O Level / IGCSE Biology chapter 12: Disease and immunity MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
36 exam-style questions on Disease and immunity, 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.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Which is an example of passive immunity?
A
a baby receives antibodies from its mother across the placenta
B
a child produces its own antibodies after having chickenpox
C
a teenager is given a measles vaccine containing weakened virus
D
an adult makes memory cells after being infected with flu
Show answer
Answer: A. Passive immunity comes from antibodies made by another individual, such as via the placenta or breast milk.
2. Which patient is most likely to benefit from a course of antibiotics?
A
a boy with a cold, to speed up his recovery
B
a man with a chest infection caused by bacteria
C
a child with influenza caused by a virus
D
a woman with HIV, to kill the virus in her blood
Show answer
Answer: B. Antibiotics kill bacteria or stop them growing, so they treat bacterial infections only. They have no effect on viruses such as those causing influenza, colds or HIV.
3. Why is it important to vaccinate a large proportion of a population?
A
antibodies pass from vaccinated people to unvaccinated people nearby
B
the vaccine also kills any vectors that carry the pathogen
C
fewer people can pass the pathogen on, so it spreads less even to unvaccinated people
D
a vaccine works only if a large group is given it at the same time
Show answer
Answer: C. If most people are immune, the pathogen finds few hosts and cannot spread easily, so even unvaccinated people are less likely to be infected.
4. What does a vaccine contain?
A
memory cells taken from a donor who is immune to the disease
B
antibodies taken from a person who has recovered from the disease
C
antibiotics that kill the pathogen before it can multiply
D
dead or weakened pathogens, or their antigens, which cause no serious illness
Show answer
Answer: D. The weakened pathogen or antigens stimulate lymphocytes to make antibodies and memory cells without causing illness.
5. A person is injected with an antigen. The antibody level in the blood peaks at 20 units after 14 days. Six weeks later the same antigen is injected again and the antibody level peaks at 200 units after 4 days. How many times higher is the second peak, and what explains the faster response?
A
10 times higher, because the first antibodies were never broken down
B
10 times higher, because memory cells respond quickly
C
180 times higher, because the first antibodies were never broken down
D
180 times higher, because memory cells respond quickly
Show answer
Answer: B. 200 ÷ 20 = 10 times higher. The second response is faster and larger because memory cells made after the first exposure recognise the antigen and divide quickly. 180 is the difference, not "how many times higher".
6. Why do antibodies against measles give no protection against chickenpox?
A
each antibody fits only the antigen it was made against
B
chickenpox pathogens have no antigens on their surface
C
measles antibodies are destroyed as soon as chickenpox enters the body
D
chickenpox is caused by a bacterium, which antibodies cannot bind to
Show answer
Answer: A. Antibodies are specific: they fit only the antigen they were made against, just as an enzyme fits only its substrate.
7. A scientist finds that a rare lung disease is caused by a fungus growing in the airways. Which word describes the fungus?
A
antigen
B
antibody
C
vector
D
pathogen
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Answer: D. A pathogen is a disease-causing organism. A vector carries a pathogen between hosts, an antigen is a molecule on a pathogen, and an antibody is a protein made by lymphocytes.
8. The number of malaria cases in a village falls sharply after villagers drain the standing water around their houses. What is the best explanation?
A
there are fewer places for mosquitoes to breed, so fewer vectors carry the parasite
B
the parasite cannot survive in dry soil
C
the villagers developed immunity because the water was drained
D
the standing water carried the parasite to people who drank it
Show answer
Answer: A. Mosquitoes breed in standing water. A vector carries the pathogen between people, so fewer mosquitoes means fewer infections. Malaria is not spread by drinking water.
9. Why are antibiotics not given to treat influenza (flu)?
A
flu is caused by a bacterium, and antibiotics work only on fungi
B
flu is caused by a virus, and antibiotics have no effect on viruses
C
antibiotics would make the flu virus stronger and more infectious
D
flu can be cured only by vaccination, not by any medicine
Show answer
Answer: B. Antibiotics kill bacteria but have no effect on viruses, so they cannot cure flu.
10. Several people in a village become ill with cholera after drinking water from the same well. Which route of transmission has most likely spread the pathogen?
A
indirect transmission, through contaminated water
B
indirect transmission, by bites from infected mosquitoes
C
direct transmission, in droplets breathed out by an infected person
D
direct transmission, by touching the skin of an infected person
Show answer
Answer: A. Cholera bacteria pass out in the faeces of infected people and reach other people through contaminated water or food. That is indirect transmission. Cholera is not spread by mosquitoes or droplets.
36, each with the answer and a short explanation, across 3 topics: Disease, Antibiotics, Immunity. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Biology chapter 12 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.
