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Biology Aqa as Essay

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Below is an essay on "Biology Aqa as" from Anti Essays, your source for research papers, essays, and term paper examples.

Explain how the defence mechanisms of the body reduce the chance of entry by a pathogen.
Epidermis of skin is dead / keratinised so pathogens cannot penetrate;
mucus in respiratory system is trapping sticky pathogens;
cilia move fluid / mucus removing pathogens;
tears / saliva / mucus contain lysozyme breaking down bacterial cell wall;
stomach contains hydrochloric acid which destroys bacteria;
blood clot prevents entry;
fluid nature of tears wash away bacteria;
vaginal acid destroys bacteria;
commensal bacteria on skin compete with pathogen;
sebum (fatty acid) inhibits bacterial growth;

Explain how the body responds both generally and specifically to pathogens that enter the blood.
action of phagocytes;
Interferon production;
body temperature increased;
ref to B or T lymphocytes;
activated by non-self-antigen;
either clone / divide by mitosis;
T helper cells role;
B plasma cells produced;
which produces antibodies;
any specific effect (e.g. immobilise /agglutinate / lysis /coat for recognition /
neutralise toxins);
T killer / cytotoxic cell;
perform produced;
memory cell produced;

Explain the role of B-lymphocytes and T-lymphocytes in the defence of the body against a virus infection.
B lymphocytes produce antibodies/involved in humoral response;
T lymphocytes involved in cell mediated immunity;
Macrophages present antigens;
(specific) B lymphocytes recognise/bind to antigen;
increase in numbers by mitosis;
produce plasma cells (which make antibodies);
antibodies bind to and clump/ agglutinate virus;
memory cells produced by 1st exposure/cloned on 2nd exposure;
T lymphocytes(helpers) produce lymphokines/chemicals;
which aid B lymphocyte cloning;
encourages phagocytes to engulf clumped virus;
killer T cells kill virus infected cells;

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