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Investigating the relationship between the transpiration rate of a shoot and the degree of opening of the stomata of its leaves

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Investigating the relationship between the transpiration rate of a shoot and the degree of opening of the stomata of its leaves I will be investigating the relationship between the transpiration rate of a shoot and the degree of opening of the stomata of its leaves. Transpiration is the loss of water vapour from the surfaces of a plant. Solar energy turns the water in the plants into a vapour causing it to evaporate into the leaf's internal air spaces before diffusing out of the stomata into the air. The water is able to evaporate out of the leaf as the leaf has a high water potential and the surrounding has a low water potential. The water molecules pass down the concentration gradient from the spongy and palisade mesophyll cells into the leaf's internal air spaces before diffusing out into the air. For this experiment, I will need to vary a factor that affects both the transpiration rate and the degree of stomata opening in order to determine the relationship. Factors that affect transpiration rate are humidity, temperature, light intensity, water supply, plant surface area, plant species and wind speed. These in fact affect both incidents because transpiration rate depends upon stomata opening to allow gas exchange. ...read more.


The reason for choosing individual plants to work on instead of just one is so that the experiment will be a fair test. I.e. if I choose one plant and start cutting shoots from it, it will gradually affect the overall transpiration rate. It is not easy to measure the rate of transpiration but I can use a potometer to measure the rate of water uptake. I know that the amount of water loss is less then the water taken up by the roots as some of the water is used for photosynthesis (Biology 1, Cambridge Press). I will move the fan 20cm at a time until the fan is 200cm away, starting with a 20cm distance. I will keep the plant in this situation for 5 minutes so that it adapts to the environment. I will then stop the fan and proceed to measuring the rate of transpiration as follows: 1. First I shall fill the capillary tube by submerging it in water. 2. Next I will cut the end of a Kniphofia shoot under water. 3. I will attach the shoot to rubber tubing connecting the plant to the capillary tube. ...read more.


While doing the experiment I will need to take a few precautions. When I am placing the Kniphofia shoot into the rubber tubing I will try not to bruise the xylem cells, as this will affect the plants uptake of water. If that happens I cannot keep the uptake of water consistent. This plan is as precise as possible. However, water is used up in photosynthesis, but this should be at a constant rate so would not affect the increase in the uptake of water (I already know that the graph is not going to go through the origin, so it will just affect how far up the y-axis it starts). It also will be fairly inaccurate as it is not easy to read how far the meniscus has travelled to any degree of accuracy smaller than 1mm, but yet this will have a large effect on the results, and 0.5mm could be as much as 5% of the distance travelled, this inaccuracy would then be multiplied by the area of a cross section of the capillary tube. It would not be very easy to improve this, unless I use a very accurate ruler, and a magnifying glass, but this seems unnecessary, as the inaccuracy would not make that great a difference to the graph. ...read more.

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