What is transpiration in biology?

What is transpiration?

Plants release water in the form of vapor from its aerial parts like stems and leaves. This water loss from plants in the form of vapor is called transpiration. These water vapors are generated from the internal tissues and occur at the exposed part of the plants.

Environmental conditions like temperature, humidity level determine the rate of transpiration.A structure in the epidermal cell of plants called stomata controls the transpiration. As compared to evaporation in surroundings, transpiration is very slow process.

On basis of the surface from which water vapor transpires, it is classified as Stomatal transpiration(Transpiration from the stomata on leaves), Cuticular transpiration(Transpiration by cuticular or epidermal cell of the leaves), Lenticular transpiration(Transpiration by the lenticels present on woody surface of plants); Bark transpiration( Transpiration through the outer cork of the stem).

Transpiration

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Types of Transpiration

There are three main types of transpiration-

  • Stomatal Transpiration: This is the most common type, accounting for about 90% of the water lost by plants. It occurs through the stomata, which are small openings on the underside of leaves. These openings allow gas exchange but also lead to water vapor loss. The rate of stomatal transpiration is influenced by factors such as light, temperature, humidity, and wind.
  • Cuticular Transpiration: This type involves water loss through the cuticle, a waxy layer covering the leaves and stems. Cuticular transpiration is typically minimal compared to stomatal transpiration, as the cuticle is designed to prevent water loss. However, in conditions of high humidity or when the stomata are closed, cuticular transpiration can become more significant.
  • Lenticular Transpiration: This occurs through lenticels, which are small openings in the bark of woody plants. Lenticels allow for gas exchange and transpiration, though the amount of water lost this way is relatively small compared to stomatal and cuticular transpiration.

Structure of Stomata

Stomata are tiny pores located on the epidermal surface of leaves. These pores are guarded by two kidney-shaped cells known as guard cells. The inner wall of the guard cell facing the stomata is thicker than the outer walls. The unique arrangement of microfibrils within the guard cells facilitates the opening and closing of the stomatal aperture.

The microfibrils are arranged radially rather than longitudinally, making it easier for the stomata to open. In a dorsiventral (dicotyledonous) leaf, there are more stomata on the lower surface compared to the upper surface. This adaptation helps in reducing water evaporation. In an isobilateral (monocotyledonous) leaf, the number of stomata is equal on both surfaces.

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Factors affecting Transpiration

Transpiration rate depends on various factors such as

  • Environmental factors like
  1. temperature
  2. relative humidity
  3. wind speed etc.
  • Plant factors like
  1. the number and distribution of stomata.
  2. Percentage of open stomata.
  3. Water status of the plant.
  4. The structure of canopy of the tree.

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Frequently Asked Questions on What is transpiration in biology?

Ans. Transpiration is the process by which plants release water vapor into the atmosphere from their leaves and other aerial parts.

Ans. Water is absorbed by roots from the soil, transported through the plant, and evaporated from the stomata in leaves into the atmosphere.

Ans. The two types of transpiration are stomatal transpiration, which occurs through the stomata, and cuticular transpiration, which occurs through the cuticle.

Ans. Transpiration helps in nutrient uptake, cooling the plant, and maintaining turgor pressure, which supports plant structure.

Ans. Transpiration is driven by factors such as light, temperature, humidity, wind, and soil water availability, which affect the opening and closing of stomata.