Immunity and the evolutionary raceEdexcel International A Level Biology: Subtopic test

1. 1
   A baby is breast-fed and receives antibodies from her mother in the milk. At eight weeks old she is also given her first dose of a vaccine against whooping cough.

   (a)

   Which type of immunity does the baby gain from the antibodies in her mother's milk?

   [1 mark]

   • AArtificial active
   • BNatural passive
   • CNatural active
   • DArtificial passive

   (b)

   Which type of immunity does the vaccine give the baby?

   [1 mark]

   • ANatural passive
   • BNatural active
   • CArtificial passive
   • DArtificial active

   (c)

   Distinguish between active and passive immunity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A traveller is bitten by a dog in a region where rabies occurs. At the clinic he is immediately injected with ready-made rabies antibodies, and is then given a course of rabies vaccine over the following weeks.

   (a)

   Why is the traveller given ready-made antibodies straight away?

   [1 mark]

   • AThey give immediate protection because the body does not need to make them
   • BThey stimulate memory cells to divide
   • CThey are a source of viral antigens
   • DThey destroy the virus without binding to it

   (b)

   What is the main reason for also giving the rabies vaccine?

   [1 mark]

   • AThe vaccine antigens destroy the virus directly
   • BThe vaccine contains plasma cells that secrete antibody
   • CIt stimulates the traveller's own immune system to make antibodies and memory cells for longer protection
   • DThe vaccine antibodies bind to the virus faster than the injected antibodies

   (c)

   Explain why the injected antibodies give the traveller only short-term protection.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Influenza viruses accumulate mutations in the genes for their surface antigens, so a new strain appears every few years. Each year a new influenza vaccine has to be produced against the strains most likely to be circulating.

   (a)

   Explain why a person who has recovered from influenza one year may become ill again when a new strain appears.

   [3 marks]

   (b)

   Use ideas about natural selection to explain why new strains of influenza virus keep arising.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Pathogens have evolved ways of avoiding the human immune system. Streptococcus pneumoniae has a polysaccharide capsule around its cell wall. Mycobacterium tuberculosis is engulfed by macrophages but prevents lysosomes from fusing with the phagosome. HIV infects and destroys T helper cells.

   (a)

   Explain how each of the three strategies helps the pathogen to avoid destruction by the immune system.

   [6 marks]

   (b)

   Explain what is meant by the evolutionary race between pathogens and their hosts, using one of the pathogens above as an example.

   [6 marks]

   Total for question 4: 12 marks

End of questions