Overview
This lecture covers all essential concepts from Cambridge IGCSE Biology Topic 10.1 Diseases and Immunity, including pathogens, transmission, body defenses, control measures, immunity types, vaccination, and cholera.
Pathogens & Disease Transmission
- Pathogens are disease-causing organisms like viruses, bacteria, fungi, protoctista, and parasitic worms.
- They cause disease by damaging cells and disrupting tissue functions, triggering symptoms and immune responses.
- Transmissible diseases can spread from one host to another via direct or indirect contact.
- Direct contact includes infection through blood, bodily fluids, needles, or sexual intercourse.
- Indirect contact involves contaminated surfaces, food, airborne droplets, or insect vectors like houseflies.
Body Defense Systems
- The skin's outer layer (epidermis) acts as a barrier against pathogens.
- Nasal hairs and mucus in the trachea/bronchi trap and remove pathogens from the air.
- Gastric juice in the stomach contains hydrochloric acid, killing most ingested bacteria.
- Ciliated cells move mucus away from the lungs.
- White blood cells destroy pathogens that enter the body.
Control Measures to Prevent Disease Spread
- Safe water supply: filter, chlorinate, or boil water to kill pathogens.
- Hygienic food preparation: cook meat well, use separate utensils, and avoid reheating food.
- Personal hygiene: wash hands after toilet use and before food handling.
- Waste disposal: use covered bins, dispose of waste by burning or burial to prevent flies/vectors.
- Sewage treatment: treat sewage before releasing into water sources.
Types of Immunity
- Active immunity: body produces antibodies after infection or vaccination; creates memory cells for long-term protection.
- Passive immunity: short-term protection from antibodies obtained from another individual (e.g., mother to child via placenta and breast milk); no memory cells produced.
Vaccination
- Vaccination introduces weakened pathogens or antigens to stimulate antibody production and memory cell formation.
- Vaccinated individuals develop long-term active immunity without developing symptoms of the full disease.
Cholera
- Cholera is caused by bacteria transmitted through contaminated water.
- Bacteria invade the small intestine, releasing toxins that lead to watery diarrhea, dehydration, and possible kidney failure.
- Treatment involves intravenous fluids, salt replacement, and antibiotics.
Key Terms & Definitions
- Pathogen — organism that causes disease.
- Transmissible disease — disease that can spread from one host to another.
- Active immunity — long-term immunity where antibodies are produced by the person's own immune system.
- Passive immunity — short-term protection using antibodies from another source.
- Vaccination — process of introducing antigens to stimulate active immunity.
- Cholera — bacterial disease causing severe diarrhea, commonly spread by contaminated water.
Action Items / Next Steps
- Review all definitions and key concepts for exams.
- Study diagrams of body defense mechanisms and immune responses.
- Prepare for next lecture on gas exchange in humans.