1. 1
   A cyclist falls and grazes her knee on the road surface. The graze bleeds for about three minutes and then stops as a clot forms. Soil bacteria from the road have entered the damaged tissue, and over the next day the area becomes red and swollen as white blood cells gather there.

   (a)

   Which statement correctly distinguishes the innate immune system from the adaptive immune system?

   [1 mark]

   • AThe innate system responds to specific pathogens and builds up a memory of them
   • BThe innate system responds to broad categories of pathogen and does not change during life
   • CThe adaptive system responds to broad categories of pathogen and does not change during life
   • DOnly the innate system involves white blood cells

   (b)

   Which sequence describes how phagocytes deal with the soil bacteria in the graze?

   [1 mark]

   • ALeave the blood by amoeboid movement, engulf bacteria by endocytosis, digest them with lysosomal enzymes
   • BLeave the blood by amoeboid movement, secrete antibodies, digest bacteria with lysosomal enzymes
   • CStay in the blood, engulf bacteria by exocytosis, digest them with enzymes from the Golgi
   • DLeave the blood by amoeboid movement, engulf bacteria by endocytosis, kill them with antibiotics

   (c)

   Outline how the clot that stopped the bleeding was formed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A patient whose blood group is Rhesus negative (her erythrocytes lack the Rhesus D antigen) was given an emergency transfusion of Rhesus positive blood. She showed no reaction at the time, but tests three weeks later found antibodies against the Rhesus D antigen in her plasma.

   (a)

   What type of molecule are most antigens, such as the Rhesus D antigen?

   [1 mark]

   • ANucleic acids
   • BPhospholipids
   • CProteins or glycoproteins
   • DSteroids

   (b)

   Which cells must be activated for her to produce anti-D antibodies?

   [1 mark]

   • APhagocytes and erythrocytes
   • BMemory cells that she was born with
   • CAny B-lymphocyte, without the need for helper T-lymphocytes
   • DB-lymphocytes specific to the D antigen, with helper T-lymphocytes activated by the same antigen

   (c)

   Explain why a second transfusion of Rhesus positive blood a year later would cause a faster and larger antibody response.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In a randomised trial of a COVID-19 mRNA vaccine, 18 200 adults received two doses of the vaccine and 18 300 adults received two doses of a placebo (salt solution). Neither the participants nor the doctors knew who had received which. Over the following two months, 8 people in the vaccine group and 162 people in the placebo group developed confirmed COVID-19. Newspapers reported the result as "vaccine 95 % effective" before the full data had been published and reviewed by other scientists.

   (a)

   Calculate the percentage of each group that developed COVID-19, and the percentage change in this rate in the vaccine group compared with the placebo group.

   [3 marks]

   (b)

   Evaluate the strength of the evidence from this trial and the way it was reported.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A man who has been infected with HIV (human immunodeficiency virus) for several years without treatment is admitted to hospital with pneumonia caused by bacteria. His doctors find that his blood contains very few helper T-lymphocytes. The bacteria isolated from his lungs are resistant to two of the antibiotics commonly used for pneumonia.

   (a)

   Outline how HIV is transmitted and explain how HIV infection has led to his inability to fight the bacterial infection.

   [6 marks]

   (b)

   Discuss the use of antibiotics in treating this patient, including why they will not treat the HIV infection and why the bacteria may be resistant.

   [6 marks]

   Total for question 4: 12 marks

End of questions