1. 1
   A student cuts her finger while gardening and also visits a friend who has a common cold. Over the next few hours, her body relies on several non-specific defences to prevent pathogens entering and causing infection: the skin forms a physical barrier over the cut, mucus and cilia line her airways to trap and remove inhaled pathogens, and hydrochloric acid in her stomach kills any pathogens she swallows.

   (a)

   Which of the following is a physical barrier against pathogen entry, rather than a chemical defence?

   [1 mark]

   • AHydrochloric acid in the stomach
   • BLysozymes in tears
   • CCilia lining the airways
   • DAntibodies produced by lymphocytes

   (b)

   Which substance in the scenario is a chemical defence that kills pathogens by altering pH, rather than acting as a physical barrier?

   [1 mark]

   • ASkin
   • BCilia
   • CMucus
   • DHydrochloric acid

   (c)

   Explain how mucus and cilia work together in the airways to protect the body from pathogens.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A group of Year 10 students is vaccinated against measles using a vaccine containing an inactive form of the measles virus. Several years later, some of these students are accidentally exposed to the live measles virus during an outbreak linked to a nearby school. Vaccinated students remain well, while unvaccinated students in the same year group become seriously ill.

   (a)

   What is the immediate effect of the antigens on the inactive measles virus when the vaccine is first injected into a student?

   [1 mark]

   • AThe antigens trigger production of antibodies specific to that antigen and the production of memory lymphocytes
   • BThe antigens directly destroy the inactive virus particles
   • CThe antigens suppress the activity of the immune system
   • DThe antigens convert the virus into a harmless bacterium

   (b)

   Why do the vaccinated students not become ill when exposed to the live measles virus during the outbreak, while the unvaccinated students do?

   [1 mark]

   • AVaccinated students no longer produce any antibodies at all
   • BTheir memory lymphocytes recognise the antigen quickly, producing antibodies faster and in greater quantity than in an unvaccinated person
   • CVaccination causes the students' skin to become thicker, blocking the virus
   • DVaccination permanently destroys the white blood cells that the virus would normally infect

   (c)

   Explain why the vaccinated students' response to the live virus during the outbreak is faster and stronger than their original response to the vaccine.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A microbiologist is investigating the effect of a new plant extract on bacterial growth. Using aseptic technique, she prepares nutrient agar plates in petri dishes, evenly spreads a bacterial culture over the surface, and places a paper disc soaked in the plant extract at the centre of each plate. After incubation, a circular clear zone with no bacterial growth forms around the disc with a diameter of 4 cm. Elsewhere in the same hospital, doctors are treating a patient's bacterial throat infection with antibiotics, having first confirmed the infection is bacterial and not viral before prescribing them.

   (a)

   Calculate the cross-sectional area of the clear zone around the disc, showing your working, and describe what this area indicates about the antibacterial effect of the plant extract. (Use $\pi = 3.14$)

   [3 marks]

   (b)

   Explain two reasons why aseptic technique must be used throughout the microbiologist's investigation, and explain why antibiotics would not have been an appropriate treatment if the patient's throat infection had instead been caused by a virus.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A local health authority is deciding whether to introduce a compulsory school vaccination programme against a serious communicable disease, aiming to vaccinate at least 95% of children to try to establish herd immunity. At the same time, hospital data shows that a strain of bacteria causing a common infection is becoming increasingly resistant to a widely used antibiotic, and doctors are reviewing their prescribing practices as a result.

   (a)

   Discuss the advantages and disadvantages of introducing this compulsory school vaccination programme, including reference to herd immunity, and evaluate whether the programme should go ahead.

   [6 marks]

   (b)

   Explain why bacteria have become resistant to the widely used antibiotic, and explain what doctors and patients should do to reduce the further development and spread of antibiotic resistance.

   [6 marks]

   Total for question 4: 12 marks

End of questions