Biology · Plant Physiology
A botanist observes that a plant kept in a dark, humid chamber for 48 hours shows no visible wilting but its xylem sap flow has nearly stopped. On shifting it to bright light, xylem flow resumes rapidly before any visible stomatal opening is recorded. Which of the following best explains this sequence?
Verified Solution4 OptionsUpdated: October 2026👁️1 View
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- 1Phototropism immediately increases the osmotic pressure in leaf cells without involving transpiration
- 2Photosynthesis produces O2 which pressurises the xylem and forces water upward
- 3Light immediately triggers K+ influx into guard cells, lowering water potential in the substomatal cavity and initiating transpiration pull even before stomata are visibly wide open
- 4Root pressure alone sustains initial sap flow upon light exposure before stomata open✓
Correct answer
Root pressure alone sustains initial sap flow upon light exposure before stomata open
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