Video Transcript
When is guttation most likely to
occur? (A) When the rate of transpiration
is at its lowest. (B) When the rate of transpiration
is at its highest. (C) Constantly throughout daylight
hours.
To answer this question, let’s
start by understanding what the key terms guttation and transpiration mean.
Sometimes, plants need to remove
excess water from their bodies. And there are two main processes
that they can use to eliminate this water: transpiration and guttation. Transpiration is the evaporation of
water from plant surfaces, like the leaves and stems, into the atmosphere. 90 percent of transpiration takes
place through small pores on the leaves, which are called stomata. The stomata are usually open during
the daytime to allow the diffusion of carbon dioxide into the leaves for
photosynthesis. For this reason, transpiration and
water loss is usually high during the daytime.
Guttation is the elimination of
excess water from the plant through structures called hydathodes, which are found on
the margins of leaves. Let’s take a closer look at this
process.
Plants usually absorb water and
mineral ions from soil into the roots. The absorption of fluids into roots
creates an upward pressure through the xylem vessels, which transports these
substances to the leaves, where any excess water can be removed through the
hydathodes. When the rate of transpiration is
high, the plant can get rid of excess water through the open stomata.
During this time, guttation is
unlikely to happen, because there is not much buildup of water in the xylem. Guttation is most likely to happen
when transpiration is at its lowest and the plant needs to eliminate large amounts
of water. This is usually at night, when the
stomata are closed. So guttation does not occur
constantly throughout daylight hours.
Now we know that the correct answer
to our question is (A). Guttation is most likely to occur
when the rate of transpiration is at its lowest.
