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Investigation Into The Rate of Water Uptake By Transpiration.

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Investigation Into The Rate of Water Uptake By Transpiration. Hypothesis: The rate of water uptake in a plant is directly proportional to the surface area of the leaves on the plant. As the surface area is reduced, the time taken for the water to travel up the stem over the same distance will increase. Background Knowledge: Plants add a considerable volume of moisture to the atmosphere. After absorbing water through their roots, the water travels up the stem to the leaves where over 99% of the absorbed water is lost through the leaves by a process named transpiration. The Sun provides the energy required to turn the water in the leaves into a vapour, causing it to diffuse out of the plant and into the atmosphere. Water evaporates from the leaves and causes a force that pulls the water up the stem. The water travels through the vessels in the vascular bundles and this flow of water is called the transpiration stream. Vascular tissue is made up of xylem and phloem. These tissues are concerned with the translocation (transport) of water and nutrients around the plant. Xylem carries mainly water and mineral salts, whereas phloem carries mainly organic solutes in solution, for example sugars. As the vascular tissue forms a transport system around the plant, a large, complex body will develop. Xylem fibres are thought to have originated from tracheids (single cells that are elongated and lignified), however they are shorter and narrower than tracheids. Overlapping walls are present at the end of the xylem. Phloem resemble xylem as they also have a tubular structure that is modified for translocation. The tubes are composed of living cells, and there are five different cell types: sieve tube elements, companion cells, parenchyma, fibres and schlerids. See Figure 1a that shows how phloem and xylem play an important role in transpiration. Figure 1b shows how gaseous exchange occurs in leaves.. ...read more.


* The sharp blade must be used with care, as it is very sharp and fingers can be cut easily. When they are not being used, the blades must be kept inside their box so that other people will not hurt themselves if they are left lying around. * I will not break any branches off the privet hedge that I will not be using for the experiment. This means that I will not be disturbing any organisms unnecessarily that live on the plant. * The apparatus must be positioned steadily on the surface. It is quite bulky, and I must be careful not to knock it over and spill the water. Predictions: I predict that if the surface area of the plant's leaves is reduced the rate of uptake will slow down. This is because the number of stomata will be reduced, and transpiration rates will be reduced. I predict that the rate will decrease in proportion to the number of leaves removed, for example if the number of leaves is reduced by 50%, the rate of uptake will be reduced by 50%. The rate of transpiration is directly proportional to the surface area of the leaves on the plant. This is assuming that all other variables will remain constant. I am assuming that there will be an equal distribution of stomata on all of the leaves, and also that the surface area of each set of 10 leaves I remove will be approximately the same. For example, each set may have a combined surface area of 50 cm?. See Figure 4 that shows how I predict the rate of uptake will change. As I am unsure of the rate at present, I have left the axis unlabelled and shown only the general trend. Method: This was carried out as stated earlier, with no changes made to the original plan. The first attempt was carried out on a different branch to the other three attempts. ...read more.


I did not take into account the stomatal distribution in either of my two experiments. This would have been an interesting variable to look at, however I found that I was short on time. I would have liked to have looked at the lower epidermis underneath a microscope, and made an approximate stomatal count. I could have seen if they were evenly spread, and if not, still made an estimated rate of uptake from my other results. My results were very pleasing overall. They followed my predicted trend and I have been able to see why, due to measuring the total surface area of the second branch. I have accounted for my anomalies as the experiment was affected by factors beyond my control. I had not realised that the air-conditioning and positioning of the apparatus would affect the experiment in such an extreme fashion. Factors such as light intensity and the temperature of the surrounding air may only change slightly, but have a larger effect on the overall experiment. I would have liked to repeat the experiment again, so that I could obtain more results. This would give me a more significant mean average, and I would have been able to leave out the anomalies in the analysis. A source of error may have been counting the number of leaves rather than the surface area. Nevertheless, it turned out that I was removing the leaves by nearly 10% each time. I would improve the experiment by measuring the stomatal distribution next time. This will allow me to calculate a more significant rate of uptake by calculating how much water is taken in through each stomatal pore. I could then estimate how much water should be taken in. If I was able to calculate the transpiration rate as well, I would be able to work out how much water was being used within the plant. Generally, this experiment was conducted well. The anomalies were not large enough to change the trend in any way, and the overall results were beneficial in proving the hypothesis correct. ...read more.

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