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Three separate experiments which are to be carried out to investigate a plant's unique property of transpiration.

Extracts from this document...

Introduction

BIOLOGY COURSEWORK - TRANSPIRATION IN PLANTS AIM: I have three separate experiments which are to be carried out to investigate a plant's unique property of transpiration. I will carry out the following three experiments to investigate transpiration: * The use of a potometer to investigate the rate of transpiration and the relationship between leaf surface area and water uptake. This experiment will take place over a double lesson. * Using a microscope to find the number of stomata on one of the Laurel leaves and then using the results to calculate the number of stomata on each leaf. * My third experiment to prove that the substance being lost from the leaves is water by using cobalt chloride paper. SCIENTIFIC BACKGROUND: Overall plant structure: The following diagram shows the overall structure of a plant, and identifies the uses of each different part of the plant: As you can see by looking at the diagram to the left, there are several key parts to the plant, all of which have a major part in the transport of water in plants (i.e. transpiration). The roots can be seen towards the bottom of the diagram. The roots suck up the water from the soil which the plant is in. They do this because of the added effects of transpiration and capillary rise. Capillary rise is where a liquid climbs up a very narrow tube, defying gravity almost. As the water evaporates from the leaf, water must fill up the xylem. This water is sucked up from the ground through the roots. It must then travel to the leaves through little vessels in the stalk. It does this by travelling through the xylem tissue in the vascular bundle. The following diagram shows these vessels in the plant and show how the water travels through the xylem. This diagram shows the microscopic vessels in the plant which transport sugar and water (through the xylem), and food substances (through the phloem). ...read more.

Middle

A brief explanation of how to set up a microscope ready for viewing the nail varnish: * Firstly you must adjust the microscope to its lowest possible magnification (this is, in our case, 8 x magnification). * You must then adjust the light mirror on the microscope so that the light from a desk lamp shines through the viewing hole in the platform. Before the object is added, the platform must be fully retracted (in the down position). * Then apply the slide. * Centre the desired object in the viewfinder and wind up the platform to focus. Also use the major and minor focus wheels to focus the desired object. * Once the desired object is focussed, you can turn the magnifying column to 20 x magnification, which is where we want it. Then re-focus the microscope at 20x magnification, using the minor focussing wheel. * Once you have focussed on the desired object, you can then begin to count the stomata in the 3 x 3 square as mentioned above. I performed this experiment 6 times to get an average number of stomata. I found that there were stomata on the underside of the leaf, but when I came to count the stomata on the top side of the leaf, the nail varnish did not seem to have any stomata imprints on it. The reason we use clear nail varnish is because it seeps into the stomata, so that is why we can see the stomata, and also, the reason it has to be clear is, when it is on the slide, the light from the mirror has to be able to shine through it. If the nail varnish were coloured, the light would not be able to shine through it and therefore, counting the stomata would be impossible. The diagram below shows roughly what you should see through the microscope when you are looking for stomata. ...read more.

Conclusion

was indeed water. I concluded from this experiment that water was indeed given off by the leaves. More water was given off from the bottom of the leaf than from the top. I know this because of the extra experiment that I have explained under the Potometer heading of the evaluation. Even though this experiment seems fairly fool proof, human error may still happen (twice in fact). When you have to dry off the paper before you begin using the lamp, human error may cause you not to dry it off enough, causing the colour-change times to be inaccurate. This could simply be solved by making sure that the paper is dry. Also, we use paper reinforcement rings to stop the paper from actually coming into physical contact with the leaf. Human error may step in when it comes to putting the prepared paper on the leaf. You have to be vigilant when resting the paper on the leaf because if it is touching the leaf, results may be wrong, due to surface wetness. What we have to remember is that this experiment is see if the evaporate is water, not surface liquid. Overall this experiment was effective, despite the fact that it was unbelievably tricky to make sure that the paper was not actually touching the leaf. OVERALL CONCLUSION: I am very satisfied with all the experiment that I have carried out to complete this coursework. I have found that there are many factors affecting transpiration in plants. I have learned that the number of leaves, their surface area and ultimately the number of stomata on them have a direct affect on the amount of water that is taken up by the plant. I have also learned that the plant gives off a substance through its stomata, which I have concluded to be water. I learned a lot about the transport in plants and transpiration while completing the scientific background part of my coursework. It has helped me to understand how and why all these things are related. Joe Harper Page 1 04/05/2007 - 1 - ...read more.

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