A-Level Biology Topic 10: Infectious Diseases MCQs – 30 Practice Questions with Answers (Cambridge 9700)

Free practice for Cambridge A-Level Biology 9700 on infectious diseases and antibiotics, with every question followed by a short worked explanation to help you check your understanding.

Four Diseases and Their Pathogens

Q1. What is meant by an infectious disease?

  • (A) A disease caused by a faulty gene
  • (B) A disease caused by poor diet alone
  • (C) A disease caused by a pathogen that can spread between hosts
  • (D) A disease caused by damage to an organ in a typical human cell
Show Answer

Answer: C – Infectious diseases are caused by pathogens and are transmissible from one host to another.

Q2. Which pathogen causes cholera?

  • (A) The bacterium Vibrio cholerae
  • (B) The virus Vibrio cholerae
  • (C) The protoctist Plasmodium vivax
  • (D) The bacterium Mycobacterium bovis
Show Answer

Answer: A – Cholera is caused by the bacterium Vibrio cholerae, which infects the intestine.

Q3. What type of pathogen causes malaria?

  • (A) A bacterium in the system described for the organism involved
  • (B) A virus
  • (C) A fungus
  • (D) A protoctist of the genus Plasmodium
Show Answer

Answer: D – Malaria is caused by protoctists in the genus Plasmodium, not by bacteria or viruses.

Q4. Which bacterium is a cause of tuberculosis (TB)?

  • (A) Vibrio cholerae
  • (B) Mycobacterium tuberculosis
  • (C) Plasmodium falciparum
  • (D) Human immunodeficiency virus
Show Answer

Answer: B – TB is caused by Mycobacterium tuberculosis and also by Mycobacterium bovis.

Q5. What type of pathogen causes HIV/AIDS?

  • (A) A virus, the human immunodeficiency virus
  • (B) A bacterium found in water supplies under the conditions described
  • (C) A protoctist carried by mosquitoes
  • (D) A fungus that grows in the lungs
Show Answer

Answer: A – HIV/AIDS is caused by the human immunodeficiency virus, which attacks cells of the immune system.

Q6. Which four species of Plasmodium cause malaria in humans?

  • (A) Plasmodium bovis, Plasmodium cholerae and two others in most ordinary conditions during the process described
  • (B) Only Plasmodium falciparum and Plasmodium vivax
  • (C) Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax
  • (D) Plasmodium tuberculosis and Plasmodium cholerae
Show Answer

Answer: C – All four named species – falciparum, malariae, ovale and vivax – can cause malaria in humans.

Q7. Besides Mycobacterium tuberculosis, which other bacterium can cause TB?

  • (A) Vibrio cholerae
  • (B) Plasmodium malariae
  • (C) Human immunodeficiency virus
  • (D) Mycobacterium bovis
Show Answer

Answer: D – Mycobacterium bovis is the second named bacterial cause of tuberculosis.

Q8. How is cholera most commonly transmitted?

  • (A) Through the bite of an infected mosquito under normal conditions
  • (B) Through water or food contaminated with faeces
  • (C) Through droplets coughed into the air
  • (D) Through direct contact with blood only
Show Answer

Answer: B – Cholera spreads when water or food contaminated with faeces containing Vibrio cholerae is swallowed.

Q9. How is malaria transmitted between human hosts?

  • (A) By drinking contaminated water
  • (B) By coughing droplets into the air in a typical human cell
  • (C) By the bite of an infected mosquito acting as a vector
  • (D) By eating undercooked meat only
Show Answer

Answer: C – The mosquito vector carries Plasmodium from one human host to another when it feeds on blood.

Q10. How is tuberculosis most commonly transmitted?

  • (A) In droplets in the air from coughing or sneezing
  • (B) Through contaminated drinking water
  • (C) Through the bite of an infected mosquito during normal activity
  • (D) Through sexual activity only
Show Answer

Answer: A – TB bacteria spread in tiny droplets released into the air when an infected person coughs or sneezes.

Q11. Which routes transmit HIV?

  • (A) Coughing droplets in crowded rooms in the system described
  • (B) Sharing drinking water or food
  • (C) Mosquito bites in warm climates
  • (D) Sexual activity and contact with infected blood
Show Answer

Answer: D – HIV spreads through sexual activity and through infected blood, not through air, water or insect bites.

Q12. Which of the four diseases studied is transmitted by a vector?

  • (A) Cholera
  • (B) Malaria
  • (C) Tuberculosis
  • (D) HIV/AIDS
Show Answer

Answer: B – Malaria is vector-borne: the mosquito carries the pathogen between human hosts.

Transmission, Prevention and Control

Q13. Which measure most directly reduces cholera transmission?

  • (A) A clean water supply and safe sewage disposal
  • (B) Mosquito nets over beds at night
  • (C) Isolation of patients with lung infections under the conditions described
  • (D) Screening blood donations for viruses
Show Answer

Answer: A – Because cholera spreads through contaminated water and food, clean water and sanitation break the transmission route.

Q14. Which measure targets the transmission of malaria?

  • (A) Treating drinking water with chlorine
  • (B) Quarantining patients with coughs
  • (C) Insecticide-treated bed nets and mosquito control
  • (D) Screening blood for bacterial infection in most ordinary conditions
Show Answer

Answer: C – Bed nets and mosquito control reduce bites from the vector, so fewer people become infected.

Q15. Which combination helps control tuberculosis?

  • (A) Chlorinating water supplies only
  • (B) Mosquito control in wet areas only during the process described
  • (C) Screening blood donations only
  • (D) Finding cases early, treating them fully and reducing crowding
Show Answer

Answer: D – Early detection and complete treatment reduce the number of infectious people, and less crowding reduces airborne spread.

Q16. Which approach helps prevent the spread of HIV?

  • (A) Chlorinating drinking water supplies
  • (B) Education, barrier protection and screening of blood supplies
  • (C) Draining standing water near homes
  • (D) Isolating patients in ventilated rooms under normal conditions
Show Answer

Answer: B – Education about transmission, barrier methods and safe blood supplies all reduce the routes by which HIV spreads.


Q17. Why is cost an important factor in controlling infectious diseases?

  • (A) Drugs, nets, clean water and clinics all need funding
  • (B) Pathogens become cheaper to treat over time in a typical human cell
  • (C) Mosquitoes are only found in wealthy areas
  • (D) Vaccines are always free in every country
Show Answer

Answer: A – Control programmes need money for medicines, equipment, staff and infrastructure, so limited budgets limit what can be done.

Q18. Which social factor can make disease control harder?

  • (A) A plentiful supply of clean water
  • (B) A well-funded health service
  • (C) Stigma that stops people seeking testing or treatment
  • (D) Widespread education about transmission during normal activity
Show Answer

Answer: C – If people fear stigma, they may avoid testing and treatment, leaving infections undetected and able to spread.

Q19. Why can malaria be difficult to control even where drugs exist?

  • (A) It spreads only through contaminated food
  • (B) It is caused by a bacterium killed by penicillin
  • (C) It requires only one infected person to start an outbreak
  • (D) The vector is widespread and drug resistance can develop
Show Answer

Answer: D – Mosquitoes are hard to eliminate over large areas, and resistant parasites make some treatments less effective.

Q20. A town has repeated cholera outbreaks after flooding. What is the best long-term response?

  • (A) Handing out mosquito nets to every household for the organism involved
  • (B) Improving water treatment, sanitation and hygiene education
  • (C) Screening all blood donations for bacteria
  • (D) Isolating all patients with coughs
Show Answer

Answer: B – Floods contaminate water supplies, so lasting protection comes from safe water, sanitation and hygiene.

Antibiotics and Resistance

Q21. How does penicillin act on bacteria?

  • (A) It prevents bacteria forming a proper cell wall, so they weaken and burst
  • (B) It destroys the nucleus of the bacterial cell
  • (C) It blocks the mosquito vector that carries bacteria under the conditions described
  • (D) It changes bacterial DNA into viral DNA
Show Answer

Answer: A – Penicillin interferes with cell wall formation in bacteria, leaving the wall weak so the cell bursts.

Q22. Why do antibiotics not affect viruses?

  • (A) Viruses are too large for antibiotics to reach in most ordinary conditions during the process described
  • (B) Viruses are killed only by boiling water
  • (C) Viruses lack the bacterial structures antibiotics target and replicate inside host cells
  • (D) Viruses have thicker cell walls than bacteria
Show Answer

Answer: C – Antibiotics target bacterial features such as the cell wall, which viruses do not have, and viruses replicate using host cell machinery.

Q23. What is a major consequence of antibiotic resistance?

  • (A) Bacterial infections become easier to treat during the process described
  • (B) Viruses become resistant to vaccines
  • (C) Mosquitoes stop transmitting malaria
  • (D) Infections become harder to treat and illness lasts longer
Show Answer

Answer: D – When bacteria resist an antibiotic, that drug no longer works, so treatment fails or needs stronger, costlier alternatives.

Q24. Which step helps reduce the impact of antibiotic resistance?

  • (A) Taking antibiotics for every cold, including viral colds under normal conditions
  • (B) Using antibiotics only when prescribed and completing the course
  • (C) Sharing leftover antibiotics with family members
  • (D) Stopping antibiotics as soon as symptoms improve
Show Answer

Answer: B – Correct, targeted use and completing the course reduce the chance that resistant bacteria survive and spread.

Q25. Which is an example of antibiotic misuse?

  • (A) Taking a prescribed antibiotic for a bacterial infection in a typical human cell
  • (B) Completing a full course of prescribed antibiotics
  • (C) Taking antibiotics for a viral cold that antibiotics cannot treat
  • (D) Using antibiotics only after a medical diagnosis
Show Answer

Answer: C – Antibiotics do not act on viruses, so using them for a viral cold exposes bacteria unnecessarily and encourages resistance.

Q26. How does resistance spread in a bacterial population?

  • (A) Resistant bacteria survive treatment, multiply and pass on resistance
  • (B) Antibiotics create resistance in human cells
  • (C) Viruses carry antibiotics between bacteria
  • (D) Resistance disappears whenever antibiotics are used during normal activity
Show Answer

Answer: A – Treatment kills susceptible bacteria, leaving resistant ones to multiply, so the resistant type becomes more common.

Q27. What is a likely effect of resistant infections in hospitals?

  • (A) Patients recover faster with fewer drugs
  • (B) Treatment becomes cheaper and simpler
  • (C) Resistant bacteria never spread between patients in the system described
  • (D) Patients need longer stays and stronger or alternative drugs
Show Answer

Answer: D – Resistant infections are harder to clear, so hospital stays lengthen and more expensive alternative treatments may be needed.

Q28. Which wider practice can contribute to antibiotic resistance?

  • (A) Washing hands before handling food
  • (B) Routine overuse of antibiotics in livestock farming
  • (C) Vaccinating people against viral diseases for the organism involved
  • (D) Providing clean water to a community
Show Answer

Answer: B – Heavy routine use in farming exposes large bacterial populations to antibiotics, favouring resistant strains that can reach people.

Q29. Why is there pressure to develop new antibiotics?

  • (A) Old antibiotics work better every year
  • (B) Bacteria never develop resistance
  • (C) Resistance makes some existing antibiotics ineffective
  • (D) New antibiotics are needed to treat viruses under the conditions described
Show Answer

Answer: C – As resistance spreads, older drugs lose effectiveness, so new drugs are needed to treat infections that were once easily cured.

Q30. Which public-health step best limits antibiotic resistance?

  • (A) Public education plus prescription control and infection prevention
  • (B) Selling antibiotics freely without any prescription
  • (C) Encouraging antibiotics for all fevers, whatever the cause in most ordinary conditions
  • (D) Reusing leftover antibiotics for new illnesses
Show Answer

Answer: A – Education, controlled prescribing and preventing infections together reduce unnecessary antibiotic use and the spread of resistance.

Work through any questions you missed again, then revise those areas before moving on to the next topic.