K325 / 2027

Infectious diseases

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Which statement separates a pathogen from its route correctly?

  1. Contaminated water is the pathogen, and a bacterium is the disease.
  2. Type 2 diabetes is transmitted when people share food and drink with an affected person.
  3. A pathogenic bacterium can enter a new host when contaminated water is swallowed.
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A pathogenic bacterium can enter a new host when contaminated water is swallowed.

This identifies both the disease-causing agent and the route into the digestive system.

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Which feature is correctly described?

  1. Viruses reproduce by dividing in water without living cells.
  2. A typical bacterium has its DNA enclosed in a nucleus with a double membrane.
  3. A virus contains genetic material enclosed in a protein coat.
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A virus contains genetic material enclosed in a protein coat.

Some also have an envelope, but the protein coat enclosing genetic material is a central feature.

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Which comparison is correct?

  1. Both are caused by viruses, because both give a fever and a cough at the start.
  2. Every lung infection is caused by pneumococcus.
  3. Influenza is viral; pneumococcal disease is bacterial; symptoms may overlap.
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Influenza is viral; pneumococcal disease is bacterial; symptoms may overlap.

Distinguish the causes even when both illnesses include cough and fever.

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Which explanation correctly links a measure to a transmission route?

  1. Clean drinking water stops respiratory transmission, because the pathogens travel in water we drink.
  2. Covering a cough reduces the release of respiratory secretions that can carry pathogens.
  3. Covering a cough makes every pathogen already inside the body disappear.
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Covering a cough reduces the release of respiratory secretions that can carry pathogens.

It interrupts the route near its source, reducing opportunities for transmission.

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Which measure most directly reduces the spread of influenza in a classroom?

  1. Asking students to eat more protein for the next week
  2. Boiling the drinking water before students drink it
  3. Giving every student antibiotics at the start of term
  4. Covering coughs and sneezes and opening windows for airflow
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Covering coughs and sneezes and opening windows for airflow

Influenza spreads in respiratory droplets; covering coughs and ventilation reduce exposure.

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Why can vaccination protect during a later encounter with the matching pathogen?

  1. It makes every white blood cell attack every pathogen equally.
  2. The vaccine leaves antibiotic in the blood, which kills the pathogen when it arrives.
  3. Memory cells enable more rapid production of specific antibodies.
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Memory cells enable more rapid production of specific antibodies.

A faster specific response can control the pathogen earlier, reducing the risk or severity of disease.

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Invented data: after a first vaccine dose, antibody levels peak at 10 units on day 14. After a second dose on day 60, they peak at 80 units on day 65. Why is the second response larger and faster?

  1. The second dose contained more antibodies than the first dose did
  2. Antibodies from the first dose stayed in the blood and doubled each week
  3. Memory cells made after the first dose quickly produce more antibodies
  4. The pathogen in the vaccine had become weaker, so it was easier to fight
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Memory cells made after the first dose quickly produce more antibodies

Memory lymphocytes recognise the antigen at once, so antibodies are made sooner and in larger amounts.

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Which explanation accounts for resistance increasing after antibiotic exposure?

  1. The human body becomes resistant, because the antibiotic was used to kill a virus instead.
  2. Every bacterium chooses to become resistant when it senses danger.
  3. Resistant bacteria survive more successfully and reproduce, passing on resistance.
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Resistant bacteria survive more successfully and reproduce, passing on resistance.

Differential survival and reproduction change the bacterial population.

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Invented data: in a hospital, 2% of one bacterial species was resistant to an antibiotic in 2015 and 30% in 2025, after heavy use. Which is the best explanation?

  1. The antibiotic killed non-resistant bacteria, so resistant ones reproduced more
  2. The antibiotic caused the bacteria to mutate so that they could resist it
  3. The bacteria learned to break down the antibiotic after meeting it once
  4. Patients became resistant to the antibiotic after taking it many times
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The antibiotic killed non-resistant bacteria, so resistant ones reproduced more

Resistant bacteria survived each course and passed on resistance, so their share rose.

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Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 7

Separate cause and route

4 marks

A fictional outbreak report states that a pathogenic bacterium was found in drinking water and that people became ill after drinking it. Identify the pathogen and transmission route. Explain one measure that interrupts that route, and contrast this disease with type 2 diabetes. [4]

Cause -> vehicle -> entry -> interruption. Then compare transmissibility.

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