ICSE Class 10 Answered

Mechanism of stomatal transpiration:

• The surfaces of spongy mesophyll cells in leaf are exposed to the intercellular spaces.
• These cells give out a thin film of water. Water from this film evaporates.
• Water vapour formed saturates the air in the intercellular spaces, diffuses into connecting intercellular spaces and reaches the sub-stomatal space. Finally, it escapes in the atmosphere through air.
• Water absorbed by roots rises up through the stem and reaches the tissues of leaves.
• The cell sap in each cell exerts a turgor pressure outward on the cell wall. This pressure forces some water out of the cell wall into the air space between the cells, i.e. intercellular space.
• Here, the water evaporates and the water vapour from intercellular spaces diffuses into the sub-stomatal space from where it finally goes out by diffusion through stomata.