Exam questions · Biology
Human Defences and Immunity
- 30 exam questions
- 97 marks
- 45 quick checks
Physical and Chemical Barriers
Just this lesson-
1 State [2 marks]
State two ways in which the skin protects the body from pathogens.
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Model answer
Any two from: it is a physical barrier of dead cells with keratin; it makes sebum which kills bacteria; it has friendly bacteria; scabs seal cuts.
Mark scheme
- First — 1 mark
- Second — 1 mark
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2 Name [2 marks]
Name the substance in tears that kills bacteria, and the acid in the stomach that kills pathogens.
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Model answer
Lysozyme, and hydrochloric acid.
Mark scheme
- Lysozyme — 1 mark
- Hydrochloric acid — 1 mark
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3 Describe [3 marks]
Describe how mucus and cilia protect the lungs from pathogens.
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Model answer
Goblet cells make mucus, which traps pathogens in the air that is breathed in. Cilia on the cells in the lining move the mucus up the airways to the throat. The mucus is then swallowed or coughed out.
Mark scheme
- Mucus traps pathogens — 1 mark
- Cilia move the mucus — 1 mark
- Swallowed or coughed out — 1 mark
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4 Explain [3 marks]
Explain how lysozyme helps to protect the eye from infection.
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Model answer
Lysozyme is an enzyme in tears. It breaks down the cell walls of bacteria, so the bacteria die. This stops them from growing on the surface of the eye.
Mark scheme
- Enzyme in tears — 1 mark
- Breaks down bacterial cell walls — 1 mark
- Bacteria are killed — 1 mark
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5 Calculate [3 marks]
In one year, 15% of non-smokers and 36% of smokers had a chest infection. Calculate how many times more likely a smoker was to have an infection. Suggest one reason.
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Model answer
36 ÷ 15 = 2.4 times. Smoke damages the cilia, so mucus and pathogens are not moved out of the lungs.
Mark scheme
- 36 divided by 15 — 1 mark
- 2.4 times — 1 mark
- Cilia damaged — 1 mark
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6 Explain [6 marks]
Explain why smokers are more likely than non-smokers to suffer from chest infections.
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Model answer
In the airways, goblet cells make mucus that traps pathogens and dust, and cilia on the cells move the mucus up to the throat so that it can be swallowed or coughed out. Chemicals in cigarette smoke paralyse and destroy the cilia. The mucus can no longer be moved, so it builds up in the lungs, together with the pathogens it has trapped. The bacteria can multiply there, which leads to infection such as bronchitis. Smokers also make more mucus, and have to cough to clear it.
Mark scheme
- Goblet cells make mucus that traps pathogens — 1 mark
- Cilia move mucus up — 1 mark
- Smoke damages the cilia — 1 mark
- Mucus is not moved — 1 mark
- Pathogens multiply in the lungs — 1 mark
- Infection such as bronchitis — 1 mark
Quick check
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1
What do goblet cells make?
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C: Mucus
Goblet cells make mucus, which traps pathogens in the airways.
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2
What is the function of cilia in the airways?
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A: To move the mucus up
Cilia move the mucus with the trapped pathogens up towards the throat.
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3
What does lysozyme do?
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D: Breaks down bacterial cell walls
Lysozyme is an enzyme that breaks down the cell walls of bacteria.
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4
Which acid in the stomach kills pathogens?
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B: Hydrochloric acid
The stomach contains hydrochloric acid, which kills most pathogens.
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5
How do platelets help to protect the body?
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C: They help to form a scab
Platelets help the blood to clot and form a scab, which seals a wound.
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6
Which is a physical barrier?
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A: The skin
The skin is a physical barrier, while lysozyme and acid are chemical defences.
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7
How does smoking increase the risk of lung infections?
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D: It damages the cilia
It damages the cilia, so mucus and pathogens stay in the lungs.
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8
Why are these defences called non-specific?
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B: They work against all pathogens in the same way
They work in the same way against all pathogens.
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9
In one study, 8% of non-smokers and 20% of smokers had infections. How many times more likely was a smoker to be infected?
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A: 2.5 times
\(20 \div 8 = 2.5\) times.
The Immune System
Just this lesson-
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
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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
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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
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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
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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
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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
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1
What is an antigen?
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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.
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2
Which cell makes antibodies?
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D: Lymphocyte
Lymphocytes make antibodies.
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3
What does a phagocyte do?
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A: Engulfs and digests pathogens
A phagocyte engulfs and digests pathogens.
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4
Why does an antibody only work against one pathogen?
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C: Its shape fits only one antigen
Its shape fits one specific antigen.
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5
What are memory lymphocytes?
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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.
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6
How does the secondary response differ from the primary response?
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A: It is faster and larger
It is faster and produces more antibodies.
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7
How do antibodies help to destroy pathogens?
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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.
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8
Why do you not usually get chickenpox twice?
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B: Memory lymphocytes destroy the virus quickly
Memory lymphocytes respond very fast and destroy the virus before symptoms appear.
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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?
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C: 4 times
\(60 \div 15 = 4\) times higher.
Immunisation
Just this lesson-
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.
Herd Immunity and Evaluating Vaccination
Just this lesson-
1 State [1 mark]
State what is meant by herd immunity.
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Model answer
Unvaccinated people are protected from a disease, because most of the population is immune, so the disease cannot spread easily.
Mark scheme
- Protection of the unvaccinated by the immunity of the rest — 1 mark
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2 State [2 marks]
State two groups of people who rely on herd immunity for protection.
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Model answer
Any two from: babies who are too young to be vaccinated; people with weakened immune systems; people for whom the vaccine does not work; people who cannot be vaccinated for medical reasons.
Mark scheme
- First — 1 mark
- Second — 1 mark
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3 Explain [3 marks]
Explain how herd immunity protects people who have not been vaccinated.
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Model answer
If most people are immune, an infected person is unlikely to meet someone who is not immune. The pathogen cannot easily pass from person to person, so the disease does not spread. The unvaccinated people are therefore not exposed to it.
Mark scheme
- Most people are immune — 1 mark
- Pathogen cannot pass on easily — 1 mark
- Unvaccinated people not exposed — 1 mark
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4 Describe [3 marks]
Describe two disadvantages of vaccination programmes.
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Model answer
Vaccines can cause side effects, which are usually mild such as soreness, but rarely can be serious. No vaccine is effective in everyone, so some vaccinated people can still get the disease. Programmes are expensive to run.
Mark scheme
- Side effects — 1 mark
- Not 100% effective — 1 mark
- Cost, or another correct point — 1 mark
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5 Calculate [3 marks]
In a city, vaccination against a disease fell from 95% to 76% of children, and cases rose from 12 to 300. Calculate how many times more cases there were, and the fall in the percentage vaccinated, in percentage points.
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Model answer
300 ÷ 12 = 25 times more cases. The fall is 95 − 76 = 19 percentage points.
Mark scheme
- 300 divided by 12 — 1 mark
- 25 times — 1 mark
- 19 percentage points — 1 mark
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6 Evaluate [6 marks]
Some parents decide not to have their children vaccinated against measles. Evaluate this decision, using ideas about herd immunity.
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Model answer
A parent may be worried about side effects, but these are usually mild, and serious ones are very rare. An unvaccinated child is at risk of measles, which can cause serious complications such as pneumonia and brain damage, and can be fatal. The child is protected only if enough other children are vaccinated, because of herd immunity. If many parents decide not to vaccinate, the level of immunity falls below about 95%, and the disease can spread, which puts babies and those who cannot be vaccinated at risk. The evidence from many studies is that the vaccine is safe, so the benefit to the child and the community is much greater than the risk. It is better to vaccinate.
Mark scheme
- Side effects are mild and serious ones rare — 1 mark
- Risk to an unvaccinated child — 1 mark
- Child depends on herd immunity — 1 mark
- If too many do not vaccinate, herd immunity is lost — 1 mark
- Vulnerable people are put at risk — 1 mark
- A reasoned conclusion using evidence — 1 mark
Quick check
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1
What is herd immunity?
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B: Protection of unvaccinated people by the immunity of others
It is the protection of unvaccinated people, because so many others are immune that the disease cannot spread.
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2
Roughly what percentage must be immune to measles for herd immunity?
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D: 95%
Measles is very infectious, so about 95% need to be immune.
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3
Who is protected by herd immunity?
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C: Unvaccinated people, because the disease cannot spread
Those who cannot be vaccinated, such as babies and people with weak immune systems, rely on it.
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4
What happens if vaccination levels fall below the threshold?
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A: Outbreaks can happen
Outbreaks of the disease can happen again.
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5
Which is a disadvantage of vaccination?
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B: It can cause mild side effects
Mild side effects, such as soreness, are common.
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6
Which disease has been eradicated by vaccination?
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C: Smallpox
Smallpox was declared eradicated in 1980.
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7
Why did measles outbreaks follow the MMR scare?
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A: Vaccination rates fell
The number of children vaccinated fell, so herd immunity was lost.
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8
Vaccination fell from 90% to 72%. What was the fall in percentage points?
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D: 18
\(90 - 72 = 18\) percentage points.
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9
A child cannot be vaccinated because they have a weak immune system. How can they be protected from measles?
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B: By herd immunity, from others being vaccinated
If most of the people around them are immune, the disease cannot spread to them, which is herd immunity.
Antibiotics
Just this lesson-
1 State [2 marks]
State two structures or processes in bacteria that antibiotics can target.
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Model answer
The cell wall, and the ribosomes (protein synthesis).
Mark scheme
- Cell wall — 1 mark
- Ribosomes / protein synthesis — 1 mark
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2 Explain [3 marks]
Explain why antibiotics can be used to treat bacterial infections without harming the cells of the patient.
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Model answer
Antibiotics attack structures and processes that bacteria have but human cells do not, such as the cell wall, or they block bacterial ribosomes. Human cells have no cell wall, and have different ribosomes, so they are not affected.
Mark scheme
- Target structures in bacteria — 1 mark
- Human cells do not have the cell wall / different ribosomes — 1 mark
- So the patient's cells are not harmed — 1 mark
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3 Explain [3 marks]
A patient has flu. Explain why the doctor does not give the patient an antibiotic.
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Model answer
Flu is caused by a virus, and antibiotics do not work against viruses. Viruses have no cell wall and live inside host cells. Giving an antibiotic would not help, and would make resistance more likely.
Mark scheme
- Flu is caused by a virus — 1 mark
- Antibiotics do not work on viruses — 1 mark
- Would increase resistance — 1 mark
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4 Describe [3 marks]
Describe how Alexander Fleming discovered penicillin.
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Model answer
In 1928 Fleming found that a dish of bacteria had been contaminated by a mould. There was a clear area around the mould where the bacteria had not grown. He realised that the mould was making a substance that killed the bacteria, which he called penicillin.
Mark scheme
- 1928, mould on a dish of bacteria — 1 mark
- Clear area around the mould — 1 mark
- Substance that kills bacteria — 1 mark
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5 Calculate [3 marks]
The diameters of the clear zones on an agar plate were: antibiotic A, 20 mm; antibiotic B, 10 mm. Calculate the area of each zone using \(\pi r^2\) (use \(\pi = 3.14\)), and state how many times larger the zone for A is than for B.
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Model answer
A has a radius of 10 mm, so its area is 3.14 × 10² = 314 mm². B has a radius of 5 mm, so its area is 3.14 × 5² = 78.5 mm². The zone for A is 314 ÷ 78.5 = 4 times larger.
Mark scheme
- Area of A = 314 mm² — 1 mark
- Area of B = 78.5 mm² — 1 mark
- 4 times larger — 1 mark
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6 Evaluate [6 marks]
Evaluate the importance of the discovery of antibiotics, and explain why it is important to use them carefully.
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Model answer
Antibiotics have saved millions of lives by curing bacterial infections that used to be fatal, such as pneumonia and wound infections, and they made surgery and cancer treatment much safer. They target structures in bacteria, so they do not harm human cells. However, they do not work against viruses, so they are useless for colds and flu. If they are overused or taken incompletely, bacteria that are resistant survive and reproduce, so resistance spreads and the drugs stop working. It is therefore important to use them only when needed, to finish the course, and to develop new ones.
Mark scheme
- Saved many lives — 1 mark
- Made surgery safer — 1 mark
- Target bacteria, not human cells — 1 mark
- Do not work on viruses — 1 mark
- Overuse leads to resistance — 1 mark
- Use carefully, complete the course — 1 mark
Quick check
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1
What do antibiotics treat?
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B: Bacterial infections
Antibiotics treat bacterial infections.
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2
How does penicillin kill bacteria?
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C: It stops cell wall formation
It stops the bacteria from building their cell wall, so they burst.
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3
Why do antibiotics not harm human cells?
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A: They target structures that human cells do not have
Human cells have no cell wall, and have different ribosomes.
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4
Who discovered penicillin in 1928?
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D: Alexander Fleming
Alexander Fleming discovered penicillin.
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5
From which organism is penicillin made?
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B: A mould
Penicillin is made by the mould Penicillium.
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6
Why do antibiotics not work against viruses?
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C: Viruses have nothing for the antibiotic to target
Viruses have no cell wall or ribosomes of their own, and live inside host cells.
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7
Which disease should NOT be treated with antibiotics?
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A: Influenza
Influenza is caused by a virus, so antibiotics do not work.
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8
A clear zone of 4 mm appears around antibiotic X and 12 mm around antibiotic Y. Which is more effective?
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D: Y
The larger clear zone shows that antibiotic Y stops more bacteria growing.
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9
A patient stops taking antibiotics after 2 days because she feels better. Why is this a problem?
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B: Some bacteria may survive, and could be resistant
Some bacteria may survive, including resistant ones, and the infection may return.