Question 1
Paper 4 short-answer style1 markState the type of organism that antibiotics are used to treat infections from. (1 mark)
Model answer
Bacteria (antibiotics treat bacterial infections).
Why this scores
One mark for 'bacteria'.
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Detailed notes on Drugs for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Antibiotics revolutionised medicine — and now we're losing them. Cambridge wants the mechanism, the resistance crisis, and how to fight back.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Drugs that target bacteria-specific structures. Discovered in 1928, transformed medicine.
The discovery.
How they work.
Antibiotics target structures or processes UNIQUE to bacteria:
Why they DON'T work on viruses.
Worked qualitative. Why is it WRONG to take antibiotics 'just in case' for a cold?
Cambridge tip. Always state 'antibiotics target BACTERIA-SPECIFIC structures'. The reason viruses are unaffected is that they LACK these structures.
Random mutations + antibiotic pressure → resistant bacteria selected → spread.
The mechanism — step by step.
1. Bacteria mutate.
2. Selective pressure.
3. Resistant bacteria multiply.
4. Resistance spreads.
Famous examples.
Why this matters.
Worked qualitative. Why is hospital MRSA particularly dangerous?
Cambridge tip. Memorise the 4-step chain: MUTATION → SELECTION → REPRODUCTION → SPREAD. Cambridge wants the mechanism, not just 'bacteria evolve'.
Use less, use right, develop new ones, prevent infection.
1. Don't use antibiotics for viral infections.
2. Complete the full course.
3. Reduce antibiotic use in livestock.
4. Improve hygiene + sanitation.
5. Develop NEW antibiotics.
6. Vaccinate.
Worked qualitative. Why is it counter-intuitive that 'doing less' might help fight bacteria?
Cambridge tip. When asked HOW to slow resistance, give 3-4 different strategies. 'Take less' alone is partial.
Verbatim phrases and definitions Cambridge mark schemes credit.
Medicinal drugs appear Paper 4 (5-7 marks). Common formats: explain antibiotic action, why not on viruses, how resistance develops. Examiner reports flag students saying antibiotics 'cause' resistance and missing 'natural selection'.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (15.2); 0610/42 May/Jun 2024 — Q16 (antibiotics); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on medicinal drugs, written exactly the way a tutor would explain them at the board.
Question
State what an antibiotic is and explain why antibiotics cannot be used to treat viral infections.
Step-by-step solution
Step 1
An antibiotic is a drug that kills bacteria or stops them growing, without harming human cells.
Step 2
Antibiotics work by attacking structures or processes that are specific to bacteria (such as the bacterial cell wall).
Step 3
Viruses are not cells and reproduce inside the body's own cells, so they do not have these bacterial structures.
Step 4
Therefore antibiotics have no effect on viruses — viral infections such as colds and flu cannot be treated with them.
Answer
An antibiotic kills bacteria (or stops them growing) by targeting bacterial structures. Viruses lack these and live inside cells, so antibiotics do not work against them.
Question
State whether an antibiotic would be an effective treatment for each: (a) a sore throat caused by bacteria; (b) influenza (caused by a virus); (c) a wound infected by bacteria.
Step-by-step solution
Step 1
(a) Bacterial sore throat → yes, antibiotics can treat it.
Step 2
(b) Influenza (a virus) → no, antibiotics do not affect viruses.
Step 3
(c) Bacterial wound infection → yes, antibiotics can treat it.
Answer
(a) Yes; (b) no; (c) yes. Antibiotics treat bacterial infections only.
Examiner tip
Prescribing antibiotics for viral infections is useless and helps resistance to develop.
Question
Suggest three ways the development and spread of antibiotic-resistant bacteria can be reduced.
Step-by-step solution
Step 1
Only use antibiotics when necessary — not for viral infections such as colds.
Step 2
Always complete the full course of antibiotics, even after feeling better, so all the bacteria are killed.
Step 3
Avoid unnecessary use of antibiotics, including limiting their use in farm animals.
Answer
Use antibiotics only when needed (not for viruses), always finish the full course, and avoid unnecessary use (including in livestock).
Question
Explain why a patient should complete the full course of an antibiotic even once they feel better.
Step-by-step solution
Step 1
When you start to feel better, most of the bacteria have been killed, but some may still be alive.
Step 2
The ones still alive are likely to be the least easily killed (most resistant).
Step 3
If you stop early, these surviving bacteria can multiply and the infection can return.
Step 4
Because the survivors were the more resistant ones, finishing the course helps to kill them too, reducing the chance of a resistant population developing.
Answer
Stopping early leaves the more resistant bacteria alive to multiply, so the infection can return and resistance can build up. Completing the course kills these survivors too.
Question
Explain how a population of bacteria becomes resistant to an antibiotic.
Step-by-step solution
Step 1
Random mutations occur in bacteria, and some of these by chance make a bacterium resistant to the antibiotic.
Step 2
When the antibiotic is used, it kills the non-resistant bacteria, but the resistant ones survive.
Step 3
The surviving resistant bacteria reproduce, passing on the resistance gene to their offspring.
Step 4
Over time the proportion of resistant bacteria increases — this is natural selection — until the whole population may be resistant and the antibiotic no longer works.
Answer
A random mutation makes some bacteria resistant; the antibiotic kills the rest but the resistant ones survive and reproduce, passing on resistance — so by natural selection the population becomes resistant.
Examiner tip
Cambridge wants 'random mutation', 'survive and reproduce / pass on the gene' and 'natural selection' — include all three.
Question
Describe how you could investigate which of three antibiotics is most effective against a particular type of bacterium.
Step-by-step solution
Step 1
Spread the bacteria evenly over the surface of a sterile agar plate.
Step 2
Place small paper discs soaked in each antibiotic (and one control disc with no antibiotic) on the agar, well spaced out.
Step 3
Incubate the sealed plate and observe the clear zones (where no bacteria grow) around the discs.
Step 4
The antibiotic with the largest clear zone has killed bacteria over the widest area, so it is the most effective. (Measure the zone diameters to compare fairly.)
Answer
Grow bacteria on agar, add discs soaked in each antibiotic (plus a control), incubate, and measure the clear zones. The biggest clear zone shows the most effective antibiotic.
Examiner tip
The clear zone (zone of inhibition) shows where the antibiotic stopped bacterial growth; a control disc with no antibiotic checks the discs themselves have no effect.
High-scoring sample answers for medicinal drugs on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State the type of organism that antibiotics are used to treat infections from. (1 mark)
Model answer
Bacteria (antibiotics treat bacterial infections).
Why this scores
One mark for 'bacteria'.
Explain why antibiotics are not effective against viruses. (2 marks)
Model answer
Antibiotics work by attacking structures or processes that are specific to bacteria, but viruses are not cells and do not have these structures (and they reproduce inside the body's own cells), so antibiotics have no effect on them.
Why this scores
Two marks: antibiotics target bacterial structures/processes; viruses are not cells / live inside host cells, so are unaffected.
State three ways the development of antibiotic-resistant bacteria can be reduced. (3 marks)
Model answer
Only use antibiotics when they are really needed (not for viral infections); always complete the full course of antibiotics prescribed; and avoid the unnecessary use of antibiotics, for example in healthy farm animals.
Why this scores
Three distinct measures from: avoid unnecessary use / not for viruses; complete the course; reduce use in agriculture.
Explain how a population of bacteria can become resistant to an antibiotic. (4 marks)
Model answer
A random mutation in a bacterium can, by chance, make it resistant to the antibiotic. When the antibiotic is used, the non-resistant bacteria are killed, but the resistant ones survive. These survivors reproduce and pass on the resistance to their offspring. Over time, by natural selection, the proportion of resistant bacteria increases until the whole population is resistant.
Why this scores
Four marks: random mutation gives resistance; antibiotic kills non-resistant bacteria; resistant survive and reproduce/pass on the gene; natural selection increases resistance.
Describe an experiment to find out which of several antibiotics is the most effective against a type of bacterium. (5 marks)
Model answer
Spread the bacteria evenly over a sterile agar plate. Place small paper discs, each soaked in a different antibiotic, onto the agar, spaced well apart, along with a control disc soaked in water only. Seal and incubate the plate. Where an antibiotic kills the bacteria, a clear zone (with no bacterial growth) appears around the disc. Measure the diameter of each clear zone: the antibiotic with the largest clear zone has prevented growth over the widest area and is therefore the most effective. The control disc should show no clear zone, confirming the effect is due to the antibiotics.
Why this scores
Five marks: bacteria spread on agar; discs of different antibiotics + a control; incubate; clear zones form; measure the zones / biggest zone = most effective.
Explain why the overuse of antibiotics has led to bacteria that are difficult to treat, and what can be done to slow this down. (6 marks)
Model answer
Within a population of bacteria, random mutations sometimes produce individuals that are resistant to an antibiotic. Each time an antibiotic is used, it kills the non-resistant bacteria but the resistant ones survive; these survivors reproduce and pass on the resistance gene to their offspring. The more often antibiotics are used — especially when used unnecessarily — the more often this selection happens, so resistant bacteria become more and more common. Eventually some bacteria become resistant to many antibiotics, so infections by them are very difficult to treat. This can be slowed down by only using antibiotics when they are really needed (not for viral infections), by patients always completing the full course so that all the bacteria are killed, and by reducing unnecessary use in medicine and in farm animals. Developing new antibiotics and using good hygiene to prevent the spread of infection also help.
Why this scores
Up to 6 marks: random mutation → resistance; antibiotic kills non-resistant; resistant survive and reproduce/pass on gene; overuse increases selection; harder to treat; control measures (use only when needed, complete the course, reduce unnecessary/agricultural use).
Definitions to memorise and the exact keywords mark schemes credit for medicinal drugs answers — sharpened from recent examiner reports for the 2026 0610 sitting.
A drug that kills bacteria or stops them growing, without harming human cells. It does not work against viruses.
When bacteria are able to survive exposure to an antibiotic. It develops through random mutation and natural selection.
A random change in the genetic material. A mutation can, by chance, make a bacterium resistant to an antibiotic.
The traps other students keep falling into on medicinal drugs questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Both bacteria and viruses are 'germs'.
How to avoid it
Antibiotics target bacteria-specific structures. Viruses are not cells and live inside host cells, so antibiotics do not work on them.
Why it happens
It sounds like the bacteria adapt on purpose.
How to avoid it
Resistance comes from RANDOM mutation. The antibiotic does not cause resistance — it selects for bacteria that are already resistant (natural selection).
Why it happens
Common patient behaviour.
How to avoid it
Stopping early leaves the more resistant bacteria alive to multiply. Always complete the full course.
The things students keep getting wrong in this sub-topic, answered.