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Effect of Surface Area on Transpiration

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Introduction

Effect of Surface Area on Transpiration Most of the water entering a plant does so via the root hairs. It travels across the root cortex to the xylem, ascends in the xylem to the leaves and is lost by evaporation from the surface of the mesophyll cells before diffusing out through the stomata. This process is called transpiration, and the flow of water from the roots to the transpiring surfaces forms the transpiration stream.. Transpiration is the loss of water vapour from the surface of a plant, and may occur from: 1) stomata: by evaporation of water from cells and diffusion of the water vapour through stomata, the pours found in the epidermis of leaves and green stems (about 90%). 2) waxy cuticles: by evaporation from the outer walls of epidermal cells through the waxy cuticle covering the epidermis of leaves and stems (about 10%, varying with thickness of cuticle). The aim of this experiment is to find out how the surface area of a plants leaves effects transpiration. Equipment: Potometer(short rubber tubing, rubber bung, graduated capillary tube), small electric fan, stand and clamp, stop clock, Vaseline, leafy shoot ( laurel). ...read more.

Middle

Consequently, depending upon temperature and humidity, transpiration is faster on a windy day than in still air. The best conditions for a higher rate of transpiration are the same as those needed for drying washing on a line: a warm, dry, sunny, windy day. Fair Test A fan will be set 1meter away from the plant, and will supply the heat and wind needed to cause the plant to transpire, thus causing water uptake by the xylem of the stalk.. The strength of the fan will remain constant as will the distance that it is set apart from the plant. The light intensity and the humidity of the room will be kept constant as much as possible. The variable that will be changed Is the surface area of the plant. This will be done by starting with 10 leaves on the plant, and then after 2 minutes of the fan blowing on the plant, 2 will be removed. The water uptake for each number of leaves will be recorded, and two will be taken away every two minutes and the results recorded until there are no leaves left. ...read more.

Conclusion

The surface areas of the leaves were measured very accurately using graph paper which enabled me to measure to the nearest mm�. Vaseline was rubbed on the ends of stems after leaves had been removed, which enabled me to minimise water loss. In spite of this there are still factors which could have altered the results. The experiment was done by many people in the same room. After the fans where switched on the temperature in the room would have gradually increased, which in theory could cause transpiration to increase as the experiment went on. Also, it was impossible to make the fan blow on all leaves equally. It is inevitable that some leaves has more heat and wind on them than others. This could cause less transpiration is some leaves, than others. Further work: Another experiment that could be done can measure the transpiration rate through the waxy cuticles of the leaves. Using the same method as the main experiment, use 4 leaves. Measure the water uptake over 2 minutes, then coat the bottom layer of each leaf(lower epidermis) thoroughly, and again measure the water uptake. There should be less water uptake when the lower epidermis is covered in Vaseline. Then cover both the upper and lower epidermis in Vaseline and measure the water uptake. Again there should be considerably less water uptake. ...read more.

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