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Summary - CCEA Unit A2 1 - Physiology and Ecosystems - Immunity
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A complete summary of CCEA A21 Immunity section, covers the entire specification in regards to immunity topics.
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ImmunityActive Immunity: The exposure to a foreign antigen resulting in memory cells being produced. Called
‘active’ as B lymphocytes are activated by foreign antigen.
- Natural: Infection occurs. B/T cells activated to destroy pathogen (delay in response). Memory cells
formed during primary response to provide long term immunity and a greater response in
subsequent infections.
- Artificial: Vaccination of weakened/dead pathogen. Activated B cells and memory cells produced.
Passive Immunity: Temporary immunity achieved when a person receives ready made pathogen
from another source. Short term immunity as no memory cells are produced.
Natural: Baby receives antibodies from mothers across the placenta in the colostrum.
Artificial: Injection of antibodies to provide immediate response to deadly venom/pathogen.
Body’s defences:
1. Barriers to entry of pathogen (non-specific)
2. Phagocytes – ingest pathogen at site of infection (non-specific)
3. Antibodies – produced to target a particular pathogen in a specific immune response.
Non-Specific Response
Defence that protects against any pathogen. Includes physical barriers to infection (tears/mucus) as
well as phagocytes (in the blood.)
Commensals: Non-specific bacteria that live on/in the body. Prevent pathogenic bacteria colonising.
Phagocytes: Polymorphs are the most common type of phagocyte in the blood and are first to arrive
at site of infection. Engulfs bacteria. Bacteria is then enclosed in vesicle called phagosome.
Lysosome: Vesicle containing hydrolytic enzymes fuse with vesicle containing pathogen. Digests
pathogen.
Specific Response
Immune response that targets a specific pathogen. Lymphocytes produce antibodies in response to
the antigen of specific pathogens. Highly effective, long-lasting immunity against anything the body
recognises as foreign.
Antigen: Proteins and glycoproteins on the surface (membrane) of a cell. A foreign antigen triggers
an immune response and antibody production.
Antibody: Protein made in response to a foreign antigen by B lymphocytes. Has 2 binding sites with a
complementary shape, to bind specifically to foreign antigen made by plasma cells. (cell lysis/clump
to be engulfed)
Memory cells- Carry an immunological memory of a specific antigen. Next time antigen in
encountered there is a greater secondary response.
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