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Exam questions · Biology · Human Defences and Immunity

The Immune System

  • 6 exam questions
  • 21 marks
  • 9 quick checks
  1. 1 Define [2 marks]

    Define the terms antigen and antibody.

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    Model answer

    An antigen is a molecule on the surface of a pathogen that the immune system recognises as foreign. An antibody is a protein made by lymphocytes that fits a specific antigen.

    Mark scheme

    • Antigen — 1 mark
    • Antibody — 1 mark
  2. 2 State [2 marks]

    State the functions of (a) a phagocyte and (b) a lymphocyte.

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    Model answer

    (a) A phagocyte engulfs and digests pathogens. (b) A lymphocyte makes antibodies.

    Mark scheme

    • Phagocyte — 1 mark
    • Lymphocyte — 1 mark
  3. 3 Explain [3 marks]

    Explain why an antibody that is made against one pathogen does not work against a different pathogen.

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    Model answer

    Antibodies have a shape that fits one specific antigen. A different pathogen has different antigens, which have a different shape. The antibody does not fit them, so it cannot bind to them.

    Mark scheme

    • Antibody shape fits one antigen — 1 mark
    • Different pathogen has different antigens — 1 mark
    • Antibody does not fit — 1 mark
  4. 4 Describe [4 marks]

    Describe how the body responds the first time that a pathogen enters the blood.

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    Model answer

    A lymphocyte that recognises the pathogen's antigen is activated, and divides many times. Many of the new cells make antibodies, which bind to the pathogen and make it clump, so that phagocytes can engulf it. Some of the lymphocytes become memory lymphocytes.

    Mark scheme

    • Lymphocyte recognises the antigen — 1 mark
    • Divides to make many cells — 1 mark
    • Antibodies made, pathogen destroyed — 1 mark
    • Memory lymphocytes made — 1 mark
  5. 5 Explain [4 marks]

    Explain why the secondary response to a pathogen is faster than the primary response.

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    Model answer

    After the first infection, memory lymphocytes remain in the body, and they already recognise the antigen. When the same pathogen enters again, they divide quickly and make a large amount of antibodies in a short time. The pathogen is destroyed before it can cause illness.

    Mark scheme

    • Memory lymphocytes remain — 1 mark
    • Recognise the antigen — 1 mark
    • Divide quickly, make more antibodies — 1 mark
    • Pathogen destroyed before illness — 1 mark
  6. 6 Evaluate [6 marks]

    The graph shows antibody concentration after a first infection at day 0, and a second infection at day 28. Describe and explain the differences between the two responses.

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    Model answer

    After the first infection, the antibody concentration rises slowly, starting at about day 4, and it reaches a low peak of about 15 units at day 14. After the second infection, the concentration rises much faster, reaching a peak in about 4 days, and the peak is much higher, at about 70 units. This is because memory lymphocytes were made during the first infection. They recognise the antigen at once, and divide quickly to make many antibodies. The second response is therefore faster and larger, which means that the person does not become ill the second time.

    Mark scheme

    • First: slow rise, low peak — 1 mark
    • Data for the first response — 1 mark
    • Second: faster, higher peak — 1 mark
    • Data for the second response — 1 mark
    • Explained by memory lymphocytes — 1 mark
    • Person does not become ill — 1 mark

Quick check

  1. 1

    What is an antigen?

    1. AA type of white blood cell
    2. BA molecule on the surface of a pathogen
    3. CA type of antibody
    4. DA drug
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    B: A molecule on the surface of a pathogen

    An antigen is a molecule on the surface of a pathogen that the immune system recognises as foreign.

  2. 2

    Which cell makes antibodies?

    1. APhagocyte
    2. BRed blood cell
    3. CPlatelet
    4. DLymphocyte
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    D: Lymphocyte

    Lymphocytes make antibodies.

  3. 3

    What does a phagocyte do?

    1. AEngulfs and digests pathogens
    2. BMakes antibodies
    3. CCarries oxygen
    4. DClots blood
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    A: Engulfs and digests pathogens

    A phagocyte engulfs and digests pathogens.

  4. 4

    Why does an antibody only work against one pathogen?

    1. AIt is made by a phagocyte
    2. BIt is too large
    3. CIts shape fits only one antigen
    4. DIt is a hormone
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    C: Its shape fits only one antigen

    Its shape fits one specific antigen.

  5. 5

    What are memory lymphocytes?

    1. ACells that forget pathogens
    2. BCells that remain and respond quickly to the same pathogen
    3. CCells that carry oxygen
    4. DCells that make mucus
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    B: Cells that remain and respond quickly to the same pathogen

    Memory lymphocytes remain after an infection, and respond quickly if the pathogen returns.

  6. 6

    How does the secondary response differ from the primary response?

    1. AIt is faster and larger
    2. BIt is slower and smaller
    3. CIt is the same
    4. DIt only happens in children
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    A: It is faster and larger

    It is faster and produces more antibodies.

  7. 7

    How do antibodies help to destroy pathogens?

    1. AThey digest pathogens
    2. BThey make mucus
    3. CThey become red blood cells
    4. DThey bind to them and help phagocytes to engulf them
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    D: They bind to them and help phagocytes to engulf them

    They clump pathogens together, so phagocytes can engulf them, and can neutralise toxins.

  8. 8

    Why do you not usually get chickenpox twice?

    1. AThe virus dies out
    2. BMemory lymphocytes destroy the virus quickly
    3. CThe skin changes
    4. DAntibiotics kill it
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    B: Memory lymphocytes destroy the virus quickly

    Memory lymphocytes respond very fast and destroy the virus before symptoms appear.

  9. 9

    A graph shows a peak at 15 units after the first infection and 60 units after the second. How many times higher is the second peak?

    1. A2 times
    2. B3 times
    3. C4 times
    4. D45 times
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    C: 4 times

    \(60 \div 15 = 4\) times higher.