2 The diagram shows the circulatory system of a fish. The lungs of a human and the gills of a fish both have a large surface area for gas exchange. capillaries of gills aorta heart capillaries of body tissues (a) (i) State two differences between the structure of the heart of a fish and the structure of the heart of a human. 1 … … 2 … … [2] (ii) Draw a ring around the correct words to complete the sentence below. higher than the same as lower than The pressure of blood in the aorta of a fish will be … the pressure of blood in the aorta of a human. [1] (b) The photograph shows an Antarctic icefish. The blood of Antarctic icefish is colourless. (i) State which component of human blood is not present in the blood of an Antarctic icefish. … [1] Antarctic icefish live in the Antarctic Ocean where the water temperature is very cold. Aerobic respiration is an enzyme-controlled reaction. More oxygen is able to dissolve in water at a lower temperature. Antarctic icefish have a larger heart, wider blood vessels and a greater volume of blood than fish of the same size that live in warmer water. (ii) Suggest how Antarctic icefish with colourless blood are able to survive in the low temperatures of the Antarctic Ocean. … … … … … … … … … … [5] [Total: 9]

2(a)(i) fish + 2 chambers AW OR human + 4 chambers AW ; fish + 2 valves AW OR human + 4 valves AW ; fish + 2 blood vessels AW OR human + 4 blood vessels AW ; fish + chambers similar size OR human + chambers different sizes ; 2 2(a)(ii) lower than ; 1 A any clear reference only to lower than 2(b)(i) red blood cells / erythrocytes / haemoglobin ; 1 2(b)(ii) less + aerobic respiration ; enzyme reactions + slower ; less + oxygen needed ; more oxygen + absorbed AW by fish ; more oxygen + plasma ; more blood / more oxygen + supplied / taken / pumped ; (to) organs / tissues / cells ; 5

5 Some laundry detergents used to wash clothes contain enzymes. These enzymes break down the molecules that cause stains. (a) Suggest enzymes that may be components of a laundry detergent that will break down stains made of: starch … fat. … [2] (b) Savinase is a protease enzyme produced by genetically engineered bacteria. The enzyme is a component of laundry detergents. The graphs show the results of an investigation into the effects of temperature and pH on the rate of Savinase activity. 0 0 rate of Savinase activity 10 20 30 40 50 temperature / °C 60 70 80 90 4 0 rate of Savinase activity 5 6 7 8 9 pH effect of temperature effect of pH 10 11 12 (i) Describe how the effect of temperature on Savinase activity differs from the effect of temperature on a protease that functions in the human stomach. … … … … … … … … [3] (ii) Suggest why laundry detergents that contain Savinase also contain chemicals that dissolve to form an alkaline solution. … … … … [2] (iii) After washing clothes using laundry detergents, the waste water is sometimes released into the environment. This waste water contains inorganic phosphate ions that are also found in fertilisers. Explain the harmful effect on aquatic life of releasing this waste water into the environment. … … … … … … … … [4] [Total: 11]

5(a) (starch) amylase ; (fat) lipase ; 2 5(b)(i) optimum AW + 60oC ; (optimum) not 37oC ; correct ref. temperature + denaturation for either enzyme ; 3 5(b)(ii) savinase / enzyme + increased rate / works faster / optimum ; prevents denaturation ; detergent more effective / clothes cleaner ; 2 5(b)(iii) pollution ; eutrophication ; two correct details of the eutrophication process for two marks ;; less oxygen available / kills + fish / consumers / animals AW ; 4

6 (a) Explain the ‘lock and key’ hypothesis of enzyme action using a named example. … … … … … … … [5] (b) Explain, using examples, why proteins are essential for all living organisms. … … … … … … … [5] [Total: 10]

6(a) any five from: enzyme + name, e.g. amylase ; substrate + name, e.g. amylose/starch ; enzyme + has an active site ; specificity of enzyme AW ; substrate fits into active site / enzyme-substrate complex formed ; named product formed ; enzyme unchanged at end of reaction ; 5 6(b) any five from: growth / new cells ; repair ; energy in absence of carbohydrates/fats ; muscle ; hair / nails / skin ; hormones ; enzymes ; antibodies ; named protein, e.g. haemoglobin, fibrinogen ; cell membrane / carrier protein ; blood clotting ; 5

1 The flow chart shows stages in the life cycle of a flowering plant. pollination pollen tube formation and fertilisation fruit and seed formation fruit and seed dispersal … plant growth and flower formation stage 1 stage 2 stage 3 stage 4 stage 5 stage 6 (a) The name of stage 5 of the life cycle has not been included in the flow chart. During this stage a radicle and a plumule are formed from a seed. (i) State, in the correct place on the flow chart, the name of stage 5. [1] (ii) Describe the role of enzymes in this stage of the plant’s life cycle. … … … … … … [3] (b) Two of the stages in the life cycle of this flowering plant may depend on the action of an animal. Identify each of these stages and for each stage describe how the action of an animal may be required. stage … action of an animal … … … … stage … action of an animal … … … … [6] [Total: 10]

1(a)(i) germination ; 1 1(a)(ii) 1 break down AW / digest / hydrolyse ; 2 amylase / maltase / lipase / other named digestive enzyme ; 3 named substrate + named product ; 4 respiration / protein synthesis ; 3 1(b) response groups may be in either order response group 1 1 (stage) 1 / one / pollination ; ONLY if marking point 1 awarded then go on to award any two from ... 2 pollen + movement / attachment ; 3 from anther + to stigma ; 4 of different flowers ; 3 response group 2 5 (stage) 4 / four / fruit dispersal / seed dispersal ; ONLY if marking point 5 awarded then go on to award any two from ... 6 eats / consumes / undigested / attachment AW ; 7 movement AW ; 8 egestion / faeces / removal AW (e.g. falls off / spat out / thrown) ; 3 6 7 8 R if any reference to pollen / pollination 8 R excretion (a)(i) To earn this mark, you must correctly state 'germination' as the name for stage 5. (a)(ii) To earn these marks, you need to state that enzymes break down/digest/hydrolyse substances, name a specific digestive enzyme (e.g., amylase), link a named substrate to its product, and mention the use of these products for respiration or protein synthesis. (b) To earn these marks, you must identify stage 1 (pollination) and then describe two aspects of it, such as pollen movement from anther to stigma, possibly between different flowers. For the second group, you must identify stage 4 (fruit/seed dispersal) and then describe two aspects of it, such as consumption by animals, movement, and egestion/removal, ensuring no reference to pollen.

4 What is a correct description of enzymes? A biological catalysts made of lipids B biological catalysts made of proteins C catalysts that slow down chemical reactions and are changed by the reaction D catalysts that speed up chemical reactions and are changed by the reaction

Answer: B To earn the mark, a student must correctly identify enzymes as biological catalysts that are made of proteins.

Cambridge O Level Biology · 5090

O-Level Biology (5090) Enzymes past paper questions

Revise O-Level Biology (5090) — 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.

51 free questions from 2017–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Enzymes in O-Level Biology 5090 exams, 2020–2025

Across 2020–2025, Enzymes accounted for 88 questions worth 661 marks in Cambridge O Level Biology (5090) papers.

By year
Year	Questions	Marks
2020	13	114
2021	9	36
2022	19	147
2023	10	73
2024	13	76
2025	24	215

Most-tested subtopics

5.2 Effects of temperature and pH481 marks
5.1 Enzyme action457 marks

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Paper 1 · 45 qs
Paper 2 · 21 qs
Paper 3 · 15 qs
Paper 4 · 7 qs

All most-tested Biology topics

2021 Oct/Nov · Paper 2 · Q2 · 9 marks
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2021 Oct/Nov · Paper 2 · Q5 · 11 marks
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2021 Oct/Nov · Paper 2 · Q6 · 10 marks
Marking scheme
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2020 Oct/Nov · Paper 2 · Q1 · 10 marks
Marking scheme
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2021 May/Jun · Paper 1 · Q4 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q4
Answer: B
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