IMMUNITY exam qs

• Describe how antibodies are produced in the body following a viral infection? [6] ANY 6

  The virus contains antigen

  virus engulfed by phagocyte/macrophage

  cytokines released by t cells

  b cells become activated

  divides to form clones

  by mitosis

  plasma b cells secrete antibodies

  antibodies are specific to antigen
• Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how. [2]

  The scientists could identify proteins

  they could then identify potential antigens
• Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus. You can assume that the B lymphocytes of a frog respond in the same way as B lymphocytes of a human. Do not include details of the cellular response in your answer. [4]

  B cell antibody binds to complementary viral antigen

  B cell clones/B cell divides by mitosis

  Plasma cells release antibodies against the virus

  B cells produce memory cells
• What do you include in 2 marker about why 2 things bind, apart from saying that they're complementary ?

  that one of the substrates has a specific tertiary structure
• Describe how HIV is replicated? [4]

  attachment protein on HIV binds to surface receptor on host cell

  viral RNA/nucleic acid enters cell

  reverse transcriptase converts RNA to DNA

  viral protein produced

  virus assembled and released from cell
• Describe how HIV is replicated once inside helper t cells? [4]

  RNA converted to DNA using reverse transcriptase

  DNA inserted into DNA of t cell

  DNA transcribed into HIV mRNA

  HIV mRNA translated into new HIV proteins (for assembly into viral particles)
• How does a phagocyte destroy a pathogen present in the blood? [4]

  phagocyte recognises foreign antigen on pathogen by surface receptors

  phagocyte engulfs pathogen

  forming phagosome and fusing with lysosome

  lysozymes digest/hydrolyse the pathogen
• What's the only difference if the Q asks how drug is released, when it still involves same phagocytosis process just with a different cell to phagocyte and thing that attaches on is a monoclonal antibody with a drug attached ?

  The only difference is that when the lysozymes hydrolyse/digest the monoclonal antibody you must say that this is when the drug is released.
• Describe the differences between active and passive immunity [5]

  Active involves memory cells, passive does not

  Active involves production of antibodies by plasma cells

  passive involves antibody introduced into body from outside

  Active is long term because antibody produced in response to antigen

  Passive is short term because antibody given is broken down

  Active can take time to develop/work, but passive is fast acting
• When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. [5] ANY 5

  Virus contains antigen from pathogen

  macrophage presents antigen on its surface

  T-cell with complementary surface receptor protein binds to antigen

  T-cell stimulates B cells

  with complementary antibody on its surface

  B cell secretes large amount of antibody

  B cell divides to form clone, all producing the same antibody
• What should you include in the mark-scheme when the Q asks about how a vaccine can provide protection against a virus?

  that some B cells become memory cells

  memory cells produce antibodies faster
• Describe how phagocytosis of a virus leads to presentation of one of its antigens? [3]

  phagosome fuses with lysosome

  virus destroyed by lysozymes

  antigen from virus are displayed on cell membrane

  (must include cell membrane to get the mark)
• AZT inhibits the enzyme that synthesises DNA from HIV RNA. Suggest and explain why AZT does not destroy HIV in the body but stops or slows the development of AIDS. [4] ANY 4

  person infected with HIV has HIV DNA in their DNA

  so new HIV particles still made

  AZT inhibits reverse transcriptase

  so AZT stops these new HIV particles from forming new HIV DNA/so AZT slows replication of HIV

  so stops destruction of more/newly infected T cells

  so immune system continues to work (and AIDS does not develop)
• During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom. Use your knowledge of the humoral immune response to explain this vaccination programme. [3]

  B cells specific to the venom reproduce by mitosis

  B cells produce memory cells and plasma cells

  The second dose produces antibodies in a higher concentration AND more quickly
• What's one word to use when including B cells or T cells in any immune response answer to ensure marking point is met?


  specific
• Describe the role of antibodies in producing a positive ELISA test. [4]

  First antibody binds/attaches/complementary in shape to antigen

  second antibody with enzyme attached is added

  second antibody attaches to antigen

  substrate added and colour changes
• Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis [2]

  Act as markers/bind to antigens

  cause agglutination/attract phagocytes
• The scientists hypothesised that memory B cells had formed in the mice 180 days after the 3rd injection. Suggest and explain a practical method the scientists could use to test this hypothesis. [2]

  Inject vaccine again/use a booster

  memory cells present if faster production and higher concentration of antibody

  OR

  add enzyme attached to second antibody against memory cell

  colour change shows memory cell present

  (not enough to just say use ELISA test)
• What are 2 marking points to always include when there's a question about ELISA tests

  That there's a second antibody used with an enzyme attached

  and when substrate added there's colour change to show that (thing you were looking for) is present