Pathogens, transmission and cholera
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 3 worked examples, 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Invisible enemies
- Pathogens
- How pathogens spread
- The body’s barriers
- Controlling the spread
- Cholera
- How the toxin works
- Treating cholera
Read the transcript of the teaching part
Last time
Before we start: last time, in Antibodies, vaccination and passive immunity, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Invisible enemies
In 1854 a doctor in London, John Snow, stopped a cholera outbreak by removing the handle of one water pump. He had worked out that the disease was spreading through dirty water. Today: what pathogens are, how they spread, how the body defends itself, and how cholera kills.
Pathogens
A pathogen is a disease-causing organism. Pathogens include bacteria, viruses, fungi and protoctists. A transmissible disease is one in which the pathogen can be passed from one host to another.
How pathogens spread
Direct contact: through blood or other body fluids, for example HIV. Indirect contact: through contaminated surfaces, food, animals, or the air, for example flu in droplets. Dirty water can carry pathogens such as cholera bacteria.
The body’s barriers
The skin is a tough mechanical barrier. Hairs in the nose trap particles. Mucus in the airways traps pathogens, and cilia sweep it away. Stomach acid kills pathogens in food. White blood cells attack any that get in.
Controlling the spread
Clean water supplies and good sanitation stop water-borne diseases like cholera. Hygienic food preparation and cooking food properly kill pathogens. Good personal hygiene, such as washing hands, and safe waste disposal also help.
Cholera
Cholera is caused by a bacterium carried in water contaminated with faeces. The bacteria multiply in the small intestine and release a toxin. The toxin causes severe diarrhoea, and the person can die from dehydration within hours.
How the toxin works
Here is the sequence the examiner wants. Each step causes the next. The key idea: chloride ions go out, so water follows by osmosis.
Treating cholera
The main treatment is oral rehydration therapy: a drink of water with salts and glucose. It replaces the water and ions lost in diarrhoea. Antibiotics can also kill the bacteria.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Cholera.
The whole chapter: Diseases and Immunity.
Chapter 10: Diseases and immunity
- Pathogens, transmission and cholera 4 min
- Active and passive immunity 4 min
Also for IGCSE Biology 0610
Which topics come up most in IGCSE Biology 0610 past papers, counted from every paper since 2004.