Transpiration-in-plants

Transpiration in plants: Types, Mechanism, Affecting factors and Significance

Transpiration in plants is the process by which plants lose water in the form of water vapor from their aerial parts, primarily through the stomata of leaves. This process is essential for plant physiology, as it drives water movement from roots to leaves and helps regulate temperature.

Water is lost by transpiration to the tune of 97–99%. The physiological loss of water as water vapour, primarily through the stomata of leaves but also by evaporation from the surfaces of leaves, flowers, and stems, is known as transpiration.

Transpiration-in-plants

Types of Transpiration

  1. Stomatal Transpiration:
    • Water vapor is lost through the stomata, tiny pores located primarily on the lower surface of the leaves.
    • Contribution: Accounts for about 85–90% of the total transpiration in plants.
  2. Cuticular Transpiration:
    • Water loss through the cuticle, a waxy layer on the leaf surface that minimizes water loss but still allows some transpiration.
    • Contribution: Accounts for around 5–10% of transpiration in plants.
  3. Lenticular Transpiration:
    • Water vapor escapes through lenticels, small openings on the bark of stems and branches.
    • Contribution: Contributes only a small amount of the total transpiration in plants.

Mechanism of Transpiration

  1. Water Uptake:
    • Water is absorbed by the plant roots from the soil through osmosis.
  2. Ascent of Sap:
    • Water travels upward through the xylem vessels from roots to leaves, primarily driven by capillary action and root pressure.
    • Cohesion-Tension Theory: Water molecules stick together (cohesion) and adhere to the xylem walls (adhesion), creating a continuous column of water from roots to leaves.
  3. Evaporation from Leaf Cells:
    • In the leaf, water moves from the xylem to mesophyll cells and evaporates from the cell walls into the intercellular spaces.
  4. Diffusion through Stomata:
    • The water vapor then diffuses from the intercellular spaces to the atmosphere through stomatal pores. This step is regulated by the opening and closing of stomata, which are controlled by guard cells.
  5. Pulling of Water:
    • As water vapor is lost from the leaf, it creates a negative pressure or suction (transpiration pull), drawing more water upward from the roots.
Plant_Transpiration

Factors Affecting Transpiration

  1. External Factors:
    • Light Intensity: Increased light causes stomata to open, leading to more transpiration.
    • Temperature: Higher temperatures increase the rate of evaporation and thus transpiration.
    • Humidity: Low humidity increases the water vapor gradient between the leaf and the atmosphere, enhancing transpiration.
    • Wind Speed: Higher wind speeds remove the saturated air around the leaf surface, increasing the rate of transpiration.
    • Water Availability: Limited water supply in the soil reduces the plant’s ability to absorb water, leading to a reduction in transpiration.
  2. Internal Factors:
    • Stomatal Density: More stomata result in higher transpiration rates.
    • Leaf Surface Area: Larger leaves with more surface area tend to lose more water.
    • Cuticle Thickness: Thicker cuticles reduce water loss through cuticular transpiration in plants.
    • Leaf Orientation: Leaves that minimize direct exposure to sunlight reduce transpiration in plants.

Significance of Transpiration

  1. Water Movement and Nutrient Transport:
    • Transpiration helps in the upward movement of water from the roots to different parts of the plant, carrying dissolved minerals and nutrients essential for growth.
  2. Cooling Effect:
    • It cools the plant by releasing water vapor, helping to maintain temperature homeostasis and prevent overheating.
  3. Maintains Turgor Pressure:
    • Water lost through it is replenished from the roots, keeping cells turgid (full of water) and maintaining the plant’s structure and rigidity.
  4. Gas Exchange:
    • The opening of stomata during transpiration in plants also allows for gas exchange, facilitating the intake of carbon dioxide needed for photosynthesis.
  5. Prevents Waterlogging:
    • By losing water through it, plants help prevent excess water from accumulating in their tissues, which can lead to waterlogging and disrupt metabolic processes.

Examples of Plants and Adaptations

  • Desert Plants (Xerophytes): Have thick cuticles, fewer stomata, and specialized leaf structures to reduce transpiration. Example: Cactus.
  • Hydrophytes: Plants in aquatic environments have a thin cuticle and more stomata to facilitate water exchange. Example: Water lilies.

In conclusion, it is an essential process in plants, regulating water balance, nutrient uptake, and temperature control. The rate of transpiration is influenced by both environmental conditions and internal plant factors, making it a crucial aspect of plant survival and growth.

Frequently Asked Questions (FAQS)

What is transpiration in plants study?

Similar to any other living thing, plants also need an excretory system to get rid of extra water from their bodies. Transpiration is the mechanism by which the extra water is removed from the plant body. Usually, it is the water evaporating off the leaf surface.

Why is transpiration important to plants?

A significant part of the energy balance of leaves is evaporative cooling, which is produced by plant transpiration. Additionally, transpiration acts as a catalyst for the movement of nutrients and water from roots to shoots.

What is transpiration in plants cycle?

Water moves from a plant’s roots to its leaves through a process called transpiration, which is a component of the water cycle. Once there, it turns into vapour and is released into the sky.

What is the pathway of transpiration in plants?

One approach is the apoplastic path, in which the water molecule remains between cells in the cell wall region without crossing membranes or entering a cell. The other two routes, known as cellular pathways, need the water molecule to physically traverse a membrane.

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