4 Use the calibration of the eyepiece graticule scale and Fig. 2.4 to calculate the actual width of the vascular bundle, shown by line X ‑ Y. Show all the steps in your working and use appropriate units. actual width of the vascular bundle = …… [3] [Total: 21]