GCSE Biology (AQA) chapter 3: Infection and response MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

40 exam-style questions on Infection and response, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

40 questions · 4 topics · 10 per test

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What chapter 3 covers

Ten Infection and response questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. Which is a chemical defence of a plant?

  1. A
    a thick layer of bark around the stem
  2. B
    poisons that deter herbivores
  3. C
    sharp thorns growing along the stem
  4. D
    a waxy cuticle on the leaf surface
Show answer

Answer: B. Poisons and antibacterial chemicals are chemical defences. Bark and the waxy cuticle are physical; thorns are mechanical.

2. Why is it difficult to develop drugs that kill viruses?

  1. A
    viruses are too large to be affected by drugs of any kind
  2. B
    viruses have thick cell walls that drugs cannot pass through
  3. C
    viruses reproduce inside body cells, so a drug that kills them may damage the cells too
  4. D
    viruses live only outside cells, where drugs cannot reach them
Show answer

Answer: C. Because viruses use the host’s cells to reproduce, it is hard to kill them without also harming the cells.

3. Why are monoclonal antibodies described as monoclonal?

  1. A
    they bind to many different antigens on the same cell
  2. B
    they are made by a single clone of cells, so are identical
  3. C
    they are all made using cells from one mouse
  4. D
    each is a single molecule made of one amino acid
Show answer

Answer: B. All the antibodies come from one clone of identical hybridoma cells, so they are identical and bind to one specific antigen.

4. Alexander Fleming noticed a clear area around a Penicillium mould growing on a plate of bacteria. What did this suggest?

  1. A
    the mould released a substance that stopped the bacteria growing near it
  2. B
    the mould had dissolved the agar in that region of the plate
  3. C
    the mould was engulfing the bacteria, as phagocytes do
  4. D
    the mould had used up all of the nutrients in that area
Show answer

Answer: A. The clear area suggested that the mould released a substance that killed the bacteria or stopped them growing; this substance became the antibiotic penicillin. Moulds do not engulf bacteria as phagocytes do.

5. How is the measles virus spread?

  1. A
    by direct sexual contact between two people
  2. B
    by inhaling droplets from sneezes and coughs
  3. C
    by mosquitoes carrying the virus between people
  4. D
    by eating food that has not been cooked properly
Show answer

Answer: B. Measles is spread by droplets in the air. It causes fever and a red skin rash; most young children are vaccinated against it.

6. Which practice increases the risk of antibiotic-resistant strains of bacteria developing?

  1. A
    completing the full course of antibiotics
  2. B
    using a specific antibiotic for a specific bacterium
  3. C
    prescribing antibiotics for viral infections
  4. D
    washing hands in hospitals
Show answer

Answer: C. Unnecessary use of antibiotics exposes bacteria to them, selecting for resistant strains. Completing the course reduces this risk.

7. The bacteria that cause tetanus release a toxin into the blood. Which part of the body’s response neutralises the toxin?

  1. A
    antitoxins made by white blood cells
  2. B
    phagocytes engulfing the toxin molecules
  3. C
    platelets forming a clot around the toxin
  4. D
    stomach acid breaking down the toxin
Show answer

Answer: A. Antitoxins made by white blood cells bind to the toxin molecules and neutralise them. Phagocytes engulf whole pathogens, not free toxin molecules, and platelets and stomach acid do not deal with toxins in the blood.

8. In preclinical testing, what is a new drug tested on?

  1. A
    human cells, tissues and live animals, before any human trials
  2. B
    a small group of healthy human volunteers
  3. C
    large numbers of patients who have the disease
  4. D
    doctors and nurses who will later prescribe it
Show answer

Answer: A. Preclinical testing uses cells, tissues and live animals, before any human trials, to check toxicity, efficacy and dose.

9. Mosquito nets stop mosquitoes biting people. In one village the number of malaria cases fell from 240 a year to 90 a year after nets were given out. What was the percentage decrease in cases?

  1. A
    37.5%
  2. B
    62.5%
  3. C
    167%
  4. D
    267%
Show answer

Answer: B. The decrease was 240 − 90 = 150 cases. 150 ÷ 240 × 100 = 62.5%. 37.5% is the new number of cases as a percentage of the old number, and 167% divides the decrease by the new number instead of the old.

10. Which drug was originally extracted from foxgloves?

  1. A
    aspirin
  2. B
    penicillin
  3. C
    digitalis
  4. D
    insulin
Show answer

Answer: C. Digitalis, a heart drug, comes from foxgloves. Aspirin was developed from willow, and penicillin from Penicillium mould.

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Ways to practise this chapter

Infection and response: questions students ask

How many Infection and response MCQs are there?

40, each with the answer and a short explanation, across 4 topics: 4.3.1.1–4.3.1.5 Communicable diseases, 4.3.1.6–4.3.1.7 Human defence systems and vaccination, 4.3.1.8–4.3.1.9 Antibiotics, painkillers and drug development, 4.3.2–4.3.3 Monoclonal antibodies and plant disease. Every chapter test draws ten of them, so you can take it many times.

Is the GCSE Biology (AQA) chapter 3 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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