Water Transportation

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Graph showing the transpiration rate in Pa/min/mm2

Discussion:

The result is supported by the theory of transpiration stated in the principal. The rates for the four conditions we used namely Ambient, Ambient + Fan, Ambient + Lamp and Lamp + Fan were different. The transpiration rate increased in ambient condition with fan and light respectively and with Fan+ lamp together, because Light intensity stimulates stomata opening and an increase in light intensity results in an increase of rate of photosynthesis. Photosynthesis requires gaseous exchange and the stomata is the pore in which gaseous exchange takes place. Therefore, an increase in photosynthesis results in an increase in stomata opening. As when the plants were supplied with wind the transpiration rate increased because the moist or humid air around the plant is quickly replaced by less humid air allowing the plant to release even more water into the atmosphere.

The rates for two plants species used were different because the surface area for two plants different as one of the plant had only one big broad leaf connected with the shoot while the other plant used had many small leaves connected with the shoot. As smaller leaves may lose less water than the larger ones.

The energy to move the water comes from capillary action which cause the transpiration pull. During evaporation of water from the leaves, not one water molecules escape through stomata but a chain of water molecules. The movement of water through the xylem is like drinking water from a straw. Drinking exerts pressure on the straw, and a chain of water molecules is drawn upward. Water molecules are polar and stick together with hydrogen bonds. Water stability to stay linked in a chain is called cohesion, and its ability to stick inside the straw or xylem vessel is adhesion. Evaporation of water at the leaves exerts tension, which pulls on a chain of water molecules. Transpiration is constant tugging or pulling of the water column from the top due to evaporation. Cohesion of water molecules and adhesion to the inside of the xylem vessel facilitate this process, as transpiration occurs, the water column is pulled upward-first within the leaf, and then from the stem and finally from the roots.

Conclusion:

The experiment was carried out successfully and I was able to measure the rate of transpiration for the two plants used in different environment conditions.

The rate of transpiration, and hence of upward movement of water in the plant, depends on several factors. Read about this topic in your text and be prepared to suggest in a lab discussion one or more possible factors and how their relative contribution to water movement may be assessed.

It is important to realize that the cut shoot may take up water faster than the intact plant under the same environmental conditions. This is because a major resistance to water uptake, located at membranes of root cells (endodermis), has been removed. Thus, a potometer connected to a cut shoot can estimate the influence of environmental and biological factors on uptake, but not the