The immune responseEdexcel A-Level Biology B: Subtopic test

1. 1
   A patient has a cut that becomes infected with bacteria. Within a few hours the area is swollen and red, and large numbers of phagocytes are seen in the tissue. Many of the first phagocytes to arrive die at the site and form pus, while other phagocytes remain active for longer.

   (a)

   Which cell is usually the first phagocyte to arrive in large numbers at a site of bacterial infection?

   [1 mark]

   • ANeutrophil
   • BB memory cell
   • CT killer cell
   • DPlasma cell

   (b)

   After a macrophage has engulfed and digested a bacterium, what does it do next in the specific immune response?

   [1 mark]

   • ASecretes antibodies
   • BDivides to form plasma cells
   • CDisplays antigens from the bacterium on its surface
   • DReleases perforin into the bacterium

   (c)

   Explain how a phagocyte destroys a bacterium after engulfing it.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Researchers infect a mouse with a virus. A few days later they find that a small number of B cells, each with surface antibodies that bind to a viral protein, have divided many times to form a large number of identical cells. Some of these cells are secreting large amounts of antibody into the blood.

   (a)

   Which term describes the repeated division of the selected B cells to form many identical cells?

   [1 mark]

   • AClonal selection
   • BClonal expansion
   • CPhagocytosis
   • DMeiosis

   (b)

   Which cells secrete the large amounts of antibody found in the mouse's blood?

   [1 mark]

   • AB memory cells
   • BT helper cells
   • CT killer cells
   • DPlasma cells

   (c)

   Explain why only a small number of B cells divided in response to the viral protein.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A virus enters the liver cells of a patient and replicates inside them. Fragments of viral protein are displayed on the surface membranes of the infected cells. The patient's blood contains antibodies against the virus, but the virus inside the liver cells is still not cleared until other cells of the immune system respond.

   (a)

   Describe how T helper cells are activated in the cell-mediated response and how they activate T killer cells.

   [3 marks]

   (b)

   Explain how T killer cells destroy infected cells, and why antibodies alone cannot clear the virus.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is vaccinated with an inactivated form of a pathogen. Three months later she is exposed to the live pathogen. A blood test after the vaccination shows a slow, small rise in antibody concentration, while after the exposure there is a much faster rise to a much higher concentration.

   (a)

   Describe how the humoral immune response develops after a pathogen first enters the body.

   [6 marks]

   (b)

   Explain why the antibody response after the exposure was faster and greater than after the vaccination, and evaluate how this makes vaccination effective.

   [6 marks]

   Total for question 4: 12 marks

End of questions