WAEC Biology 2012 Theory — Question 5

Model answer

(a)(i) Disease is a state of infirmity or lack of wellbeing. (ii) Symptoms of a disease are those observable manifestations of the disease, for instance, painful urination is a symptom of gonorrhea. (b)(i) Physical barriers that prevent pathogens from penetrating the body of an organism include the skin and mucus membranes. Chemical barriers include sebum and mucus, which are chemical examples of such. (ii) Vaccination works basically by stimulating the immune system to recognize and combat pathogens, by introducing molecules from the pathogen into the body. (c) Antibodies are produced in response to the presence of a foreign substance (i.e. antigen) and are proteinous in nature. Antigens are substances which invoke immune responses; they are proteins but may also be lipids, polysaccharides or even nucleic acids, and cause disease or allergic reaction. Antibodies protect the body by lysis of antigenic materials. (Lysis means the breakdown or rupture of the membrane of a cell.) (d)(i) The causative agent of malaria is Plasmodium spp. (ii) The causative agent of cholera is Vibrio cholerae. (iii) The causative agent of AIDS is Human Immuno-deficiency Virus (HIV).