Plant Structures: Stomata and Transpiration

Stomata are minute openings, typically found on the undersides of leaves, that allow for exchange of gases, including water vapour, carbon dioxide, and oxygen.
Each stoma is surrounded by two specialised parenchyma cells known as guard cells. These cells expand and contract to open or close the stomata.
Transpiration is the process by which water is lost from the plant to the atmosphere through the stomata. This process cools the plant and helps to maintain its water balance.
The water evaporates from the surface of the plant’s leaves and is replaced by water drawn up from the roots - this is known as a transpiration stream.
A number of environmental factors can influence the rate of transpiration, including the light intensity, temperature, air flow and moisture of the surrounding environment.
In hot, dry and windy conditions, the rate of transpiration increases. This happens because the gradient between the moisture inside the leaf and the dry air outside it increases, therefore the water inside the leaf is drawn out more rapidly.
High light intensity, one of the factors influencing transpiration, stimulates guard cells to open the stomata. This increases the rate of photosynthesis and consequently transpiration.
The closing of the stomata at night reduces water loss through transpiration while the process of photosynthesis is inactive.
Plants manage their water needs by closing stomata during high heat or drought conditions or having fewer stomata overall. Different species have adaptations specific to their environmental conditions.
Understanding of these principles is key to understanding the physiological activities and adaptations of plants which are essential for their survival.