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2024 AQA AS BIOLOGY 7401/ 2 Paper 2
Verified Question Paper and Marking Scheme Attached
June 2024
BIOLOGY
Paper 2
Thursday 23 May 2024 Morning Time allowed: 1 hour 30 minutes
Materials
For this paper you must have:
- a ruler with millimetre measurements
- a scientific calculator.
Instructions
- Use black ink or black ball-point pen.
- Fill in the boxes at the top of this page.
- Answer all questions.
- You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages.
- If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s).
- Show all your working.
- Do all rough work in this book. Cross through any work you do not want to be marked.
Information
- The marks for the questions are shown in brackets.
- The maximum mark for this paper is 75. For Examiner’s Use Question Mark 1 2 3 4 5 6 7 8 9 TOTAL
Do not write outside the Answer all questions in the spaces provided.^ box (^0 1). 1 Water has a high heat capacity and a large latent heat of vaporisation. Describe the importance of each of these properties to living organisms. [2 marks] High heat capacity Large latent heat of vaporisation (^0 1). 2 Figure 1 shows that water loss from a porous pot can cause the upward movement of water. Figure 1
Do not write outside the box (^0 2). 1 Figure 2 shows an image of a red blood cell at a magnification of × 5500 Figure 2 Calculate the actual diameter in μm of the red blood cell between points P and Q. Show your working. [2 marks] Answer μm
Do not write outside the box (^0 2). 2 A haemocytometer is a special microscope slide that can be used to determine the mean number of red blood cells in 0.004 mm^3 of blood.
- A researcher prepared a 10 –^3 dilution of a sample of blood from an adult.
- Using a haemocytometer, the researcher determined that the mean number of red blood cells in 0.004 mm^3 of the diluted blood sample was 21 The volume of blood in the body of the adult was 4.8 dm^3 Calculate the total number of red blood cells in the body of this adult. Show your working. [2 marks] Answer (^0 2). 3 The solution used to dilute the blood had to have the same water potential as the blood. Explain why. [2 marks] Question 2 continues on the next page Turn over ►
Do not write outside the box (^0 3). 1 Describe how you would use cell fractionation and ultracentrifugation to obtain a sample of mitochondria from muscle tissue. [4 marks] Question 3 continues on the next page Turn over ►
Do not write outside the box (^0 3). 2 Mitochondrial respiratory capacity is a measure of maximum ATP production in a mitochondrion. Scientists investigated the effect of a resistance exercise training (RET) programme on the respiratory capacity of mitochondria in skeletal muscle tissue. RET develops muscle strength. The scientists:
- took samples of muscle tissue from 11 young males before and after a 12 - week RET programme
- recorded the respiratory capacity of the mitochondria in the samples of muscle tissue. Figure 3 shows some of the scientists’ results. The error bars represent ± 2 standard deviations from the mean, which includes over 95% of the data. Figure 3
Do not write outside the box [1 mark] (^0 4). 2 The genome of an adenovirus is a single, linear molecule of double-stranded DNA. Adenoviruses use eukaryotic host cells to transcribe their genes in protein synthesis. The process of transcription of adenovirus genes is similar to the process of transcription of genes in eukaryotes. Scientists investigated the process of transcription of this viral DNA. Figure 4 shows one of the experiments carried out by these scientists. Figure 4 (^0 4). 1 Where does transcription occur in a eukaryotic cell?
Do not write outside the Looking at the results of the experiment in Figure 4 , the scientists concluded that^ box splicing had taken place. Use Figure 4 to describe and explain why the scientists’ conclusion was justified. [3 marks] (^0 4). 3 Describe and explain how the results of the experiment in Figure 4 would differ if the scientists had used prokaryotic DNA. [2 marks] (^0 4). 4 Errors in the precise location of splicing in the DNA molecule can lead to mutations. Explain why. [1 mark] Turn over ►
Do not write outside the box (^0 5). 4 A student used an optical microscope to observe a piece of tissue from the lower surface of an orchid leaf. The piece of leaf tissue observed was very thin. Explain why this was important. [2 marks] (^0 5). 5 The student produced a biological drawing of the leaf tissue they viewed through an optical microscope. Give three ways the student could ensure they produce a correct biological drawing of the leaf tissue. Assume the student uses a sharp pencil. [3 marks] 1 2 3 Turn over ►
Do not write outside the
. 1 Disinfectants are used to kill microorganisms on non-living surfaces. A student investigated the effect of different concentrations of disinfectant X on the growth of Bacillus subtilis. The student: - added 5 cm^3 of a different concentration of disinfectant X to 5 different test tubes - added 5 cm^3 of distilled water to another test tube - added 2 cm^3 of a culture of B. subtilis to all 6 test tubes - incubated the test tubes at 25 °C for 24 hours - used a colorimeter to record the percentage of light absorbed by the contents of each tube. Table 2 shows the student’s results. Table 2 Percentage concentration of disinfectant X
Percentage light absorbance 100 100 87 52 10 10 The student prepared the different concentrations of disinfectant X. Describe how the student made 5 cm^3 of the 60% concentration using distilled water and undiluted disinfectant. box [1 mark]
Do not write outside the box (^0 7). 1 Edwards’ syndrome is a condition resulting from an extra chromosome 18. A chromosome mutation in the second meiotic division is the most frequent cause of Edwards’ syndrome. Explain how a chromosome mutation in the second meiotic division could result in an extra chromosome 18. In your answer, name the type of chromosome mutation which would result in the extra chromosome. [2 marks] (^0 7). 2 Complete trisomy 18 is the most common type of Edwards’ syndrome. This occurs when all the cells of the body have an extra chromosome 18. Explain why all the cells of the body have an extra chromosome 18. [2 marks]
Do not write outside the box (^0 7). 3 Mosaic trisomy 18 is another type of Edwards’ syndrome. This occurs due to a chromosome mutation after fertilisation. In mosaic trisomy, the body has cells with an extra chromosome 18 and cells with the correct number of chromosomes. Explain how cells with different numbers of chromosomes are produced in mosaic trisomy. [1 mark] (^0 7). 4 The age of the female parent is a factor linked to the risk of a child having Edwards’ syndrome. Which statistical test should be used to test whether this link is statistically significant? Tick (✓) one box. [1 mark] Correlation coefficient Chi-squared Student’s t-test Question 7 continues on the next page Turn over ►
Do not write outside the box (^0 8) Lyme disease is most frequently caused by the bacterium Borrelia burgdorferi. Lyme disease can be difficult to diagnose. Figure 5 shows an ELISA test that is used to find out if a person has antibodies to B. burgdorferi. Figure 5 A false positive in this test is a result which incorrectly indicates that antibodies to B. burgdorferi are present. (^0 8). 1 Failure to thoroughly wash the well in Step 4 can result in a false positive. Explain why. [2 marks] Turn over ►
Do not write outside the box (^0 8). 2 A false positive can be produced if a person has been infected by another bacterium that causes a disease called syphilis. Suggest why. [1 mark] (^0 8). 3 A false negative in this test is often produced if a person is tested within 2 weeks of being infected with B. burgdorferi. Explain why. [2 marks] (^0 8). 4 Sometimes, symptoms of Lyme disease can persist for 6 months following antibiotic treatment. This condition is known as Post-Treatment Lyme Disease Syndrome (PTLDS). Scientists investigated the symptoms experienced by a large number of PTLDS patients and a control group. During a 2 - week period, they asked all the participants:
- if they had experienced symptoms of PTLDS
- to record the intensity of these symptoms. The scientists used a statistical test to determine if there was a difference in the intensity of symptoms of PTLDS between these two groups.
