A student set up the calibrated bubble potometer shown in the diagram to investigate the rate of water uptake in a leafy shoot. The capillary tube has a constant internal cross-sectional area of 0.80 mm². During a 15-minute experimental trial under standard laboratory conditions (22 °C, still air), the air bubble moved a total distance of 75 mm along the scale.
Define the term transpiration.
Calculate the rate of water uptake by the leafy shoot in mm³ min⁻¹. Show your working.
State one essential precaution taken when assembling the apparatus to ensure valid, reliable measurements.
The leafy shoot was subsequently placed in a chamber with high air temperature (35 °C) and an operating electric fan.
Predict and explain the effect of these combined conditions on the rate of bubble movement.
If the cut stem is lifted completely out of the water beaker while remaining in this warm, windy chamber, explain why the leaves soon wilt.
Outline the role of companion cells in the phloem tissue during the translocation of sugars to growing shoot tips.