Question 75

A leafy shoot that had been standing in still air is placed in front of a running fan. What happens to its rate of transpiration, and why?

It rises, because moving air sweeps humid air away from the poresCorrect answer
It falls, because the moving air cools the leaf down
It rises, because the wind forces water back out through the pores
It is unchanged, because air outside cannot affect what happens inside a leaf

Explanation

Vapour builds up just outside the pores and slows further escape once the air there is nearly saturated, so moving air raises the loss by carrying that vapour away and keeping the difference large. The cooling explanation runs the physics backwards, because cooling on its own slows evaporation rather than speeding it up, and air cannot be forced into a leaf through pores that vapour is streaming out of.

Explanation

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