GCSE BIOLOGY • SPECIFICATION 1.3

Infection & Response

Aligned to AQA GCSE Biology (8461/8464). Wording consistent with AQA mark schemes.

Mastering the defense mechanisms and the development of medical treatments.

1. Pathogens and Communicable Disease

Exam Definition (Pathogen):

"Microorganisms that cause infectious (communicable) disease. They can infect plants or animals."

Pathogen TypeHow they cause illness
BacteriaReproduce rapidly inside the body. They produce toxins that damage tissues.
VirusesLive and replicate inside cells, damaging them as new virus particles are released.

Essential Disease Profiles

  • Measles (Viral): Fever and red skin rash. Spread by inhalation of droplets.
  • HIV (Viral): Damages the immune system by attacking white blood cells. Leads to AIDS.
  • Salmonella (Bacterial): Fever, cramps, vomiting caused by toxins in food.
  • Gonorrhoea (Bacterial): STD. Treated with antibiotics, but antibiotic resistance is increasing.
  • Malaria (Protist): Spread by a vector (mosquito). Causes recurrent fevers.
2. Human Defence Systems
Non-Specific Defences:
  • Skin: Physical barrier + antimicrobial secretions.
  • Nose: Hairs and mucus trap particles.
  • Trachea/Bronchi: Mucus traps pathogens; cilia move mucus up to the throat to be swallowed.
  • Stomach: Hydrochloric acid kills pathogens.
The Immune System (WBCs):
  1. Phagocytosis: Engulfing and digesting pathogens.
  2. Antibody Production: Antibodies have a specific shape that binds to one antigen only.
  3. Antitoxin Production: Neutralise toxins made by bacteria.
3. Vaccination & Herd Immunity

Mechanism of Vaccination:

  1. Introduce small quantities of dead/inactive pathogens (or antigens from them).
  2. Stimulates white blood cells to produce antibodies.
  3. If the same pathogen re-enters, WBCs respond rapidly to produce antibodies in large quantities.

Herd Immunity (The Logic Chain)

When most people are immune, fewer hosts are available so transmission is reduced, protecting those who cannot be vaccinated.

[Image of herd immunity concept]
4. Drug Discovery and Development
StageFocusPurpose
PreclinicalCells, tissues, animalsTest for toxicity and efficacy.
Phase 1Healthy volunteersCheck for side effects (safety).
Phase 2 & 3PatientsPhase 2 tests efficacy; Phase 3 finds optimum dose and compares with placebo.

Q: Explain the purpose of a "double-blind trial".

Neither the doctor nor the patient knows who has the drug or the placebo. This removes bias and prevents the placebo effect.
5. Monoclonal Antibodies (Triple Only)

The Hybridoma Process:

1. Mouse lymphocytes stimulated to make a specific antibody.
2. Combined with a tumour cell to form a hybridoma.
3. Hybridoma produces identical monoclonal antibodies.

Limitation:

Monoclonal antibodies can cause side effects in some patients, which has limited their use in clinical treatments.

Final Exam Guardrail

• Antibiotics cannot kill viruses because viruses have no cell structures (e.g. cell wall) for antibiotics to target.
• Digitalis originates from Foxgloves; Aspirin from Willow; Penicillin from Penicillium mould.
• For Vaccination marks, always mention the "rapid" production of antibodies upon re-infection.
• For Monoclonal marks, ensure you mention that the hybridoma cell can both divide and make the antibody.

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