The stomata are primarily
meant for absorption of CO2 but these also help in exchange of
gases, but at the same time water vapors also escape through stomata. Thus
transpiration is described as necessary evil because it is an inevitable
process but potentially harmful. Loss of water can lead to wilting, serious
desiccation, and often death of a plant, if there is shortage of water. There
is good evidence that even mild water stress results in reduced growth rate,
and reduction in yield.
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| Transpiration |
However, transpiration is
beneficial to the plants in several ways.
1) Mineral Absorption: Minerals absorbed in water are absorbed into
the roots; move up through the plant in the transpiration stream.
2) Optimum Turgidity: In some plants if transpiration is not allowed
to occur, plants become very turgid, do not grow well and there is shortage of
water in their cells.
3) Energy Exchange: When water is evaporated from the exposed surface
of cells of leaves, it exerts a cooling effect on plant.
4) Effect on Growth and Development: Transpiration is a necessary
factor in the normal growth of some plants e.g. pear, sunflower.
5) Absorption of Water: Water is conducted or transported in upward
direction in most tall plants due to transpiration.
6) Exchange of Gases: Wet surface of leaf cells allow gaseous
exchange.
The evaporation of water
from the surface of leaf cells in actively growing plants is called
Transpiration. Thus more water enters the plant from the soil. The water enters
the plant in the form of liquid but when it is on the surface of the leaves, it
converts into gaseous form due to evaporation. The cohesive properties of water
(hydrogen bonding between adjacent water molecules) allow the column of water
to be ‘pulled’ up through the plants as water molecules are evaporating at the
leaf surface. This process has been termed the Cohesion Theory of Sap Ascent in
plants.
The proper description of why transpiration is a necessary evil would be ~
ReplyDeleteThe loss of excess water in the form of water vapour through evaporation from the surface of the internal tissues of the aerial parts of plants especially leaves, is known as Transpiration.
Since water is one of the most important compounds needed for various important life processes, a loss of water by transpiration is obviously harmful. This harmful effect becomes dangerous when excessive transpiration leads to the wilting of the plants. To reduce the loss of water, several practices are commonly employed by the farmers and the gardeners. One of them is to remove the weeds from the vicinity of the crop plants. These weeds transpire a lot of water and also utilize soil minerals, thus depleting the soil of its two important constituents, the water and the mineral salts.
If it is not done, the crop plants would only be stunted. To minimize the transpiration during the summer months, the green houses are whitewashed to cut down the light intensity and the temperature. Interior of the green houses is sprayed with water to saturate the atmosphere with humidity and thus decrease the transpiration. In propagation of plants by cutting or in trans-plantation of seedlings, some of the leaves are removed to reduce the transpiration and thus avoid wilting. Besides wilting, other harmful effects of excessive transpiration include inhibition of protein synthesis and breakdown of proteins and retardation of metabolic processes like photosynthesis. This is the reason why Transpiration is often called as necessary evil.
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ReplyDeleteVery good...this is very interesting and useful for our study and also this is very important for us.. thank you so much for your support and..
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