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Measuring rate of water uptake by a leafy shoot

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Introduction

Measuring rate of water uptake by a leafy shoot. The water uptake can be measured easily and because very high proportion of the water taken up by a stem is lost in transpiration, it enables the rate of transpiration to be measured. Key Factors to be kept Constant: - * Temperature - room temperature (approximately 25�C) * Wind speed - No artificial wind was produced to affect results * Light intensity - Extra light was not used * Humidity - it was not humid on the day experiments were conducted The water uptake for the control Experiment. Time (minutes) Initial meniscus position of the air bubble (cm) Final meniscus position of the air bubble (cm) Water uptake (Distance moved) (cm) Total water uptake (cm) 1 10.0 10.7 0.7 0.7 2 10.7 11.5 0.8 1.5 3 11.5 12.3 0.8 2.3 4 12.3 13.0 0.7 3.0 5 13.0 14.0 1.0 4.0 6 14.0 14.8 0.8 4.8 The water uptake when Vaseline is applied on the top surface of the leaves. Time (minutes) Initial meniscus position of the air bubble (cm) Final meniscus position of the air bubble (cm) Water uptake (Distance moved) (cm) Total water uptake (cm) 1 6.0 6.6 0.6 0.6 2 6.6 7.2 0.6 1.2 3 7.2 7.9 0.7 1.9 4 7.9 8.5 0.6 2.5 5 8.5 9.2 0.7 3.2 6 9.2 9.7 0.5 3.7 Time (minutes) ...read more.

Middle

Stomata are pores surrounded by specialized cells (guard cells). These pores allow water to escape by diffusion into the air. As the water evaporates from the leaf by water evaporating from the surface of the parenchyma and escaping out through the stomata into the atmosphere, water from the xylem in the leaf replaces it. As water leaves the xylem, more is sucked up from below. A negative gradient in hydrostatic pressure forms, causing a column of water to rise up the plant. This is known as the transpiration pull. This means that transpiration directly affects the rate of water uptake. If this did not occur, the plant will wilt, and if water loss continues without being replaced, it will suffer plasmolysis. (Biology 1 text book and 'Biology - AS in a week). When both surfaces were covered with Vaseline, the Vaseline was applied over the stomata as well. By covering the stomata it meant that this would prevent water from escaping by diffusion, so this will reduce transpiration, which then led to a decrease in water uptake. The fact that both sides were now preventing any water from evaporating from the leaves of the plant means that this experiment had to have a lower water uptake, which it did. ...read more.

Conclusion

For all three T-tests, the pattern that is similar is that the probabilities are all below the critical value, which is 0.05. This means that I can reject the "null" hypothesis that there is no difference between the means for each T-test and that the results only occurred by chance. I can assume that there is a significant difference between the means and the difference is real. There is not a big difference between each individual reading either which means that my results must be quite accurate. From the tests I can also see that the mean for the control test is greatest (0.8000), then the mean for the experiment with Vaseline on top (0.6167) and the lowest mean was for the experiment with Vaseline on both sides (0.4500). The standard deviation also shows this trend 0.1095 for the control, 0.0753 for the Vaseline on top, and 0.0548 for the one with Vaseline on both surfaces. The variance also supported this, 0.0120 for the control experiment, 0.0057 for the Vaseline on top, and 0.0030 for the one with Vaseline on both sides. The results from the T-tests support the trend showed by the graph, and this is supported by the background information. ...read more.

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