AQA AS BIOLOGY Paper 1 FOR MAY 2023

AQA AS BIOLOGY Paper 1 Monday 15 May 2023 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. Answer all questions in the spaces provided. box . Describe the primary structure of all proteins. [2 marks] 0 1 . 2 This question is about the genetic code. Define universal, non-overlapping and degenerate. [3 marks] Universal Non-overlapping Degenerate Figure 1 shows a transmission electron microscope (TEM) image of a Streptococcus bacterium. Figure 1 . Describe how the appearance of the area containing DNA in a TEM image of a eukaryotic cell would differ from that shown in Figure 1. box [2 marks] . Describe one difference between the structure of DNA in a prokaryotic cell and in a eukaryotic cell. [1 mark] Question 2 continues on the next page Turn over ► . Streptococcus bacteria can infect the lungs when air is breathed in and cause lung disease. box Describe the mechanism of breathing that causes air to enter the lungs. [3 marks] . Some strains of Streptococcus bacteria are more likely to cause lung disease than other strains. Strains that do not cause lung disease are quickly destroyed by phagocytes. Phagocytes are stimulated when they bind to murein on Streptococcus bacteria. Each strain of Streptococcus bacteria has a capsule of different thickness from the others. Suggest how Streptococcus bacteria with a thicker capsule are more likely to survive and so cause lung disease. [2 marks] . Figure 2 shows a fatty acid that contains 20 carbon atoms and four double bonds. Figure 2 box On Figure 2, draw a box around the R group of the fatty acid. [1 mark] 0 3 . 2 Figure 3 shows a triglyceride. Figure 3 Describe two differences between the structure of the triglyceride shown in Figure 3 and a phospholipid. [2 marks] 1 2 Question 3 continues on the next page Turn over ► . Explain why phospholipids can form a bilayer but triglycerides cannot. [3 marks] box . Figure 4 shows two fatty acids, A and B. Figure 4 A B Scientists fed rats a diet with added fish oil for 4 months. They obtained samples of red blood cells from the rats before starting this diet (0 months) and after 4 months on this diet. For each red blood cell sample, they separated the cell-surface membranes and measured: • the percentage of phospholipids containing each of the fatty acids A and B • the fluidity of the membrane. Table 1 shows the scientists’ results. box Table 1 Time sample of red blood cells obtained / months Mean percentage of phospholipids containing fatty acid A Mean percentage of phospholipids containing fatty acid B Mean fluidity of the membrane / arbitrary units 0 19.8 1.7 31 4 11.7 9.0 97 Suggest why the fluidity of the membrane was higher after 4 months. Use all the information provided in the question. [3 marks] Turn over for the next question *07* Turn over ► Scientists investigated the activation of T lymphocytes. The scientists studied two types of cell: • naïve T cells, which are T cells that have not yet been in contact with a foreign antigen • activated helper T cells, which are T cells that have been activated by a foreign antigen. Figure 5 shows electron microscope images of the two types of cell. Figure 5 Naïve T cell Activated helper T cell The activated helper T cell has a volume of 463 μm3 box . Calculate the volume of the naïve T cell shown in Figure 5. Then calculate how many times larger the activated helper T cell volume is compared with the naïve T cell volume. Assume the cell is spherical. Use line PQ to measure the diameter of the naïve T cell. 4 Volume of a sphere = 3 πr3 where π is 3.14 Show your working. [3 marks] Volume of naïve T cell μm3 Number of times larger the activated helper T cell volume is compared with the naïve T cell volume . State one feature that shows the images in Figure 5 were taken with an electron microscope and not an optical microscope. box Explain your answer. [2 marks] . State one role of a helper T cell. [1 mark] . The rate of translation is increased in T cells activated by antigens. Describe the role of tRNA in translation. [2 marks] Turn over for the next question Turn over ► A student investigated the effect of changing surface area on the rate of diffusion of a solution into the centre of agar blocks. She used agar coloured by an indicator. The indicator is pink at pH > 8 and colourless at pH 8 and pH < 8 She cut blocks in different shapes as shown in Figure 6. Figure 6 . Complete Table 2 to show the surface area and the surface area to volume ratio for the two shapes. Table 2 Shape Surface area / cm2 Volume / cm3 Surface area to volume ratio C 64 : 1 D 64 : 1 [2 marks] box . The student put the blocks into an acidic solution. The acidic solution caused the blocks to gradually turn from pink to colourless. She recorded the time taken for the blocks to turn completely colourless. She repeated this three times. Table 3 shows the student’s results. Table 3 Shape Time for block to turn colourless / s Mean time for block to turn colourless / s Block 1 Block 2 Block 3 Block 4 C 3490 1200 3540 3530 D 1680 1500 1590 1610 1595 After collecting the data, the student noticed that shape C, block 2 was damaged. box Calculate the mean for shape C. [1 mark] . Suggest what the student should have done when she saw that shape C, block 2 was damaged. [1 mark] 0 5 . 4 State three variables the student controlled in order to obtain valid results. [2 marks] 1 2 3 Question 5 continues on the next page Turn over ►