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The Immune System

Primary defences


This is a physical barrier that blocks pathogens from entering the body and also acts as a
chemical barrier by producing chemicals that are antimicrobial and can lower pH which
inhibits the growth of pathogens.

Mucous Membranes

They protect body openings that are exposed…

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This activates the T lymphocyte causing it to divide and differentiate into different types
of T lymphocytes that carry out different functions.
Some of these activated T lymphocytes release substances to activate B lymphocytes.
Some of these activated T lymphocytes attach to antigens on a pathogen and kill the

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They also have a hinge reigion which allows flexibility when the antibody binds to the

They also have constant regions which are the same in all antibodies. There are Disulfide
bridges to hold the polypeptide chains together.

How Antibodies Help to Clear an Infection

A way they help clear…

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The secondary response often gets rid of the pathogen before you begin to show any

Primary response Secondary response

Pathogen Enteres for the first time Enters for a second time

Speed of Slow Fast

Cells activated B and T lymphocytes Memory cells

Symptoms Yes No



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