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How water uptake of a plant is affected by the number of leaves

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Introduction

GCSE BIOLOGY COURSEWORK: Planning I will investigate how the water uptake of a plant is affected by the number of leaves using a potometer. To make it a fair test I will ensure that all factors remain constant except for the one that is manipulated. Same: Piece of plant, air pressure, light intensity/wavelength, wind speed and temperature, all done in the same lesson. Different: Leaf area/stomatal density. This is the easiest and most independent variable. For accuracy I will use Vaseline to seal the cuts where I have cut off leaves to stop water from escaping and complete the experiment in one lesson so other factors do not change too much e.g. temperature etc. Safety * Laurel is poisonous so hands should be washed thoroughly afterwards. * Glass is breakable. It should be pulled from the holder, not levered. * Glass should be put on the desk somewhere where it can't roll off. * Secateurs are sharp so care should be taken not to cut fingers. Equipment I will use a potometer. This will be connected to a plant at the top and a beaker of water at the bottom. The removal of the leaves will be done with secateurs and cut will be sealed with Vaseline. ...read more.

Middle

before recording them to increase accuracy. GCSE BIOLOGY COURSEWORK: Analysis The evidence shows that the fewer leaves the plant has, the less water it takes up. The graph shows strong negative correlation. The less leaf area left, the less water taken up. Conclusion Water is lost through the stomata on the underside of the leaves. There are about 75 stomata per mm2. Quote from Green, Stout and Taylor biology book: "Stomata: by evaporation of water from cells and diffusion of the water vapour through stomata, the pores found in the epidermis of leaves and green stems (about 90 %*)." *90% of water is lost through the leaves. The other 10% is through lenticels. The rest of the plant (not the leaves) is not 100% waterproof. 60072(total leaf area)/7(number of leaves=8581.714283. So the average leaf area is about 8581.7mm2. The average number of stomata per leaf was 643628.5714. This is a large area for water to be lost through. The results show us that when we remove leaves, less water is lost. This is because there is less stomata for water to be lost through. The top-side of the leaf has no stomata. Diagram of how water is lost through stomata Contours of equal concentration of water molecules; steeper potential gradient=closer contours and faster rate of diffusion. ...read more.

Conclusion

Air turbulence would be kept to a minimum by closing all windows and doors and making sure that no one enters while I am doing the experiment. Another problem which I will address from the first experiment is that cutting off the leaves gave the plant shock affecting the readings. To combat this I would cover the leaves with cling film instead of cutting them off. This would cause no distress to the plant so the readings will be more accurate. The plant and apparatus would be weighed first, then I would see how the mass changes as water is sucked from the beaker. The balance would be accurate enough to detect the small weight change. I would wait for the plant to settle down and for the water uptake to become constant. I would perhaps measure the weight change in one minute and repeat six times to increase accuracy. Before I cover the leaves with cling film I will weigh the cling film first. This will stop the weight of the cling film from affecting the readings. This method would be more accurate than the last because the balance is more accurate than judging from a scale as in the last experiment. There would be no errors such as parallax with this experiment and no stress to the plant because of leaves being cut off, making this experiment much more reliable than the original. ?? ?? ?? ?? GCSE Biology Coursework 1 ...read more.

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