In vascular plants, scaling up to larger sizes requires transport of water under tension through the xylem. During dry periods, saplings are vulnerable to xylem cavitation (hydraulic failure), which occurs when the negative pressure (tension) inside the xylem vessels becomes too high, causing air bubbles to form and block water flow.
Which combination of environmental conditions creates the highest tension within the xylem of a sapling, maximizing the risk of hydraulic failure?
Low wind speed and high relative humidity
Low wind speed and low relative humidity
High wind speed and low relative humidity
High wind speed and high relative humidity
17 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.