3 The table shows the mass of each component in 250 cm3 of cow’s milk. component mass / g carbohydrate 11 fat 8 protein 8 (a) (i) A 250 cm3 drink of cow’s milk provides 14% of the total mass of protein required each day in the diet of an average adult human. Calculate the total mass of protein required in the diet of an average adult human each day. You must state your answer to one decimal place and include correct units. … [3] (ii) State two important uses of protein in the diet. 1 … 2 … [2] (b) The table below lists four components of a balanced diet for an average adult human. For each component listed, the percentage of the daily requirement provided by 250 cm3 of milk is shown. component percentage of daily requirement provided by 250 cm3 of milk vitamin C 0 vitamin D 30 calcium 30 iron 0 Discuss how a 250 cm3 drink of cow’s milk contributes to the health of an adult human for each of the components listed in the table. … … … … … … … … [4] [Total: 9]

3(a)(i) 57 ; (57).1 ; g ; 3 3(a)(ii) growth / new cells / protoplasm ; repair ; muscle ; hair / nails / skin / keratin ; hormones / named hormone ; enzymes / named enzyme ; antibodies ; haemoglobin / collagen ; membrane component ; 2 3(b) no/lacks vitamin C + gums / scurvy / immunity AW / wound healing ; vitamin D + prevents rickets / bones / teeth / absorb calcium ; calcium + prevents rickets / bones / teeth / blood clotting ; no/lacks iron + haemoglobin / red blood cells / anaemia / lack of energy ; 4

4 The kapok tree is a flowering plant that grows rapidly to become one of the tallest trees in a tropical rainforest ecosystem. Climbing plants wind up its stem and the tree provides a habitat for insect-eating birds and frogs. Bats feed on the nectar from its flowers and pollinate them so they can produce small, light seeds. Insects feed on its leaves and when the leaves fall to the ground they will come into contact with soil bacteria and fungi. (a) (i) Use the information provided to draw a food chain for this tropical rainforest in the space provided. The chain should contain three organisms. [2] (ii) Suggest and explain ways in which being tall may be helpful for the survival of this tree species. … … … … [3] (iii) Explain why the bacteria and fungi found in the rainforest soil are important in this ecosystem. … … … … [3] (b) Every year large areas of tropical rainforest are destroyed by burning. A large percentage of the mass of a kapok tree is made of the element carbon. (i) Name one substance, found in plants but not in animals, that contains carbon. … [1] (ii) Explain how burning trees contributes to global warming. … … … … [2] [Total: 11]

4(a)(i) kapok / tree + insect + frog / bird ; arrow in correct direction from kapok / tree / leaves / plant at start ; 2 4(a)(ii) any three from: gets light / reduced + competition for light ; photosynthesis ; exposed to wind ; for seed dispersal ; easier for bats to find flowers ; 3 4(a)(iii) any three from: decomposition / decay / decomposers / break down (organic matter) ; use of enzymes ; carbon / nitrogen / nutrients + recycled / returned to soil ; carbon / nitrogen / named nutrient used by plants ; 3 4(b)(i) starch / cellulose / chlorophyll / sucrose ; 1 4(b)(ii) any two from: releases carbon dioxide / carbon dioxide into the atmosphere ; greenhouse gas ; traps thermal energy / causes temperature to increase ; removal of carbon sink AW ; 2

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 Cells have membranes which can allow molecules to enter and leave the cell. You are going to carry out an investigation into the movement of glucose and protein molecules through a membrane. You are provided with: • a piece of Visking tube that acts in a similar way to a cell membrane. It has a knot tied in one end to seal it. It has been soaked in distilled water to make it easier to handle. • a large test-tube • two solutions, A and B. Use the following method: • Half-fill the large test-tube with solution A. • Take the Visking tube out of the distilled water. • Hold the end of the tube without the knot and use your finger and thumb to rub it so that the tube opens. If you cannot open the end of the tube raise your hand for help to do this. • Measure 15 cm3 of solution B and add it to the inside of the Visking tube through the open end. • Check that the contents are not leaking from the knotted end of the tube. • Carefully rinse the outer surface of the Visking tube using distilled water and the container labelled waste water. • Place the Visking tube into the large test-tube containing solution A so that it appears as shown in the diagram. The open end of the Visking tube should be folded over the top edge of the large test-tube. • Check the levels of solution A in the large test-tube and solution B in the Visking tube. If solution A is below the level of solution B, add extra solution A to the large test-tube so that they are at the same level. solution B large test-tube solution A Visking tube knot Record the time … • Leave this apparatus for 25–30 minutes. Continue with questions (a)(i), (a)(ii) and 2 during this time. You are provided with Benedict’s solution to test for glucose and biuret reagent to test for protein. (a) (i) Describe how you will carry out the tests for glucose and protein. glucose … … protein … … [2] (ii) Decide how you will label four test-tubes to use for testing solutions A and B for glucose and for protein. • Label the test-tubes and record the labels in the table. • Carry out the tests for glucose and protein on solutions A and B. If you need hot water raise your hand when you require it. Caution: water will be hot. Complete the table by recording your observations and conclusions. solution test test-tube label observation conclusion A glucose protein B glucose protein [5] • After 25–30 minutes remove the Visking tube from the large test-tube and place it in the waste water container. (b) (i) Record the time and then calculate the total time that the Visking tube was in the large test-tube. time that Visking tube was placed in large test-tube … time that Visking tube was removed from large test-tube … length of time Visking tube was immersed in solution A … minutes [2] (ii) Test a sample of the solution from the large test-tube for glucose and another sample for protein. Raise your hand if more hot water is needed. Record your observations and conclusions in the table. test observation conclusion glucose protein [3] (iii) State two variables you should have controlled so that these repeat tests on solution A produced results that were comparable with those in the table in (a)(ii). 1. … … 2. … … [2] (iv) Describe and explain what the results of all the tests you have done show about the permeability of the Visking tube. … … … … … … [3] (v) Suggest why it was important to rinse the outside of the Visking tube before placing it in the large test-tube containing solution A. … … [1] [Total: 18]

1(a)(i) glucose (Benedict’s) + heat ; protein add biuret ; 2 1(a)(ii) sol test t-t label observation conclusion A glucose – blue no glucose / -ve/ none / absent protein – blue no protein / -ve / none /absent B glucose – green / yellow orange / red glucose present / + ve protein – purple / lilac / mauve protein present / + ve all cells completed ; labels: GA, PA, GB, PB ORA ; observations: as expected with only colours recorded ; conclusions: no glucose + no protein in A ; glucose + protein in B ; 5 A glu A and pro B etc. 1(b)(i) three times recorded ; total time between 25 and 30 minutes + correct calculation based on candidate’s times ; 2 1(b)(ii) colours correctly recorded ; glucose present / consistent with observation ; protein not present / consistent with observation ; 3 1(b)(iii) same temperature for Benedict’s ; same time in hot water ; same volumes, of Benedict’s / biuret / reagents / solution / used ; same concentration, of Benedict’s / biuret / reagents / used ; 2 1(b)(iv) permeable to glucose ; not permeable / impermeable to protein ; semi-permeable / partially permeable ; 3 1(b)(v) to ensure there is no solution B on the outside of the tube AW ; 1

Cambridge O Level Biology · 5090

O-Level Biology (5090) Biological molecules past paper questions

Revise O-Level Biology (5090) — Biological molecules 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.

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

Biological molecules in O-Level Biology 5090 exams, 2020–2025

Across 2020–2025, Biological molecules accounted for 38 questions worth 330 marks in Cambridge O Level Biology (5090) papers.

By year
Year	Questions	Marks
2020	3	20
2021	5	49
2022	3	21
2023	7	34
2024	11	120
2025	9	86

Most-tested subtopics

4.1 Biological molecules314 marks

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Paper 1 · 16 qs
Paper 2 · 10 qs
Paper 3 · 8 qs
Paper 4 · 4 qs

All most-tested Biology topics

2021 Oct/Nov · Paper 2 · Q3 · 9 marks
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2021 Oct/Nov · Paper 2 · Q4 · 11 marks
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2021 Oct/Nov · Paper 2 · Q6 · 10 marks
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2021 Oct/Nov · Paper 3 · Q1 · 18 marks
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2021 May/Jun · Paper 1 · Q8 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q8
Answer: A
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