Theory question 107
Microorganisms and Health(For candidates in Nigeria only)
(a) Explain the following terms: (i) disease; (ii) symptoms of diseases.
(b)(i) List two physical and two chemical barriers that prevent pathogens from penetrating the body of an organism.
(ii) Explain how vaccination protects the body from contracting infectious diseases.
(c) Distinguish between an antibody and an antigen.
(d) Name the causative agents of: (i) Malaria; (ii) Cholera; (iii) AIDS.
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(a)(i) Disease: a condition in which the normal functioning of the body or part of it is disturbed, so the organism is unwell.
(ii) Symptoms: the signs or changes (e.g. fever, pain, rash, diarrhoea) felt or seen that show a person has a particular disease.
(b)(i) Physical: intact skin; mucus in the nose/airways; cilia; hairs in the nose; blood clotting; tears washing the eye. Chemical: hydrochloric acid in the stomach; lysozyme in tears and saliva; sebum/sweat; acidic vaginal secretions.
(ii) A vaccine contains dead or weakened germs or their toxoids; when introduced it stimulates the body to make antibodies and memory cells without causing the disease; if the real germ later enters, memory cells quickly produce large amounts of antibodies that destroy it before illness develops.
(c) An antigen is a foreign substance (usually protein on a germ's surface) that stimulates the body to make antibodies; an antibody is a protein made by white blood cells (lymphocytes) that combines with and neutralises a specific antigen.
(d)(i) Plasmodium (a protozoan, carried by female Anopheles mosquito); (ii) Vibrio cholerae (a bacterium); (iii) HIV (human immunodeficiency virus).
Antigen = the trigger; antibody = the body's response.