Question

Certain plants roll up during midday

Answer 1

Are you familiar with Transpiration ???
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It's the loss of water , isn't it ?
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What does it cause ?
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Whatever work was done by the plant to get the water to the leaves gets waste due to OVER transpiration.
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So , to stop over transpiration the leaves of the certain plants gets rolled.
This is carried out by ABA (Absisic acid ).
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Hope you get it.