Transpiration ,types, factor affecting and its significance. DPG Degree College, Gurgaon

1. TRANSPIRATION
NISHA KATARIA

2. Transpiration
 the loss of water from a plant in the form of water vapor.
 Water is absorbed by roots from the soil and transported as a liquid to the leaves
via xylem.
 In the leaves, small pores allow water to escape as a vapor.

3. How do plants show transpiration?
 Water drops appear inside the walls of the
bell jar containing potted plant .
 whereas no water drops appear in the bell
jar without a plant.
 This demonstrates that water is evaporated
from the surface of leaves.
 in presence of sunlight.

4. TYPES
STOMATAL TRANSPIRATION
CUTICULAR TRANSPIRATION
LENTICULAR /LETICELLATE
TRANSPIRATION
BARK TRANSPIRATION

5. Stomatal Transpiration:
 Stomatal transpiration constitutes about 50-97% of the total transpiration.
 It occurs through the stomata.
 Water vapours , pass outwardly through stomata by diffusion.
 More water evaporates from the internal cells to replace the outgoing water vapours .
 The stomatal transpiration continues till the stomata are kept open.

6. Cuticular Transpiration:
 It occurs through the cuticle or epidermal cells of the leaves,other exposed parts of the plant.
 In herbaceous shade loving plants where the cuticle is very thin, the cuticular transpiration may be up
to 50% of the total.
 Cuticular transpiration continues throughout day and night.

7. Lenticular or Lenticellate Transpiration:
 It is found only in the woody branches of the trees where lenticels occur.
 The lenticular transpiration is only 0.1% of the total transpiration.
 It, continues day and night because lenticels have no mechanism of closure.
 The lenticels connect the atmospheric air with the cortical tissue of the stem through the
intercellular spaces present amongst the complementary cells.

8. This type of transpiration occurs through corky covering of the stems.
 Bark transpiration is very little but its measured rate is often more than lenticular
transpiration due to larger area.
 Like cuticular and lenticular types of transpiration, bark transpiration occurs
continuously during day and night.
Bark Transpiration:

9. Factors Affecting Transpiration:
Carbon Dioxide:
Stomatal mechanism is sensitive to carbon dioxide
concentration. Stomata close in the presence of high
concentrations of CO2.
Oxygen:
This gas is essential for the opening of stomata. Its
deficiency quickens stomatal closure.
Hormones:
ABA causes stomatal closure whereas cytokinins are
essential for the intake of K+.
ABA works only in the presence of CO2.

10. Light:
stomata open when exposed to illumination and close in the
dark.
Temperature:
When all other factors are equal, stomatal opening increases with
rise in temperature up to 25°- 30°C and decreases at still higher
temperatures.
Mineral deficiencies:
With the deficiency of any of minerals such as, nitrogen,
phosphorus and potassium, the stomatal movements become
sluggish. Different ions affect the stomatal aperture differently.
Mechanical shock:
Various types of shocks, such as rough handling of leaves may
result in stomatal closure. It is found that stomata may close in
light when nearby tissue is wounded.

11. Significance of Transpiration:
There are three possible advantages of transpiration to the plants
and these are discussed below:
I. Transport of minerals:
High transpiration rates cause high rates of mineral absorption.
when the mineral in the soil are in abundance then the rate of
transpiration is vital for their translocation.
II. Lowering of leaf temperature:
 Transpiration of water from a surface of the leaf lowers the
temperature of that organ; the molecules having highest kinetic
energy are the first to evaporate.
III. Optimum turgidity:
In the absence of transpiration, plants tend to become over turgid and
will cease to grow. Similarly when the water potential becomes highly
negative growth also stops.