1 (a) Fig. 1.1 shows some of the organs of the human body. … X … … Fig. 1.1 (i) Complete the labels in Fig. 1.1 to show the names of the organs. [3] (ii) One function of organ X is digestion. State one other function of organ X. … [1] (iii) Name the organ that pumps blood around the body. … [1] (iv) Name the part of the body where egestion occurs. … [1] (b) Enzymes are involved in digestion. Fig. 1.2 is a graph that shows the effect of pH on the activity of three enzymes. 1 0 2 3 4 5 6 pH enzyme activity enzyme A enzyme B enzyme C 7 8 9 10 11 Fig. 1.2 (i) Describe the effect of pH on enzyme A. Use data from the graph in your answer. … … … … [2] (ii) The mouth has an average pH of 6.7. Identify which enzyme in Fig. 1.2 is found in the mouth. Explain your answer. enzyme … explanation … … [2] (iii) Enzymes are involved in the clotting of blood. Circle the component of blood which is also involved in clotting. plasma platelets red blood cells white blood cells [1] [Total: 11]

1(a)(i) lung(s) ; liver ; large intestine ; 3 1(a)(ii) absorption ; 1 1(a)(iii) heart ; 1 1(a)(iv) anus ; 1 1(b)(i) activity increases then decreases (as pH increases) ; maximum activity at pH 2 ; 2 1(b)(ii) B ; maximum activity at pH 6.5 / other enzymes do not work at pH 6.7 ; 2 1(b)(iii) platelets (circled) ; 1

4 (a) A student investigates the effect of temperature on enzyme activity. They use an enzyme called amylase to breakdown starch into a reducing sugar. They measure the activity of the enzyme at different temperatures. Fig. 4.1 is a graph of their results. rate of reaction / arbitrary units temperature / °C 0 0 10 20 30 40 50 60 5 10 15 20 25 30 35 Fig. 4.1 (i) Describe the effect of temperature on the enzyme activity shown in Fig. 4.1. Include data from the graph in your answer. … … … … [2] (ii) Complete this sentence to define the term enzyme. Enzymes are … that function as biological … . [2] (iii) Enzymes are transported in the blood plasma. State the molecule in red blood cells that transports oxygen. … [1] (b) Glucose is made by plants during photosynthesis, transported as sucrose and stored as starch. Fig. 4.2 shows apparatus used to investigate one factor that affects photosynthesis. green plant chemical used to remove carbon dioxide from the glass jar water glass jar air tight bung sunlight Fig. 4.2 (i) Place a tick (✓) in one box to show the factor being investigated in Fig. 4.2. carbon dioxide chlorophyll light water [1] (ii) The plant is left for 48 hours in the glass jar. After 48 hours a leaf is prepared and then tested using iodine solution. Complete these sentences about the expected result. When placed on the leaf the iodine solution will be … in colour. This is because the plant does not make any … . [2] (iii) State the name of the ions needed to make chlorophyll. … [1] [Total: 9]

4(a)(i) as temperature increases, rate increases then falls ; peak or optimum (rate) at 40°C / maximum rate 34 (arbitrary units) ; OR activity increases, to 40°C / from a rate of 8 to 34 ; above 40°C the activity decreases / decreases from 34 ; 2 4(a)(ii) proteins ; catalysts ; 2 4(a)(iii) haemoglobin ; 1 4(b)(i) carbon dioxide  chlorophyll light water ; 1 4b(ii) orange / brown ; starch ; 2 4(b)(iii) magnesium ; 1 (a)(i) You need to describe the trend of the rate increasing then falling as temperature increases, and include specific data from the graph, such as the peak or optimum rate at 40°C or the maximum rate of 34 arbitrary units. (a)(ii) You must correctly identify enzymes as 'proteins' and state that they function as biological 'catalysts'. (a)(iii) You need to state 'haemoglobin' as the molecule in red blood cells that transports oxygen. (b)(i) You must correctly identify 'carbon dioxide' and 'water' as the reactants and 'chlorophyll' and 'light' as the conditions for photosynthesis. (b)(ii) You need to state that the iodine solution will turn 'orange' or 'brown' and that this indicates the presence of 'starch'. (b)(iii) You must identify 'magnesium' as the mineral ion needed to make chlorophyll.

4 (a) Table 4.1 shows the mass of protein in some different food types. Table 4.1 food type mass of protein in 100 g of food / g beans 6.9 cheese 25.4 eggs 12.5 fish 23.5 lentils 7.6 meat 32.0 nuts 21.1 (i) Identify the food type that contains the most protein in 100 g of food. … [1] (ii) The recommended daily intake of protein for an adult male is 56 g. A man eats 25 g of nuts. Calculate the percentage of the recommended daily intake of protein he has eaten. Give your answer to 2 significant figures. …% [3] (iii) Some people only eat vegetable proteins. Suggest why eating nuts can be an important part of their diet. Use the information in Table 4.1 to help you. … … [1] (b) Proteins are digested in the stomach. (i) Mechanical digestion and chemical digestion both take place in the stomach. Compare mechanical digestion and chemical digestion. … … … … [2] (ii) Hydrochloric acid is found in the stomach. State why chemical digestion in the stomach requires the presence of hydrochloric acid. … … [1] [Total: 8]

4(a)(i) meat ; 1 4(a)(ii) 9.4 / 9.5(%) ;;; MP1 21.1 ÷ 4 / = 5.275 / 5.3 ; MP2 (5.275 ÷ 56) × 100 / = 9.42 OR (5.3 ÷ 56) × 100 / = 9.46 ; MP3 answer given as two significant figures 9.4 or 9.5 % ; 3 4(a)(iii) higher in protein than, the other vegetable based proteins / beans / lentils OWTTE ; 1 4(b)(i) any two from: both types break down, food / protein ; the idea that mechanical digestion results in smaller pieces (of food) AND idea that chemical digestion results in smaller molecules ; chemical digestion involves enzymes / mechanical digestion does not use enzymes ; chemical digestion produces soluble molecules / mechanical digestion may not result in soluble molecules ; 2 4(b)(ii) (provides an acidic pH) for enzymes / for enzymes to work ; 1

4 (a) Fig. 4.1 is a graph showing the effect of temperature on the activity of an enzyme. 16 12 8 4 0 18 14 10 6 2 45 50 55 60 65 70 75 temperature / °C enzyme activity / arbitrary units Fig. 4.1 (i) Identify the temperature when this enzyme is most active. … °C [1] (ii) Explain why enzyme activity increases between 45 °C and 55 °C in Fig. 4.1. … … … … [2] (b) Protease enzymes are found in the stomach of humans. (i) State the role of protease enzymes in the stomach. … … … [2] (ii) Fig. 4.2 shows how changing pH affects the activity of three enzymes, A, B and C. enzyme activity 1 7 14 A B C pH Fig. 4.2 Describe the evidence from Fig. 4.2 that shows that enzyme A is the protease enzyme from the stomach. … … … [2] (c) The process of photosynthesis occurs in plants. Complete the balanced equation for photosynthesis. light … CO2 + … … … + … O2 chlorophyll [2] [Total: 9]

4(a)(i) 60 (°C) ; 1 4(a)(ii) correct reference to gain of energy ; increase in frequency of collisions / more effective collisions ; 2 4(b)(i) break down proteins ; to form amino acids ; 2 4(b)(ii) stomach, is acidic / has a low pH ; only enzyme A works, in acidic conditions / at low pH ; 2 4(c) (light) 6(CO2) + 6H2O C6H12O6 + 6(O2) ;; (chlorophyll) reactants correct = 1 mark products correct = 1 mark 2

Cambridge IGCSE Combined Science · 0653

IGCSE Combined Science (0653) Enzymes past paper questions

Revise IGCSE Combined Science (0653) — Enzymes with real Cambridge past-paper questions grouped by topic, each shown with its marking scheme. Working one topic at a time targets exactly the skill each question tests.

122 free questions from 2016–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Enzymes in IGCSE Combined Science 0653 exams, 2020–2025

Across 2020–2025, Enzymes accounted for 133 questions worth 678 marks in Cambridge IGCSE Combined Science (0653) papers.

By year
Year	Questions	Marks
2020	15	53
2021	24	120
2022	22	107
2023	26	139
2024	23	143
2025	23	116

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B5.1 Enzymes607 marks

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Paper 1 · 29 qs
Paper 2 · 42 qs
Paper 3 · 16 qs
Paper 4 · 28 qs
Paper 5 · 7 qs
Paper 6 · 11 qs

All most-tested Combined Science topics

2021 Feb/Mar · Paper 3 · Q1 · 11 marks
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2021 May/Jun · Paper 3 · Q4 · 9 marks
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2021 May/Jun · Paper 4 · Q4 · 8 marks
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2021 May/Jun · Paper 4 · Q4 · 9 marks
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2021 May/Jun · Paper 1 · Q3 · 1 mark
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Mark scheme — 2021 Paper 1 Q3
Answer: D
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