Question 1
Paper 1A style
What is the role of thrombin in blood clotting?
- It is released from platelets to start the clotting cascade
- It converts fibrinogen into fibrin
- It binds erythrocytes together directly
- It converts fibrin into fibrinogen
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Answer: B [1]
Question 2
Paper 1A style
Which of the following is a zoonosis transmitted to humans by the bite of a mosquito?
- Rabies
- Tuberculosis
- Japanese encephalitis
- AIDS
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Answer: C [1]
Question 3
Paper 1A style
Why are antibiotics not effective against viral infections?
- Viruses are too small to absorb antibiotics
- Viruses have no metabolism of their own for antibiotics to block
- Viruses have cell walls made of a different material from bacteria
- Antibiotics are broken down by the host's immune system
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Answer: B [1]
Question 4
Paper 2A style
Outline how antibodies against a specific antigen are produced.
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- antigen (glycoprotein / protein) on surface of pathogen [1]
- specific B-cell binds / interacts directly with the antigen [1]
- helper T-cell activated by the same antigen [1]
- contact with activated helper T-cell activates the B-cell [1]
- activated B-cell divides by mitosis [1]
- forms a clone of plasma cells [1]
- plasma cells secrete the (same) specific antibody [1]
- [max 4]
Question 5
Paper 1B style
The table shows weekly COVID-19 cases per 100 000 adults in one region, in vaccinated and unvaccinated adults. The data are for practice. (a) Calculate the percentage change in cases among unvaccinated adults from week 1 to week 8. [2] (b) Calculate the percentage difference between the case rates of unvaccinated and vaccinated adults in week 8. [2] (c) Suggest one reason, other than vaccination, why cases fell in both groups between week 4 and week 8. [1] (d) Evaluate the claim that these data prove that vaccination reduces infection. [2]
| Week | Unvaccinated adults | Vaccinated adults |
|---|---|---|
| 1 | 420 | 150 |
| 4 | 610 | 190 |
| 8 | 280 | 70 |
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- (a) (280 − 420) ÷ 420 × 100 [1]
- (a) = −33.3% / a decrease of 33% [1]
- (b) mean of the two rates = (280 + 70) ÷ 2 = 175 [1]
- (b) |280 − 70| ÷ 175 × 100 = 120% [1]
- (b) Accept (280 − 70) ÷ 280 × 100 = 75% (lower in vaccinated adults) for [1] max only if unvaccinated adults are clearly stated as the reference value
- (c) social distancing / lockdown / mask wearing / more people immune after infection / seasonal change / less testing OWTTE [1]
- (d) supports: vaccinated adults had fewer cases than unvaccinated in every week [1]
- (d) but correlation does not prove causation / data are from one region only [1]
- (d) groups may differ in age / behaviour / testing rate / only three weeks shown / no statistical test [1]
- [max 7]
Question 6
Paper 2A style
Explain why a person infected with HIV for several years is likely to develop opportunistic infections.
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- HIV infects and kills (certain types of) lymphocytes / helper T-cells [1]
- number of helper T-cells falls over time [1]
- fewer B-cells activated, so fewer antibodies produced [1]
- immune system cannot fight pathogens normally controlled / this is AIDS [1]
- [max 3]
Question 7
Paper 2B style
Explain how strains of pathogenic bacteria resistant to several antibiotics evolve, and why careful use of antibiotics is needed.
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- variation in the bacterial population [1]
- resistance arises by random mutation / gene for resistance [1]
- resistance genes can be transferred between bacteria on plasmids [1]
- antibiotic kills susceptible bacteria [1]
- resistant bacteria survive: natural selection [1]
- resistant bacteria reproduce rapidly / binary fission, passing on resistance gene [1]
- proportion of resistant bacteria in the population increases [1]
- exposure to several antibiotics selects multiresistant strains [1]
- careful use slows the emergence of multiresistant bacteria [1]
- eg prescribe only for bacterial infections / not for viral infections [1]
- eg complete the course / avoid routine use in livestock / hospital hygiene [1]
- [max 6]
Question 8
Paper 2A style
Outline how vaccination of a large proportion of a population can prevent an epidemic.
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- vaccine contains antigens / DNA or RNA coding for antigens [1]
- stimulates a primary immune response without causing the disease [1]
- memory cells produced / retained, giving immunity [1]
- on infection, memory cells give a rapid secondary response, eliminating the pathogen [1]
- if a sufficient percentage is immune, transmission is greatly impeded: herd immunity [1]
- protects people who cannot be vaccinated / are not immune [1]
- [max 4]