WAEC Biology 2021 Theory — Question 17

Model answer

(i) Irritability is that characteristic of living organisms by which they are aware of, and able to respond to, stimuli. (ii) Euglena moving towards light — positive phototaxis. Opening/closing of Mimosa leaves — nastism. Mosquitoes avoiding repellants — negative chemotaxis. Earthworm moving away from light — negative phototaxis. Sperm cell moving towards chemical substances of an ovum — positive chemotaxis. Four o'clock plant opening at 4:00pm — nastism. Shoot of bean seedling growing towards sunlight — positive phototaxis (phototropism).