LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- describe transmission
- explain body defences
- compare active and passive immunity
- explain vaccination and cholera
THE BIG IDEA
How pathogens spread and how barriers, immune cells and vaccination protect the body.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
01
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
- Skin blocks entry; nasal hairs and mucus trap particles; stomach acid kills many swallowed microbes.
- White cells engulf pathogens or make antibodies.
- Clean water, food hygiene, personal hygiene, waste disposal and sewage treatment break transmission routes.
02
SECTION 02
Immunity and vaccination
Pathogen antigens have specific shapes. Complementary antibodies bind them, destroying pathogens or marking them for phagocytes.
DETAILED EXPLANATION
- Active immunity follows infection or vaccination and forms memory cells.
- 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.
1antigen exposure→
2lymphocytes→
3antibodies→
4memory cells→
5rapid secondary response
03
SECTION 03
Cholera
Cholera bacteria in contaminated water release toxin that causes chloride secretion into the small intestine.
DETAILED EXPLANATION
- Lower gut water potential draws water in by osmosis.
- Diarrhoea removes water and ions, causing dehydration.
- Safe water and sanitation prevent transmission.
1toxin→
2chloride secretion→
3osmosis into gut→
4diarrhoea→
5dehydration
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.