WAEC Biology 2025 Theory — Question 3

Model answer

Paramecium: Excretory structure - Contractile vacuole; Mechanism - Osmoregulation and internal water balance; Adaptation - Regulates internal water balance and expels excess water. Planaria: Excretory structure - Flame cells; Mechanism - Ciliary movement and diffusion; Adaptation - Extensive branching increases surface area for excretion. Leaf of plant: Excretory structure - Stomata; Mechanism - Transpiration; Adaptation - Stomata open to allow water vapour to escape. Earthworm: Excretory structure - Nephridium; Mechanism - Filtration and diffusion; Adaptation - Tubular structures in segments efficiently remove nitrogenous waste.