Specific immune responseEdexcel International A Level Biology: Subtopic test

1. 1
   A patient is infected with a bacterium that carries a protein on its cell surface membrane which the patient's immune system has not met before. Within days the patient's blood contains proteins that bind only to this bacterial protein and to no other molecule.

   (a)

   What name is given to the bacterial surface protein that triggers the immune response?

   [1 mark]

   • AAntibody
   • BInterferon
   • CLysozyme
   • DAntigen

   (b)

   Which statement about the proteins that bind to the bacterial protein is correct?

   [1 mark]

   • AThey have a variable region whose shape is complementary to one specific antigen
   • BThey are carbohydrates secreted by macrophages
   • CThey are enzymes that hydrolyse the antigen
   • DThey are secreted by killer T cells to lyse infected cells

   (c)

   Explain why these proteins bind only to this bacterial protein.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student is infected with a virus for the first time. Antibodies against the virus appear in her blood after about ten days and reach a modest concentration. Several months later she is exposed to the same virus again. Within two days the antibody concentration in her blood is much higher than before, and she does not become ill.

   (a)

   Which type of cell is mainly responsible for the faster and larger response when the student meets the virus for the second time?

   [1 mark]

   • AMacrophages
   • BNeutrophils
   • CMemory B cells
   • DMast cells

   (b)

   During the first infection, which cell displays viral antigens on its surface membrane in order to activate T helper cells?

   [1 mark]

   • APlasma cell
   • BAntigen-presenting cell
   • CRed blood cell
   • DKiller T cell

   (c)

   Explain why the antibody concentration rises faster during the second exposure to the virus.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient has a very low count of T helper cells. He suffers frequent severe infections, and he also produces much less antibody than a healthy person after exposure to a new pathogen.

   (a)

   Explain how T helper cells normally enable B cells to produce antibodies.

   [3 marks]

   (b)

   Explain why the patient is more likely to suffer severe infections by viruses that replicate inside body cells.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient is infected with a virus for the first time. Macrophages engulf some viral particles, and some of the patient's body cells become infected. Later, blood tests show large numbers of plasma cells and killer T cells specific to the virus, together with some memory cells. The patient recovers.

   (a)

   Describe how the first infection leads to the production of antibodies against the virus.

   [6 marks]

   (b)

   Explain how killer T cells and memory cells help the patient to recover from this infection and to resist a second infection by the same virus.

   [6 marks]

   Total for question 4: 12 marks

End of questions