Biology 2023 · Oct/Nov

There were several different species of algae growing in the mid-shore zone.

Some algae were exposed to the air at low tide, but most grew in rock pools.

The distribution and abundance of the algae differed on the shore between the low-water mark (LWM) and the high-water mark (HWM).

Large rock pools appeared to have more species of algae than small rock pools.

Large rock pools were deeper than small rock pools. The student decided to investigate the relationship between the depth of rock pools and the species diversity of the algae in the rock pools in the mid-shore zone. The student selected 32 rock pools at random. Approximately half the rock pools were small and half were large. The depth of each rock pool at its deepest point was measured and the number of different species of algae in each rock pool was counted.

State two variables that have been standardised in the investigation. 1 2

The results of the investigation are shown in Fig. 1.3. 0 10 20 30 40 depth of rock pool / cm species diversity / number of species of algae 50 60 70 80 The student used the Spearman's rank correlation to analyse the data in Fig. 1.3.

State a null hypothesis for this investigation.

The student calculated the Spearman's rank correlation coefficient (r ) as 0.628. Table 1.1 shows some of the critical values for the Spearman's rank correlation test. Table 1.1 number of pairs of measurements critical values p = 0.05 (5%) p = 0.01 (1%) 30 0.362 0.467 31 0.356 0.459 32 0.350 0.452 33 0.345 0.446 34 0.340 0.439 Discuss, with reference to Table 1.1, the conclusions that can be made from the analysis of the data collected by the student.

State one reason why Pearson's linear correlation coefficient is not appropriate for analysing the data shown in Fig. 1.3.

One important feature of scientific reports is that they provide enough information for other researchers to repeat each investigation. Explain why it is difficult for researchers to repeat this investigation of species diversity in rock pools from the information provided.

The student noticed that part of the rocky shore had no rock pools. The student observed that the species of algae were not distributed equally on this part of the rocky shore from the LWM to the HWM. Describe an investigation to find out how the distribution and abundance of the different species of algae varies on a rocky shore with no rock pools from the LWM to the HWM. Your method should be set out in a logical order and be detailed enough for another person to follow. [7] [Total: 16] 2 Abscisic acid (ABA) is a plant hormone that influences the growth and development of plants. Salicylic acid (SA) is a plant hormone that interacts with other plant hormones, such as ABA, to influence growth and development in plants. Scientists investigated the effects of ABA and SA on shoot growth in seedlings of rice, Oryza sativa. The scientists germinated some rice grains and divided the young seedlings into four batches, A to D, each containing 9 seedlings of the same length. The seedlings were put into trays containing a seedling growth medium. The shoots in each batch of seedlings were sprayed once with a different solution: batch A - water batch B - 2 μmol dmABA batch C - 2 μmol dm ABA + 1.0 mmol dm batch D - 1.0 mmol dm The seedlings were then put into a growth chamber with constant conditions of light, temperature and humidity. The length of the shoot on each seedling was measured one day after spraying and five days after spraying. Fig. 2.1 shows two seedlings taken at random from each batch five days after being sprayed. cm / mm A water B ABA C ABA + SA D SA The mean results of the investigation are shown in Fig. 2.2. day 1 day 5 mean shoot length / mm A waterB ABAC ABA + SAD SA A waterB ABAC ABA + SAD SA

Seedlings do not always grow straight. Suggest how the measurements of shoot length of the rice seedlings can be made as accurately as possible.

There were nine seedlings in each batch. The standard deviation for the length of seedlings in batch D (sprayed with SA only) at day 5 is 5 mm. The formula for calculating standard error (SE) is: SE = s = sample standard deviation n = sample size (number of observations) The formula for calculating the 95% confidence interval (95% CI) is: 95% CI = x ± (2 × SE) x = mean

Calculate the 95% CI for batch D (treated with SA only) at day 5. 95% CI = mm

The values for 95% CI were used to add error bars for batches C and D at day 5. These error bars did not overlap. State what can be concluded from this.

Use the information in Fig. 2.2 to suggest and explain the effects of ABA and SA on the growth of the rice seedlings over five days.

The scientists delivered the plant hormones to the rice seedlings by spraying the shoots. A student suggested that the rice seedlings could take up ABA and SA in the roots and transport the hormones to tissues in the shoot to give similar results to those in Fig. 2.2. Outline a method to test this suggestion. Question 2 continues on page 12

ABA and SA are reported in the scientific literature to be involved in the control of the mitotic cell cycle. Cyclin-dependent kinases (CDKs) are enzymes involved in the control of the mitotic cycle. The gene CDKB2 codes for one of these kinase enzymes. Genes KRP4 and CycD6 code for proteins that regulate the activity of CDKs. The scientists investigated the effect of ABA and SA on gene expression. Microarrays were used to measure the relative quantities of mRNA produced by transcription of the three genes, CDKB2, KRP4 and CycD6, in the cells of the seedlings that were sprayed by ABA and SA. The relative quantity of mRNA produced is a measure of the level of gene expression. Fig. 2.3 shows the effects of ABA alone, SA alone and ABA and SA combined on the expression of the three genes. Error bars show standard deviation (n = 3).

Complete Table 2.1 to show how the expression of the three genes is affected by the presence of ABA alone and SA alone, shown in Fig. 2.3. Use only these descriptions to complete the table: large increase small increase large decrease small decrease no change Table 2.1 gene effect on gene expression ABA only SA only CDKB2 KRP4 CycD6 [3] CycD6 0.00 0.50 1.00 1.50 2.00 2.50 3.00 mean relative quantities of mRNA A waterB ABAC ABA + SAD SA KRP4 0.00 0.50 1.00 1.50 2.00 2.50 3.00 mean relative quantities of mRNA A waterB ABAC ABA + SAD SA CDKB2 0.00 0.50 1.00 1.50 2.00 2.50 3.00 mean relative quantities of mRNA A waterB ABAC ABA + SAD SA

Fig. 2.3 also shows the results of spraying the seedlings with the mixture of ABA and SA (batch C) on the expression of the three genes. The scientists made two conclusions about the effects of the mixture of ABA and SA (batch C) on the expression of the genes KRP4 and CycD6. Conclusion 1: SA counteracts the stimulation of gene expression of KRP4 by ABA. Conclusion 2: SA does not reverse the effect of ABA on gene expression of CycD6. State and explain whether the evidence from Fig. 2.3 fully supports, partially supports or does not support each of these conclusions. conclusion 1 conclusion 2 [2] [Total: 14] 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. Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge.