Question
In the following experimental set-up, a twig of a succulent plant (Crassula) was inserted in the glass tube. The apparatus was kept in sun light for 6 hours. The inserted bubble will:
Options
Solution
Sol. Key concept: CAM physiology reduces daytime transpiration in succulent plants.
A potometer estimates water uptake through the movement of an air bubble in a water-filled capillary. Evaporation from the leaves creates a transpiration pull that draws water towards the shoot; faster water uptake produces faster bubble movement.
Crassula is a CAM succulent. Its stomata generally open at night and close during the day, allowing carbon dioxide uptake with reduced water loss. Its thick cuticle also limits evaporation.
In the idealized six-hour sunlight experiment, water uptake due to transpiration is therefore taken as negligible, so the intended answer is c, no movement.
Correction / clarification: Daytime water loss is not literally zero in every living CAM plant: cuticular loss, imperfect stomatal closure and apparatus effects can cause a small movement. Treat c as the idealized official-key answer, not an absolute experimental law.
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