Cambridge A Level Biology 9700 — 2024 May/June Paper 5 · Variant 2

1 Tree plantations are areas where trees are planted for a particular purpose. Some tree plantations increase the supply of wood for construction and fuel. In many plantations, fast‑growing, alien tree species are planted. Undergrowth is found in and around plantations, increasing plant biodiversity. Undergrowth is mainly made up of indigenous (native) small plants and shrubs. Fig. 1.1 shows part of a plantation of eucalyptus trees. eucalyptus trees small plants and shrubs in undergrowth Fig. 1.1 Bangladesh has many tree plantations as part of a national tree‑planting programme. Two fast‑growing, alien tree species planted in Bangladesh are acacia, Acacia auriculiformis, and eucalyptus, Eucalyptus camaldulensis. Acacia and eucalyptus are considered to be invasive species as they outcompete indigenous tree species such as sal tree, Shorea robusta, and mango, Mangifera indica. Scientists carried out an investigation into the biodiversity of plant species in the undergrowth in plantations of alien trees compared with the undergrowth in plantations of indigenous trees. The hypothesis that the scientists tested was stated as: The undergrowth in plantations of alien tree species will have a lower biodiversity of plant species than the undergrowth in plantations of indigenous tree species. (a) (i) Identify the independent variable in this investigation. ........................................................................................................................................... ..................................................................................................................................... [1] For the investigation, plantations were selected within the same region of Bangladesh with the same environmental conditions. • Three plantations of each tree species were selected: acacia, eucalyptus, sal tree and mango. • A plot measuring 36 m by 36 m was studied within each plantation. • For each plot, belt transects were used to collect the data needed to determine Simpson’s index of diversity (D). For each type of plantation, Simpson’s index of diversity (D) was calculated for the plant species in the undergrowth. Each plot was studied in April, July and November. (ii) Identify two variables the scientists standardised in this investigation. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) The scientists used belt transects to investigate the undergrowth of each plot. Describe how you could use belt transects to collect the data needed to determine Simpson’s index of diversity (D) of the undergrowth in each of the plots. Your method should be set out in a logical order and be detailed enough to let another person follow it. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [5] Table 1.1 shows the Simpson’s index of diversity (D) values the scientists obtained for the different plantations during April, July and November. Table 1.1 month Simpson’s index of diversity (D) for undergrowth plant species in plantation acacia eucalyptus sal tree mango April 0.90 0.87 0.94 0.90 July 0.86 0.86 0.94 0.86 November 0.87 0.83 0.94 0.88 mean 0.88 0.85 0.94 0.88 ± s ± 0.02 ± 0.02 ± 0.00 ± 0.02 s = standard deviation (c) State and explain whether the data in Table 1.1 support the hypothesis: The undergrowth in plantations of alien tree species will have a lower biodiversity of plant species than the undergrowth in plantations of indigenous tree species. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] In China, a different group of scientists investigated whether the roots of invasive plant species produce chemicals that have an effect on the growth of other plants. The scientists prepared an extract of the roots of staghorn sumac, Rhus typhina. Staghorn sumac is an invasive plant species. The scientists prepared a stock solution of the root extract with a concentration of 10 mg cm–3. The scientists then used the stock solution to prepare solutions with different concentrations of root extract. (d) (i) Describe how the scientists could use the stock solution to prepare 50 cm3 of solutions of the root extract with concentrations of 2.5 mg cm–3 and 7.5 mg cm–3. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] In some regions of China, marigold plants, Tagetes erecta, are grown commercially. In the investigation into the effect of staghorn sumac root extract on the growth of marigolds, the scientists carried out the procedure described in step 1 to step 5. step 1 Prepare five containers, each with five marigold plants grown from seed. step 2 Add 20 cm3 of distilled water to one of the containers. This is the control. step 3 Add 20 cm3 of the root extract concentrations to the other four containers, so that each container has a different concentration of root extract. step 4 Repeat step 2 and step 3 each day for 60 days. step 5 After 60 days, remove the marigold plants from the soil and untangle the roots. Measure the length of the longest root for each plant. The scientists replicated this procedure twice and calculated the mean maximum root length for the control and for the root extract concentrations. The results are shown in Table 1.2. Table 1.2 root extract concentration mean maximum root length after / mg cm–3 60 days / mm control 163.0 2.5 153.2 5.0 156.4 7.5 152.0 10.0 141.6 (ii) Using the data in Table 1.2, calculate the percentage change in the mean maximum root length between the control and the roots treated with 10 mg cm–3 root extract concentration. Show your working and record your answer to 3 significant figures. percentage change .......................................................... [3] (e) A student suggested that this investigation could be improved. With reference to the method used and the data in Table 1.2, state and explain three ways to improve confidence in the results. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (f) To investigate the effect of the different root extract concentrations on the diversity of the microorganisms in soil, the scientists: • took samples of soil from each of the containers • identified and counted the number of species of microorganism present in the samples • calculated the Simpson’s index of diversity (D) values for the species of microorganism in each of the soil samples. State two variables the scientists should have standardised when taking the soil samples. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 19]

Mark scheme: 1(a)(i) species of tree or type of tree ; 1 1(a)(ii) any two from: 1 (same) number of / 3, plantations for each tree species ; 2 (same) size/area of, plot/(sampling)area / 36 m x 36 m / 1296m2 ; 3 (same / used a) belt transect (same method in all plots/plantations) ; 4 (same) months / seasons (of the year) or sampling at the same times ; 2 Question Answer Marks 1(b) any five from: using a belt transect: 1 use of tape / line / string, and quadrat (to create belt transect) ; 2 selecting a start point for the, transect / placement of tape / line / string or all transects same length, in plots / plantations / repeats ; 3 same (size) quadrat ; 4 sample at / use quadrat at, regular intervals / stated distances along the, tape / line / string / transect or continuous belt transect ; collecting data: 5 method to identify each of the plant (species in the quadrat) ; 6 count / record / note the number of (individuals), each plant species (n) (in each quadrat / at each sampling point) or estimate percentage (%) cover of each plant species (in each quadrat) ; 7 use at least 3 different transects (in each plot) ; 8 named hazard and risk and precaution ; e.g. (see table below) 5 Question Answer Marks 1(b) hazard risk precaution plants / fungi falling trees / branches hard hat thorns gloves / goggles / mask / long trousers / PPE irritant / allergy infection (spores) antihistamines / cover skin / first aid equipment (named) animal(s) parasite bites / infection / attack / stings / allergy antivenom / antihistamine / trained, professionals / medics, available / insect repellent / gloves / goggles / mask / PPE / cover skin plantation terrain trip hazard correct footwear / watch where you are walking / use walking sticks getting lost work in group / maps / use GPS / guide poachers being attacked / shot trained, professionals/ medics, available 1(c) any one from: (does not support) 1. acacia and mango have the same means or acacia and mango have similar, D values / index or mango and invasive species have overlapping, D values / index / means +/- SD ; (does support / partially support) 2. sal tree has the highest, D value / index / mean or sal tree has greater, D values / Index / mean, than both alien species ; 1 Question Answer Marks 1(d)(i) concentration / mg cm-3 volume of stock solution / cm3 volume of (distilled) water / cm3 7.5 37.5 12.5 ; 2.5 12.5 37.5 ; 2 1(d)(ii) 1 correct processes and correct figures ; 2 (correct) answer to 3 significant figures ; ecf if mp1 is incorrect 3 decrease / minus (number) ; 3 Question Answer Marks 1(e) any three from: improvement impact 1 More, intermediate / smaller values / intervals appropriate examples accepted better idea of the, trend / pattern / effect ; 2 exclude anomalous results improve reliability ; 3 repeat reading for 2.5 / 5.0 / 7.5 mg cm-3 (any of these 3 might be anomalous) check the anomaly / improve reliability ; 4 repeat investigation at least twice or repeat with more marigolds better idea of trend / improve reliability / reduce effect of anomalies ; 5 (calculate) standard error / standard deviation / confidence intervals / statistical analysis check for significance (difference between the means) / checking accuracy ; 6 use marigold clones exclude genetic effects / improve validity ; 7 use Vernier calliper more precise measurements ; 8 measure the mass of all the roots improve reliability ; 3 1(f) any two from: 1 (same) mass of soil ; 2 sample from same depth ; 3 sampled at the same time ; 4 sample from same, distance from roots / position in the pot ; 2

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2 Tumours may be described as benign or malignant. Malignant tumours can lead to greater complications for the person with the tumour. Early identification of tumours, particularly malignant tumours, is important for effective treatment. Benign tumour cells and malignant tumour cells can look similar when viewed using a light microscope. Some scientists wanted to develop a diagnostic test to identify tumour cells as benign or malignant. The scientists investigated whether the diameter of the cell nucleus could be used to identify the type of tumour cell as benign or malignant. The scientists used a light microscope with a calibrated eyepiece graticule to measure the diameter of the nuclei of stained tumour cells. Fig. 2.1 shows a photomicrograph of stained tumour cells viewed using a light microscope. An eyepiece graticule was placed across the nucleus of one of the tumour cells. 100 90 80 70 cell surface 60 membrane 50 nucleus 40 30 cell X 20 eyepiece 10 graticule 0 image magnification ×400 Fig. 2.1 The calibration of the eyepiece graticule scale is: one eyepiece graticule division = 320 nm (a) Use the calibration of the eyepiece graticule scale to calculate the actual diameter of the nucleus of cell X, shown in Fig. 2.1. Show your working and state your answer in µm. actual diameter of the nucleus of cell X = ................................................... µm [3] (b) For the investigation into whether the diameter of the nucleus could be used to identify the type of tumour cell, tumours of the thyroid gland (an endocrine gland) were used. For the diagnostic test the scientists carried out a procedure using two different stains. step 1 50 people diagnosed with benign tumours and 24 people diagnosed with malignant tumours were selected. step 2 A sample of tumour cells was removed from the thyroid gland of each person. step 3 The cells were stained with either Papanicolaou stain (Pap) or haematoxylin and eosin stain (H&E). step 4 Samples were viewed using a light microscope with a magnification of ×400. step 5 In each sample, the diameters of 100 nuclei were measured. step 6 The measurements were made by one of the scientists who did not know the type of tumour cell they were measuring. Table 2.1 shows the results of the investigation. Table 2.1 category mean nuclear standard standard diameter / µm deviation / µm error / µm total benign cells (50 people) 5000 cells: 7.3 ± 0.8 ± 0.011 • Pap‑stained cells (41 people) 4100 cells 7.3 ± 0.7 ± 0.011 • H&E‑stained cells (9 people) 900 cells 7.2 ± 1.0 ± 0.033 total malignant cells (24 people) 2400 cells: 9.0 ± 0.6 ± 0.122 • Pap‑stained cells (18 people) 1800 cells 9.0 ± 0.7 ± 0.016 • H&E‑stained cells (6 people) 600 cells 8.8 ± 0.5 ± 0.020 (i) Suggest how the scientists can standardise the method of measuring the diameter of the 100 nuclei in step 5, so that valid comparisons can be made between benign and malignant tumour cells. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Identify one variable that the scientists have standardised in step 1 to step 6, other than details of the method of measurement of the nuclei. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (iii) The scientists used a t‑test to compare the mean nuclear diameter of the Pap‑stained cells and the H&E‑stained cells in Table 2.1. State a null hypothesis for the t‑test. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1]

Mark scheme: 2(a) 1 correct counting / correct number of divisions / 28 ± 2 ; 2 for correct conversion(s) to micrometres ; 3 correct answer / 8.96 / 8.32–9.6 ; 3 2(b)(i) measure the, widest / narrowest / longest, part of the each nucleus ; 1 2(b)(ii) any one from: 1 (same) magnification /  400 ; 2 (same) number of / 100 nuclei (measuring) per, person ; 3 (sample from / same) thyroid / gland ; 4 same / one, scientist (measuring the diameter) ; 5 idea that: type of tumour cell is unknown ; 1 2(b)(iii) there is no difference, in / between the (mean) nuclear diameters of, the Pap-stained cells and H&E- stained cells ; 1 2(b)(iv) accept null hypothesis or there is no significant difference ; 1 2(b)(v) state 1 idea that this technique can be used to distinguish between benign and malignant cells or the mean nuclear diameter of benign cells is smaller than in malignant cells / ora ; explain 2 mean  2 SE, do not overlap or there is a significant difference in the mean nuclear diameters of benign cells and malignant cells ; 2 Question Answer Marks 2(b)(vi) disadvantages  time consuming (prepping / counting / measuring)  labour intensive  shortage of skilled scientists  invasive  only thyroid / one tissue, used  human error – due to, small values / very close values / large numbers counted impact:  infection / bleeding  pain  tissue damage  metastasis  anxiety  delayed treatment  unnecessary treatment  idea of misdiagnosis  possibly not feasible on large scale  may not be true of other tumours 2

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