WJEC GCSE Biology 3 Microbes and Disease

Microbes and disease, prevention, antibiotics etc

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  • Created on: 22-05-12 17:19
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Megan Nolan
Triple Biology Revision Notes:
Microbes and Disease
Pathogens Causing Illness:
A pathogen is a disease causing organism, such as a virus, bacteria or fungi. They can cause illness in
three different ways:
Toxins- Harmful substances produced by pathogens that poison the body's tissue/ enzymes
Reproduction- Pathogens can `hijack' a cell, taking the resources it needs to reproduce itself
and consequently damaging them
Immune Response- Sites of infection often become swollen, sore and hot as there is
increased blood flow
Pathogens are also spread in many different ways, including:
Through food and water e.g. Cholera
Insect bites e.g. Malaria
Airborne droplets e.g. Flu
Direct contact e.g. HIV/ STIs
Indirect contact e.g. Salmonella (food poisoning)
Natural defences against Disease:
Non- specific-
Skin- The skin has a number of dead layers which acts as a barrier against all microorganisms
Blood clots- If the skin is broken or damaged, platelets make a net at the side of the cuts, trapping
red blood cells, which clot and form a scab (made from dead cells)
Mucus- The breathing system produces a sticky liquid- mucus- which covers the lining of the organs
and tubes to trap microorganisms, cilia then `waft' the liquid up the throat or to the stomach
Stomach acid- Acidic conditions kill anything foreign
Ingesting white blood cells- The white blood cell surrounds the microbe and ingests it; surrounds it
before digesting it
Producing antitoxins- Some white blood cells also produce antitoxins, they match up to the toxins
produced by the bacteria, and neutralise them
Producing antibodies- As well as the antitoxins, white blood cells can release antibodies, a protein
which neutralises the bacteria itself. (See: Antibodies and Antigens)
Antibodies and Antigens:
Antigens are proteins found on the outside of bacteria; each bacteria has a unique antigen. They
trigger a response from a white blood cell which then secretes antibodies, which are specific to each
type of antigen. Antibodies attach to antigens and stop the bacteria from producing toxins. They can
also cause bacteria to clump together, preventing attacks on other cells, or destroy the bacteria cell
containing the antigen.

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Megan Nolan
Immunisation can prevent many diseases, but often has moral issues for the patient, such as the risk
of side effects. For example, new mothers must decide whether their baby has the MMR vaccination.
There are lots of possible side effects, such as autism, measles, mumps, rashes, fits or seizures and
allergic reactions.…read more

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Megan Nolan
Antibiotics, such as penicillin, are placed on an agar plate cover in bacteria.
If the antibiotic responds to the bacteria, a zone of inhibition will be clear
around the antibiotic. The zone of inhibition is where the bacteria have
been destroyed. The larger this zone, the more effective the antibiotic.
Antibiotics work by killing the infecting bacteria and are used regularly by
doctors for bacterial disease.…read more



A clear set of well written notes on immunisation, defence against disease and antibiotics which wold be useful for any GCSE Biology or science student needing to study these topics. Team them up with a set of flashcards and a quiz or two for a complete set of resources.

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