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GCSE · Biology

B3 Infection and Response

AQA 8461/8462/8463 · Calculator allowed · about 105 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Different pathogens cause different communicable diseases. For each disease below, identify the type of pathogen that causes it.

(a)Which type of pathogen causes Salmonella food poisoning?(1)

A) Virus
B) Bacterium
C) Fungus
D) Protist

(b)Which type of pathogen causes measles?(1)

A) Virus
B) Bacterium
C) Fungus
D) Protist

(c)Which type of pathogen causes malaria?(1)

A) Virus
B) Bacterium
C) Fungus
D) Protist

(d)Which type of pathogen causes rose black spot?(1)

A) Virus
B) Bacterium
C) Fungus
D) Protist

(Total for Question 1 is 4 marks)

Communicable diseases are caused by pathogens and can spread between organisms.

(a)Define the term 'communicable disease'.(1)

(b)State two ways that pathogens can be spread between people.(2)

(Total for Question 2 is 3 marks)

Measles is a viral disease that mainly affects children in the UK, most of whom are vaccinated against it using the MMR vaccine.

(a)Name the type of pathogen that causes measles.(1)

(b)Describe two symptoms of measles.(2)

(c)Explain why most children in the UK are vaccinated against measles, even though most children who catch measles recover fully.(2)

(Total for Question 3 is 5 marks)

Salmonella and gonorrhoea are both bacterial diseases with very different methods of transmission and prevention.

(a)State how a person could become infected with Salmonella bacteria.(1)

(b)Describe two symptoms of salmonella food poisoning.(2)

(c)In the UK, poultry are routinely vaccinated against Salmonella. Explain how this reduces cases of salmonella food poisoning in humans.(2)

(d)Gonorrhoea is a sexually transmitted bacterial infection. Many strains are now resistant to the antibiotic penicillin. Suggest two ways the spread of gonorrhoea can be reduced.(2)

(Total for Question 4 is 7 marks)

Malaria is caused by a protist pathogen and is spread by a vector.

(a)Name the vector that spreads the protist pathogen that causes malaria.(1)

(b)Describe how the mosquito spreads the protist pathogen between people.(2)

(c)Suggest two methods, other than drug treatment, that could reduce the spread of malaria in an area.(2)

(Total for Question 5 is 5 marks)

A gardener in Cheshire notices a mosaic pattern of yellow and dark green patches on the leaves of her tomato plants and suspects Tobacco Mosaic Virus (TMV).

(a)State one symptom of TMV infection in plants, other than the mosaic pattern on the leaves.(1)

(b)Explain how TMV infection could reduce the yield of the gardener's tomato plants.(2)

(c)Describe how the gardener could confirm that the plants have TMV rather than a mineral deficiency.(2)

(Total for Question 6 is 5 marks)

The human body has several non-specific defence systems that act as barriers to prevent pathogens entering the body.

(a)Describe how the skin acts as a defence against pathogens.(2)

(b)Describe how the nose acts as a defence against pathogens.(2)

(c)Describe how the trachea and bronchi act as a defence against pathogens.(2)

(Total for Question 7 is 6 marks)

If a pathogen enters the body, white blood cells help to defend against it in several ways.

(a)Describe how phagocytosis destroys pathogens in the body.(2)

(b)Describe how lymphocytes destroy pathogens using antibodies.(2)

(c)Some bacteria produce toxins. Describe how white blood cells counteract this.(2)

(Total for Question 8 is 6 marks)

Explain how vaccinating a large proportion of a population against measles can protect individuals who have not been vaccinated. In your answer, refer to what happens in the body after a person is vaccinated, and how this leads to herd immunity.

(Total for Question 9 is 6 marks)

Required practical: A student investigated the effectiveness of two antibiotics, A and B, against a bacterial culture using agar plates and paper discs soaked in each antibiotic. The student measured the diameter of the clear zone (zone of inhibition) around each disc after 48 hours of incubation. The table shows the results for three repeats of Antibiotic B: Repeat 1 = 21 mm, Repeat 2 = 23 mm, Repeat 3 = 22 mm. The mean diameter of the zone of inhibition for Antibiotic A was found to be 16 mm.

(a)State three aseptic techniques the student should use when setting up this investigation, and give the purpose of each.(3)

(b)Explain why the agar plates were incubated at 25 degC rather than at 37 degC.(2)

(c)Calculate the mean diameter of the zone of inhibition for Antibiotic B.(2)

(d)Calculate the area of the zone of inhibition for Antibiotic B, using your answer to part (c). Give your answer to 3 significant figures. (area of a circle = π x r²)(3)

(e)The mean diameter of the zone of inhibition for Antibiotic A was 16 mm. Calculate the area of this zone, to 3 significant figures, and use both calculated areas to determine which antibiotic was more effective. Explain your reasoning.(3)

(f)Suggest one improvement to the method that would increase the reliability of this conclusion.(2)

(g)Explain the purpose of including a control disc, soaked in sterile water only, in this investigation.(2)

(Total for Question 10 is 17 marks)

MRSA is a strain of bacteria that is resistant to many antibiotics, including methicillin. Explain how the population of antibiotic-resistant bacteria such as MRSA can increase over time.

(Total for Question 11 is 5 marks)

New medicinal drugs must be extensively tested and trialled before they can be used.

(a)Describe how a new drug is tested before it is given to human volunteers, and explain why this stage is necessary.(3)

(b)A new drug passes preclinical testing. Explain why it is first given at a very low dose to a small number of healthy volunteers in a clinical trial.(2)

(c)In a later stage of the trial, patients are given either the new drug or a placebo, and neither the patients nor the doctors know who has received which, until the trial ends. State the name given to this type of trial.(1)

(d)Explain why a placebo is used, and why the trial is double-blind.(2)

(Total for Question 12 is 8 marks)

Monoclonal antibodies are produced using hybridoma cells. Describe how hybridoma cells are produced and used to make a monoclonal antibody.

(Total for Question 13 is 5 marks)

Monoclonal antibodies have many uses, including in pregnancy testing and cancer treatment.

(a)Describe how a home pregnancy test uses monoclonal antibodies to detect pregnancy.(3)

(b)Explain how monoclonal antibodies can be used to treat cancer with fewer side effects than conventional chemotherapy.(3)

(Total for Question 14 is 6 marks)

Plants have physical, chemical and mechanical defences against pathogens and pests. Give one example of each type of defence, and briefly explain how it helps protect the plant.

(a)Physical defence(2)

(b)Chemical defence(2)

(c)Mechanical defence(2)

(Total for Question 15 is 6 marks)

A vaccination programme against Disease X was introduced in a country. The number of new cases reported was 8400 in Year 1 (before the programme) and 1260 in Year 3 (after the programme).

(a)Calculate the percentage decrease in the number of new cases between Year 1 and Year 3.(3)

(b)Suggest one reason, other than vaccination, why the number of cases might have decreased.(1)

(Total for Question 16 is 4 marks)

A microbiologist grew a culture of bacteria in a flask. A fixed dose of antibiotic was added to the flask at time = 4 hours. The table shows the total number of bacteria and the number of antibiotic-resistant bacteria in the culture over time. Time (hours): 0, 2, 4, 6, 8, 10. Total bacteria (million per cm3): 4, 8, 16, 10, 6, 5. Resistant bacteria (million per cm3): 0.1, 0.2, 0.4, 3, 5, 4.8.

(a)Calculate the mean rate of decrease in the total bacteria population between 4 and 6 hours, in million bacteria per cm3 per hour.(2)

(b)Calculate the percentage of the total bacterial population that was antibiotic-resistant at t = 10 hours.(2)

(c)Explain the trend shown in the number of resistant bacteria after the antibiotic was added at t = 4 hours.(2)

(Total for Question 17 is 6 marks)

A new viral disease has emerged. Scientists can respond by developing either a vaccine or a monoclonal antibody based treatment. Evaluate the use of vaccination compared with monoclonal antibody treatment in controlling the spread of this viral disease in a population.

(Total for Question 18 is 6 marks)

Mark scheme · B3 Infection and Response

Question 1

(a) B1 B (bacterium)
(a) Answer: B
(b) B1 A (virus)
(b) Answer: A
(c) B1 D (protist)
(c) Answer: D
(d) B1 C (fungus)
(d) Answer: C

Question 2

(a) B1 a disease that can be spread from one organism/person to another (oe)
(a) Answer: A disease caused by a pathogen that can be passed from one organism to another.
(b) B1 any one correct method of transmission, e.g. direct contact
(b) B1 any second correct method of transmission, e.g. water, air/droplets, contaminated food, animal vectors, bodily fluids/sexual contact
(b) Answer: Any two of: direct contact; contaminated water; air/droplet infection; contaminated food; animal vectors; bodily fluids.

Question 3

(a) B1 virus
(a) Answer: Virus
(b) B1 fever
(b) B1 red skin rash (allow cough, red eyes)
(b) Answer: Fever and a red skin rash (any two accepted symptoms).
(c) B1 measles can be fatal or cause serious complications, e.g. encephalitis (swelling of the brain) (oe)
(c) B1 vaccination protects the individual and contributes to herd immunity, reducing spread to vulnerable people who cannot be vaccinated
(c) Answer: Although most children recover, measles can occasionally be fatal or cause serious complications; vaccination also reduces spread to those who cannot be vaccinated (herd immunity).

Question 4

(a) B1 eating food contaminated with the bacteria (oe)
(a) Answer: By eating food contaminated with Salmonella bacteria.
(b) B1 fever
(b) B1 abdominal cramps / vomiting / diarrhoea (any one)
(b) Answer: Any two of: fever; stomach cramps; vomiting; diarrhoea.
(c) B1 vaccination reduces the number of poultry/eggs infected with (or carrying) the bacteria
(c) B1 this reduces the chance of the bacteria being passed on to humans through contaminated poultry meat or eggs
(c) Answer: Fewer poultry carry the bacteria, so fewer contaminated eggs/meat reach humans, reducing human infection rates.
(d) B1 using a barrier method of contraception, e.g. a condom
(d) B1 treating both/all sexual partners with an appropriate antibiotic
(d) Answer: Using barrier contraception (e.g. condoms) and ensuring all sexual partners are treated with an effective antibiotic.

Question 5

(a) B1 mosquito (allow Anopheles mosquito)
(a) Answer: Mosquito
(b) B1 the mosquito feeds on (bites) an infected person, taking in the protist along with the blood
(b) B1 the mosquito then bites/feeds on an uninfected person, transferring the protist into their blood
(b) Answer: A mosquito bites an infected person and picks up the protist, then bites another person and transfers the protist to them.
(c) B1 using mosquito nets (ideally treated with insecticide) while sleeping
(c) B1 using insect repellent, spraying insecticide, or removing/treating standing water where mosquitoes breed (any one)
(c) Answer: Using insecticide-treated mosquito nets and removing standing water/using insect repellent to reduce mosquito bites.

Question 6

(a) B1 stunted growth (allow reduced yield)
(a) Answer: Stunted growth of the plant.
(b) B1 the mosaic pattern reduces the area of leaf that is green/contains chlorophyll
(b) B1 this reduces the rate of photosynthesis, so less glucose is available for growth, resulting in smaller plants/less fruit
(b) Answer: Damaged, discoloured leaf tissue photosynthesises less, so less glucose is made for growth, reducing plant size and fruit yield.
(c) B1 use a testing kit containing monoclonal antibodies that bind specifically to TMV antigens/proteins (oe)
(c) B1 or take a sample and compare the symptoms/pathogen with a reference database or send to a laboratory for analysis
(c) Answer: Use a monoclonal-antibody-based detection kit specific to TMV, or compare symptoms/sample against a reference database in a laboratory.

Question 7

(a) B1 acts as a physical barrier to pathogens
(a) B1 produces sebum, an oily antimicrobial secretion, which inhibits the growth of pathogens on the skin's surface
(a) Answer: It is a physical barrier and secretes antimicrobial sebum that inhibits pathogen growth.
(b) B1 hairs trap large particles/pathogens
(b) B1 mucus traps pathogens/particles
(b) Answer: Hairs and mucus in the nose trap pathogens and dust particles.
(c) B1 lined with mucus, which traps pathogens
(c) B1 lined with cilia, which waft/sweep the mucus (and trapped pathogens) up to the throat to be swallowed
(c) Answer: Mucus traps pathogens and cilia sweep the mucus up to the throat to be swallowed.

Question 8

(a) B1 a white blood cell (phagocyte) engulfs the pathogen
(a) B1 the pathogen is then digested/destroyed by the phagocyte
(a) Answer: A phagocyte engulfs the pathogen and digests/destroys it.
(b) B1 lymphocytes produce antibodies that are specific/complementary to antigens on the surface of the pathogen
(b) B1 antibodies bind to the antigens, leading to destruction of the pathogen or clumping so it can be more easily engulfed by phagocytes
(b) Answer: Lymphocytes make antibodies specific to the pathogen's antigens; the antibodies bind and help destroy or clump the pathogen.
(c) B1 lymphocytes produce antitoxins
(c) B1 antitoxins neutralise the toxins produced by the bacteria
(c) Answer: Lymphocytes produce antitoxins, which neutralise the bacterial toxins.

Question 9

Level 1 (1-2): Simple statements are made about vaccination or about herd immunity, with little detail and little or no linkage between ideas.
Level 2 (3-4): The process of vaccination in the body is described, with some description of herd immunity. Some logical linkage between points is shown.
Level 3 (5-6): A detailed, coherent explanation links the body's response to vaccination with herd immunity in the population, showing a clear chain of reasoning throughout.
Indicative content:
- Vaccination involves injecting a small/dead/inactive quantity of the pathogen (or its antigens)
- This stimulates white blood cells (lymphocytes) to produce antibodies specific to the antigens
- Memory lymphocytes remain in the blood after vaccination
- If the person is later exposed to the live pathogen, memory cells enable rapid production of antibodies (secondary response)
- The pathogen is destroyed before the person becomes ill, so they do not develop symptoms and cannot pass the disease on
- If a large enough proportion of the population is vaccinated, the pathogen cannot spread easily because there are fewer people it can infect
- This reduces the overall spread of the disease, protecting unvaccinated individuals (e.g. babies, those who cannot be vaccinated) - herd immunity

Question 10

(a) B1 sterilise the inoculating loop by passing it through a flame - kills unwanted microorganisms before use
(a) B1 tape the lid of the petri dish without sealing it completely - reduces contamination from airborne microorganisms while allowing some air in for aerobic respiration
(a) B1 work near a lit Bunsen burner (or use a sterile bench) - creates an updraught of air, reducing the chance of airborne microorganisms settling on the culture
(a) Answer: Flame the inoculating loop; tape (not seal) the petri dish lid; work near a lit Bunsen burner - each reduces contamination by unwanted microorganisms.
(b) B1 37 degC is close to human body temperature
(b) B1 incubating at this temperature would encourage the growth of pathogens that could be harmful to humans in a school laboratory
(b) Answer: 25 degC avoids growing microorganisms that thrive at body temperature (37 degC), which could be harmful pathogens to humans.
(c) M1 (21 + 23 + 22) / 3
(c) A1 22 (mm) cao
(c) Answer: 22 mm
(d) M1 radius = 22 / 2 = 11 (mm)
(d) M1 area = π x 11²
(d) A1 380 mm² (3 sf) ft from (c)
(d) Answer: 380 mm² (3 s.f.)
(e) M1 radius = 16 / 2 = 8 (mm); area = π x 8²
(e) A1 201 mm² (3 sf)
(e) B1 Antibiotic B is more effective, because it produced a larger zone of inhibition (area), showing it killed/inhibited bacteria over a larger area
(e) Answer: Area for A = 201 mm² (3 s.f.); Antibiotic B is more effective, as its zone of inhibition covers a larger area (380 mm² vs 201 mm²).
(f) B1 increase the number of repeats for Antibiotic A (only a mean is given, with no repeats shown)
(f) B1 this reduces the effect of anomalous results/random error, allowing a more reliable mean to be calculated
(f) Answer: Carry out more repeats for Antibiotic A, so a more reliable mean can be calculated and anomalies have less effect.
(g) B1 shows that any zone of inhibition is caused by the antibiotic and not by another factor (e.g. the paper disc or the water itself)
(g) B1 allows a valid/fair comparison to be made between the antibiotics tested
(g) Answer: It confirms that any clear zone seen is due to the antibiotic (not the disc or water), allowing a fair comparison between antibiotics.

Question 11

B1 mutations occur naturally/randomly in bacterial DNA
B1 some mutations may result in bacteria being resistant to an antibiotic
B1 when the antibiotic is used, non-resistant bacteria are killed, but resistant bacteria survive (selection pressure)
B1 surviving resistant bacteria reproduce, passing on the resistance allele/gene to their offspring
B1 over many generations, the proportion of resistant bacteria in the population increases (natural selection); overuse or incomplete courses of antibiotics increase the rate at which this happens
Answer: Indicative content - award any 5 of the marking points listed, max 5 marks.

Question 12

(a) B1 tested in the laboratory on human cells and tissues, then on live animals (preclinical testing)
(a) B1 this tests for toxicity and finds a suitable dosage before human trials
(a) B1 this protects human volunteers from unnecessary harm before any human testing takes place
(a) Answer: Drugs are first tested on cells/tissues and live animals (preclinical testing) to check for toxicity and find a safe dose, protecting future human volunteers.
(b) B1 to test for/check for any side effects or toxicity in humans
(b) B1 a low dose and small number of people minimises the risk/harm to volunteers if there is an unexpected adverse reaction
(b) Answer: A low dose in few healthy volunteers checks for side effects/toxicity while minimising risk if there is an unexpected reaction.
(c) B1 double-blind trial
(c) Answer: A double-blind trial.
(d) B1 the placebo allows a comparison to be made, so any improvement caused by the drug itself can be identified, rather than the placebo effect
(d) B1 the double-blind design prevents bias from patients' or doctors' expectations affecting the results or how they are interpreted
(d) Answer: The placebo lets researchers separate real drug effects from the placebo effect; being double-blind stops patient or doctor expectations biasing the results.

Question 13

B1 a mouse (or other animal) is injected with the chosen antigen, stimulating an immune response
B1 lymphocytes in the mouse produce the antibody that is specific/complementary to that antigen
B1 the lymphocytes are fused/combined with a tumour (myeloma) cell to produce a hybridoma cell
B1 the hybridoma cell can both divide/multiply (from the tumour cell) and produce the specific antibody (from the lymphocyte)
B1 hybridoma cells are cloned to produce many identical cells, all producing the same (monoclonal) antibody, which is then collected and purified
Answer: Indicative content - award any 5 of the marking points listed, max 5 marks.

Question 14

(a) B1 the test contains monoclonal antibodies (bound to a coloured dye) that are specific/complementary to the hormone hCG, found in the urine of pregnant women
(a) B1 if hCG is present, it binds to the antibody-dye complex, forming an antibody-antigen complex that moves along the test strip
(a) B1 this complex binds to a second set of fixed antibodies at the test window, concentrating the dye and producing a visible line/colour change
(a) Answer: Dye-linked monoclonal antibodies bind specifically to hCG in urine; this complex binds to a second fixed antibody in the test window, concentrating the dye to show a positive result.
(b) B1 monoclonal antibodies are produced that bind specifically to antigens found only on the surface of cancer cells (and not healthy cells)
(b) B1 a toxic drug or radioactive substance can be attached to the antibody, and is delivered directly/only to the cancer cells
(b) B1 healthy cells are not targeted/damaged, so there are fewer side effects than with chemotherapy, which affects healthy cells too
(b) Answer: Because the antibodies bind only to cancer-cell antigens, an attached drug/radioactive substance is delivered specifically to cancer cells, sparing healthy cells and reducing side effects compared with chemotherapy.

Question 15

(a) B1 e.g. a waxy cuticle on the leaf surface, or a cellulose cell wall
(a) B1 acts as a barrier that prevents pathogens from entering the plant tissue
(a) Answer: The waxy cuticle (or cellulose cell wall) acts as a physical barrier preventing pathogen entry.
(b) B1 e.g. production of antibacterial chemicals or poisons
(b) B1 these kill pathogens directly or deter herbivores/insects from feeding on the plant
(b) Answer: Plants produce antibacterial chemicals or poisons that kill pathogens or deter herbivores from feeding.
(c) B1 e.g. thorns, hairs, leaves that droop or curl when touched, or mimicry
(c) B1 these deter animals/insects from eating or landing on/laying eggs on the plant
(c) Answer: Thorns or hairs deter animals from eating the plant; drooping/curling leaves deter feeding insects.

Question 16

(a) M1 decrease = 8400 - 1260 = 7140
(a) M1 (7140 / 8400) x 100
(a) A1 85% cao
(a) Answer: 85% decrease
(b) B1 e.g. improved sanitation/hygiene, improved treatment or isolation of infected individuals, public health campaigns raising awareness
(b) Answer: For example, improved sanitation/hygiene or better isolation/treatment of infected individuals.

Question 17

(a) M1 (16 - 10) / 2
(a) A1 3 million per cm3 per hour cao
(a) Answer: 3 million bacteria per cm3 per hour
(b) M1 (4.8 / 5) x 100
(b) A1 96% cao
(b) Answer: 96%
(c) B1 non-resistant bacteria are killed by the antibiotic, so the total population falls after t = 4 hours
(c) B1 resistant bacteria survive and can reproduce, so they make up an increasing proportion of the (smaller) surviving population
(c) Answer: The antibiotic kills non-resistant bacteria, so resistant bacteria form an increasing share of the shrinking population as they survive and reproduce.

Question 18

Level 1 (1-2): Statements are made with limited reasoning; little or no reference to both vaccination and monoclonal antibodies.
Level 2 (3-4): Some relevant points are made about both vaccination and monoclonal antibodies, with some reasoning or justification; a partial conclusion may be given.
Level 3 (5-6): A well-reasoned, balanced evaluation is given, covering both vaccination and monoclonal antibodies, with a justified conclusion supported throughout by scientific reasoning.
Indicative content:
- Vaccination stimulates the body's own immune system to produce antibodies and memory cells, giving long-term protection
- Vaccination can be given to a large proportion of the population, reducing spread through herd immunity, so is more suitable for preventing a wider outbreak/pandemic
- Vaccination takes time (weeks) to produce full immunity and does not directly help someone who is already seriously ill
- Monoclonal antibodies can be produced to target the virus's antigens specifically and could be given as an immediate treatment to patients who are already infected
- Monoclonal antibody treatment does not rely on the patient's own immune response, so it may act faster or be more suitable for patients with a weakened immune system
- Monoclonal antibody treatment does not give long-term immunity and would need to be manufactured and administered repeatedly, which may be more costly and harder to produce at scale than a vaccine
- A balanced conclusion might use vaccination to prevent spread in the wider population, alongside monoclonal antibodies to treat those already infected

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