Transpiration

Transpiration (Group B)

Transpiration
The loss of water in the form of water vapours from the leaves and aerial parts of plant is called transpiration.

Types of Transpiration

• Stomatal transpiration- Occurs through stomata
• Cuticular transpiration- Occurs through surface of stem and leaves
• Lenticular transpiration- Occurs through lenticels

Occurs mainly through openings called stomata.

Stomata are the minute openings found in the epidermal layer of the leaves. A stoma is surrounded by two bean shaped guard cells which regulate its opening and closing. 

Stomatal Transpiration
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In plants, water is absorbed through the roots, This absorbed water has to be transported throughout the plant's body for various physiological functions. It rises up in the stem through xylem and reaches the tissues of leaves through veins. The mesophyll cells of the leaves have their surfaces exposed to the intercellular spaces. Some amount of water forms a thin layer over these surfaces. The water from this film gets evaporated and form water vapours. These water vapours can diffuse through the intercellular space and reach the sub stomatal space and finally escape through stomata.

Regulation of Stomatal Transpiration

• Stomata:

  • Open in the day and close during the night

  • Also contribute in the exchange of O₂ and CO₂

  • Opening and closing of stomata is influenced by the turgidity of the guard cells.

• Inner walls of the guard cells (towards stomatal opening): Thick and elastic

• When turgidity increases within two guard cells flanking each stomatal pore, the thin outer walls bulge out, and the inner walls assume a crescent shape.

• Radial orientation of microfibrils in the cell wall of the guard cells makes it easier for the stoma to open.

• When turgidity decreases within the guard cells, the inner walls regain their original shape, the guard cells become flaccid and stoma…