Water transport in plantsAQA A-Level Biology: Mind map

Exam questions on Water transport in plants

1. A student examined a longitudinal section of the stem of a sunflower with a light microscope. The mature xylem vessels contained no cytoplasm, had no end walls between neighbouring vessel elements, and had walls thickened with lignin.
   Explain why the walls of xylem vessels need to be strong.2 marks
2. A scientist fitted a sensitive instrument to the trunk of a pine tree and recorded its diameter over several days. The diameter was smallest in the afternoon, when the air was warm, dry and sunny, and largest in the early morning. The change in diameter was about 0.5 mm.
   Explain why the trunk diameter was smaller in the afternoon than in the early morning.2 marks
3. A student set up a potometer with a leafy shoot from a laurel plant cut under water, and measured the distance moved by an air bubble in a capillary tube of internal radius 0.5 mm. In still air, the bubble moved 12 mm in 5 minutes. When a fan blew air across the leaves, the bubble moved 30 mm in 5 minutes.
   Calculate the rate of water uptake in the moving air, in mm³ min⁻¹.3 marks