2023 SASS Bio Prelims P2

Preliminary Examination 2023/4Exp/Biology Paper 2 3 [Turn over Section A [50 marks] Answer all questions. Write your answers in the spaces provided. 1 Aplastic anaemia is a rare blood disorder where stem cells in the bone marrow are damaged. Fig. 1.1 depicts the blood samples taken from a healthy individual and an individual with aplastic anemia. Fig. 1.1 (a) State one difference that can be observed in the two blood samples in Fig. 1.1. ………………………………………………………………………………………… ………………………………………………………………………………………[1] (b) Individuals with aplastic anemia may often experience light -headedness, especially when active or standing up. Explain why. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………[3] (c) Suggest an effect that aplastic anemia can have on the heart. Explain your answer. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………..…………………….[2] [Total: 6] red blood cell white blood cell red blood cell white blood cell healthy individual individual with aplastic anemia

Preliminary Examination 2023/4Exp/Biology Paper 2 4 2 Camellia sinensis is a widely grown plant as its leaves are used to make tea. A photomicrograph of a section through the midrib of the tea leaf is shown in Fig. 2.1. Fig. 2.1 (a) State the structural differences between (i) tissues A and B ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………[2] (ii) tissues C and D ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………[2] D A B C

Preliminary Examination 2023/4Exp/Biology Paper 2 5 [Turn over (b) The lower epidermis of the leaf contains many minute open ings called stomata. The opening and closing of each stoma is regulated by the guard cells surrounding it. In the space below, draw a labelled diagram of a pair of guard cells surrounding a single stoma. [3] (c) Camellia sinensis is mainly cultivated in tropical climates as it prefers a moist growing location. Explain how this affects the rate of transpiration of the plant. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [2] [Total: 9] 3 Fig. 3.1 shows the respiratory system of a human. Fig. 3.1 B A C

Preliminary Examination 2023/4Exp/Biology Paper 2 6 (a) Describe the process of inhalation and how it involves structures A, B and C. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [4] (b) Suggest and explain the effect of having low levels of carbonic anhydrase on gaseous exchange in an individual. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [3] (c) Cystic fibrosis is a genetic disorder which results in the build-up of thick, sticky mucus that affects various organ systems in the body. Explain the effects this condition will have on an individual’s respiratory system. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [2] [Total: 9]

Preliminary Examination 2023/4Exp/Biology Paper 2 7 [Turn over 4 Fig. 4.1 depicts the changes in a follicle during the menstrual cycle. Fig. 4.1 (a) Identify the structures labelled A and B. A …………………………..………… B ………………………..…………… [2] (b) A woman is trying to conceive a baby. (i) If the process labelled X takes place on the 14th day of a 28-day month, suggest a time period where she would have a good chance of getting pregnant. Explain your answer. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… …………………………………………………………………………..… [3] (ii) Explain the limitations to this method of family planning. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………...…... [2] [Total: 7] A B X

Preliminary Examination 2023/4Exp/Biology Paper 2 8 5 Canavan disease is an inherited disease caused by a mutation in the gene for the enzyme aspartoacylase, which acts to break down the brain chemical known as N - acetyl-aspartate (NAA) . Studies have suggested that if NAA is not broken down properly, the resulting chemical imbalance interferes with the formation of the myelin sheath as the nervous system develops. (a) Describe how a mutation in the gene results in a deficiency of the enzyme. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [3] (b) Suggest a symptom that would be observed in an individual with the disease. Explain your answer. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [2] (c) Canavan disease is inherited as an autosomal recessive trait. (i) Explain what is meant by the term ‘recessive trait’. ………………………………………………………………………………… …………………………………………………………………………..… [1] (ii) Using the symbol N to represent the dominant allele and n to represent the recessive allele, draw a genetic diagram to show how a mother and father who do not have the disease, can have a child with the Canavan disease. Mother Father phenotype of parents ………….…… ………….…… genotype of parents ………….…… ………….…… gametes …… .…… …… .…… genotype of offspring ……..… .……..… ……..… .……..… phenotype of offspring ……..… .……..… ……..… .……..… [4] [Total: 10]

Preliminary Examination 2023/4Exp/Biology Paper 2 9 [Turn over 6 Fig. 6.1 shows the four stages of mitosis in an animal cell. (a) Using the letters P, Q, R and S, list the correct order of the stages. ………………………………………………………………………………….… [1] (b) State the diploid number of chromosomes in this cell. ………………………………………………………………………………….… [1] (c) Non-disjunction refers to the failure of sister chromatids to separate properly during mitosis. Using the letters P, Q, R and S, identify the stage at which non- disjunction occurs. Explain your answer. ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………..… [2] (d) Compare and contrast between mitosis and meiosis. …………………………………………………………………………….……….… …………………………………………………………………………….……….… …………………………………………………………………………….……….… …………………………………………………………………………….……….… …………………………………………………………………………….……….… …………………………………………………………………………….……….… …………………………………………………………………………….………. [