Video Transcript
The diagram given shows the process
of transpiration in a plant. What is the scientific term given
to the pores in the leaf that allow water vapor to diffuse out of the plant?
Transpiration is the process in
which water vapor is lost from the leaves of a plant. In fact, more than 90 percent of
the water that plants absorb through their roots is lost each day by
transpiration. So why does it happen? The big advantage of transpiration
is that it provides the force known as transpiration pull to transport water up the
stem of a plant in the xylem vessels. This ensures plants get all the
water they need to carry out photosynthesis. However, if too much water is lost
through transpiration, this can damage plant tissues.
Let’s have a closer look at the
structure of a leaf to see exactly how transpiration happens. This diagram shows a cross section
through a leaf, detailing the cells that make up its lower surface. The xylem vessels are shown in
blue, and the spongy mesophyll cells are shown in green. We can also see a pore on the
bottom surface of the leaf. This pore is called a stoma, which
has the plural stomata. Each leaf has many stomata, and
they’re predominantly found on its lower surface. The main reason that leaves have
stomata is so that carbon dioxide can diffuse from the atmosphere into the air
spaces between the spongy mesophyll cells. This carbon dioxide then diffuses
into leaf cells, where it’s used as a reactant for photosynthesis.
As well as allowing carbon dioxide
to move into leaves, stomata also facilitate transpiration. Water that has been transported to
the leaf in the xylem vessels moves through the spongy mesophyll cells and into air
spaces near the stomata. In the air spaces, this water
evaporates into a gas called water vapor. The water vapor then diffuses
through the stomata and out of the leaf. It’s important to note that the
stomata are not always open. For example, at night, when there’s
no light available for photosynthesis, leaves can close their stomata in order to
conserve water.
We have therefore determined that
the scientific term given to the pores in the leaf that allow water vapor to diffuse
out of the plant is stomata.
