Exam questions · Biology · Human Defences and Immunity
Immunisation
- 6 exam questions
- 19 marks
- 9 quick checks
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1 State [1 mark]
State what a vaccine contains that triggers the production of antibodies.
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Model answer
Antigens from the pathogen (an inactive or weakened pathogen).
Mark scheme
- Antigens — 1 mark
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2 State [2 marks]
State two reasons why a person who has been vaccinated does not become ill when they meet the live pathogen.
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Model answer
Memory lymphocytes are already present, and so the body makes a secondary response that is fast and large. The pathogen is destroyed by the antibodies before it can cause the disease.
Mark scheme
- Memory lymphocytes present — 1 mark
- Fast secondary response — 1 mark
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3 Explain [3 marks]
Explain why a vaccine made from an inactive pathogen does not cause the disease.
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Model answer
The pathogen has been killed or inactivated, so it cannot reproduce in the body or make toxins. It still carries the antigens, so the immune system makes antibodies, but the person does not become ill.
Mark scheme
- Pathogen is inactive / cannot reproduce — 1 mark
- Still has antigens — 1 mark
- Antibodies made, no illness — 1 mark
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4 Explain [4 marks]
Explain why a new influenza vaccine has to be made each year.
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Model answer
The influenza virus mutates often, so the antigens on its surface change. The memory lymphocytes made against last year's strain do not recognise the new antigens, so they do not give protection. A new vaccine is needed that matches the strains that are expected.
Mark scheme
- Virus mutates — 1 mark
- Antigens change — 1 mark
- Existing memory lymphocytes do not recognise them — 1 mark
- New vaccine matches the new strain — 1 mark
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5 Calculate [3 marks]
In a trial, 4000 people were given a vaccine and 4000 were given a placebo. 8 of the vaccinated people and 160 of the placebo group caught the disease. Calculate the percentage reduction in the number of cases in the vaccinated group, compared with the placebo group.
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Model answer
The reduction is 160 − 8 = 152 cases. 152 ÷ 160 × 100 = 95%.
Mark scheme
- Reduction of 152 — 1 mark
- Divides by 160, times 100 — 1 mark
- 95% — 1 mark
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6 Explain [6 marks]
Describe how a vaccine gives long-term protection against a disease, and explain why the second dose of some vaccines gives a better response than the first.
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Model answer
A vaccine contains an inactive form of the pathogen, with its antigens. Lymphocytes recognise them and divide, making antibodies in a primary response, and some become memory lymphocytes. These stay in the body for a long time. If the real pathogen arrives, the memory lymphocytes make a fast secondary response, producing a large amount of antibodies, and the pathogen is destroyed before the person is ill. A second dose of the vaccine causes a secondary response, because memory lymphocytes from the first dose respond fast. This makes a bigger increase in antibodies and more memory cells, which makes the protection stronger and longer lasting.
Mark scheme
- Inactive pathogen with antigens — 1 mark
- Primary response, antibodies — 1 mark
- Memory lymphocytes made — 1 mark
- Fast secondary response to the real pathogen — 1 mark
- Second dose gives a secondary response — 1 mark
- Stronger, longer protection — 1 mark
Quick check
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1
What does a vaccine contain?
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C: An inactive form of a pathogen
A vaccine contains an inactive or weakened pathogen, or its antigens.
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2
What does a vaccine make the body produce?
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A: Antibodies and memory lymphocytes
The body makes antibodies and memory lymphocytes in response to the antigens.
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3
Why does a vaccinated person not become ill when exposed to the pathogen?
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D: Memory lymphocytes make a fast response
Memory lymphocytes give a fast secondary response, so the pathogen is destroyed quickly.
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4
Why does the flu vaccine change each year?
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B: The virus mutates and its antigens change
The flu virus mutates, so its antigens change.
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5
Who made the first vaccine, for smallpox?
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A: Edward Jenner
Edward Jenner developed the first vaccine, in 1796.
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6
What is a placebo?
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C: A substance with no effect
A placebo is a harmless substance that has no effect, used for comparison.
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7
What is the purpose of a booster dose?
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B: To increase immunity
It raises the level of memory lymphocytes, to keep immunity high.
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8
10 of 1000 vaccinated people and 100 of 1000 unvaccinated people caught a disease. What is the percentage reduction in cases?
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D: 90%
The reduction is 90 out of 100 cases, which is 90%.
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9
Why does the measles vaccine work for life, while the flu vaccine needs updating?
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A: Measles virus changes little, flu virus mutates often
The measles virus changes very little, so the same antigens remain, but the flu virus mutates often.