Cambridge IGCSE Biology 0610: Drugs – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover topic 15 (Drugs), section 15.1, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028. Questions without a label use Core content (Papers 1 and 3); questions or parts marked “(Extended)” use the Supplement outcome 15.1.5 on resistant bacteria such as MRSA, tested on Papers 2 and 4, together with natural selection from topic 18. A calculator is useful for questions 7, 8 and 9.

Before you start, you may want the Drugs study guide or the Drugs revision notes. The course hub lists every topic, and the checklist lets you tick off each outcome. For a quick check of the whole course, try the free Core diagnostic or Extended diagnostic.

Questions

1. State what is meant by the term drug. [2]

2. A student has a bacterial chest infection and is given a course of antibiotics. Describe how the antibiotic helps the student to recover. [3]

3. The table shows four illnesses and the type of pathogen that causes each one.

Illness	Type of pathogen
Cholera	bacterium
Measles	virus
Influenza (flu)	virus
Infected cut on the hand	bacterium

(a) State the two illnesses in the table that could be treated with antibiotics. [1] (b) Explain why antibiotics would not help a person with the other two illnesses. [2]

4. Some bacteria are resistant to antibiotics.

(a) State what is meant by a resistant bacterium. [1] (b) State how antibiotic resistance affects the treatment of bacterial infections. [1]

5. For each substance, state whether it is a drug under the 0610 definition, and give a reason.

(a) a paracetamol tablet that is swallowed [1] (b) insulin made by a person’s own pancreas [1] (c) insulin injected by a person whose pancreas does not make enough [1]

6. (Extended) A patient in hospital has a wound infected with Staphylococcus aureus. The patient is given an antibiotic. Two weeks later, almost all of the S. aureus in the wound are resistant to that antibiotic. Explain how this change happened. [4]

7. Health workers in one region recorded the number of antibiotic prescriptions per 1000 people and the percentage of samples of a bacterium that were resistant, over five years.

Year	Prescriptions per 1000 people	Resistant samples / %
1	900	6
2	1000	8
3	1100	11
4	850	10
5	700	8

(a) Describe the changes in the percentage of resistant samples over the five years. [2] (b) Calculate the percentage decrease in prescriptions between year 3 and year 5. Give your answer to one decimal place. (calculator allowed) [2] (c) (Extended) Suggest an explanation for the relationship between the number of prescriptions and the percentage of resistant samples. [3]

8. A single bacterium that is resistant to an antibiotic divides once every 25 minutes.

(a) Calculate how many resistant bacteria there would be after 150 minutes, assuming all of them survive. (calculator allowed) [2] (b) Suggest why this rate of reproduction matters when a resistant bacterium enters a hospital ward. [1]

9. A group of doctors’ surgeries introduced a policy of prescribing antibiotics only when essential. Before the policy, 36 out of 240 samples of a bacterium from patients were resistant. One year after the policy started, 21 out of 250 samples were resistant.

(a) Calculate the percentage of resistant samples before and after the policy. Give each answer to one decimal place. (calculator allowed) [2] (b) (Extended) Explain how prescribing antibiotics only when essential can limit the development of resistant bacteria. [4] (c) Suggest one reason why these results do not prove that the policy caused the change. [1]

10. State two ways in which bacteria differ from viruses that explain why antibiotics kill bacteria but do not affect viruses. [2]

11. (Extended) A person with a cold visits a doctor and asks for antibiotics. The doctor refuses. Explain why the doctor refuses, using your knowledge of antibiotics, viruses and natural selection. [6]

Answers

1. Any substance taken into the body [1] that modifies or affects chemical reactions in the body [1]. [2]

Examiner insight: The two marks are for the two halves of the definition, so an answer that says only “a substance that changes the body” scores at most one; learn the syllabus wording exactly.

2. The antibiotic kills the bacteria (or stops them growing) [1]. It acts on structures or processes in bacterial cells that human cells do not have, so body cells are not harmed [1]. With fewer bacteria, the immune system can destroy the rest and the infection clears [1]. [3]

Examiner insight: “Kills germs” or “fights the infection” is too vague for the first mark; the word bacteria is needed, and “kills” must be clearly applied to the pathogen, not the illness.

3. (a) Cholera and the infected cut – both needed [1]. (b) Measles and flu are caused by viruses [1]; antibiotics kill bacteria but do not affect viruses [1].

Examiner insight: In part (a) one mark for two answers means both must be correct; in (b) the second mark needs the idea that antibiotics have no effect on viruses, and “work less well” is not credited.

4. (a) A bacterium that is not killed by (is not affected by) the antibiotic [1]. (b) It reduces the effectiveness of antibiotics, so the infection may not be cured by that antibiotic [1].

Examiner insight: Using “immune” instead of “resistant” is not credited, because immunity describes the human body’s defences in 0610 topic 10.

5. (a) Drug – it is taken into the body and affects chemical reactions in the body [1]. (b) Not a drug – it is made by the body, not taken into the body [1]. (c) Drug – it is taken into the body (by injection) and affects chemical reactions in the body [1].

Examiner insight: Each mark needs the decision and a reason tied to the definition; parts (b) and (c) test whether you apply “taken into the body” rather than judging by the name of the substance.

6. (Extended) A few bacteria already had a mutation that made them resistant [1]. The antibiotic killed the non-resistant bacteria [1]. The resistant bacteria survived and reproduced, passing on the resistance (allele/gene) to their offspring [1]. So the proportion of resistant bacteria in the wound increased; this is natural selection [1]. [4]

Examiner insight: An answer that says the antibiotic “made the bacteria mutate” or that the bacteria “got used to it” loses the first mark, as the mutation must be random and present before selection.

7. (a) The percentage of resistant samples increased from 6 % to a peak of 11 % in year 3 [1], then decreased to 8 % by year 5 [1].

(b) Decrease = 1100 − 700 = 400 [1]; (400 ÷ 1100) × 100 = 36.4 % [1].

(c) (Extended) As prescriptions increased (years 1 to 3), the percentage resistant increased, and as prescriptions fell, the percentage resistant fell [1]. More antibiotic use kills more non-resistant bacteria, so resistant bacteria are selected and reproduce more [1]. With fewer prescriptions there is less selection pressure, so resistant bacteria have less advantage and their proportion falls [1].

Examiner insight: In (a) a trend mark needs data quoted with units (%) and the turning point identified; in (b) a correct answer with no working still scores both marks, but a wrong answer with the correct subtraction shown earns one.

8. (a) Number of divisions = 150 ÷ 25 = 6 [1]; 2⁶ = 64 bacteria [1]. (b) A resistant population could build up very quickly and spread to other patients, where the antibiotic would not cure the infection [1].

Examiner insight: A common slip is to multiply (6 × 2 = 12) instead of doubling six times; showing the number of divisions first earns the method mark even if the power is miscalculated.

9. (a) Before: (36 ÷ 240) × 100 = 15.0 % [1]; after: (21 ÷ 250) × 100 = 8.4 % [1].

(b) (Extended) Some bacteria have a mutation giving resistance [1]. Each time an antibiotic is used, non-resistant bacteria are killed and resistant ones survive and reproduce – natural selection [1]. Prescribing only when essential means fewer occasions when resistant bacteria are selected [1], so resistant strains are less likely to develop and spread, and antibiotics remain effective [1].

(c) Any one: other factors may have changed at the same time (for example better hygiene); the samples came from different patients; only one year of data after the policy [1].

Examiner insight: In (a) both percentages are needed to the stated one decimal place, so “15 %” for the first loses its mark; in (b) the final mark is only given if you link back to prescribing only when essential.

10. Bacteria are cells with their own cell wall and chemical reactions that antibiotics act on, but viruses are not cells and have none of these [1]. Viruses reproduce only inside host cells using the host’s machinery, whereas bacteria reproduce on their own [1]. [2]

Examiner insight: “Two ways” means two separate differences, each stated as a comparison; writing “viruses are smaller” is true but not creditworthy here because it does not explain the antibiotic’s lack of effect.

11. (Extended) A cold is caused by a virus [1]. Antibiotics kill bacteria but do not affect viruses, so the antibiotic would not treat the cold [1]. Taking the antibiotic would still expose the bacteria in the person’s body to it [1]. Any bacteria with a resistance mutation would survive while non-resistant ones are killed [1]. The resistant bacteria would reproduce and pass on resistance, increasing the proportion of resistant bacteria (natural selection) [1]. Using antibiotics only when essential limits this, so antibiotics stay effective for infections such as MRSA that need them [1]. [6]

Examiner insight: A six-mark “Explain” needs six distinct creditworthy points in a logical chain; repeating “antibiotics don’t work on viruses” in several ways earns the same mark only once.

Where marks are usually lost

• Writing “germs” or “microbes” instead of bacteria when saying what antibiotics kill.
• Saying antibiotics “work less well” on viruses rather than do not affect them.
• Using “immune” for bacteria. The correct word is resistant.
• Saying the antibiotic causes the mutation, or that bacteria “adapt” or “get used to” it as individuals.
• Describing natural selection but never linking back to using antibiotics only when essential.
• Giving only half of the definition of a drug.
• Quoting a trend without figures or units, or missing the turning point in the data.
• Rounding a percentage to the wrong number of decimal places when the question states one.
• Treating a correlation in data as proof of cause.

Next steps

• Review the Drugs revision notes for the method box on resistance.
• Reread the Drugs study guide for anything you got wrong.
• Go to the Cambridge IGCSE Biology course hub and the printable checklist.
• Try all free 10-minute diagnostics, including the 0610 Core and Extended ones.
• Book a free trial class.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), Cambridge Assessment International Education, part of Cambridge University Press & Assessment. Topic 15 Drugs, section 15.1.