IGCSE Biology: Drugs Practice Questions
A drug is any substance taken into the body that modifies or affects chemical reactions in the body. IGCSE focuses on antibiotics and resistance, and on the effects of alcohol, tobacco smoke and misused drugs such as heroin.
Topic 15 of Cambridge IGCSE Biology 0610 is short, but antibiotic resistance appears very often because it links directly to natural selection. The trap is describing bacteria as choosing to become resistant. The questions below train the correct evolutionary wording alongside the recall content.
What you need to know for Drugs
- DrugAny substance taken into the body that modifies or affects chemical reactions in the body.
- AntibioticsDrugs that kill or stop the growth of bacteria. They have no effect on viruses, which have no cell structures or metabolism of their own for the antibiotic to act on.
- Antibiotic resistanceRandom mutation produces a resistant bacterium. When antibiotics are used, non-resistant bacteria are killed and the resistant one survives, reproduces and passes on the resistance allele, so the resistant population increases.
- AlcoholA depressant. It slows reaction time, impairs judgement and reduces self control. Long term heavy use damages the liver, which has to break the alcohol down.
- Tobacco smokeTar paralyses and destroys cilia and causes excess mucus, leading to smoker's cough, bronchitis and lung cancer. Carbon monoxide binds to haemoglobin and reduces oxygen transport. Nicotine is addictive and increases heart rate.
- HeroinA powerful depressant that is highly addictive. Injection with shared needles risks transmitting HIV and other blood borne infections.
IGCSE Biology Drugs questions and answers
4 exam-style questions written to the 0610 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
A patient with influenza asks for antibiotics. Explain why antibiotics will not help.
Show the worked answer
- Influenza is caused by a virus, not a bacterium.
- Antibiotics work by disrupting structures and processes found only in bacterial cells, such as the bacterial cell wall or bacterial protein synthesis.
- Viruses have no cell wall and no metabolism of their own. They reproduce inside the patient's own cells, so there is nothing for the antibiotic to act on.
- Taking antibiotics unnecessarily also increases the risk of antibiotic resistant bacteria developing.
Explain how a population of bacteria becomes resistant to an antibiotic.
Show the worked answer
- Within a population of bacteria there is variation, caused by random mutation.
- A mutation may by chance produce a bacterium that is resistant to the antibiotic. The mutation happens whether or not the antibiotic is present.
- When the antibiotic is used it kills the non-resistant bacteria. The resistant bacterium survives.
- The surviving resistant bacterium reproduces rapidly, and because reproduction is asexual its offspring inherit the resistance allele.
- Over time the proportion of resistant bacteria in the population increases until the antibiotic is no longer effective. This is natural selection.
State three named components of tobacco smoke and describe one harmful effect of each.
Show the worked answer
- Tar. It paralyses and destroys the cilia lining the airways, so mucus is not swept away. Mucus accumulates, causing smoker's cough and bronchitis, and tar contains carcinogens that cause lung cancer.
- Carbon monoxide. It binds irreversibly to haemoglobin in red blood cells, so less haemoglobin is available to carry oxygen and less oxygen reaches the tissues.
- Nicotine. It is addictive, which makes stopping difficult, and it increases heart rate and narrows blood vessels, raising blood pressure.
- Any three of these with a matched effect will score.
Explain why alcohol increases the risk of a road accident.
Show the worked answer
- Alcohol is a depressant, meaning it slows down the transmission of nerve impulses.
- Reaction time increases, so a driver takes longer to respond to a hazard and the stopping distance increases.
- Judgement is impaired, so drivers misjudge speeds and distances.
- Self control is reduced, so drivers take risks they would normally avoid.
Common mistakes in this topic
- Saying antibiotics kill viruses.
- Describing bacteria as choosing or trying to become resistant.
- Confusing tar with nicotine when describing effects.
- Calling alcohol a stimulant. It is a depressant.
- Forgetting that failing to complete a course of antibiotics allows partially resistant bacteria to survive and multiply.
Exam tips
- Antibiotic resistance answers must use the natural selection sequence: variation, mutation, selection, survival, reproduction, inheritance.
- Use the word random for the mutation. It is often worth a mark on its own.
- Learn the three tobacco smoke components with one effect each. That is a standard six mark question.
- For any drug question, distinguish between short term effects and long term effects if the question separates them.
- Link needle sharing to HIV transmission when discussing injected drugs.
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Drugs FAQs
Why do antibiotics not work against viruses?
Antibiotics target structures and processes unique to bacterial cells, such as the bacterial cell wall or bacterial ribosomes. Viruses are not cells, have no cell wall and no metabolism of their own, and reproduce inside the host's cells. There is therefore nothing for an antibiotic to act on.
How does antibiotic resistance develop?
Random mutation in a bacterium can produce resistance by chance, independently of any antibiotic. When the antibiotic is used, non-resistant bacteria are killed while the resistant one survives, reproduces rapidly and passes on the resistance allele. The resistant proportion of the population therefore increases. This is natural selection.
What are the main harmful components of tobacco smoke?
Tar paralyses and destroys cilia, causes a build up of mucus leading to bronchitis, and contains carcinogens causing lung cancer. Carbon monoxide binds to haemoglobin and reduces the oxygen carrying capacity of the blood. Nicotine is addictive and raises heart rate and blood pressure.
Why should a course of antibiotics be finished?
Stopping early leaves the more resistant bacteria alive, because they take longer to be killed. Those survivors then reproduce and pass on their resistance, making the infection harder to treat and increasing resistance in the wider bacterial population.
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Written to the published Cambridge IGCSE Biology (0610) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.