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[h] iGCSE Biology Notes Diseases and immunity
[q] What is a pathogen?
What are pathogens?
[a]
- A pathogen is an organism that causes disease.
- The pathogen is the organism, the disease is disorder of the sufferer.
- A pathogen is either a virus, bacterium, fungus, protist, prion or a multicellular parasite .
- All pathogens have proteins on their cell surface, which wen call antigens. These have very specific shapes.
[q] How can disease be spread?
What are the ways diseases can spread?
[a] A transmissible/communicable disease is on that can be transferred from one organism to another.
[q] What are the ways disease be spread?
[a]
- Directly: By skin-to-skin contact, sexual contact, blood or other bodily fluids
- Indirectly: Via water, air, contaminated surfaces or food or by an animal vector.
[q] How can we prevent this spread?
Talk the person next to you!
[a]
1. Sexual contact
2. Skin-to-skin contact
3. Bodily fluids/blood
4. Food
5. Water
6. Airborne
7. Vector
8. Contaminated surfaces
[q] How can we prevent this spread?
[a]
- 1. Contraception like condoms or abstinence
- 2. Self-isolation, avoid contact, personal hygiene
- 3. Use sterilised needles and medical equipment
- 4. Regularly clean cooking tools, use different chopping boards to avoid cross-contamination (hygienic)
- 5. Clean water supply that is treated (like with chlorine/UV/ozone) and sewage treatment
- 6. Masks
- 7. Mosquito nets and spray, kill the vectors/control vector population
- 8. Regularly disinfect surfaces, waste disposal
[q] What are the body’s non-specific defences?
What are the body’s first barrier to disease?
Skin as a barrier
[a] Skin, a water-proof barrier than can repair itself and seal cuts by clotting blood
[q] Nose hairs as a barrier
[a] Nose hairs, traps particles that contain pathogens
[q] Mucus as a barrier
[a] Mucus, produced by goblet cells in your trachea and bronchi, is sticky and traps pathogens
[q] Stomach acid as a barrier
[a] Stomach acid, kills most pathogens that enter the stomach
[q] Ear wax and Tears as a barrier
[a] Honourable mentions: ear wax and tears
[q] Types of immunity
What are the body’s first barrier to disease?
[a]
- The two types of immunity
- Immunity can be active or passive.
[q] Active immunity
[a] Active immunity is a long-term defence against pathogens by the body creating antibodies and memory cells.
[q] Passive immunity
[a] Passive immunity is a short-term defence against pathogens by antibodies being given by another organism, like via the placenta during pregnancy or via breastfeeding after birth.
[q] Passive immunity
Why do we need passive immunity?
[a]
- Passive immunity is essential has baby’s immune systems are not yet fully developed.
- This means they are at greater risk of disease
- However, passive immunity does not generate memory cells, so it is short term.
[q] The active immune response
What are the steps to the immune response?
[a]
1. A pathogen enters the body
2. Lymphocytes will detect the foreign antigens on the pathogen, and eventually produce antibodies that are a complimentary shape.
3. These antibodies bind to the pathogen’s antigens, directly killing them or marking them for destruction.
4. Memory cells are produced which will remember this antigen so antibodies can be produced faster in the next exposure, granting long-term immunity
[q] What is vaccination?
How does vaccination spread disease spread?
[a]
- A vaccine contains a weakened/inactive form of the pathogen, or just the antigens
- It triggers an immune response as normal, are eventually results in memory cells being created granted long term immunity
- Herd immunity is where if around 95% of a population is vaccinated, those who are unvaccinated are unlikely to get the disease as the vaccinated act as barriers between them since they can’t catch or spread the pathogen.
[q] What is cholera?
What is cholera?
[a]
- Cholera, Vibrio cholerae, is a bacterial disease.
- It is waterborne which means it is spread by dirty, infected water.
- The symptoms include diarrhoea, dehydration and loss of important ions (minerals) from the blood.
[q] How does cholera cause disease?
What is cholera?
[a]
- Cholera bacteria release a toxin that causes chloride ions to be secreted into the lumen of the small intestine.
- This means the water potential in the small intestine lumen is now lower.
- This then means water will move by osmosis from the blood (high water potential) into the small intestine lumen (lower water potential)
- This leads to watery faeces (diarrhea), excess water loss (dehydration) and loss of important ions like the chloride ions
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