WAEC Biology 2019 Theory — Question 5

Model answer

(a)(i) Lightening is essential to the nitrogen cycle as it causes nitrogen and oxygen to combine forming nitrogen oxides. These oxides are further oxidized to eventually produce nitrogen(IV)oxide, which then dissolves in rain water to form HNO2 and HNO3. These nitrates are utilized by plants. (ii) Nitrosomonas acts on ammonia or ammonium compound, converting it into nitrite. NB: The eventual conversion of nitrite into nitrate is by another bacterium known as Nitrobacter. (iii) Azotobacter (and other bacteria such as Rhizobium leguminosarium) help in nitrogen fixation. These bacteria help to fix atmospheric nitrogen into the soil. The relationship between azotobacter and these plants is said to be mutualistic because the bacteria obtain nutrient and shelter from the plant. (b)(i) The malpighian tubules are the excretory structures in insects. (ii) The excretory organ in earthworm is the nephridium. (c)(i) Hepatitis is the inflammation of liver cells. It may occur as a result of infection. (ii) Kidney stones are hard deposits of minerals and acid salts that stick together in concentrated urine. They are usually painful when passed through the urinary tract. (d)(i) The lack of sense receptors in the skin of human will cause: Inability to detect pain; Inability to detect heat; Inability to detect pressure; Inability to detect touch. (ii) The layers of the epidermis are the horny or cornified layer, granular layer and the malpighian layer. (e)(i) Metamorphosis refers to the series of gradual changes that occur during the development of an animal from the zygote to the adult stage. (ii) Type of metamorphosis: Grasshopper - Incomplete; Cockroach - Incomplete; Butterfly - Complete; Mosquito - Complete; Housefly - Complete.