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GCSE · Biology

B3b Human Defences, Vaccination and Drug Development

AQA 8464 · Calculator allowed · about 90 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Vaccination Coverage and Whooping Cough Cases

Original scenario written for Revision Library, styled on the format of UK public health vaccination-coverage reporting (e.g. UKHSA/NHS data summaries). No copied text or figures.

Whooping cough (pertussis) is a bacterial infection that can be serious in young babies. In one country, a national vaccination programme against whooping cough was introduced. Before the programme began, 84000 cases of whooping cough were recorded per year. Several years after the programme began, this fell to 3150 cases per year.

At a secondary school in the same country, 1500 students attend. School nurse records show that 88% of these students have received the MMR (measles, mumps and rubella) vaccine. Public health guidance states that at least 95% vaccination coverage is generally needed to achieve herd immunity against measles within a school-sized population.

The human body has several physical and chemical defences that stop pathogens entering the body, before the immune system needs to respond. State the function of each of the following defences against pathogens: (i) the skin (ii) stomach acid (iii) mucus produced in the airways.

(Total for Question 1 is 3 marks)

White blood cells are central to the body's specific immune response against pathogens. Describe the different roles of phagocytes and lymphocytes in defending the body against pathogens.

(Total for Question 2 is 3 marks)

The trachea (windpipe) and bronchi are lined with goblet cells, which produce mucus, and with cells that have cilia on their surface. Explain how the ciliary escalator helps to prevent lung infections.

(Total for Question 3 is 4 marks)

Painkillers and antibiotics are both medicines used to treat illness, but they work in very different ways.

(a)State what painkillers do to relieve the symptoms of an illness.(2)

(b)Dr Aleksander Nowak, a GP in Cardiff, sees a patient with symptoms of a common cold. Explain why he would not prescribe antibiotics for this patient.(2)

(Total for Question 4 is 4 marks)

Phagocytosis is the process by which a phagocyte destroys a pathogen. Describe the main stages of phagocytosis.

(Total for Question 5 is 4 marks)

Lymphocytes respond to specific pathogens by producing antibodies and antitoxins.

(a)Explain why a particular antibody will only bind to one specific type of antigen.(2)

(b)Describe the difference between the roles of antibodies and antitoxins when the body defends itself against a bacterial infection.(3)

(Total for Question 6 is 5 marks)

Vaccination programmes aim to protect not just the people who are vaccinated, but also the wider population. Explain what is meant by the term 'herd immunity', and explain why it protects people who cannot be vaccinated.

(Total for Question 7 is 3 marks)

Use the information in the source about whooping cough cases to answer this question. Calculate the percentage decrease in the number of whooping cough cases per year after the vaccination programme began. Give your answer to 3 significant figures.

(Total for Question 8 is 3 marks)

Use the information in the source about MMR vaccination coverage at the school to answer this question.

(a)Calculate the number of students at the school who have NOT been vaccinated against MMR.(2)

(b)State and explain whether herd immunity against measles has been achieved at this school.(2)

(Total for Question 9 is 4 marks)

When a person is vaccinated, they are given a small, safe dose of a dead, inactivated or harmless part of a pathogen, which contains specific antigens. Explain, using ideas about the primary and secondary immune response, how vaccination can give a person long-term protection against a serious disease.

Figure (to be drawn): Optional graph: antibody concentration in the blood (y-axis) plotted against time (x-axis), showing a small, slow first peak shortly after vaccination (primary response), and a much larger, faster second peak if the same pathogen is encountered again later (secondary response).

(Total for Question 10 is 6 marks)

Antibiotics, such as penicillin, are medicines that treat bacterial infections.

(a)Explain why antibiotics cannot be used to treat a viral infection such as the common cold.(2)

(b)Evaluate the risk to public health caused by doctors overprescribing antibiotics.(2)

(Total for Question 11 is 4 marks)

A student is investigating bacterial growth. A culture starts with 400 bacterial cells. Under ideal conditions, the population doubles every 20 minutes. Calculate the number of bacterial cells present after 100 minutes, assuming growth continues at this rate with no antibiotic present.

(Total for Question 12 is 3 marks)

Required practical: investigating the effect of antibiotics on bacterial growth using agar plates. A student investigated the effectiveness of two antibiotics by placing paper discs soaked in antibiotic X and antibiotic Y onto an agar plate that had been spread with a lawn of a harmless species of bacterium. The plate was incubated, and the size of the clear zone (zone of inhibition) around each disc was measured after 48 hours.

Figure (to be drawn): Diagram of a Petri dish containing agar and a bacterial lawn, with two antibiotic discs (X and Y) placed on the surface, each surrounded by a clear zone of inhibition.

(a)State two aseptic techniques the student should have used when setting up this investigation, and explain the purpose of each.(2)

(b)Suggest why the agar plate was incubated at a maximum of 25 C in the school laboratory, rather than at 37 C (normal human body temperature).(2)

(c)The clear zone (zone of inhibition) around disc X was circular, with a radius of 6 mm. Calculate the area of this zone of inhibition. Give your answer to 3 significant figures.(3)

(d)The zone of inhibition around disc Y had an area of 78.5 mm^2. Using your answer to part (c), compare the effectiveness of antibiotics X and Y against this bacterium.(2)

(e)Suggest one way the reliability of this investigation could be improved, and evaluate why your suggestion would increase confidence in the conclusion.(4)

(Total for Question 13 is 13 marks)

Before a new medicinal drug, such as a new painkiller, can be prescribed by doctors, it must go through an extensive testing and trialling process. Describe the main stages involved in developing and testing a new medicinal drug, from preclinical testing through to clinical trials.

(Total for Question 14 is 5 marks)

Clinical trials of a new drug are often designed to include a placebo group and are carried out double-blind. Explain why a placebo is used, and why the trial is carried out double-blind.

(Total for Question 15 is 4 marks)

A pharmaceutical company has developed a new painkiller and wants to bring it to market for doctors to prescribe. Evaluate the process the company must follow to test and trial this new painkiller before it can be prescribed by doctors, including reference to safety, effectiveness and appropriate dosage.

(Total for Question 16 is 6 marks)

Monoclonal antibodies are identical antibodies, produced by clones of a single type of white blood cell, that are specific to one particular antigen. Describe how monoclonal antibodies are produced, including the role of hybridoma cells.

(Total for Question 17 is 5 marks)

Monoclonal antibodies have several important uses in medicine and research.

(a)Describe two different uses of monoclonal antibodies, explaining in each case how their specificity for one antigen makes that use possible.(3)

(b)Evaluate one limitation of using monoclonal antibodies to treat disease.(2)

(Total for Question 18 is 5 marks)

Mark scheme · B3b Human Defences, Vaccination and Drug Development

Question 1

B1 skin - acts as a physical barrier to pathogens (and produces sebum, an antimicrobial oil, on its surface) (oe; either point)
B1 stomach acid - kills most pathogens/bacteria that are swallowed with food or drink (oe)
B1 mucus (produced in the airways/nose) - traps pathogens (and dust/particles) before they can reach the lungs (oe)
Answer: Skin: physical barrier that also produces antimicrobial sebum. Stomach acid: kills swallowed pathogens. Mucus in the airways: traps pathogens before they reach the lungs.

Question 2

B1 phagocytes are white blood cells that engulf and digest pathogens (phagocytosis) (oe)
B1 lymphocytes are white blood cells that produce antibodies specific to a particular antigen on a pathogen (oe)
B1 lymphocytes can also produce antitoxins, which neutralise toxins produced by some pathogens (oe)
Answer: Phagocytes engulf and digest pathogens; lymphocytes produce antibodies (and antitoxins) specific to a particular pathogen.

Question 3

B1 mucus (produced by goblet cells lining the trachea/bronchi) traps pathogens and other particles breathed in with air (oe)
B1 cilia are hair-like structures on the surface of the cells lining the airways (oe)
B1 cilia beat together in a coordinated, wave-like motion (oe)
B1 this moves the mucus (containing trapped pathogens) up and away from the lungs towards the throat, where it is swallowed or coughed out, so fewer pathogens reach/infect the lungs (oe)
Answer: Mucus traps inhaled pathogens; the coordinated beating of cilia sweeps the mucus up and out of the airways towards the throat, so fewer pathogens reach the lungs.

Question 4

(a) B1 painkillers relieve symptoms such as pain (oe)
(a) B1 they do this without killing the pathogen / without treating the underlying cause of the illness (oe)
(a) Answer: Painkillers relieve symptoms such as pain, but do not kill the pathogen causing the illness.
(b) B1 a cold is caused by a virus, and antibiotics are not effective against/do not kill viruses (oe)
(b) B1 viruses reproduce inside the body's own cells, making them very difficult to target with a drug without also damaging the patient's own cells (oe); allow: prescribing antibiotics unnecessarily also contributes to antibiotic resistance
(b) Answer: A cold is caused by a virus, and antibiotics only work against bacteria; viruses reproduce inside the body's own cells, making them very difficult to target without harming the patient's own cells.

Question 5

B1 the phagocyte recognises the pathogen as foreign (e.g. by antigens on its surface) and moves towards it (oe)
B1 the phagocyte engulfs/surrounds the pathogen (oe)
B1 the pathogen becomes enclosed within a vesicle inside the phagocyte (oe)
B1 enzymes are released into the vesicle, which digest/destroy the pathogen (oe)
Answer: The phagocyte recognises and moves towards the pathogen, engulfs it into a vesicle, then releases enzymes that digest and destroy it.

Question 6

(a) B1 the antibody has a binding site with a shape that is complementary to the antigen (oe)
(a) B1 only an antigen with a matching/complementary shape can bind to that antibody (oe)
(a) Answer: An antibody's binding site has a shape complementary to one specific antigen, so it will only bind to (and be triggered by) that matching antigen.
(b) B1 antibodies bind to antigens on the surface of the pathogen itself (oe)
(b) B1 this can label the pathogen for destruction by phagocytes, or cause pathogens to clump together (agglutinate) (oe)
(b) B1 antitoxins instead bind to and neutralise toxins released by the pathogen, making them harmless, rather than acting on the pathogen itself (oe)
(b) Answer: Antibodies bind to antigens on the pathogen itself (marking it for destruction, or causing it to clump); antitoxins instead bind to and neutralise the toxins the pathogen releases.

Question 7

B1 herd immunity is when a large enough proportion of a population is immune to (e.g. vaccinated against) a disease that the disease cannot spread easily through the population (oe)
B1 this means people who are not vaccinated (e.g. babies, or people who cannot be vaccinated for medical reasons) are much less likely to come into contact with an infected person (oe)
B1 so they are indirectly protected from catching the disease, even though they are not immune themselves (oe)
Answer: Herd immunity is when enough of a population is vaccinated/immune that a disease cannot spread easily; this indirectly protects unvaccinated individuals because they are much less likely to encounter an infected person.

Question 8

M1 decrease = 84000 - 3150 (= 80850)
M1 percentage decrease = (decrease / original) x 100 = (80850 / 84000) x 100
A1 96.3% (awrt 96.2-96.3%) cao
Answer: 96.3% (accept 96.2% to 96.3%)

Question 9

(a) M1 unvaccinated = 100% - 88% = 12%; number = 12% of 1500 (= 0.12 x 1500)
(a) A1 180 (students) cao
(a) Answer: 180 students
(b) B1 no, herd immunity has not been achieved (ft: must be consistent with the coverage figure used, but the correct answer is 'no')
(b) B1 because the school's vaccination coverage (88%) is below the 95% threshold stated as being needed for herd immunity (oe; must compare both figures)
(b) Answer: No - the school's coverage of 88% is below the 95% threshold needed for herd immunity.

Question 10

B1 the antigens in the vaccine trigger a primary immune response (oe)
B1 lymphocytes produce antibodies specific to that antigen, but this response is relatively slow and produces a low concentration of antibodies (oe)
B1 memory lymphocytes (memory cells) are produced and remain in the blood for a long time after vaccination (oe)
B1 if the person later encounters the same/live pathogen, the memory cells recognise the antigen rapidly (oe)
B1 this triggers a faster secondary immune response, producing antibodies more quickly and in much greater quantity than the primary response (oe)
B1 the pathogen is destroyed before the person shows symptoms of the disease, so they are immune (oe)
Answer: Vaccination triggers a primary response, producing antibodies and memory cells; on later exposure to the real pathogen, memory cells trigger a much faster, larger secondary response that destroys the pathogen before symptoms develop, giving long-term immunity.

Question 11

(a) B1 antibiotics kill bacteria (or stop bacteria growing/reproducing) by a mechanism that specifically targets structures/processes found in bacterial cells (e.g. the bacterial cell wall) (oe)
(a) B1 viruses do not have this bacterial target and reproduce inside the body's own cells, so antibiotics have no effect on them (oe)
(a) Answer: Antibiotics work by targeting structures/processes found only in bacterial cells (such as the cell wall); viruses lack these targets and reproduce inside human cells, so antibiotics cannot affect them.
(b) B1 overuse of antibiotics increases the rate at which bacteria develop and spread antibiotic resistance, through natural selection: resistant bacteria survive and reproduce, passing on the resistance gene (oe)
(b) B1 this can lead to infections that are difficult or impossible to treat with existing antibiotics, which is a serious risk to public health (oe); allow reference to the need to develop new antibiotics
(b) Answer: Overprescribing antibiotics speeds up the evolution of antibiotic-resistant bacteria (by natural selection), which can create infections that existing antibiotics can no longer treat - a serious public health risk.

Question 12

M1 number of doublings = 100 / 20 (= 5)
M1 number of cells = 400 x 2⁵ (= 400 x 32)
A1 12800 (cells) cao
Answer: 12800 cells

Question 13

(a) B1 e.g. sterilise the Petri dishes, agar and equipment (for example, using an autoclave) before use - to kill any microorganisms already present, preventing contamination of the culture (oe; accept any one valid technique with a correct purpose)
(a) B1 e.g. flame the neck of the bottle containing the bacterial culture (and the inoculating loop) immediately before and after use - to kill microorganisms in the air that could fall in and contaminate the culture, or that could escape (oe; accept any one different valid technique with a correct purpose)
(a) Answer: Any two of: sterilising equipment/agar before use; flaming the culture bottle neck and inoculating loop; working near a Bunsen flame; taping (not sealing) the lid - each to prevent unwanted microorganisms contaminating or escaping the culture.
(b) B1 37 C is the temperature at which many pathogens that could harm humans grow best/fastest (oe)
(b) B1 incubating at a lower temperature (25 C or below) reduces the risk of culturing/growing such pathogens, while still allowing the (harmless) bacterium used in this investigation to grow (oe)
(b) Answer: Incubating below 25 C avoids growing conditions that favour pathogens that could infect humans (which grow best near body temperature, 37 C), keeping the investigation safer while still allowing the test bacterium to grow.
(c) M1 area = π x r²
(c) M1 area = π x 6² (= π x 36)
(c) A1 113 mm² (awrt 113 mm²) cao
(c) Answer: 113 mm²
(d) B1 antibiotic X produced a larger zone of inhibition (113 mm², allow ft from the candidate's answer to (c)) than antibiotic Y (78.5 mm²) (oe; must show or state a clear numerical comparison)
(d) B1 a larger zone of inhibition means the bacterium is more strongly inhibited by / more sensitive to that antibiotic, so antibiotic X is more effective against this bacterium than antibiotic Y (oe)
(d) Answer: Antibiotic X (zone area 113 mm²) is more effective than antibiotic Y (zone area 78.5 mm²), because a larger zone of inhibition shows the bacterium is more strongly inhibited by antibiotic X.
(e) B1 valid improvement, e.g. test each antibiotic against more than one species/strain of bacterium (oe; accept: repeat the investigation several times for each antibiotic and calculate a mean zone area)
(e) B1 reason linked to the chosen improvement, e.g. this shows whether the pattern (X more effective than Y) applies generally, rather than being specific to just one type of bacterium (oe; if repeats chosen: reduces the effect of anomalous results/random error on the mean)
(e) B1 further valid related point, e.g. testing a wider range of antibiotic concentrations on the discs would show whether the difference depends on dose, not just the antibiotic used (oe)
(e) B1 correctly links the suggested improvement to increased confidence in the conclusion (e.g. explicitly states that this would make it more certain that antibiotic X really is more effective, rather than the difference being due to chance or to the specific bacterium tested) (oe)
(e) Answer: Test each antibiotic against more than one species/strain of bacterium (or repeat the investigation and calculate a mean zone area for each antibiotic); this shows whether antibiotic X really is more effective in general, increasing confidence that the difference is real rather than due to chance or to the one bacterium tested.

Question 14

B1 preclinical testing is carried out on cells and tissues in the laboratory, to test for toxicity and efficacy (oe)
B1 preclinical testing is then carried out on live animals, to test for toxicity, an appropriate dosage, and efficacy in a whole living organism (oe)
B1 if preclinical testing is successful, clinical trials on humans can begin, starting with a small number of healthy volunteers given a very low dose, to test for harmful side effects (oe)
B1 if considered safe, trials continue on patients who have the illness, using a range of doses, to find the optimum dose that is most effective with the fewest side effects (oe)
B1 the drug and trial results are peer reviewed by other scientists, and the drug must pass regulatory approval, before doctors can prescribe it (oe)
Answer: Preclinical testing on cells/tissues, then live animals, checks toxicity, dosage and efficacy; clinical trials on healthy volunteers at a low dose test safety, then patients are tested across a range of doses to find the optimum dose; results are peer reviewed and approved before the drug can be prescribed.

Question 15

B1 a placebo is a substance that looks/tastes identical to the drug being tested but contains no active ingredient (oe)
B1 comparing patients given the drug with patients given the placebo allows researchers to see whether the drug itself is responsible for any improvement, rather than the placebo effect or patients simply expecting to feel better (oe)
B1 in a double-blind trial, neither the patient nor the doctor/researcher assessing them knows who has received the drug or the placebo until the trial ends (oe)
B1 this reduces bias, because the doctor's or patient's expectations cannot influence how symptoms are reported or assessed (oe)
Answer: A placebo (identical in appearance but with no active ingredient) lets researchers separate the drug's real effect from the placebo effect; carrying out the trial double-blind, so neither patient nor assessor knows who received the drug, prevents expectation or bias from affecting the results.

Question 16

Level 1 (1-2): Basic, isolated statement(s) about testing a drug, for example a simple reference to preclinical or clinical testing. Little or no evaluation of why the process is needed. The answer may lack scientific detail or structure.
Level 2 (3-4): Clear description of most of the main stages of drug testing (preclinical and clinical), with some correct reference to features such as placebo use or double-blind design. Some attempt to evaluate why stages are necessary, though the reasoning may be incomplete or not fully linked together.
Level 3 (5-6): A detailed, logically structured description of the full testing and trialling process, from preclinical testing through to clinical trials, correctly referencing placebo use and double-blind design. A well-reasoned evaluation is given, clearly weighing the need for patient safety and reliable results against the time and cost of bringing a new drug to patients.
Indicative content:
- Preclinical testing is carried out on cells and tissues in the laboratory, to check for toxicity before any human exposure.
- Preclinical testing is then carried out on live animals, to test for toxicity, an appropriate dosage range, and efficacy in a whole organism.
- Clinical trials begin with a small number of healthy human volunteers, given a very low dose, to check the drug does not cause harmful side effects.
- If safe, trials continue on patients with the condition, using a range of doses, to find the optimum dose that gives the greatest benefit with the fewest side effects.
- A placebo may be given to a control group so that the drug's real effect can be separated from the placebo effect or natural recovery.
- Trials are often double-blind, so neither the patient nor the doctor/researcher knows who has received the drug or placebo, reducing bias in the results.
- Large-scale trials involving many patients help to identify rare side effects and confirm the drug works across different types of patient.
- Volunteers and patients must give informed consent and can withdraw at any time, which protects patient welfare during testing.
- Results are peer reviewed by other scientists, and the drug must pass regulatory approval, before doctors can prescribe it.
- The lengthy, multi-stage process balances patient safety and reliable evidence of effectiveness against the delay and cost of bringing a new painkiller to patients who need it.

Question 17

B1 a mouse (or other suitable animal) is exposed to the chosen antigen, which stimulates its lymphocytes to produce the specific antibody needed (oe)
B1 lymphocytes that produce this antibody are collected/extracted from the animal (oe)
B1 these lymphocytes are fused with a tumour (myeloma) cell to form a hybridoma cell (oe)
B1 the hybridoma cell combines the ability to divide/proliferate indefinitely (like a tumour cell) with the ability to produce the specific antibody (like the lymphocyte) (oe)
B1 hybridoma cells are cloned and cultured/grown in large quantities to produce a large amount of identical (monoclonal) antibody (oe)
Answer: A mouse is exposed to the chosen antigen so its lymphocytes make the matching antibody; these lymphocytes are fused with a myeloma (tumour) cell to form a hybridoma cell, which both divides indefinitely and produces the antibody; hybridoma cells are then cloned and cultured to produce large quantities of identical, monoclonal antibody.

Question 18

(a) B1 pregnancy testing - the antibody used binds specifically to hCG (a hormone found in the urine of pregnant women), producing a visible colour change/line if hCG is present (oe)
(a) B1 cancer treatment/diagnosis - antibodies can be produced that bind specifically to antigens found only on cancer cells; they can carry a toxic drug, radioactive substance, or marker directly to the cancer cell without affecting normal healthy cells (oe)
(a) B1 a further valid use, e.g. in research/laboratory diagnosis, to measure or detect the amount of a specific substance (such as a hormone or a pathogen's antigen) in a blood or other sample (oe); accept any two of these three uses, credited once each, up to 3 marks
(a) Answer: Any two of: pregnancy testing (antibody binds specifically to hCG); cancer diagnosis/treatment (antibody binds only to cancer-cell antigens, allowing targeted drug/radioactive delivery); laboratory diagnosis/research (antibody binds specifically to the substance being measured/detected). In each case, specificity for one antigen means only the target substance/cell is detected or affected.
(b) B1 identifies a valid limitation, e.g. monoclonal antibodies (originally produced using mouse cells) can trigger an immune/allergic reaction in the patient, because the patient's immune system recognises them as foreign (oe; accept other valid limitations, e.g. high cost/time of production)
(b) B1 expands with a linked evaluative consequence, e.g. this can cause side effects such as fever, can limit the dose that can safely be given, or requires the antibody to be 'humanised', increasing production cost and time (oe)
(b) Answer: Monoclonal antibodies can be recognised as foreign by the patient's immune system (as they are often produced using mouse cells), triggering side effects or an allergic reaction; this can limit the safe dose or require costly, time-consuming 'humanising' of the antibody before use.

Human Defences, Vaccination and Drug Development - Worksheets, Questions and Revision