The meaning of 'transpiration' in botanical terms
is the passage of water through a plant from the
roots through the vascular system to the
atmosphere
In a plant, glucose and water
travels through miniature tubes
throughout the plant.
The tube that carries the
food is called the Phloem.
The tube that carries the
water is called the Xylem
Both the Xylem and the
Phloem are contained in
one big tube called the
Vascular Bundle
As water is getting
transported around
the plant through
the xylem it will
eventually reach
the leaves
When it does some water
will be used in the process of
photosynthesis by the
chloroplasts
However, a percentage
of the water will be lost
as it escapes through the
stomata.
The stomata is a hole bordered by guard cells
that allows gas exchange. There are hundreds
of these on a single leaf.
The stomata opens and
closes allowing carbon
dioxide to come in and
oxygen to come out.
When the stomata does
open the water can escape
into the atmosphere and evaporate.
The stomata is
visible as pores
on the leaf.
Stomata
Transpiration in a plant can
be measured by a potometer
Potometer
Plants in the desert, for
example a cactus get very little
water so they cannot afford to
lose any through transpiration.
The way they avoid this is that through a process
of evolution, the leaves have curled up tightly
over millions of years until the leaves have
eventually become spikes.
What this prevents is any water vapour
getting lost; as because the leaves have
curled so much there is no place for the
water vapour to escape and so it stays
in the leaf ready to be used for
photosynthesis.