Describe: Transpiration.

(N/A) $ \Rightarrow $ Transpiration is the evaporative loss of water by plants.
$ \Rightarrow $ It occurs mainly through the stomata in the leaves.
$ \Rightarrow $ Besides the loss of water vapour in transpiration, exchange of oxygen and carbon dioxide in the leaf also occurs through pores called stomata.
$ \Rightarrow $ Normally, stomata are open in the daytime and close during the night.
$ \Rightarrow $ The immediate cause of the opening or closing of the stomata is a change in the turgidity of the guard cells.
$ \Rightarrow $ Opening and closing of stomata: The inner wall of each guard cell, towards the pore or stomatal aperture, is thick and elastic.
$ \Rightarrow $ When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape, and stomata open.
$ \Rightarrow $ The opening of the stoma is also aided due to the orientation of the microfibrils in the cell walls of the guard cells.
$ \Rightarrow $ Cellulose microfibrils are oriented radially rather than longitudinally, making it easier for the stoma to open.
$ \Rightarrow $ When the guard cells lose turgor due to water loss, the elastic inner walls regain their original shape, and the stoma closes.
$ \Rightarrow $ Usually, the lower surface of a dorsiventral (often dicotyledonous) leaf has a greater number of stomata, while in an isobilateral (often monocotyledonous) leaf, they are about equal on both surfaces.
$ \Rightarrow $ Transpiration is affected by several external factors: $ (1) $ Temperature, $ (2) $ Light, $ (3) $ Humidity, $ (4) $ Wind speed.
$ \Rightarrow $ Plant factors affecting transpiration:
$ \Rightarrow $ Number and distribution of stomata.
$ \Rightarrow $ Percent of open stomata.
$ \Rightarrow $ Water status of the plant.
$ \Rightarrow $ Canopy structure.