Plants lose water from their above-ground surfaces through transpiration. most of this water is lost from stomata, small openings in the leaves. excess water loss can have a negative effect on the growth, development, and reproduction of a plant. the first sign of this water loss is plant wilting, as water leaves the large central vacuole of the above-ground plant cells. severe water loss can be fatal. environmental factors have a major impact on the rate of plant transpiration.
consider the graph above, noting the rate of transpiration as atmospheric humidity increases. compare this process of osmosis of water from plant cells themselves.
a) increasing humidity leads to reduced transpiration due to decreased difference in water vapor pressure between leaf and atmosphere. osmosis increases as the concentration gradient reaches equilibrium.
b) increasing humidity leads to increased transpiration due to increased difference in water vapor pressure between leaf and atmosphere. similarly, osmosis increases with a difference in concentration gradient.
c) there is a indirect relationship between relative humidity and transpiration; as humidity increases, transpiration decreases. the same is true on a cellular level. as the concentration gradient increases, osmosis decreases.
d) increasing humidity leads to reduced transpiration due to decreased difference in water vapor pressure between leaf and atmosphere. similarly, osmosis decreases as the concentration gradient inside and out of the cell reaches equilibrium.