Transpiration Essay

Transpiration is the loss of water vapour from the leaves of plants; a process that begins when water is carried from the roots of a plant to small pores on the underside of leaves, where the majority of it is changed to water vapour and released into the atmosphere (United States Geological Survey (USGS), 2014). Transpiration has three major roles in the life of a plant. The first is to transport water and other essential minerals around the plant. Plants use xylem vessels, which are vertically elongated vessels with lignified walls, to transport water and dissolved minerals from the roots to the leaves, where they can be used for photosynthesis and cell growth (Roberts, King, 1987). Phloem vessels transport carbohydrates, created during photosynthesis, from the leaves to the rest of the plant to be used in growth (Whiting, 2010). Plants also use transpiration as an evaporative cooling system. This is possible because the process of evaporation is an endothermic reaction; it requires energy to break the hydrogen bonds between liquid water molecules, changing them to free water molecules, or, water vapour. This energy is taken from the leaf in the form of heat, which, in turn, cools the plant (Plant and Soil Sciences, 2014). Transpiration also helps to keep the plant stiff and upright. As water leaves the plant, via evaporation, more is brought up through the roots, maintaining a constant amount of water in the plant pushing against the cell walls; this is known as turgor pressure (Whiting, 2010).

The process of transpiration is a cycle. As the water in the leaves of the plant is heated by the sun, some of the molecules break their cohesive bonds, separating from the rest of the water; this is known as evaporation (Spencley, Eva...

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...n more carbon dioxide for photosynthesis (Plant and Soils Sciences, 2014). While this may be beneficial to the plant, the more stomata that are open the more water the plant loses. If there is a lack of water in the soil and the plant is releasing too much vapour the plant may begin to wilt and eventually die (USGS, 2014). Plants are also known to drop leaves when water is unavailable. Stomata are present on all above-ground parts of the plant but are most abundant on the underside of the leaf (Domingos, 2012).

This investigation will focus on finding the differences in the number, position and sizes of stomata and the effects on the rate of transpiration. More specifically it will compare the stomata of Geranium and Ixora and their ability to transpire. How do the stomata of Geranium and Ixora differ and what effect does this have of their rate of transpiration?