Igcse Model Questions Vol1 2019 Biology Question 37

Plant A has a leaf surface area of \(150\ \text{cm}^2\) and its stomata remain open for \(6\) h per day, with a transpiration rate of \(0.5\ \text{g cm}^{-2}\text{h}^{-1}\). Plant B has a leaf area of \(100\ \text{cm}^2\), stomata open for \(3\) h per day, and a transpiration rate of \(0.4\ \text{g cm}^{-2}\text{h}^{-1}\). When stomata are open, each square centimetre of leaf gains carbon dioxide at a rate of \(2\ \text{mg cm}^{-2}\text{h}^{-1}\). Determine which plant has the higher water‑use efficiency (ratio of total CO\(_2\) gain to total water loss) and calculate that efficiency for the more efficient plant, expressing the answer in grams of CO\(_2\) per gram of water (to three significant figures).