Transpiration: Definition, Types, Factors, and Significance

Transpiration: Definition, Types, Factors, and Significance

Transpiration: Definition,

 Even while plants receive a lot of water from the soil, very little of it is used by the plant. Water vapours are produced when surplus water is lost from a plant’s aerial portions. This process is known as Transpiration.

The evaporation of water from plants is known as Transpiration. As much as 99.5% of the water received by a plant’s roots is not used for growth or metabolism, instead, it is excess water that transpires out of the plant. Maintaining the environment’s moisture levels depends heavily on transpiration. Up to 10% of the moisture in the Earth’s atmosphere is caused by plants transpiring water. English botanist and biologist Stephen Hales (1677–1761) made the first measurement of transpiration. He developed a revolutionary technique for assessing the emission of water vapour by plants after seeing that plants “imbibe” and “perspire” substantial amounts of water in comparison to animals. He discovered that water and dissolved nutrients were continuously transported upward from the roots by a process known as Transpiration, which originated from the leaves. According to recent studies, a plant’s roots can release up to 99% of the water they absorb as water vapour into the atmosphere. The principal locations of transpiration are called Leaf Stomata, which are two guard cells that together produce a tiny pore on the surface of leaves. The guard cells can regulate the rate of transpiration to prevent water loss and govern how the stomata open and close in response to diverse environmental cues. Stomata prefer to close in the presence of internal water shortage and darkness, increasing transpiration in the presence of illumination, an abundant water supply, and an ideal temperature. To reduce evaporation or when there is a lot of carbon dioxide gas present—even though the plant probably has plenty for photosynthesis—many plants cover their stomata.

Transpiration is of three types

1. Stomatal Transpiration

Stomata are the primary conduits for transpiration. Typically, stomata are more densely packed on the lower sides of leaves. Among monocots. For instance, there is an equal distribution of grass on both sides. While they are found on the upper surface of aquatic plants with floating leaves.

2. Cuticular Transpiration

Even though some water may leak through the cuticle, it is water-resistant. It may make up no more than 10% of the overall transpiration.

3. Lenticular Transpiration

Woody stems may lose some water through lenticels, a process known as lenticular transpiration.

Factors affecting Transpiration Rate

A. External Factors

1. The atmospheric moisture

When relative humidity is high in a humid environment, the transpiration rate declines. It’s because the atmosphere is moister and slows down the diffusion of water vapour through stomata from the intercellular spaces of the leaves to the outer atmosphere. As a result of low RH and an absence of moisture-saturated air in a dry atmosphere, transpiration rates rise.

2. Temperature

A rise in temperature causes the rate of transpiration to increase by

1. lowering the relative humidity

2. Opening of stomata widely

3. Wind

i. When there is no wind or only a slight breeze, the rate of transpiration does not change.

ii. The rate of transpiration increases when the wind is flowing gently because it removes moisture from the area around the plant’s transpiration parts. This makes it easier for water vapour to diffuse from the intercellular spaces of the leaves to the outer atmosphere through stomata.

iii. The rate of transpiration decreases when the wind is blowing erratically because it hinders the outward diffusion of water vapour from the transpiring region and may even seal the stomata.

4. Light

Light causes the stomata to open, which raises the temperature. This increases the rate of transpiration. Stomatal transpiration is nearly completely stopped in the dark as a result of stomata closing.

5. Easily accessible soil water

If there is not enough water in the soil for the roots to easily absorb, the rate of transpiration will fall.

6. CO2

A rise in atmospheric CO2 concentration (Ova the typical concentration), especially inside the leaf causes stomatal closure, which slows transpiration.

B. Internal factors

1. Internal water conditions

It is necessary for transpiration. A drop in transpiration rate will occur in plants that are not getting enough water. Because water absorption cannot keep up with increased transpiration for extended periods, plants frequently experience internal water deficits.

2. Structural features

The amount of transpiration depends on the quantity, size, position, and movement of stomata. Stomata are closed and stomatal transpiration is monitored in the dark. Reduced stomatal transpiration is facilitated by sunken stomata. To control transpiration, xerophytes’ leaves shrink in size or even fall off. Reduced cuticle transpiration is caused by thick cuticles and wax coatings on exposed portions.

Significance of Transpiration

A significant portion of the energy used by plants to absorb enormous amounts of water is ultimately lost through transpiration. Some people believe that plants can benefit from transpiration. Others believe it to be an undesirable process that cannot be stopped.

Advances in transpiration

1. The role of water movement is crucial in the upward movement of water or the ascent of sap in plants.

2. Role in the absorption and translocation of mineral salts

The processes for absorbing water and mineral salts are wholly unrelated. Therefore, the absorption of mineral salts is unrelated to transpiration. However, after the plants have absorbed the mineral salts, transpiration through the movement of water in the xylem elements may help with their further translocation and distribution.

3. Temperature regulation’s function

The leaves use some of the light energy they collect for photosynthesis, the remainder is converted to heat energy, which raises their temperature. The temperature of the plants is mostly regulated by transpiration. Rapid water evaporation from the plant’s aerial parts through transpiration lowers their temperature and keeps them from overheating.

Transpiration As a Necessary Evil,

1. When the rate of transpiration is high and the soil is water-deficient, the plants may experience an internal water deficit that affects metabolic functions.

2. To control transpiration, many xerophytes must undergo structural modifications and adaptations.

3. To prevent water loss, deciduous trees must lose their leaves in the fall.

However, despite the numerous drawbacks, plants must transpire because of their unusual internal structure, especially that of their leaves. Although primarily intended for gaseous exchange for respiration, P.S., etc., their interior structure is such that it cannot prevent water from evaporating. As a result, several scientists, including Curtis (1926), have referred to transpiration as a necessary evil.

Frequently Asked Questions

Question: What is the transpiration process?

Ans: The evaporation of water from plants is known as Transpiration

Question: What is transpiration and its function?

Ans: Water vapours are produced when surplus water is lost from a plant’s aerial portions. This process is known as


1. The role of water movement is crucial in the upward movement of water or the ascent of sap in plants.

2. Role in the absorption and translocation of mineral salts

3. Temperature regulation’s function

Question: What factors affect transpiration?

Ans: The Atmospheric Moisture, CO2, Light, Wind, and Temperature

Question: What happens if transpiration stops?

Ans: Water will no longer be moving upward from roots

Question: Do plants transpire at night?

Ans: Yes Plants transpire in the Daytime as well as Night

Question: What happens if transpiration does not happen?

Ans: The water from the roots will not move upwards. 

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