Transpiration of plants - How transpiration occurs

Transpiration of plants - How transpiration occurs

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Transpiration is another very important function performed by the leaves and concerns almost all the water absorbed by the roots which, once it reaches the leaves, is expelled as water vapor through particular openings called stomata, which open and close according to the greater or less need for the plant to transpire.

Transpiration plays a decisive role in the life of plants in fact it is only thanks to it that

the carbon dioxide of the air is captured and conveyed inside the plant tissues

(enters the cells only when dissolved in water) to carry out photosynthesis,

as well as oxygen

for the development of respiration: without continuous transpiration, plants would not capture carbon dioxide and oxygen so photosynthesis and respiration would not take place.

The perspiration allows the

constant arrival of water and mineral salts to the leaves

from the roots because in fact it is a loss of water that the plant compensates with the intake of new water by the roots, thus also facilitating the absorption of mineral salts (this is why it is important never to lack the right amount of water to plants) Transpiration

regulates the temperature of the plants

keeping them fresh by preventing fabrics from reaching high temperatures. In fact, if we touch a flower or a leaf in the middle of summer, we perceive them fresh and this thanks to transpiration.

The fertility of the soil itself is influenced by transpiration, in fact, about 60% of the water that falls to the ground with the rain is transpired, thus preventing the soil from becoming marshy making the air humid thus regulating the rains and therefore

improving soil fertility



sf. [sec. XVII to transpire]. Act and effect of transpiration in particular, in biology, a process by which living organisms, animals or plants, eliminate water vapor at the level of the surfaces in contact with the external environment. In the animal organism, transpiration occurs almost exclusively at the level of the skin and lungs and is related to thermoregulation, while in plants it is essentially an evaporation of the water absorbed at the level of the roots.

Agricultural botany - Transpiration and gas exchanges Atlas of Botany

The water absorbed by the roots goes up along the xylem vessels (woody) to the leaves as indicated in the drawing below.
During the day, when the temperature is higher, there is the maximum loss of water through transpiration. The stomata are small openings present in large numbers mainly on the underside of the leaf. Through these openings the water vapor exits into the external environment. The fact that stomata are almost exclusively on the part of the leaf not directly exposed to the sun is not accidental: this mechanism allows to reduce the loss of water during the hot hours. Some dryland plants have developed very special systems to minimize the loss of water through their leaves.

Through the stomata, all gaseous exchanges take place: the water coming from the xylem comes out in the form of vapor (transpiration), due to photosynthesis, carbon dioxide enters and oxygen is eliminated.

1.cuticle 2.epidermis 3.mesofillo 4lower epidermis 5.cuticle 6.xilema 7. gaps in tissue 8. palisade fabric. Gas exchanges (source Iprase Trentino)

The stomata
The stomata open when the guard cells accumulate potassium ions (red dots) which reduce the water potential causing water to enter the cell by osmosis. The cells swollen with water become turgid and fold into a "bean" shape, increasing the width of the stomatal opening. A leakage of potassium ions from the guard cells, on the contrary, increases the water potential: the water escapes from the stomatal cells which collapse and flatten approaching until the stomatal opening is completely closed.



Transpiration, which favors the circulation of lymph in the tissues and represents a means of defense against excessive heating of the environment, occurs mainly by means of the stomata, which are found both on the leaves and on the young stems, and of the lenticels. The stomatal openings can be very numerous and communicate with the intercellular spaces inside the leaf, where the air is saturated with water vapor that has formed from the humid surfaces of the mesophyll cells. Stomatal loss represents more than 90% of transpiration water. Transpiration is influenced by various factors, one of the most important of which is temperature: in fact, the evaporation rate of water doubles for every 10 ºC increase in temperature. Since evaporation determines a cooling of the leaf surface, its temperature does not increase as rapidly as the ambient temperature, in this way transpiration has a protective function against external environmental factors. Obviously, the humidity of the air also influences the phenomenon, since if it is saturated with water vapor, further evaporation is slowed down. The presence of wind, on the other hand, accelerates the transpiration processes by rapidly eliminating the layers of air rich in humidity that form near the leaf surface. The presence of a thick tomentum in plants living in windy environments would be explained just as an attempt to protect against the wind, thanks to the stabilization of the layer of air in contact with the surface of the leaves, with consequent reduction of transpiration. The stomata in the upper plants are subject to closing and opening movements that allow to regulate transpiration. If the general turgor of the organ falls below the threshold value typical of each individual species, the lumen of the stoma narrows until it disappears, regardless of any other opening and closing mechanism. The stomatal cells are then sensitive to light, temperature and the concentration of carbon dioxide, as if this increases too much in the intercellular spaces of the mesophyll, the stomata close. In relation to the influence exerted by all the various external factors and since these vary during the day it is evident that the trend of perspiration will change over the 24 hours. In general, by far the largest part of the water is transpired during the day, while the nocturnal share covers only approx. 3% of the total. During the first hours of the morning the transpiration value is very low, then it begins to increase with the rising of the sun and with the concomitant increase in the air temperature. Together with an increase in temperature there is also a decrease in the humidity of the air, which favors the further increase of transpiration which reaches its maximum in the midday hours and then abruptly decreases and shortly after sunset reaches the low values ​​that it will maintain in the night. Whenever anomalies occur in environmental conditions, especially as regards light and temperature, the value of transpiration shows even considerable fluctuations compared to the aforementioned norm.

What is meant by potential evapotranspiration?

Potential evapotranspiration represents the evaporation that would occur if the water removed from the ground were available without limitations because it is continuously renewed. The potential evapotranspiration value can be much greater than the real one since in reality the water lost due to evapotranspiration is not renewed immediately, but only intermittently with the rains. Most tools for calculating the evapotranspiration value provide only the potential value.

The transpiration of plants

The transpiration of plants occurs through the pores and stomata of the leaves and is a phenomenon linked to photosynthesis: the stomata, in order to be able to take on carbon dioxide, keep the stomata open from which the water escapes. Many plants keep their stomata open during the day and closed at night, therefore the transpiration value will be higher during the day. 99% of the water absorbed by the roots is lost by transpiration, while only 1% enters the plant constitution

What are the effects of plant transpiration on the climate?

The amount of latent heat dissipated by transpiration from plant surfaces is quite high. This implies that the presence of large green areas in an urban environment contributes considerably to making summer overheating situations less critical. For example, the presence of a tree-lined square of 100 meters by 100 meters can transpire up to 50,000 liters of water per day, absorbing about 30,000 kcal, energy that would otherwise be absorbed by the buildings that would re-emit it in the form of heat. In terms of temperatures, it has been estimated that plant transpiration can decrease the air temperature up to 5-6 ° C compared to areas without plants and built up.

Hi, I would like to know roughly what transpiration in plants is, what is it for? When and why does it happen? Can it be considered as an adaptation or is it just breathing in plants? Greetings to all, Ele.

In terrestrial plants, water ensures cell turgor and is of vital importance for the water balance and nourishment of the plant. When the water is insufficient, withering occurs, which continues over time and leads to withering and therefore to the death of the plant.

As for the nutritional elements, each plant must absorb a considerable volume of water from the soil, to meet its needs in macro (N, P, K, S, Ca, Mg, Fe) and micro elements (B, Mn, Cu , Zn, I).

Overall, the water cycle in the plant has three phases: root absorption,
lymph circulation,

Transpiration, that is, the evaporation of water at the leaf level, causes the temperature to drop in the leaves. Furthermore, a drop in pressure is generated with consequent recall of water, or rather of raw sap, which rises from the roots through the vessels of the wood.

Transpiration occurs through the stomata, organs responsible for gaseous exchanges and which are normally present in the lower face of the leaves. Through them, CO is absorbed2 and emission of O2, with simultaneous transpiration, i.e. evaporation of H.2OR.

In particularly dry environments, plants implement a whole series of adaptations that allow the gas exchange necessary for photosynthesis, but limit the loss of water to the maximum.

For example, in some cacti, the stomata all collect in epidermal depressions at the bottom of which there are areoles, which with their fluff limit the loss of moisture during transpiration.

Mediterranean plants are evergreen, but they have to cope with low summer water availability and defend themselves from excessive transpiration: for these reasons their leaves are small and typically stiff, due to the presence of highly mechanically resistant fabrics, called "sclerenchyma". In addition, their skin is covered with materials such as cutins and waxes, which retain water inside and reflect much of the incident light. It is to the high reflection of light that we owe the characteristic brightness of the leaves of many Mediterranean.

The needle-like leaves are adapted to both cold and drought induced by the inability to use ice water. They have a thick external waxy coating and the stomata are located in a deep hollow that runs the entire length of the needle.

Video: Stomata. Opening and Closing of Stomata. Class 10. Biology. ICSE Board. Home Revise


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