PLMGSS 2025 Sec 3 EOY G3 Pure Biology Paper 2

[Turn over BIOLOGY 6093/02 Paper 2 2 Oct 2025 Changes 1 hour 30 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A (60 marks) Answer all questions. Write your answers in the spaces provided. Section B (10 marks) Answer one question. Write your answers in the spaces provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. _______________________________________________________________________________ This document consists of 22 printed pages. CANDIDATE NAME CLASS CLASS INDEX NUMBER TG Subject Teacher For Examiner’s Use Section A Section B 7 8 Total Paya Lebar Methodist Girls’ School (Secondary) End-of-year Examination 2025 Secondary 3 Express/G3

2 Section A [60 marks] Answer all questions in this section. Write your answers in the spaces provided. 1 Fig. 1.1 shows a drawing of a cell from the lining of the small intestine. The lumen is the space inside the intestine where food is digested. Fig. 1.1 (a) State the names of labelled structures A and C in Fig. 1.1 and describe the role of each structure in the intestinal cell. A…………..………..…………..…………………………………………………….……...… .….…………..………..…………....…………………………………………………….…….. .….……………..………..…………..…………………………………………………….…… ...……….………..………..…………..…………………………………………………….….. C…………..………..…………..…………………………………………………….……...… …..…………..………..….………..…………………………………………………….……... ….……………..………..…………..…………………………………………………….……. ..……….………..………..…………..……………………………………………………... [4]

[Turn over 3 (b) Cholera is a transmissible disease that causes watery faeces. The cholera bacterium can survive in the large intestine and reduces the absorption of water. The bacterium releases a toxin that interacts with receptors on the surface of cells causing the release of chloride ions into the lumen of the intestine. Fig. 1.2 shows the effect of the toxin. The arrows indicate the direction of movement of the molecules. Fig. 1.2 Suggest how cholera causes watery faeces. …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[3] chloride ions

4 (c) Scientists have found that there are different types of starch which have molecules of different shapes. Some molecules are digested rapidly and others are digested slowly. The graph in Fig. 1.3 shows the effect on the concentration of glucose in the blood after eating two types of starch. Fig.1.3 (i) Both graph lines show an initial increase in blood glucose concentration followed by a decrease. Suggest two reasons why the blood glucose concentrations decrease. 1…………..………..…………………..…………………………………………….……...….. ……………………..…..…………………..…………………...………………………….…… 2……………..………..…………..……………………………………………………………... ………………………..…..…………..…………………………...…………………………. [2] (ii) Use information from Fig. 1.3 to suggest which type of starch is healthier to have in the diet. Give a reason for your answer. …………………..…..…………………..…………………...………………………….……… …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[2] [Total: 11m]

[Turn over 5 2 The liver is responsible for the breakdown of alcohol. Fig. 2. 1 shows a computer model of the enzyme responsible for breaking down alcohol. Fig. 2.1 (a)(i) Enzymes have a specific three–dimensional shape. Explain why the shape of an enzyme is important. …………………..…..…………………..…………………...………………………….……… …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[2] (ii) Describe and explain the effect of increasing the temperature from 25oC to 35oC on the activity of the enzyme above. …………………..…..…………………..…………………...………………………….……… …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[3]

6 (b) Pineapples contain a mixture of protease enzymes called bromelain. The effect of changing pH on the activity of the enzyme bromelain was investigated. The results of this investigation are shown in Fig. 2.2. Fig. 2.2 To assist digestion, some people swallow bromelain in the form of a powder with their food. Use the information in Fig. 2.2 and your knowledge of the human digestive system to discuss the effectiveness of using bromelain in this way. …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………………..…………………………………………….……...…… …………………..…..…………………..…………………...………………………….……… …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[5] [Total: 10m]

[Turn over 7 3 (a) The alveolus is the gas exchange surface in humans. For efficient oxygen uptake, a steep diffusion gradient is maintained between the alveolar air and the blood. State two ways how the steep diffusion gradient for oxygen is maintained at the gas exchange surface. …………..………..…………..…………………………………………………….……...…… …………………..…..…………..…………………………...………………………….……… …………..………..……………..………………………………………………….……......[2] (b) A person who wanted to begin a fitness programme did some vigorous exercise. A fitness trainer took a drop of blood from the person’s finger before, during and after vigorous exercise and tested it for lactic acid. The results of the tests for lactic acid are shown in Fig. 3.1. Fig. 3.1

8 Describe and explain the changes in blood lactic acid concentration shown in Fig. 3.1. ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... .................................................................................................................................... [5] (c) The concentration