A leafy shoot is sealed inside a clear bag, so the air around it soon becomes very humid. What happens to the rate of transpiration, and why?

Explanation

Water vapour leaves a leaf by diffusing from the very moist air inside it into drier air outside, and damp surrounding air shrinks that difference, so the movement slows down. Reading the extra moisture as extra water for the plant to lose confuses the air outside the leaf with the water inside it, since the leaf supplies its own water and only the steepness of the gradient has changed.