AQA GCSE Biology coverage

Infection and response

Section 4.3
13 spec leafs

Notes and three levels of exam-style practice for each registered specification leaf in this section.

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4.3.1.1

Communicable (infectious) diseases

  • Pathogens are microorganisms that cause infectious disease; they may be viruses, bacteria, protists or fungi and may infect animals or plants.
  • Pathogens can spread by direct contact, through water or through the air, so prevention must interrupt the relevant route of transmission.
  • Bacteria and viruses may reproduce rapidly inside the body: bacteria may release toxins that damage tissues, whereas viruses reproduce inside cells and damage those cells.
  • A common error is to suggest one control for every disease; effective controls depend on whether transmission is by contact, contaminated water, airborne droplets or another route.

Tier 1 · Easy

2 marks
ORIGINAL

Define a pathogen and name one group of pathogen.

Tier 2 · Standard

4 marks
ORIGINAL

Compare how bacteria and viruses can make a person ill after entering the body.

Tier 3 · Hard

6 marks
ORIGINAL

A disease spreads when infected people cough near others and when unwashed hands touch shared surfaces. Explain both routes of transmission and suggest a suitable way to reduce each route.

4.3.1.2

Viral diseases

  • Measles causes fever and a red skin rash, can be fatal if complications arise, and spreads when droplets from coughs or sneezes are inhaled; vaccination reduces risk.
  • HIV may first cause a flu-like illness and, unless controlled by antiretroviral drugs, attacks immune cells until late-stage infection or AIDS leaves the body unable to deal with other infections or cancers.
  • HIV spreads through sexual contact or exchange of body fluids such as blood, whereas tobacco mosaic virus infects plants and produces a mosaic pattern of leaf discolouration.
  • Tobacco mosaic virus reduces photosynthesis and therefore plant growth; a common error is to describe the mosaic pattern as merely cosmetic rather than linking it to reduced photosynthesis.

Tier 1 · Easy

2 marks
ORIGINAL

Name the viral disease associated with each sign: a red skin rash in a child, and a mosaic pattern on plant leaves.

Tier 2 · Standard

3 marks
ORIGINAL

Explain why a tomato plant infected with tobacco mosaic virus may grow less than an uninfected plant.

Tier 3 · Hard

6 marks
ORIGINAL

Compare measles and HIV in terms of transmission, effects on the body and one way each disease can be controlled.

4.3.1.3

Bacterial diseases

  • Salmonella food poisoning is caused by bacteria ingested in contaminated food or food prepared in unhygienic conditions.
  • Salmonella bacteria and their toxins can cause fever, abdominal cramps, vomiting and diarrhoea; UK poultry are vaccinated to help control its spread.
  • Gonorrhoea is a bacterial sexually transmitted disease that may cause a thick yellow or green discharge and pain when urinating, and it spreads by sexual contact.
  • Gonorrhoea can be controlled with suitable antibiotics and barrier contraception such as condoms, but many strains are resistant to penicillin, so it is wrong to assume that any antibiotic will cure it.

Tier 1 · Easy

2 marks
ORIGINAL

State one symptom of Salmonella food poisoning and one symptom of gonorrhoea.

Tier 2 · Standard

4 marks
ORIGINAL

Explain how vaccinating poultry and hygienic food preparation can reduce the spread of Salmonella to people.

Tier 3 · Hard

5 marks
ORIGINAL

A patient with gonorrhoea is infected by a strain resistant to penicillin. Explain why penicillin may fail and how treatment plus barrier contraception can reduce disease and transmission.

4.3.1.4

Fungal diseases

  • Rose black spot is a fungal disease in which purple or black spots develop on leaves, which may then turn yellow and drop early.
  • Loss and damage of leaves reduce photosynthesis, so the infected rose has less material available for growth.
  • Rose black spot spreads through the environment in water or by wind.
  • Fungicides and removing and destroying affected leaves can control rose black spot; simply removing leaves without destroying them may leave fungal material able to spread.

Tier 1 · Easy

2 marks
ORIGINAL

Name the pathogen group that causes rose black spot and state one visible symptom.

Tier 2 · Standard

3 marks
ORIGINAL

Explain why rose black spot can reduce the growth of an infected plant.

Tier 3 · Hard

5 marks
ORIGINAL

A gardener finds rose black spot on several plants during wet, windy weather. Explain why the disease may spread quickly and propose a control programme.

4.3.1.5

Protist diseases

  • Malaria is caused by protist pathogens and produces recurrent episodes of fever; the disease can be fatal.
  • The malarial protist has a life cycle that includes a mosquito, which acts as a vector carrying the pathogen between hosts.
  • Mosquito nets reduce transmission by preventing infected mosquitos from biting people.
  • Preventing mosquitos from breeding reduces the vector population; a common error is to call the mosquito the pathogen rather than the vector.

Tier 1 · Easy

2 marks
ORIGINAL

State the type of pathogen that causes malaria and name its vector.

Tier 2 · Standard

3 marks
ORIGINAL

Explain how sleeping under mosquito nets can reduce the spread of malaria.

Tier 3 · Hard

5 marks
ORIGINAL

A region gives families mosquito nets and removes pools of standing water. Explain why the combined strategy should control malaria better than either action alone.

4.3.1.6

Human defence systems

  • The skin forms a non-specific physical barrier that reduces entry of pathogens, while the nose traps particles and microorganisms before they travel further into the respiratory system.
  • The trachea and bronchi produce mucus that traps pathogens, and cilia move the mucus towards the throat so it can be swallowed.
  • Hydrochloric acid in the stomach kills many pathogens that are swallowed, providing another non-specific defence.
  • If pathogens enter the body, white blood cells defend it by phagocytosis, by producing specific antibodies and by producing antitoxins that counteract bacterial toxins.

Tier 1 · Easy

2 marks
ORIGINAL

State two ways white blood cells defend the body against pathogens.

Tier 2 · Standard

4 marks
ORIGINAL

Explain how the nose, trachea and bronchi help prevent airborne pathogens from reaching the lungs.

Tier 3 · Hard

6 marks
ORIGINAL

A bacterium enters through a cut and releases a toxin. Explain how the body's defences normally prevent entry and how white blood cells respond once the skin barrier has been crossed.

4.3.1.7

Vaccination

  • Vaccination introduces a small quantity of a dead or inactive form of a pathogen to stimulate white blood cells to produce antibodies without causing the full disease.
  • If the same pathogen enters later, white blood cells respond rapidly and produce the correct antibodies, preventing illness.
  • Immunising a large proportion of a population reduces transmission because a pathogen has fewer susceptible hosts to infect.
  • A vaccine response is specific to the pathogen's antigens, so it is a misconception that one vaccination gives protection against every infectious disease.

Tier 1 · Easy

2 marks
ORIGINAL

State what is introduced during vaccination and which response it stimulates.

Tier 2 · Standard

4 marks
ORIGINAL

Explain why a vaccinated person usually responds more effectively when exposed later to the same pathogen.

Tier 3 · Hard

6 marks
ORIGINAL

Evaluate a programme intended to vaccinate a large proportion of the population against a serious communicable disease.

4.3.1.8

Antibiotics and painkillers

  • Antibiotics such as penicillin help cure bacterial disease by killing infective bacteria inside the body, and specific bacteria must be treated with an effective specific antibiotic.
  • Antibiotics have greatly reduced deaths from bacterial infectious diseases, but antibiotic-resistant bacterial strains are an increasing concern.
  • Antibiotics do not kill viruses, and it is difficult to develop drugs that kill viruses without also damaging the body's tissues because viruses reproduce inside cells.
  • Painkillers and other symptom-relieving medicines may make a patient feel better but do not kill the pathogen, so symptom relief is not the same as curing the infection.

Tier 1 · Easy

2 marks
ORIGINAL

State the difference between the action of an antibiotic and the action of a painkiller during an infectious disease.

Tier 2 · Standard

4 marks
ORIGINAL

A patient has a viral infection and asks for an antibiotic and a painkiller. Explain what each medicine could and could not do.

Tier 3 · Hard

5 marks
ORIGINAL

Explain why identifying whether an infection is bacterial or viral matters before treatment, and why a bacterial infection may still require a carefully chosen antibiotic.

4.3.1.9

Discovery and development of drugs

  • Traditional medicines include digitalis from foxgloves and aspirin from willow, while Fleming discovered penicillin from Penicillium mould; most modern drugs are synthesised, although their starting chemicals may come from plants.
  • Potential drugs are tested for toxicity, efficacy and dose before use, beginning with preclinical laboratory tests on cells, tissues and live animals.
  • Clinical trials use healthy volunteers and patients, begin with very low doses, and continue to find the optimum dose only if the drug is found to be safe.
  • Double-blind trials compare a drug with a placebo while reducing expectation and observer bias, and results are scrutinised through peer review; a common error is to treat early safety testing as proof that a drug is effective.

Tier 1 · Easy

2 marks
ORIGINAL

Name the natural source associated with aspirin and with penicillin.

Tier 2 · Standard

4 marks
ORIGINAL

Describe how a potential new medicine moves from preclinical testing into clinical trials.

Tier 3 · Hard

6 marks
ORIGINAL

Explain why a clinical trial may be double blind and include a placebo group, and why its results should be peer reviewed before the drug is widely used.

4.3.2.1

Producing monoclonal antibodies (biology only) (HT only)

  • Higher tier: in separate biology, monoclonal antibodies are produced by a single clone of cells and are specific to one binding site on one protein antigen.
  • Higher tier: mouse lymphocytes are stimulated to produce a particular antibody and then combined with tumour cells to form hybridoma cells.
  • Higher tier: a hybridoma combines the lymphocyte's ability to make the antibody with the tumour cell's ability to divide repeatedly.
  • Higher tier: single hybridoma cells are cloned so all the cells make the same antibody, which is then collected and purified; cloning a mixed population would not guarantee one monoclonal antibody.

Tier 1 · Easy

2 marks
ORIGINAL

Higher tier: state what makes an antibody monoclonal and describe its antigen specificity.

Tier 2 · Standard

4 marks
ORIGINAL

Higher tier: describe how lymphocytes and tumour cells are used to produce a large quantity of one monoclonal antibody.

Tier 3 · Hard

6 marks
ORIGINAL

Higher tier: explain why neither a normal antibody-producing lymphocyte nor a tumour cell alone is ideal for mass production, and why a single hybridoma is cloned before the antibody is purified.

4.3.2.2

Uses of monoclonal antibodies (biology only) (HT only)

  • Higher tier: in separate biology, monoclonal antibodies can be used in diagnostic tests such as pregnancy tests and in laboratories to measure hormones or other blood chemicals and to detect pathogens.
  • Higher tier: a fluorescent dye attached to a monoclonal antibody allows researchers to locate a specific molecule in a cell or tissue when the antibody binds to it.
  • Higher tier: a monoclonal antibody can carry a radioactive substance, toxic drug or cell-division inhibitor to cancer cells by binding to their specific antigens while limiting harm to other cells.
  • Higher tier: monoclonal antibodies have produced more side effects than expected and are not as widely used as first hoped, so their targeting benefit must be evaluated against possible harms.

Tier 1 · Easy

2 marks
ORIGINAL

Higher tier: state two uses of monoclonal antibodies other than treating cancer.

Tier 2 · Standard

4 marks
ORIGINAL

Higher tier: explain how a fluorescent monoclonal antibody can help a researcher locate a particular protein in a tissue sample.

Tier 3 · Hard

6 marks
ORIGINAL

Higher tier: a cancer treatment attaches a toxic drug to a monoclonal antibody. Explain how the treatment works and evaluate one advantage and one limitation.

4.3.3.1

Detection and identification of plant diseases (biology only)

  • Higher tier: in separate biology, plant disease may be detected from stunted growth, leaf spots, decay, growths, malformed stems or leaves, discolouration or the presence of pests.
  • Higher tier: an affected plant can be identified using a gardening manual or website, by laboratory identification of the pathogen, or with a testing kit containing monoclonal antibodies.
  • In separate biology, plant problems may be caused by viral, bacterial or fungal pathogens or by insects; required examples are tobacco mosaic virus, rose black spot and aphids.
  • Nitrate deficiency causes stunted growth because nitrate ions are needed for protein synthesis, whereas magnesium deficiency causes chlorosis because magnesium ions are needed to make chlorophyll.

Tier 1 · Easy

2 marks
ORIGINAL

Name the ion deficiency that causes stunted growth and the ion deficiency that causes chlorosis.

Tier 2 · Standard

3 marks
ORIGINAL

Higher tier: a plant has malformed, discoloured leaves. Describe three ways a grower could identify the cause rather than relying on the symptoms alone.

Tier 3 · Hard

6 marks
ORIGINAL

Higher tier: a crop has patches of discoloured leaves, some visible aphids and reduced growth. Explain why the symptoms alone do not prove one cause and outline how the grower could distinguish infection, insect damage and ion deficiency.

4.3.3.2

Plant defence responses (biology only)

  • In separate biology, physical defences against microorganisms include cellulose cell walls, a tough waxy cuticle on leaves and layers of dead cells around stems that can fall off.
  • Plants may produce antibacterial chemicals against microorganisms and poisons that deter herbivores as chemical defences.
  • Mechanical adaptations include thorns and hairs that deter animals, leaves that droop or curl when touched, and mimicry that tricks animals.
  • A common error is to describe every defence as physical; AQA distinguishes physical barriers, defensive chemicals and mechanical adaptations.

Tier 1 · Easy

2 marks
ORIGINAL

State one physical and one chemical plant defence response.

Tier 2 · Standard

4 marks
ORIGINAL

Explain how a tough waxy cuticle and layers of dead cells around a stem defend a plant from microorganisms.

Tier 3 · Hard

6 marks
ORIGINAL

A plant has a waxy leaf surface, produces an antibacterial chemical, grows hairs and curls its leaves when touched. Classify each response and explain how the combination protects the plant.