Transpiration: Mechanism, Types, Factors
aff ecting transpiration, Biological signifi cance and
Disadvantages
Plants absorb a large quantity of water from the soil by root hairs and only a small part (1-2%) of this
water is utilized by them in their life processes.
The remaining large part (98-99%) of water is lost in the form of vapor from internal tissues.
The process of loss of water in the form of vapor through the exposed aerial parts of the plants is
called transpiration.
Transpiration is regulated by vital activities of protoplasm and some structural peculiarities of the
transpiring organs.
Why transpiration is called a necessary evil?
Transpiration facilitates the upward movement of water and minerals absorbed by roots but at the same
time if water loss through transpiration is more than the absorption of water, it can cause wilting and
even death of the plant. Hence, transpiration is called a necessary evil.
Mechanism of transpiration:
The mesophyll cells of the leaf withdraw water from the xylem tissue by osmotic diffusion and become
turgid.
From the surface of the turgid cells, water gets evaporated into the intercellular spaces.
This vapor present in intercellular spaces becomes saturated and diffuses outwardly to the environment
where the air is unsaturated.
Water vapor diffuses through stomata, cuticle and lenticel.
The rate of this water loss is reduced just after heavy rainfall as the atmospheric air is usually saturated
with vapor in such cases.
Types of Transpiration:
Depending upon the plant parts involved, transpiration is classified into the following three types:
1. Stomatal Transpiration:
Transpiration occurring through stomata is called stomatal transpiration.
The stomata constitute the major pathway through which 90% of water vapor is lost by the
aerial parts of the plant.
Stomata are minute pores found on the epidermis between two guard cells.
These stomata allow water vapor to escape through them into the atmosphere.
Stomata are found on leaves, young stem, flowers and fruits.
In isobilateral leaves, the stomata are equally distributed on both upper and lower surfaces,
whereas, in dorsiventral leaves, they are found on the lower surface.
2. Cuticular Transpiration:
The loss of water vapor through the cuticle or cuticular surface of the plant parts is called
cuticular transpiration.
aff ecting transpiration, Biological signifi cance and
Disadvantages
Plants absorb a large quantity of water from the soil by root hairs and only a small part (1-2%) of this
water is utilized by them in their life processes.
The remaining large part (98-99%) of water is lost in the form of vapor from internal tissues.
The process of loss of water in the form of vapor through the exposed aerial parts of the plants is
called transpiration.
Transpiration is regulated by vital activities of protoplasm and some structural peculiarities of the
transpiring organs.
Why transpiration is called a necessary evil?
Transpiration facilitates the upward movement of water and minerals absorbed by roots but at the same
time if water loss through transpiration is more than the absorption of water, it can cause wilting and
even death of the plant. Hence, transpiration is called a necessary evil.
Mechanism of transpiration:
The mesophyll cells of the leaf withdraw water from the xylem tissue by osmotic diffusion and become
turgid.
From the surface of the turgid cells, water gets evaporated into the intercellular spaces.
This vapor present in intercellular spaces becomes saturated and diffuses outwardly to the environment
where the air is unsaturated.
Water vapor diffuses through stomata, cuticle and lenticel.
The rate of this water loss is reduced just after heavy rainfall as the atmospheric air is usually saturated
with vapor in such cases.
Types of Transpiration:
Depending upon the plant parts involved, transpiration is classified into the following three types:
1. Stomatal Transpiration:
Transpiration occurring through stomata is called stomatal transpiration.
The stomata constitute the major pathway through which 90% of water vapor is lost by the
aerial parts of the plant.
Stomata are minute pores found on the epidermis between two guard cells.
These stomata allow water vapor to escape through them into the atmosphere.
Stomata are found on leaves, young stem, flowers and fruits.
In isobilateral leaves, the stomata are equally distributed on both upper and lower surfaces,
whereas, in dorsiventral leaves, they are found on the lower surface.
2. Cuticular Transpiration:
The loss of water vapor through the cuticle or cuticular surface of the plant parts is called
cuticular transpiration.
