Biology

What is a microorganism?

A single celled organism e.g. bacteria, they cannot be seen without a microscope. There are good microorganisms and bads ones.

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What is a pathogen?

A microorganism that an cause disease. For something to be a microorgansim it must enter the host and cause damage to the host tissue. Pathogens= Bacteria, Fungi, Viruses.

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Interfaces are common sources of entry for pathogens. What do they include?

1) Gas exchange surface- Pathogens cause influenza and bronchitis infect this way. 2) Digestive system- Food and water carry pathogens into the stomach and intestines.

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What are the bodies 3 natural defenses of pathogens?

1) A mucous layer that covers exchange surfaces and forms a thick sticky layer. 2) Production of enzymes that break down pathogens. 3) Production of stomach acid which kills microorgansims.

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How do pathogens cause disease?

By damaging host tissue- man pathogens break down the membranes of the host cells. By producing toxins- most pathogens produce toxins.

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TIP!

It is the pathogen that causes the symptoms and not the disease e.g. the bacterium that casues cholera enters the body and this leads to diarrhoea.

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When do correlations occur?

When a change in one of two variables is reflected by the change in the other variable.

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If a correlation is shown that for example between drinking alcohol and breast cancer, can we conclude that drinking alcohol is the cause of breast cancer?

No, becasue it suggests this is the case but there is NO ACTUAL EVIDENCE to prove it. There has to be a clear CAUSAL CONNECTION between the two variables. Evidence would also need to be shown that no other factor influences the data e.g. stress level

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Biology

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