AQA GCSE Biology 8461: Infection and response – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover section 4.3 Infection and response (4.3.1.1 to 4.3.3.2) of the AQA GCSE Biology (8461) specification, for teaching from September 2016 and exams from 2018 onwards. The topic is assessed on Paper 1, which is set at Foundation and Higher Tier. Question 10 and part 11(a) test content the specification marks (HT only), and are labelled Higher tier only. Everything else is for both tiers.

Learn the content first in the Infection and response study guide and the revision notes. The course hub is AQA GCSE Biology, and the printable checklist lists every point.

Questions

1.

(a) State what is meant by a pathogen. [1] (b) Give the type of pathogen that causes each of these diseases: gonorrhoea, malaria, rose black spot, tobacco mosaic virus. [2]

2. Explain how bacteria and viruses cause illness once they are inside the body. [4]

3. Describe how the trachea and bronchi, and the stomach, defend the body against pathogens. [4]

4. A country started vaccinating young children against measles. The number of measles cases each year fell from 2400 to 180.

(a) Calculate the percentage decrease in measles cases. [2] (b) Explain how the measles vaccine stops a vaccinated child becoming ill if they later meet the measles virus. [4] (c) Some years later, fewer parents had their children vaccinated and cases rose again. Explain why cases rose, even among some people who could not be vaccinated. [2]

5. Salmonella food poisoning is caused by bacteria.

(a) Describe how Salmonella bacteria are spread to people. [2] (b) Explain why poultry in the UK are vaccinated against Salmonella. [2] (c) Give two symptoms of Salmonella food poisoning. [2]

6. A gardener checks a rose bed. Of 180 leaves, 27 have purple or black spots.

(a) Calculate the percentage of leaves with spots. [2] (b) Explain why rose black spot reduces the growth of the plants. [2] (c) Describe two ways the gardener could treat the disease. [2]

7.

(a) Give two ways HIV is spread. [2] (b) Explain why a person with late stage HIV infection (AIDS) may die from infections that a healthy person would survive. [3]

8. A company tests a new drug for a skin condition. In a clinical trial, 400 patients received the drug and 400 received a placebo. After 12 weeks, 312 patients in the drug group and 188 in the placebo group had improved.

(a) Calculate the percentage of patients who improved in each group. [2] (b) Explain why some patients were given a placebo. [2] (c) Before this trial, the drug was given at very low doses to healthy volunteers. Explain why. [2] (d) Describe the testing that is done before any clinical trial. [2]

9. A patient with flu asks a doctor for antibiotics.

(a) Explain why the doctor refuses. [2] (b) The doctor suggests a painkiller. Explain why this helps the patient but does not cure the flu. [2] (c) Suggest why it is difficult to develop drugs that kill viruses. [1] (d) Gonorrhoea is caused by a bacterium. Explain why resistant strains of gonorrhoea are a concern, and give one way to reduce its spread without using antibiotics. [2]

10. (Higher tier only)

(a) Describe how monoclonal antibodies are produced. [4] (b) A pregnancy test strip contains mobile monoclonal antibodies attached to blue beads. These antibodies bind only to a hormone found in the urine of pregnant women. Further along the strip is a line of fixed antibodies that bind only to the hormone–antibody complex. Explain why a blue line appears on the strip only if the woman is pregnant. [3] (c) Give one reason monoclonal antibodies are not yet as widely used as was first hoped. [1]

11. A tomato grower finds that some plants are stunted and have leaves with a mottled pattern of discolouration. Small insects are feeding on the stems.

(a) (Higher tier only) Describe two ways the grower could identify the cause. [2] (b) Stunted growth can also be caused by an ion deficiency. Name the ion and explain why its deficiency causes stunted growth. [2] (c) Describe two physical defences that help plants resist invasion by microorganisms. [2] (d) Some plants produce poisons. Explain how this defends the plant. [1]

12. Measles and malaria are both serious diseases that can be fatal. Compare how the spread of each disease is controlled, and explain why each method works. [6]

Answers

1. (a) A microorganism that causes infectious disease [1] (b) Gonorrhoea: bacterium and malaria: protist [1]; rose black spot: fungus and TMV: virus [1] Examiner insight: In (b) each mark usually needs a pair correct; “germ” or “microbe” is not accepted as a pathogen type.

2. Bacteria reproduce rapidly inside the body [1]; bacteria may produce toxins [1]; toxins damage tissues and make you feel ill [1]; viruses live and reproduce inside cells, causing cell damage [1] Examiner insight: Two separate processes are being tested; an answer about toxins only, however detailed, is capped at the bacteria marks.

3. Trachea and bronchi make mucus that traps pathogens [1]; cilia move the mucus up and away from the lungs [1]; the stomach produces hydrochloric acid [1]; which kills pathogens in food and drink [1] Examiner insight: Cilia “trap” pathogens is a common wrong statement; mucus traps, cilia move the mucus.

4. (a) (2400 − 180) ÷ 2400 × 100 [1] = 92.5% [1] (b) The vaccine contains a small quantity of dead or inactive measles virus [1]; this stimulates white blood cells to produce antibodies [1]; if the live virus enters later, white blood cells respond quickly [1]; and produce the correct antibodies, destroying the virus before illness develops [1] (c) A smaller proportion of the population is immune, so the virus has more hosts to spread between [1]; people who cannot be vaccinated were protected only because those around them were immune, so they are now more likely to meet the virus [1] Examiner insight: In (b), “the vaccine contains antibodies” contradicts the mark scheme and loses the first marking point; the vaccine contains the pathogen, not the antibodies.

5. (a) Bacteria are ingested in food [1]; or in food prepared in unhygienic conditions [1] (b) Vaccinated poultry do not become infected [1]; so the bacteria are not passed on in chicken or eggs eaten by people [1] (c) Any two from fever, abdominal cramps, vomiting, diarrhoea [1] [1] Examiner insight: In (b) you must link the vaccination of the birds to reduced spread to humans; “to keep the chickens healthy” alone gets one mark at most.

6. (a) 27 ÷ 180 × 100 [1] = 15% [1] (b) Spots reduce the green area of the leaf, and leaves drop early [1]; so less photosynthesis takes place and less glucose is available for growth [1] (c) Spray with a fungicide [1]; remove and destroy the affected leaves [1] Examiner insight: “Use antibiotics” or “use pesticide” in (c) gains nothing, because black spot is a fungus.

7. (a) Sexual contact [1]; exchange of body fluids such as blood, for example drug users sharing needles [1] (b) HIV attacks the body’s immune cells [1]; the immune system becomes so badly damaged [1]; that it can no longer deal with other infections or cancers [1] Examiner insight: “HIV kills you” earns no credit; the marks are for the chain from immune cell damage to failure to fight other infections.

8. (a) Drug: 312 ÷ 400 × 100 = 78% [1]; placebo: 188 ÷ 400 × 100 = 47% [1] (b) Patients may improve just because they believe they are being treated [1]; comparing with the placebo group shows whether the drug itself has an effect [1] (c) To check whether the drug is safe, or toxic [1]; before larger doses are given to patients [1] (d) Preclinical testing in a laboratory [1]; using cells, tissues and live animals [1] Examiner insight: Each calculation in (a) is marked separately, so show both divisions; a single “31% more” with no working scores nothing here.

9. (a) Flu is caused by a virus [1]; antibiotics cannot kill viral pathogens [1] (b) A painkiller treats the symptoms, such as aches [1]; but it does not kill the pathogen [1] (c) Viruses live inside cells, so a drug that kills them may also damage the body’s tissues [1] (d) Resistant strains are no longer killed by the antibiotic, so infections are harder to treat [1]; use a barrier method of contraception such as a condom [1] Examiner insight: In (d), saying “the person becomes resistant” is marked wrong; resistance belongs to the bacteria.

10. (a) Mouse lymphocytes are stimulated to make a particular antibody [1]; lymphocytes are combined with a tumour cell to make a hybridoma cell [1]; a single hybridoma cell is cloned, giving identical cells that divide and all make the same antibody [1]; the antibody is collected and purified [1] (b) If the hormone is present, it binds to the mobile antibodies on the blue beads [1]; the hormone–antibody complex moves along the strip and binds to the fixed antibodies [1]; so the blue beads collect at the line; with no hormone, the mobile antibodies are not bound and are not held there [1] (c) They cause more side effects than expected [1] Examiner insight: In (b) the marks depend on using the information given; answers that name the hormone but ignore the fixed antibodies rarely get beyond one mark.

11. (a) Look up the signs in a gardening manual or website [1]; take an infected plant to a laboratory to identify the pathogen, or use a testing kit containing monoclonal antibodies [1] (b) Nitrate ions [1]; are needed for protein synthesis, and therefore growth [1] (c) Cellulose cell walls [1]; a tough waxy cuticle on leaves, or layers of dead cells (bark) that fall off [1] (d) The poison deters herbivores, so fewer animals eat the plant [1] Examiner insight: In (b), naming magnesium is wrong; magnesium deficiency causes chlorosis, not stunted growth.

12. Measles is spread by inhaling droplets from sneezes and coughs [1]; it is controlled by vaccinating young children [1]; so they become immune and the virus has fewer hosts to spread to [1]; malaria is caused by a protist carried by mosquitoes, the vector [1]; spread is controlled by stopping mosquitoes breeding [1]; and by using mosquito nets to avoid being bitten, so the protist cannot be passed on [1] Examiner insight: A “compare” answer needs both diseases covered; six points about measles alone would be capped, because the method for each disease must be linked to how it is spread.

Where marks are usually lost

• Writing that a vaccine contains antibodies or kills the pathogen directly.
• Stating that antibiotics treat viral diseases such as measles, flu or HIV.
• Describing resistance as a property of the patient, not the bacteria.
• Confusing antibodies (bind to pathogens) with antitoxins (neutralise toxins).
• Giving the wrong pathogen type for a named disease, especially malaria or black spot.
• Leaving out “less photosynthesis, so less glucose for growth” when explaining plant disease damage.
• Dividing by the new value instead of the original value in a percentage decrease.
• Omitting the purpose of a placebo, or muddling preclinical testing (cells, tissues, animals) with clinical trials (volunteers and patients).
• (Higher tier only) Leaving the hybridoma cell or single-cell cloning out of monoclonal antibody production.

Next steps

• Infection and response revision notes
• Infection and response study guide
• AQA GCSE Biology course hub
• Printable AQA GCSE Biology checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

AQA GCSE Biology (8461) specification, Version 1.0, for teaching from September 2016 and exams from 2018 onwards (AQA), section 4.3 Infection and response.