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B5 · HealthAQA GCSE Biology · 8461 (Triple)

Communicable Diseases & Defences

Pathogens (bacteria, viruses, fungi, protists), transmission routes, physical and chemical barriers, white blood cells. Paper 1.

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CognitoCommunicable diseases and pathogens
CognitoThe immune system
Key facts & methods

Types of pathogen

  • Bacteria: single-celled prokaryotes. Reproduce rapidly inside body. Produce toxins that damage cells. Treated with antibiotics.
  • Viruses: not cells. Reproduce inside host cells, destroying them. Not treated by antibiotics. Antiviral drugs available for some.
  • Fungi: e.g. athlete's foot, rose black spot. Produce spores. Antifungal treatments.
  • Protists: single-celled eukaryotes. E.g. malaria (Plasmodium), spread by mosquito vectors.
  • Key diseases: measles (virus), HIV (virus), salmonella (bacteria), gonorrhoea (bacteria), malaria (protist), rose black spot (fungus).

Transmission routes

  • Direct contact: touching infected person/surface (e.g. athlete's foot).
  • Droplet infection: airborne from coughs/sneezes (e.g. influenza, measles, TB).
  • Sexual contact: HIV, gonorrhoea.
  • Water/food: cholera (contaminated water), salmonella (contaminated food).
  • Vectors: organisms that carry pathogens without being harmed. Mosquito → malaria, Aphid → TMV in plants.

Physical and chemical defences

  • Skin: physical barrier — prevents entry of pathogens.
  • Nose hairs and mucus: trap pathogens before they enter lungs.
  • Cilia: move mucus (with trapped pathogens) away from lungs.
  • Stomach acid: kills most pathogens in food/drink (pH 2).
  • Tears: contain lysozyme enzyme that destroys bacteria.

White blood cells (immune response)

  • Phagocytes: engulf and digest pathogens (phagocytosis). Non-specific defence.
  • Lymphocytes: produce antibodies — proteins that bind to specific antigens on pathogens.
  • Antibodies cause agglutination (clumping), neutralisation or trigger further immune responses.
  • Memory cells: remain after infection. Allow faster, stronger response if same pathogen encountered again → immunity.
  • Antitoxins: neutralise toxins produced by bacteria.
Exam questions — 5 questions · 11 marks · AQA 8461 style
Show all reasoning — the AI marks against the AQA mark scheme. Partial credit for correct biology even if wording differs.
1 markPathogen typeAQA 8461 style

Malaria is caused by which type of pathogen?

A Virus
B Bacteria
C Fungus
D Protist
1 markAntibioticsAQA 8461 style

Why are antibiotics ineffective against viral infections?

A Viruses are too small for antibiotics to work on
B Antibiotics work on bacterial cell processes (e.g. cell wall synthesis) which viruses do not have
C Antibiotics are always destroyed by the immune system
D Viruses are protected by the host cell
3 marksPhysical defencesAQA 8461 P1 style

Describe THREE ways the human body prevents pathogens from entering or surviving inside it, before the immune system responds. (3 marks)

Hint: Think about barriers that stop entry (skin, mucus/cilia) and defences that kill pathogens that do get in (stomach acid, lysozyme).
+30 XP
4 marksImmune responseAQA 8461 style

Explain how lymphocytes protect the body against a specific pathogen, and why a second infection with the same pathogen produces a faster response. (4 marks)

Hint: Cover: recognition → antibody production → action of antibodies → memory cells → faster secondary response.
+40 XP
1 markMemory cellsAQA 8461 style

Why do memory cells allow a faster immune response to a second infection?

A They produce antitoxins rather than antibodies
B They are already programmed to produce the specific antibody and are present in large numbers, ready to divide rapidly
C They destroy the pathogen by phagocytosis before antibodies are needed
D They prevent the pathogen from reproducing inside cells

Module complete! 🎉

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