Cambridge O Level Biology 5090: Disease and immunity (5090) – 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 12, Disease and immunity, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028: every section, 12.1 Disease, 12.2 Antibiotics and 12.3 Immunity. The syllabus is not tiered, so every question applies to every candidate.

Revise first with the study guide and the revision notes. The course hub and the printable checklist list the other topics, and the free 10-minute diagnostics help you decide what to revise next. A calculator is useful for questions 6, 7, 8 and 10.

Questions

1. Describe what is meant by:

(a) a pathogen [1] (b) a transmissible disease. [1]

2. Which of these is one of the body’s barriers to the entry of pathogens?

• A antibodies in the blood
• B phagocytes in the lungs
• C acid in the stomach
• D memory cells in the blood [1]

3. Malaria is common in a low-lying area with many ponds and flooded fields.

(a) Explain why the mosquito is described as a vector. [1] (b) Explain how a person catches malaria from someone who already has the disease. [3] (c) The local council plans to fill in small ponds, spray a thin film of oil on larger ponds, and give out insecticide-treated bed nets. Explain how each of these three measures reduces malaria, with reference to the mosquito’s life cycle. [4]

4.

(a) State the type of pathogen that HIV is. [1] (b) Describe two ways in which HIV is transmitted. [2] (c) Outline how HIV affects the immune system, and explain why this may lead to AIDS. [3] (d) Suggest why a doctor does not prescribe antibiotics to treat HIV infection. [1]

5. A flood breaks a town’s sewage pipes and stops its water treatment. Within a week, many people have cholera.

(a) Suggest why the flood led to an outbreak of cholera. [3] (b) A patient’s blood is tested. Explain why the concentration of ions in the blood is low. [2]

6. An adult volunteer’s reaction time was measured three times in a ruler-drop test before and after drinking alcohol, under supervision.

Trial	Before alcohol / s	After alcohol / s
1	0.24	0.31
2	0.26	0.35
3	0.25	0.33

(a) Calculate the mean reaction time before and after alcohol. [2] (b) Calculate the percentage increase in mean reaction time. [2] (c) Use the results to explain why drinking alcohol before driving is dangerous. [1] (d) State two other effects of excessive alcohol consumption. [2]

7. A study recorded the mean birth weight of babies. Mothers who did not smoke had babies with a mean birth weight of 3.40 kg. Mothers who smoked during pregnancy had babies with a mean birth weight of 3.15 kg.

(a) Calculate the difference as a percentage of the non-smokers’ mean, to one decimal place. [2] (b) Explain how carbon monoxide in tobacco smoke could reduce birth weight. [2] (c) Name the component of tobacco smoke that is addictive and the component that contains carcinogens. [2]

8. A hospital tested bacteria from infected wounds. In the first year, 18 of 240 samples were resistant to a commonly used antibiotic. After several years of heavy use of that antibiotic, 150 of 200 samples were resistant.

(a) Describe what is meant by a drug. [1] (b) Calculate the percentage of resistant samples in each test. [2] (c) Explain the increase in resistant samples. [3] (d) State how the development of resistant bacteria such as MRSA can be minimised. [1]

9.

(a) Explain why an antibody against the measles pathogen does not protect against the polio pathogen. [2] (b) Describe two ways in which antibodies lead to the destruction of a pathogen. [2]

10. A school has 4000 pupils. 95% have been vaccinated against a transmissible disease.

(a) Calculate how many pupils have not been vaccinated. [1] (b) Outline how vaccination gives a pupil long-term immunity. [3] (c) Explain why the unvaccinated pupils are unlikely to catch the disease. [2]

11.

(a) Give the two ways in which a baby can acquire antibodies from its mother. [2] (b) Explain the importance of breast-feeding for a newborn baby. [2] (c) Explain why the protection from these antibodies lasts only a few months. [2]

12. A woman had chickenpox as a child. Years later she has a baby.

(a) Compare the immunity the woman has against chickenpox with the immunity her newborn baby has against it. [4] (b) Explain the role of vaccination in controlling the spread of transmissible diseases, and suggest why clean water and hygiene are still needed to control cholera. [4]

Answers

1. (a) A disease-causing organism [1]. (b) A disease in which the pathogen can be passed from one host to another [1]. [2] Examiner insight: “A germ” or “something that makes you ill” is too vague; the word organism is needed in (a).

2. C [1] [1] Examiner insight: A, B and D act after a pathogen has entered, so none of them is a barrier.

3. (a) It carries the pathogen from one person (host) to another [1]. (b) A female mosquito bites the infected person and takes in blood containing the parasite [1]. The parasite develops in the mosquito [1]. When the mosquito bites another person, the parasite passes into that person’s blood [1]. (c) Filling in ponds removes the still water where eggs are laid and larvae develop [1]. Oil stops larvae and pupae reaching air at the surface, so they die [1]. Bed nets stop adult mosquitoes biting people at night [1], and the insecticide kills adults that land on them [1]. [8] Examiner insight: In (c) each measure must be tied to the life-cycle stage it targets; restating the measures gains nothing.

4. (a) A virus [1]. (b) Any two [2]: unprotected sexual intercourse; sharing needles; transfusion of infected blood; mother to baby across the placenta, at birth or in breast milk. (c) HIV decreases the number of lymphocytes [1], so the ability to produce antibodies falls [1]. The immune system is weakened, so other pathogens cause infections the body cannot fight, which is AIDS [1]. (d) Antibiotics do not affect viruses [1]. [7] Examiner insight: “Through blood” alone is too vague for (b); name the situation, such as shared needles or a transfusion.

5. (a) Faeces containing cholera bacteria entered the water from the broken pipes [1]. The water was not treated, so the bacteria were not killed [1]. People drank the water or used it to prepare food [1]. (b) The toxin causes chloride ions to be secreted into the small intestine [1], and ions are lost from the body in the diarrhoea [1]. [5] Examiner insight: In (a), “dirty water” earns nothing on its own; say how the bacteria got into the water and why they survived.

6. (a) Before: (0.24 + 0.26 + 0.25) ÷ 3 = 0.25 s [1]. After: (0.31 + 0.35 + 0.33) ÷ 3 = 0.33 s [1]. (b) (0.33 − 0.25) ÷ 0.25 × 100 [1] = 32% [1]. (c) The reaction time is longer, so a driver takes longer to brake or steer in an emergency [1]. (d) Any two [2]: acts as a depressant; reduced self-control; damage to the liver; social implications such as violence or family breakdown. [7] Examiner insight: Allow error carried forward in (b) from wrong means in (a), but units (s) are expected on the means.

7. (a) 3.40 − 3.15 = 0.25 kg [1]; 0.25 ÷ 3.40 × 100 = 7.4% [1]. (b) Carbon monoxide combines with haemoglobin, so the mother’s blood carries less oxygen [1]. Less oxygen reaches the fetus across the placenta, so it grows less [1]. (c) Addictive: nicotine [1]. Carcinogens: tar [1]. [6] Examiner insight: “Carbon monoxide is poisonous” is not enough in (b); the mark needs haemoglobin and the drop in oxygen carried.

8. (a) Any substance taken into the body that modifies or affects chemical reactions in the body [1]. (b) 18 ÷ 240 × 100 = 7.5% [1]; 150 ÷ 200 × 100 = 75% [1]. (c) Some bacteria were already resistant [1]. The antibiotic killed the non-resistant bacteria, but the resistant ones survived [1]. The survivors reproduced, so resistant bacteria became more common [1]. (d) Use antibiotics only when essential [1]. [7] Examiner insight: Answers saying the bacteria “got used to” or “became immune to” the antibiotic do not gain the survival marks in (c).

9. (a) Each pathogen has its own antigens with a specific shape [1]. The antibody has a complementary shape that fits only measles antigens, so it cannot bind to polio antigens [1]. (b) Antibodies bind and directly destroy the pathogen [1]; or they mark it for destruction by phagocytes [1]. [4] Examiner insight: “Same shape” instead of “complementary shape” usually loses the second mark in (a).

10. (a) 4000 × 0.05 = 200 pupils [1]. (b) Weakened pathogens or their antigens are given [1]. The antigens stimulate lymphocytes to produce antibodies [1]. Memory cells are produced, giving long-term immunity [1]. (c) Most pupils are immune, so few become infected or pass the pathogen on [1]. The pathogen has very few hosts to spread through, so it is unlikely to reach an unvaccinated pupil [1]. [6] Examiner insight: In (b), memory cells are the link to “long-term”; an answer that stops at antibodies explains only the first response.

11. (a) Across the placenta [1]; in breast milk [1]. (b) A newborn’s own immune system is not yet producing many antibodies [1]. Antibodies in breast milk protect it from pathogens the mother has met, while it is most vulnerable [1]. (c) This is passive immunity, so no memory cells are produced [1]. The antibodies are broken down and the baby cannot make more of them [1]. [6] Examiner insight: Only the two routes in the syllabus are credited in (a); vaccination of the baby is active, not passive.

12. (a) The woman has active immunity; the baby has passive immunity [1]. The woman’s own lymphocytes made her antibodies; the baby’s antibodies came from her, across the placenta or in milk [1]. The woman has memory cells; the baby has none [1]. Her immunity is long-term; the baby’s is short-term [1]. (b) Vaccinated people do not become ill and do not pass the pathogen on [1]. If enough of the population is vaccinated, the pathogen cannot spread, which is how a disease can be controlled [1]. Cholera is spread by bacteria in contaminated water [1], so a clean water supply, sewage treatment and hand washing stop the bacteria reaching people whether or not they are immune [1]. [8] Examiner insight: In a “compare” question each mark needs both sides stated; “the woman has memory cells” alone does not complete the comparison.

Where marks are usually lost

• Naming the mosquito as the cause of malaria rather than the vector.
• Giving control measures without linking them to a stage of the mosquito life cycle.
• Vague transmission routes such as “blood” or “dirty water”.
• Leaving chloride ions or osmosis out of a cholera explanation.
• Missing units on means, or wrong rounding.
• Saying bacteria “become immune” instead of describing survival of resistant bacteria.
• Writing that antibiotics treat viral diseases such as HIV.
• Leaving memory cells out of an explanation of long-term immunity.
• Giving memory cells to passive immunity.
• One-sided answers to “compare” questions.

Next steps

• Revision notes for this topic
• Study guide for this topic
• Human gas exchange practice
• Cambridge O Level Biology course hub
• Printable checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), Topic 12: Disease and immunity, published by Cambridge Assessment International Education.