WAEC Biology 2020 Theory — Question 3

Model answer

(a) Disease/Causative Organism/Vector/Control table: Cholera - Vibrio cholerae / Housefly / By maintaining food hygiene. Trypanosomiasis (Sleeping sickness) - Trypanosome / Tsetsefly / Elimination of Tsetsefly. Malaria - Plasmodium spp / Female anopheles mosquito / Elimination of mosquito, use of mosquito net. Ringworm - Tinea spp, Microsporum, Trichophyton, Epidermophyton / Kittens, puppies, cows, goats (infected animals and persons) / Maintaining good hygiene, avoiding contact with infected persons, animals capable of spreading ringworm to people. (b)(i) Salting is a very effective method of food preservation. Use is made of normal edible salt. Salting is used because most bacteria, fungi and other potentially pathogenic organisms cannot survive in a highly salty environment, due to the hypertonic nature of salt, causing the microorganisms to lose water through osmosis and die. (ii) Food irradiation refers to the treatment of foods by exposing them to ionizing radiation. Non-ionizing radiation has a considerable health risk if not controlled. Irradiation inactivates the micro-organisms in food, preventing spoilage. (iii) Meats and fish are the most common food types that are preserved by smoking. The food is exposed to smoke from burning or smouldering material, most often wood, during the drying process. Also, the reduced water content makes it unfavourable for micro-organisms to survive in the food.