Biology 9700/53 May/June 2024: question paper and mark scheme

Question

Blood vessels must be able to withstand and maintain varying blood pressures. There are several methods that could be used to determine the strength of a blood vessel. One method is called the circumferential tensile strength (CTS) test, as shown in Fig. 1.1. clamp stand hook ring of blood vessel mass hanger 10 g masses Fig. 1.1 The ring of blood vessel, shown in Fig. 1.1, was cut from a length of artery or vein that was prepared by removing surrounding tissues. A student wanted to use the apparatus in Fig. 1.1 to determine the mass needed to break an artery and the mass needed to break a vein. (a) (i) Identify the independent variable and the dependent variable in this investigation. independent variable …… dependent variable …… [1] (ii) The student was provided with lengths of a large artery, lengths of a large vein and standard laboratory apparatus. Describe how the student could use the CTS test to determine the mass needed to break an artery and the mass needed to break a vein. Your method should be set out in a logical order and be detailed enough to let another person follow it. …… [6] Another student investigated how the length of a ring of vein and the length of a ring of artery increases as more mass is added. The student used the apparatus shown in Fig. 1.2 with the ring of vein. clamp stand hook ring of vein part of metre rule mass hanger 10 g masses Fig. 1.2 The results for the ring of vein are shown in Table 1.1. Table 1.1 mass added / g length of ring of vein / mm percentage increase in length of ring of vein 0 21 0 10 36 20 38 81 30 40 90 40 41 50 41 (b) (i) Complete Table 1.1 by calculating the percentage increase in length of the ring of vein for 10 g, 40 g and 50 g. [2] (ii) Explain why the student calculated the percentage increase in length of the ring of vein. …… [1] (iii) On the grid in Fig. 1.3, plot a graph of the data shown in Table 1.1. Fig. 1.3 [3] (iv) The student carried out the same investigation using a muscular artery instead of a vein. Predict the shape of the curve you would expect for the muscular artery. On Fig. 1.3: • sketch the curve you predicted for the muscular artery • label this curve with the word artery. [2] (v) Explain the shape of the curve you sketched for the muscular artery in Fig. 1.3. …… [2] (vi) Another student suggested that the experiment should be repeated with more rings from the same blood vessels. Suggest two other ways the student could modify the method to improve the quality of the results. …… [2] [Total: 19]

Question

Gibberellins are a group of plant hormones that are involved in the elongation of plant stems. A student investigated the effect of two different concentrations of a gibberellin, known as GA3, on stem elongation of 10-day old pea seedlings. The student was given a stock solution of GA3 with a concentration of 2.85 × 10–4 mol dm–3. (a) Describe a method the student could use to make a solution of GA3 with a concentration of 1.90 × 10–6 mol dm–3 and state the dilution factor used. …… [2] (b) In the investigation, the student: • used the two concentrations of GA3: 2.85 × 10–4 mol dm–3 (high concentration GA3) and 1.90 × 10–6 mol dm–3 (low concentration GA3) • applied the high concentration GA3 to one batch of 10-day-old pea seedlings • applied the low concentration GA3 to another batch of 10-day-old pea seedlings • applied distilled water to a third batch of 10-day-old pea seedlings, as a control • standardised all other variables • measured the length of the stem of each seedling every two days until the seedlings were 20 days old • calculated the rate of stem elongation in cm day–1. State one way in which the student could standardise the measuring of stem length. …… [1] (c) The results of the investigation are shown in Table 2.1. Table 2.1 age of seedling mean stem length mean stem mean stem length / days with high length with low with distilled water concentration GA3 concentration GA3 added / cm added / cm added / cm 10 2 2 2 12 4 2 3 14 7 5 4 16 6 12 7 18 20 15 8 20 25 21 8 rate of stem elongation 2.3 0.6 (i) Complete Table 2.1 by calculating the rate of stem elongation in cm day–1 for the seedlings with low concentration GA3 added. [1] (ii) A scientist stated that they did not have enough confidence in the results in Table 2.1 to make any conclusions. State one reason to support the statement made by the scientist. …… [1] (iii) Describe how the student could modify the investigation to increase confidence in the results. …… [1] (d) The student found a study on the internet that considered the effect of different wavelengths of light on the concentration of two types of gibberellins, GA1 and GA8, in pea plants. In the study, 60 pea seeds were germinated and kept in the dark (no light) for seven days. The pea seedlings were divided into four batches of 15: • batch 1 remained in the dark • batch 2 was exposed to blue light (470 nm) • batch 3 was exposed to red light (680 nm) • batch 4 was exposed to far-red light (750 nm). After 4 hours the concentrations of GA1 and GA8 in the seedlings were measured. Table 2.2 shows the results. Table 2.2 batch wavelength of colour of mean GA1 concentration mean GA8 concentration light / nm light ± standard deviation ± standard deviation / ng g–1 fresh mass / ng g–1 fresh mass 1 – dark 2.87 ± 0.72 3.07 ± 0.10 2 470 blue light 0.21 ± 0.05 3.90 ± 0.13 3 680 red light 0.31 ± 0.10 5.03 ± 0.21

Question

750 far-red light 1.38 ± 0.26 4.00 ± 0.72 The student calculated the standard error (SE) and 95% confidence intervals (95% CI) for the data shown in Table 2.2. The formulae that the student used were: s SE = n 95% CI = x ± (2 × SE) key to symbols s = standard deviation n = sample size (number of observations) x = mean Table 2.3 shows the calculated values for SE and 95% CI for the data from Table 2.2. Table 2.3 batch SE for GA1 mean ± 95% CI for SE for GA8 mean ± 95% CI for / ng g–1 fresh mass GA1 / ng g–1 fresh mass GA8 / ng g–1 fresh mass / ng g–1 fresh mass 1 0.186 2.87 ± 0.37 0.026 3.07 ± 0.05 2 0.013 0.21 ± 0.03 0.034 3.90 ± 0.07 3 0.026 0.31 ± 0.05 0.054 5.03 ± 0.11 4 …… …… 0.186 4.00 ± 0.37 Complete Table 2.3 to show the calculated values for SE and mean ± 95% CI for the data from far-red light for GA1 (batch 4). [2] (e) Fig. 2.1 shows the bar chart of the results from the study. 5.00 Key 4.00 GA1 mean 3.00 gibberellin GA8 concentration / ng g–1 fresh mass 2.00 1.00 1 2 3 4 batch Fig. 2.1 Use Fig. 2.1, Table 2.2 and Table 2.3 to state three conclusions about the effect of different wavelengths of light on the concentrations of GA1 and GA8 in plants. …… [3] [Total: 11] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

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