Igcse Model Questions Vol1 2020 Biology Question 8

Two desert plant species, A and B, differ in two leaf adaptations that affect transpiration. Species A has a stomatal density of \(150\) stomata mm\(^{-2}\) and a cuticle thickness of \(5\) µm. Species B has a stomatal density of \(80\) stomata mm\(^{-2}\) and a cuticle thickness of \(12\) µm. Experimental data show that the transpiration rate \(W\) (in mg h\(^{-1}\) per unit leaf area) is directly proportional to stomatal density and inversely proportional to cuticle thickness, i.e. \(W = k \dfrac{D}{T}\), where \(D\) is density and \(T\) is thickness (in µm). If species A loses \(120\) mg h\(^{-1}\) under standard conditions, determine:\n\n(a) the constant \(k\);\n(b) the expected transpiration rate of species B;\n(c) the percentage reduction in water loss from A to B;\n(d) assuming only one adaptation changes at a time, calculate the individual percentage reductions due to (i) the lower stomatal density alone and (ii) the thicker cuticle alone, and state which adaptation contributes more to the overall reduction.