Antigens and phagocytosisAQA A-Level Biology: Subtopic test

1. 1
   Influenza viruses carry two types of glycoprotein on their surface, haemagglutinin and neuraminidase. The genes coding for these proteins mutate frequently. Every year public health scientists predict which strains will be common and a new seasonal influenza vaccine is produced.

   (a)

   Which definition of an antigen is correct?

   [1 mark]

   • AA molecule, usually a protein, that stimulates an immune response
   • BA protein produced by plasma cells that binds to a pathogen
   • CAn enzyme in lysosomes that digests bacterial cell walls
   • DA cell that engulfs pathogens by phagocytosis

   (b)

   A person who caught influenza last winter catches it again this winter. Which is the most likely explanation?

   [1 mark]

   • AThe person's antibodies from last winter were destroyed by lysozymes
   • BInfluenza viruses are bacteria and so are not recognised by the immune system
   • CThe person's immune system cannot recognise any antigens on viruses
   • DThe antigens on this year's strain are different, so memory cells from last year's infection are not complementary to them

   (c)

   Explain why a new influenza vaccine has to be produced each year.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A patient with kidney failure receives a kidney from an unrelated donor. Without drugs that suppress the immune system, the patient's immune system would attack the transplanted kidney.

   (a)

   Why would the patient's immune system attack the transplanted kidney?

   [1 mark]

   • AThe donor kidney cells contain DNA, which the patient's cells do not
   • BThe donor cells carry surface proteins that differ from the patient's own and are recognised as non-self
   • CThe donor kidney cells have no surface proteins
   • DThe kidney cells are carrying a toxin released by the patient's own phagocytes

   (b)

   The immune system also responds to other cells that carry non-self antigens. Which of the following would NOT be identified as non-self?

   [1 mark]

   • AA virus-infected body cell of the patient displaying viral antigens
   • BA cancer cell of the patient with an abnormal surface protein
   • CA healthy cell of the patient with the patient's normal surface proteins
   • DA toxin released by a bacterium

   (c)

   Explain why finding a donor with a very close tissue match reduces the risk of the kidney being rejected.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Neutrophils, a type of phagocyte, were mixed with Staphylococcus aureus bacteria and viewed under a microscope. After a few minutes bacteria could be seen inside membrane-bound vacuoles in the neutrophils. A rare inherited condition causes a patient's neutrophils to engulf bacteria normally, but the bacteria survive inside the neutrophils and the patient suffers repeated infections.

   (a)

   Describe how a neutrophil ingests and destroys a bacterium.

   [3 marks]

   (b)

   Suggest an explanation for the survival of the bacteria inside the neutrophils of the patient with the inherited condition.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital immunology laboratory is investigating two linked problems. During one winter an influenza outbreak affected many people who had been vaccinated against influenza the previous year. Some of these patients then developed bacterial pneumonia, and the laboratory studied how neutrophils from one of them responded to the bacterium. Within minutes of mixing, bacterial cells were seen inside the neutrophils. Later, fewer bacteria were present and fragments of bacterial cell wall were found in the neutrophil cytoplasm.

   (a)

   Explain why many people who had been vaccinated against influenza the previous year caught influenza during the outbreak.

   [6 marks]

   (b)

   Explain these observations about the patient's neutrophils and the bacterium, including how the neutrophils recognised the bacterium.

   [6 marks]

   Total for question 4: 12 marks

End of questions