`star` Opening of Stomata
`star` Factors affecting Transpiration


● `color{violet}("Transpiration")` is the `color{brown}("evaporative loss")` of water by `color{violet}("plants.")`

● It occurs mainly through the `color{brown}("stomata")` in the `color{violet}("leaves.")`

● Besides the `color{brown}("loss of water vapour")` in transpiration, exchange of `color{brown}("oxygen and carbon dioxide")` in the leaf also occurs through pores called stomata `color{brown}("(sing. : stoma).")`

● Normally `color{violet}("stomata")` are open in the `color{brown}("day time")` and close during the `color{brown}("night.")`

● The immediate cause of the opening or `color{violet}("closing of the stomata")` is a change in the `color{brown}("turgidity")` of the guard cells.

● The `color{brown}("inner wall")` of each guard cell, towards the pore or `color{brown}("stomatal aperture,")` is thick and elastic.

● When turgidity increases within the two guard cells flanking each `color{violet}("stomatal aperture")` or pore, the thin outer `color{brown}("walls bulge out")` and force the inner walls into a `color{brown}("crescent shape. ")`

● The opening of the stoma is also aided due to the `color{brown}("orientation of the microfibrils")` in the cell walls of the `color{violet}("guard cells.")`

● `color{violet}("Cellulose microfibrils")` are `color{brown}("oriented radially")` rather than longitudinally making it easier for the `color{violet}("stoma")` to open.

● When the guard cells lose turgor, due to `color{brown}("water loss (or water stress)")` the elastic inner walls regain their `color{violet}("original shape, the guard cells")` become `color{brown}("flaccid")` and the `color{violet}("stoma closes")` .

● Usually the lower surface of a `color{brown}("dorsiventral")` (often dicotyledonous) leaf has a greater number of `color{violet}("stomata")` while in an `color{brown}("isobilateral ")` (often monocotyledonous) leaf they are about equal on both surfaces.


● Transpiration is affected by several external factors:

`color{green}(star \ \ "Temperature")`

`color{green}(star \ \ "Light")`

`color{green} (star \ \ "Humidity")`

`color{green}( star \ \ "Wind speed.")`

● Plant factors that affect transpiration include:

`color{green}( star \ \ "Number and distribution of stomata,")`

`color{green} (star \ \ "Number of stomata open,")`

`color{green}(star \ \ "Per cent, water status of the plant,")`

`color{green} (star \ \ "Canopy structure etc.")`