Transpiration Stomata

Gas exchange processes of plants, in particular exchange of water vapor (transpiration), is to a large extent mediated by the stomata. Transpiration can be considered a physical process depending on vapor pressure gradients between the... 

The pathway of least resistance for gases to cross an epidermis—and thus to enter or to exit from a leaf—is through the adjustable space between a pair of guard cells (Fig. 1-2). This pore, and its two surrounding guard cells, is called a stoma or stomate (plural stomata and stomates, respectively). When they are open, the stomatal pores allow for the entry of CO2 into the leaf and for the exit of photosynthetically produced O2. The inevitable loss of water vapor by transpiration also occurs mainly through the stomatal pores, as we will discuss in Chapter 8 (Section 8.1B). Stomata thus serve... 

The leaf epidermis has small pores, called stomata, which open up for photosynthetic gas exchange and transpiration. Stomata are scattered throughout the epidermis, but are typically more numerous on the lower leaf surface. Each individual stoma (pore) is surrounded by a pair of specialized epidermal cells, called guard cells. In most species, the guard cells close their stomata during the night to prevent transpirational water loss, and open their stomata during the day so they can take up carbon... 

In photosynthesis, CO2 generally enters the leaves or stems of biomass through the stoma, the small intercellular openings in the epidermis. These openings provide the main route for both photosynthetic gas exchange and for water vapor loss in transpiration. At least three different biochemical pathways can occur during CO2 reduction to sugars (Rabinovitch, 1956 Loomis cf al, 1971 Osmond, 1978). 

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