LEARNING OBJECTIVES
What you will be able to do
- describe transmission
- explain body defences
- compare active and passive immunity
- explain vaccination and cholera
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How pathogens spread and how barriers, immune cells and vaccination protect the body.
Communicable disease depends on a pathogen, a route of transmission and a susceptible host. Prevention works by interrupting one or more of those links.
Immune responses become easier to explain when antigen recognition, antibody production and memory-cell formation are treated as a sequence.
SECTION 01
Transmission and defence
Pathogens cause disease and may pass directly through contact or fluids, or indirectly through air, food, water, animals and surfaces.
DETAILED EXPLANATION
- White cells engulf pathogens or make antibodies.
- Clean water, food hygiene, personal hygiene, waste disposal and sewage treatment break transmission routes.
SECTION 02
Immunity and vaccination
Pathogen antigens have specific shapes. Complementary antibodies bind them, destroying pathogens or marking them for phagocytes.
DETAILED EXPLANATION
- Vaccines provide weakened pathogens or antigens, causing antibodies and a faster later response.
- Passive immunity transfers ready-made antibodies across placenta or in breast milk. It is short-lived and forms no memory cells.
- Vaccination reduces susceptible hosts and therefore disease spread.
SECTION 03
Cholera
Cholera bacteria in contaminated water release toxin that causes chloride secretion into the small intestine.
DETAILED EXPLANATION
- Diarrhoea removes water and ions, causing dehydration.
- Safe water and sanitation prevent transmission.
STEP-BY-STEP EXAM EXAMPLE
Explaining a faster secondary immune response
- A first antigen exposure activates a small number of matching lymphocytes.
- These cells divide, produce antibodies and form memory cells.
- A later exposure activates the memory cells rapidly.
- Antibody concentration rises sooner and to a higher level.
Answer: Memory cells make the secondary response faster and stronger.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Transmission may be direct or indirect.
- Antibodies fit specific antigens.
- Active immunity forms memory cells.
- Cholera toxin causes osmotic water loss.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- describe transmission
- explain body defences
- compare active and passive immunity
- explain vaccination and cholera