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Summary Topic 10: Disease and Immunity
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Topic 10: Disease and Immunity: IGCSE Biology course notes which will help you study for your papers. By studying these notes I achieved a 9 - A* on my Igcse
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TOPIC 10: DISEASE AND IMMUNITY10.1 SPREAD OF DISEASE
→Pathogen: a disease-causing organism.
→Transmittable disease: a disease in which the pathogen can be passed from one host to another.
-Pathogens are passed on from one host to another and therefore the diseases they cause are known as transmissible diseases
-Pathogens can be passed on from host to host in different ways, including:
→Direct contact – the pathogen is passed directly from one host to another by transfer of body fluids such as blood or semen
(i.e. HIV, gonorrhoea, hepatitis B & C). Diseases passed through direct contact are known as contagious diseases.
→Indirect contact – the pathogen leaves the host and is carried in some way to another, uninfected individual. (i.e.
contaminated surfaces, food, by animals, air…).
VIRUSES
BACTERIA
PROTOCTISTA
FUNGI
Defences against Pathogens
-There are 3 main ways in which the body defends itself against disease:
1. Mechanical barriers – structures that make it difficult for pathogens to get past them and into the body
a) Skin – covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins
to heal itself, often by forming a scab.
b) Hairs in the nose – these make it difficult for pathogens to get past them further up the nose so they are not inhaled into
the lungs
2. Chemical barriers – substances produced by the body cells that trap / kill pathogens before they can get further into the body
and cause disease
a) Mucus – made in various places in the body, pathogens get trapped in the mucus and can then be removed from the body
(by coughing, blowing the nose, swallowing etc.)
b) Stomach acid – contains hydrochloric acid which is strong enough to kill any pathogens that have been caught in mucus in
the airways and then swallowed or have been consumed in food or water
3.Food hygiene – you can prevent food poisoning (through bacteria) by understanding the conditions which bacteria need to
live and reproduce and keep them under control. Prevent food poisoning by:
a) Keep your own bacteria and viruses away from food by washing your hands, keeping hair out, never sniff/cough…
b) Keep animals away from food. Animals are more likely to have bacteria on them than you (houseflies, rats…) so cover
your food.
c)Don’t keep foods at room temperature for long periods. If there are a few bacteria they will start growing and
reproducing, so keep your food in the fridge (slow down growth and reproduction) and cook at high temperature (kill bacteria)
d) Keep raw meat away from other food. Raw meat often contains bacteria (killed when cooked) and these may get onto
other foods and that’s the problem.
4. Personal hygiene – Keeping your body clean to prevent the risk of passing on or getting transmittable diseases. If oil, sweat
and dirt are left on skin for too long bacteria can start breeding (reproducing) – wash regularly. (also mouth as there are millions
of bacteria in your mouth).
5. Waste disposal – Rubbish in land field sites is rotten by decomposers such as bacteria producing a gas called methane which
can spread. (to prevent this methane can be collected and used as a fuel)
6. Sewage treatment – untreated sewage is called raw sewage and it contains bacteria and other microorganisms which are
likely to be pathogens and so those who are in contact with raw sewage may get ill – cholera / poliomyelitis.
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