Why do a plant's leaves feel cool?

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Discussion Overview

The discussion centers around the phenomenon of why plant leaves feel cool to the touch, exploring the underlying mechanisms and contributing factors. It includes aspects of plant physiology, particularly focusing on evaporative cooling and the role of water in leaves.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that plant leaves feel cool and questions the reason behind this sensation.
  • Another participant proposes that evaporative cooling from water loss through the leaves contributes to the cooler temperature compared to room temperature.
  • A third participant elaborates on the role of stomates in water evaporation, which not only cools the leaves but also facilitates metabolic processes and the uptake of CO2 for photosynthesis.
  • Additionally, one participant suggests that the high water content in leaves acts as a heat sink, contributing to the cool sensation beyond evaporation.

Areas of Agreement / Disagreement

Participants present multiple viewpoints regarding the reasons for the coolness of leaves, indicating that there is no consensus on a single primary explanation. Various factors such as evaporative cooling and water content are discussed, but the discussion remains unresolved regarding which is the most significant.

Contextual Notes

The discussion does not clarify the relative importance of the proposed mechanisms, and assumptions about the environmental conditions affecting leaf temperature are not explicitly stated.

EnumaElish
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Plant leaves are cool to the touch. In fact, that's one way of verifying whether it's a real plant. Can anyone explain why living plants feel cool?
 
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Plants evaporate water through their leaves and evaporative cooling keeps them a little cooler than room temperature.
 
Leaves have openings - stomates. When the stomates are open the plant loses water by evaporation to the atmosphere, as Turbo says. This has several important effects. One is to allow the leaf's metabolic machinery to operate at temperatures that would normally slow it down: air-condtioning.

It also moves water from the roots up the stem, along with minerals. The stomates also allow CO2 into the leaf for photosynthesis to build more plant tissues. Plants are a net sink for carbon dioxide.
 
I would suggest that the primary reason that leaves feel cool is that, evaporation aside, they are full of water, which is an excellent heat sink.
 
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