3.6.1Additional lessons
Pathogens — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 70 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Types of Pathogen
A pathogen is an organism or virus that causes disease.
Bacteria
- Bacteria Prokaryotic cells that cause diseases such as cholera and tuberculosis, although most bacteria are harmless or useful.
Fungi
- Fungi Some fungi infect skin or other tissues, for example the fungus that causes athlete's foot.
Protists
- Protists Single-celled eukaryotes such as Plasmodium, the protist that causes malaria.
Viruses
- Viruses Non-cellular particles that reproduce only inside host cells, using the host's cell machinery to make more viruses.
Archaea
- Archaea No archaea are known to cause disease in humans.
Part 2 of 5Infectious and Non-infectious Disease
Infectious (communicable)
- Infectious (communicable) These diseases are caused by pathogens and can be passed from one host to another, like cholera, malaria and tuberculosis.
Non-communicable
- Non-communicable These diseases are not caused by a transmissible agent, and examples include cancer, cardiovascular disease and malnutrition.
Signs and symptoms
- Signs and symptoms Each disease has a recognisable set of signs and symptoms, which helps with diagnosis and with finding the cause.
Aim of control
- Aim of control The best outcome is eradication, but control usually focuses on stopping transmission and treating the infected.
| Feature | Infectious | Non-infectious |
|---|---|---|
| Cause | Pathogen | Genes, diet, environment or lifestyle |
| Spread between people | Yes | No |
| Example | Cholera | Cardiovascular disease |
Part 3 of 5Snow and Cholera
1
Cholera is caused by the bacterium Vibrio cholerae, which spreads through contaminated drinking water and food.
2
Infected people pass large numbers of bacteria in their faeces, and these contaminate water supplies if sanitation is poor.
3
In 1854 John Snow mapped cholera deaths in Soho in London and found they clustered around one water pump.
4
The pump handle was removed, the outbreak ended, and the case supported the idea that disease can be carried in water.
5
This led to the provision of clean water and safe sewage disposal, which are still the main defences against cholera.
Part 4 of 5Semmelweis and Childbed Fever
Both examples are used to show how careful observation leads to progress.
1
Childbed fever is a bacterial infection of the reproductive tract that killed many women after childbirth in the nineteenth century.
2
Ignaz Semmelweis noticed that deaths were much higher in the ward staffed by doctors who came from dissections than in the ward staffed by midwives.
3
He introduced hand washing with a disinfectant before examining patients, and the number of deaths fell sharply.
4
His work showed that careful observation and comparison can identify a cause before the pathogen itself is known.
Part 5 of 5Exam Checklist & Tips
3.6.1 – Key Points for the Exam
- Pathogen An organism or virus that causes disease.
- Infectious disease A disease caused by a pathogen that can spread between hosts.
- Non-communicable disease A disease not caused by a transmissible pathogen.
- Vibrio cholerae The bacterium that causes cholera.
Common Mistakes
- Writing that all bacteria are pathogens; most are harmless and many are useful.
- Stating that viruses are cells; they are non-cellular.
- Calling cancer an infectious disease because it is serious.
- Saying Snow discovered the cholera bacterium; he showed water was the route of spread.
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