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Do you want to create an amazing science fair project for your next exhibition? You are in the right place. Read the below given article to get a complete idea on transpiration: 1. Meaning of Transpiration 2. Kinds of Transpiration 3. Mechanism 4. Factors 5. Regulation 6. Significance 7. Modifications.
Contents:
- Science Fair Project on the Meaning of Transpiration
- Science Fair Project on the Kinds of Transpiration
- Science Fair Project on the Mechanism of Transpiration
- Science Fair Project on the Factors Affecting Transpiration
- Science Fair Project on the Regulation of Transpiration
- Science Fair Project on the Significance of Transpiration
- Science Fair Project on the Modifications for Transpiring Plants
Science Fair Project # 1. Meaning of Transpiration:
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The plants absorb sufficient quantity of water from the soil by means of their root hairs. Some part of this water is used up in the metabolic activities going on within the plant body and the rest of it evaporates from the stem and leaves. The evaporation of the water from the aerial parts of the plant is known as transpiration.
Many authors described this phenomenon of transpiration from time to time in the following words:
‘Transpiration is the loss of water in the form of water vapour from stem and leaves’.
‘The loss of water vapour from aerial parts of living plants is known as transpiration’.
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‘Transpiration is giving off of water vapour from the surface of a plant.’
The transpiration differs from ordinary evaporation this way that the former is controlled by the protoplasm whereas latter does not. The transpiration is a metabolic activity, which is controlled by protoplasm and may be reduced or increased where needed by the nature.
Science Fair Project # 2. Kinds of Transpiration:
In general, there are three kinds of transpiration viz.:
(a) Cuticular,
(b) Lenticular, and
(c) Stomatal.
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The cuticular transpiration takes place through the cuticle found on the surface of the stem and leaves. The lenticular transpiration takes place through the lenticels found upon the stem. During night the stomata remain closed and the plants transpire through lenticels and cuticle. The stomatal transpiration is the most important.
This takes place through the stomata situated on the leaves and sometimes on the green stems. The number of stomata is usually always greater on the lower surface of the leaf. About 90 to 97% of the transpiration takes place through the stomata.
Science Fair Project # 3. Mechanism of Transpiration:
About 90 to 97% of the transpiration takes place through stomata, and 3 to 10% through the cuticle. The lenticular transpiration is negligible. Here the mechanism of stomatal transpiration has been given in detail. As we know well the water rises up in the stem of the plant through xylem vessels.
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From the xylem vessels of the veins of the leaves, the water diffuses to the mesophyll tissue making gradually the assimilatory cells, fully turgid.
The moist cellular walls release the water in the form of vapour which reaches the intercellular spaces. This way, the intercellular spaces become more saturated than the outer atmosphere. As the intercellular spaces are interconnected with the sub-stomatal chambers, they also become saturated with water vapour.
The outer atmosphere is comparatively drier than the inner tissues and therefore, the water vapour diffuses from the sub-stomatal chambers to the outside through the stomata.
The outer air remains in close contact of the leaves, evaporating the water from their surfaces. This process goes on continuously. The stomatal transpiration is controlled by the guard cells of the stomata.
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Science Fair Project # 4. Factors Affecting Transpiration:
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The transpiration is affected by several external and internal factors.
They are as follows:
External Factors:
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a. Light:
The light affects indirectly the transpiration. The rate of transpiration is always higher in light than in darkness. The main reason is that the stomata remain open in the presence of light or in the day time, and the transpiration takes place through them.
In the absence of light or in the night, the stomata remain closed, and the transpiration is checked. During night only lenticular and cuticular transpiration takes place. The leaves receive heat from the sun, which accelerates the rate to some extent.
b. Atmospheric Moisture:
Both the dryness and the humidity of the atmosphere affect the transpiration. When the atmosphere is very dry, then the water evaporates very rapidly from the surface of the leaves. On the other hand, in saturated atmosphere the rate of transpiration is quite slow.
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c. Wind Velocity:
When wind blows very fast, the rate of transpiration also becomes very high, and on becoming the atmosphere calm and quiet, the transpiration lessens sufficiently due to moist air in close contact of the transpiring plants.
d. Air Temperature:
As the atmospheric temperature rises, the rate of transpiration also rises. In high temperatures the water evaporates from the leaf surface quite rapidly. In dry and hot air the rate of transpiration rises further.
e. Solar Radiation:
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This factor is deeply related to the transpiration. The temperature of the leaves rises due to solar radiation, thus increasing the rate of transpiration. This way, solar radiation affects the transpiration indirectly.
f. Soil Environment:
This factor also affects the transpiration indirectly. The soil environment is much related to the water absorption. We know well, that the transpiring mesophyll cells of the leaves receive water from the soil.
This way, the factor affecting the absorption of water from the soil, such as:
(i) Soil water content,
(ii) Concentration of soil solution,
(iii) Soil temperature, and
(iv) Oxygen of soil air, etc., affect the transpiration indirectly. If there is enough of absorption of water, the transpiration takes place to a greater extent, on the other hand if the absorption of water is less the transpiration is also less.
Internal Factors:
a. The Root System:
If the roots reach deep in the soil up to the moist layers, the root hairs absorb sufficient quantity of water and at the same time the transpiration increases from the aerial parts of the plants. On the other hand, if the root system of the plant remains confined in the upper layers of the soil, there is less absorption of water and less transpiration.
b. The Stem:
As we know that the water rises from the roots to the stem and leaves through the xylem vessels, and therefore, the rate of transpiration much depends upon the narrowness and broadness of the xylem vessels present in the stem. If the xylem vessels are sufficiently broad, the rate of transpiration increases, and if they are narrow there is comparatively less transpiration.
c. Leaf Structure:
The leaves of many xerophytes are too much divided and this way the total leaf area becomes very much decreased. Sometimes, some plants completely lack the leaves, and the stems of such plants become flat, leaf like, angular or rounded and green.
They are called phylloclades, e.g., phylloclades of Ruscus, Opuntia, etc. Less amount of water is transpired from the surface of the phylloclades. The leaves of Asparagus are scale-like and the cladodes are developed for photosynthesis. Very less amount of water transpires from the surface of these cladodes.
Several leaves bear the special adaptations to check the excessive transpiration. These leaves also differ anatomically from the ordinary typical leaves. Sometimes in certain leaves a waxy substance accumulates on the epidermis and the cuticle becomes quite thick, which checks the excessive transpiration.
The leaves of other plants bear special cavities or depressions. The stomata are situated in these depressions which are usually surrounded by hairs. These special adaptations check transpiration to a large extent, e.g., Nerium, Banksia, etc.
In addition to these, the epidermis becomes multilayered, e.g., Nerium, Ficus, etc., which lessens the transpiration. In several xerophytic plants, the cells of epidermis are radially elongated, which retard excessive transpiration.
The sunken stomata are found in xerophytic leaves which help in retarding the transpiration. The leaves of certain xerophytes become infolded, and the stomata are protected from the direct gusts of wind, thus decreasing the rate of transpiration, e.g., Ammo-phila arenaria. This way, the leaves bear several special adaptations which check the excessive transpirations.
Science Fair Project # 5. Regulation of Transpiration:
Plants maintain wonderful balance between the intake and outgo of water. The aquatic plants are so adapted that they can transpire any amount of water, because the loss may be readily made good by absorption. Land plants regulate transpiration having cutinised epidermal cells, deposition of waxy and resinous matters, etc., and also by the suberised corky bark in the old stems.
These are all contrivances for reducing transpiration. Plants growing in very dry situations like deserts (xerophytes) have their transpiration rates reduced to the minimum not because of any inherent peculiarities of their structure and physiological behaviour but due to the only fact that the water supply of the soil in which they grow is so low that very little absorption of water can occur.
Their leaf surfaces are extremely reduced. They are rolled or folded, have very thickly developed cuticle on epidermis together with dense hairy outgrowths and coating of waxy matters. Stomata usually remain sunken.
Leaves are often modified into spines as in Opuntia. It should be mentioned that stomatal regulation of transpiration is only significant, when the aperture is almost closed. Once the stomata are even half open, there is no question of regulation, but environmental factors such as humidity, temperature, etc., are much more important.
Science Fair Project # 6. Significance of Transpiration:
Transpiration is regarded as the natural accompaniment of the physiological processes involving gaseous exchange between the internal tissues and the outer atmosphere. It is unavoidable because, when the stomata will open for gaseous exchange they must allow water vapour to pass out.
Transpiration is positively dangerous for the plants having limited water supply. For ordinary plants transpiration must, however, be considered as a necessary evil, because the metabolic processes taking place in plants are certainly intimately related with transpiration.
It has been conclusively proved that there is no relationship between the rate of transpiration and absorption of nutrient matters. The whole structure of the leaf was not possibly meant to check transpiration.
A thin flat surface provided with large intercellular spaces ending in numerous openings (stomata) was never intended for checking transpiration but rather for facilitating gaseous exchange. Transpiration, of course, facilitates the mass movement of inorganic salts through the conducting channels.
It is considered to have a cooling effect on plants, as considerable amount of heat is used in converting liquid into vapour, but the difference in temperature brought about is certainly not great to have any significant effect on the transpiration rates.
Science Fair Project # 7. Modifications for Transpiring Plants:
(a) Potometer kept in atmosphere of high humidity.
(b) Potometer kept under the fan.
(c) Potometer kept in higher temperature.
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(d) Potometer kept in dark.
(a) Potometer Kept In Atmosphere Of High Humidity:
Here the air bubble moves with a slow speed. Stomatal transpiration is caused by the diffusion of water vapours from the intercellular spaces of the mesophyll cells into the outer atmosphere through the stomata. This condition is only possible when outer atmosphere possesses less humidity or less vapour contents.
Here in the given condition the outer atmosphere is of higher humidity, so the loss of water from the leaves is negligible and consequently the transpiration is lowered. Therefore higher the humidity of air, lower is the transpiration.
(b) Potometer Kept Under The Fan:
Here the air bubble will move with a greater speed. The running fan causes to increase the rate of transpiration by sweeping away the water vapours that are present in the vicinity of transpiring plant. Therefore in this area the humidity of air becomes lower and the rate of transpiration is promoted.
(c) Potometer Kept In Higher Temperature:
Here the air bubble moves with a faster speed. Temperature has an indirect influence on the rate of transpiration.
Increase in temperature causes the following effects:
(i) Stomata get widened with the increase in temperature. So the loss of water is more, increasing the rate of transpiration.
(ii) A rise in temperature decreases the relative humidity of surrounding air. The drier the air, the more rapid is transpiration.
(d) Potometer Kept In Dark:
The air bubble does not move at all. It is due to fact that the stomata get closed when it is dark. Lowering of pH value (pH – 5) favours in closing of stomata. In dark the reducing osmotically active sugars change into the osmotically inactive starch. So the pH value lowers to 5 and the stomata are closed. On closing the stomata, no transpiration takes place, hence, the air bubble remains stable.