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Flashcards · 5090 · Topic 12
Disease and immunity flashcards
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Topic 12: Disease and immunity
- Pathogen and transmissible disease (O Level)
- Pathogen: a disease-causing organism. Transmissible disease: a disease in which the pathogen can be passed from one host to another.
- Direct contact (transmission)
- Blood or other body fluids.
- Indirect (transmission)
- Contaminated surfaces or food, animals, the air.
- Malaria: pathogen, vector and control
- Pathogen: Plasmodium, a single-celled parasite. Vector: the female mosquito. Control: drain or cover still water, oil films, larva-eating fish, insecticides, treated bed nets, repellent.
- HIV: transmission
- Unprotected sex, shared needles, infected blood transfusion, mother to baby (pregnancy, birth, breast milk).
- How the cholera bacterium causes dehydration
- Its toxin causes chloride ions to be secreted into the small intestine; the water potential of the gut contents falls; water moves into the gut by osmosis; diarrhoea causes dehydration and loss of ions.
- Effects of nicotine, tar and carbon monoxide in tobacco smoke
- Nicotine: addictive; raises heart rate and blood pressure. Tar: carcinogens; stops cilia working. Carbon monoxide: combines with haemoglobin, so less oxygen is carried.
- Antibiotics and resistance
- Antibiotics kill bacteria but do not affect viruses. Resistant bacteria (e.g. MRSA) survive and reproduce; resistance is minimised by using antibiotics only when essential.
- Active vs passive immunity
- Active: defence by antibody production in the body; memory cells, long-term. Passive: short-term defence by antibodies acquired from another individual (across the placenta, in breast milk); no memory cells.
- How vaccination gives long-term immunity
- Weakened pathogens or their antigens are given. The antigens stimulate lymphocytes to produce antibodies, and memory cells are produced, giving long-term immunity.
- How antibodies destroy pathogens
- Antibodies with a shape complementary to the pathogen's antigens bind to them. This directly destroys the pathogen or marks it for destruction by phagocytes.
- Effect of HIV on the immune system
- It reduces the number of lymphocytes, so fewer antibodies are produced and the immune system is weakened.