A-level BIOLOGY Paper 2

A-level BIOLOGY Paper 2 Friday 14 June 2024 Morning Time allowed: 2 hours 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 91. IB/M/Jun24/G4006/E7 7402/2 Answer all questions in the spaces provided. box 0 1 Figure 1 shows a drawing of a neuromuscular junction. Figure 1 0 1 . 1 Name the parts labelled A to D. [2 marks] A B C D 0 1 . 2 Following the release of acetylcholine into a neuromuscular junction, a muscle contraction occurs. Describe the sequence of events, following the release of acetylcholine, that leads to stimulation of this contraction. Do not include in your answer the events following the release of calcium ions in the myofibril. [4 marks] 0 1 . 3 Inhibitory synapses cause hyperpolarisation in postsynaptic neurones. Explain how this inhibits synaptic transmission. [2 marks] Turn over ► 0 2 . 1 Figure 2 shows part of a relaxed myofibril. Figure 2 The myofibril represented in Figure 2 has 34 sarcomeres. The length of every sarcomere is 2 µm After contraction of this myofibril, the length of each sarcomere changed by 20%. Use the information provided to calculate the length of the myofibril after contraction. Give your answer in mm and in standard form. Show your working. [2 marks] Answer mm . Which statement correctly describes the changes in length in a sarcomere when a myofibril contracts? box Tick () one box. [1 mark] H-zone decreases, I-band increases, A-band decreases H-zone increases, I-band decreases, A-band decreases H-zone decreases, I-band decreases, A-band no change H-zone increases, I-band increases, A-band no change 0 2 . 3 Fast muscle fibres have a higher concentration of glycogen than slow muscle fibres. Explain how the difference in glycogen concentration is related to the different properties of these muscle fibres. [4 marks] Turn over ► 0 3 . 1 A biologist investigated photosynthesis. They: • measured the percentage of light absorbed by a plant when it was exposed to different wavelengths • measured the rate of photosynthesis at each wavelength of light. Figure 3 shows the results they obtained. Figure 3 Using Figure 3, what can you conclude about the relationship between: [2 marks] the percentage of light absorbed and the rate of photosynthesis the colour of light and the rate of photosynthesis 0 3 . 2 Give three environmental factors that should be controlled when measuring the rate of photosynthesis in this investigation. Do not include features of the plant in your answer. [2 marks] 1 2 3 0 3 . 3 Describe how the products of the light-dependent reaction are used in the light-independent reaction to produce triose phosphate. Do not include the role of ribulose bisphosphate (RuBP) in your answer. [3 marks] Turn over ► 0 4 . 1 In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g. Explain how you would determine if the genotype of a grey fly is homozygous or heterozygous for body colour. [2 marks] 0 4 . 2 In fruit flies, males are XY and females are XX. A cross between a grey-bodied male fly and a black-bodied female fly produced some black-bodied females. Explain how this shows that the gene for body colour is not sex-linked. [1 mark] 0 4 . 3 A population of fruit flies contained 19% grey-bodied flies. Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G. Show your working. [2 marks] Answer % 0 4 . 4 In fruit flies, a gene for wing shape has a dominant allele for curly wings, R, and a recessive allele for normal wings, r. The alleles for this gene are on a different pair of chromosomes from the gene for body colour. Fruit flies that are homozygous dominant for curly wings do not survive beyond the embryo stage. A curly-winged fly, homozygous for grey body colour was crossed with a curly-winged, black-bodied fly. Complete the genetic diagram to show all the possible genotypes and the ratio of phenotypes expected to develop into adults from this cross. [3 marks] Phenotypes of parents Curly-winged, grey-bodied, × Curly-winged, black-bodied Turn over ► 0 5 . 1 A weed is a plant growing where it is not wanted. Fat hen is a weed which grows in some crop fields. Describe how you could estimate the number of fat hen plants in a field. [5 marks]