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Summary OCR A Level Biology- Defence Against Pathogens ALL revision notes you will need!
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Pathogen and Communicable disease A level biology notes. For OCR spec. This all the information you will need for this topic. It checks all boxes in the OCR A Level Biology Specification as well. Written in form that is easy to remember- and can be ACTIVELY RECALLED!. Information is split into mi...

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  • January 5, 2021
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Defence Against Pathogens
What are the non-specific defences that animals have?
The skin, mucous memebranes, blood clotting, Inflammation, Wound
Repair, Explusive Reflexes.

Is the skin a phyical or chemical barrier?
The skin acts as a physical barrier, blocking pathogens from entering the
body. It also acts as a chemical barrier by producing chemicals that are
antimicrobial (which destroy or slow down the growth of
microoraganisms) and can lower the pH, inhibitng the growth of
pathogens.

Give examples of defences that the skin carries out

Skin cells secrete fattly acids, such as oleic acid, that can kill some
bacteria. Fatty acids also lower the pH of the skin, creating an acidic
environment that is difficult for pathogens to colonise.

Skin cells also secrete lysozyme, an enzyme which catalyses the
breakdown of carbohydrates in the cell walls of some bacteria.

What do the mucous membranes do?

These protect body openings that are exposed to the environment (such
as the mouth, nostrils, ears, genitals and anus). Some memebranes secrete
mucus- a stickly substance that traps pathogens and contains
antimicrobial enzymes.

Give an example of a defence that the mucous membrane carriers out?

If you breathe in air that contains pathogens, most of them will be trapped
in the mucus lining in the lung epithelium (the outer layer of cells in the
passages to the lungs). Thses cells also have cilia (hair-like structures) that
beat and move the mucus up the trachea to the throat and mouth, where
it's removed.

A blood clot is a mesh of protein (fibrin) fibres. Blood clots plug wounds to
prevent pathogen entry and blood loss.


Defence Against Pathogens 1

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