A grower switches on a humidifier beside cucumber plants in a brightly lit glasshouse. The humidifier does not wet the leaves. Light intensity, temperature and air movement remain constant.
The rate of transpiration decreases.
Which statement explains why?
The humid air makes water enter through the stomata by osmosis faster than it leaves.
The humid air reduces the water vapour concentration gradient, so diffusion out of the leaves slows.
The humid air stops active transport of water by root cells, so less reaches the leaves.
The humid air causes water to condense in the xylem, so movement through the stem slows.
114 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.