2. 1. Importance of
Transpiration
2. Process of
Transpiration
3. Role of Stomata in
the Process
4. Factors Affecting
Transpiration
5. Xerophytes
3. 1.Transpiration
Transpiration is the loss of water by evaporation in
terrestrial plants. It then enters the atmosphere
and becomes a part of the water cycle.
5. The Importance of
Transpiration
The process of transpiration is a very
important procedure for plants.
It creates a negative pressure gradient that helps
draw water and minerals up through the plant from
its roots.
Helps to keep the plant cool on hot weather - a
method of evaporative cooling.
It supports photosynthesis and encourages the
exchange of gases, helping maintain levels of CO2
and O2 in the atmosphere.
It also-
plays an significant role in the water cycle and
releases approx 10% of water back into the
environment.
produces 200 to 1,000 lb (90–450 kg) of water for
each pound of solid material produced by the plant.
Creates water vapor that forms into fog and clouds.
6. 2.The Process of
Transpiration
Water enters into the root hair
cells by osmosis.
The root hair cell is hypertonic
(higher osmotic pressure) than
the surrounding soil water and
means that it has a lower water
molecule concentration.
Water moves from cell to cell
through the root cortex by
osmosis along a concentration
gradient; this means that each
cell is hypertonic to the one
before it.
In the centre of the root the
water enters the xylem vessels.
Water may move by diffusion
through the cell walls and
intercellular spaces.
7. 3. Role of Stomata
The pores in the stoma play an essential
role in the process of transpiration.
The two guard cells control the opening
and closing of the pore .
The rate is dependant upon the opening
time and the number of stomata present.
In sunlight the stomates are open and
the sun provides the energy that keeps
moving all of the way to the stomata
where water changes form from a liquid
to a vapor. At night, the cells remain
closed.
The stomata release water in the
atmosphere, which is then broken down
into oxygen and hydrogen. In return, the
atmosphere gives carbon-dioxide to the
plant to complete its process of
photosynthesis.
The number of stomata varies in from
plant to plant. In xerophytes the number
of stomata will be less as compared to
the other plants. This reduces the water
loss and helps the plant to survive in very
dry conditions. The plant may also close
its leaves if there is excesive sunlight, to
save the water from transpiration. All
these activities form a part of plant
biology.
8. Transpiration
Stomata also allow controlled release of
water molecules into the atmosphere.
Although the plant cannot afford to lose
too much water to the environment, the
plant must have a way to carry water and
minerals from the roots, up the stem, and
out to the leaves. Transpiration is the
loss of water through the stomata. By
allowing some water molecules to
escape the leaves through the stomata,
Plants have a balancing act to follow -
they have to let in enough carbon dioxide
for photosynthesis and enough oxygen
for cellular respiration, without losing too
much water. So, stomata open and close
in response to environmental cues.
Temperature, humidity, the concentration
of carbon dioxide, and even the presence
or absence of light affects the turgor of
the guard cells, which controls the
opening and closing of the stomata.
9.
10.
11. 6.Factors affecting
Transpiration
Factors effecting transpiration rate
The opening and closing of the stomata is
controlled by the guard cells.
In light, guard cells take up water by osmosis
and become turgid. Because their inner
walls are rigid they are pulled apart, opening
the pore. In darkness water is lost and the
inner walls move together closing the pore.
Because of this, the transpiration rate is
increased by an increase in light intensity.
The rate of transpiration can be affected by
several factors:
The opening and closing of the stomata by
the guard cells (stomatal rhythm) - In
light, guard cells take up water by osmosis
and become turgid. Because their inner walls
are rigid they are pulled apart, opening the
pore. In darkness water is lost and the inner
walls move together closing the pore.
Because of this, the transpiration rate is
increased by an increase in light intensity.
Plants which live in extreme environments
have adaptations to control their transpiration
rate.
12. 6. xerophytes
Desert plants have a real challenge to Water is transported from the roots to the
minimize water loss, since their environment leaves through a vein structure known as the
is so hot and dry. Xylem. Water and minerals are 'sucked up'
Xerophytes live in deserts where water is as water evaporates from the leaves of
scarce and evaporation is rapid, or in windy plants in a process known as Transpiration.
habitats where evaporation can also be The process of transpiration- Transpiration is
rapid. Their typical features are: a process of emission of water from the plant
deep roots to reach water far underground with the help of small openings known as
shallow spreading roots to collect occasional stomata. Stomata are small openings or
rainfall pores which are present in the aerial part of
the plants like in the
leaves reduced to spines with minimum leaves, stem, flowers, etc. But leaves
surface area for transpiration constitute the major portion of stomata.
reduced number of stomata to reduce
transpiration rate
rolled leaves, leaf hairs and stomata sunk in
pits to trap moist air, increasing humidity and
slowing diffusion of water vapour from the
stomata
waxy leaf cuticle which is impermeable to
water (preventing evaporation)
stomata opening at night and closed at
midday when evaporation rate would be
highest (reversed stomatal rhythm).
storage of water in succulent tissues
13. 5. Factors Affecting
Transpiration
Factors affecting the rate of transpiration.
High temperature may result in the opening of stomata and
hence, increases the transpiration.
In the normal procedure, plant gets water from the soil. If plant
does not get water from the soil, the stomata remains closed.
The rate of humidity is inversely proportional to the rate of
transpiration. That means when humidity
increases, transpiration decreases.
Light increases the temperature which in turn, increases
transpiration.
Transpiration increases with the wind but high winds result in
the closing of stomata which reduces transpiration.
Leaf structure, type of stomata, root and shoot ratio, etc., may
also affect the rate of transpiration.
