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Experiment to Compare Stomata Density in Different Dicotyledonous

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Experiment to Compare Stomata Density in Different Dicotyledonous Aim: To investigate if stomata density on leaves in different dicotyledonous plants is effected by there country/ eco-system of origin. I will also compare the upper and lower epidermis stomata density to see were it lies. Information on stomata and Hypothesis Based Upon this Information: Diagram 1: Structure of a leaf. The lower and upper epidermis along with the stem of a plant may contain stomata. These are openings through which gases are exchanged with the atmosphere and water is lost, this is called transpiration. Carbon dioxide is need in the process of photosynthesis. Carbon dioxide is diffused in through the stomata for photosynthesis and some carbon dioxide is produced through respiration along with the production of water which transpires out. These openings are surrounded by specialized crescent shaped guard cells, which changes their size and shape to change the size of the stomatal openings. This regulates the gas exchange e.g. open more gas exchange, closed no gas exchange. These guard cells have different stimulus to active or deactivate the openings; light, CO2 concentration, humidity and wind speed. The epidermis is covered with a waxy coating called the cuticle, which functions as a waterproofing layer and which helps to reduces water loss from the plant surface through evaporation. Transpiration (evaporation of water from plant surfaces) happens mostly from the surface openings, the stomata. Stomata transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the surfaces of the epidermal cells of the leaves. The Leaf is the principal food-making part of a plant. Not all leaves are green; many have additional pigments that produce colours other than green. The shapes and structure of leaves are adapted to the conditions which they live in. Stomata represent a hazard to a plant in that they may cause excessive transpiration of water from the leaf. ...read more.


Tally counter: So that I count the number of stomata easily and so I can record my results easily, without relaying on human memory. Risk Factor: There is very little danger, if any in this experiment. The risk factors are: 1. Clear nail varnish fumes are toxic to human. To counter this risk a well ventilated room shall be used to avoid inhalation of excess fumes. 2. Care in applying the varnish should also be taken to avoid spillages on to human skin, eyes or clothing. If the varnish comes in contact with eyes wash immediately at labelled eye wash stations and seek immediate medical attention. 3. If consumption of nail varnish occurs seek immediate medical attention 4. The pointed tweezers are sharp ended, thus care in carrying these should be taken to avoid accidents. Preliminary Method: 1. Prepare an epidermal impression by coating the upper and lower leaf surface with a thinish coat of clear nail varnish. 2. Wait for approximately 15 minutes or until the vanish is completely dry. Then peel off the dried layer of nail varnish very carefully using a pair of thin ended tweezers. (Alternatively, with some plants you can peel off an epidermal strip directly, which can be mounted in water on a slide and place under the microscope) 3. Place the impression on to a glass slide a smooth out any bubbles. 4. Place another glass slide over the top of the impression to hold it secure. 5. Using a microscope at a set magnification (to be decided through preliminary experiment) count the stomata that you can see. Making sure you do not move the slide at any time. Record these results and then recount this area at least three times, and then move the slide on to another area and count the stomata there, recounting three times. 6. Do this for each the lower and upper epidermis and for a variety of plants making sure you record all results. ...read more.


One of the biggest problems that I had to over come in this investigation was the correct removal of the nail polish (epidermis impression), or even a large enough piece to use from the leaf surface. There where 3 plants that I could not obtain any epidermis impression from and one plant, the eucalyptus, that I could not obtain a upper epidermis impression from. Also, some of the plants took more than coating of nail varnish to obtain an impression. The plants that I could obtain no epidermis impression from was the blackberry/ bramble, geranium and honeysuckle leaves. The bramble was like the geranium covered in millions of hairs that meant the nail varnish came off in little pieces that were too small to use, or the hairs came off in the nail varnish making the image under the microscope fuzzy and they covered many of the stomata. This would have made the results were inaccurate. Also, with the geranium and with he honeysuckle the leaves had no waxy cuticle to them. This meant that the nail varnish was absorbed into the leaf and did not dry, instead the leaf when dark green, soggy and very fragile, making it impossible to gain an epidermis impression like this. For the eucalyptus obtaining the lower epidermis impression was very difficult and when it came to the upper epidermis I just could not get a piece large enough. I found that, although the leaves did have some waxy cuticle , he nail polish just did not come off, and the leaf seemed to absorb it. Other plants that I had trouble with was the primrose, which like the geranium, soaked up the nail varnish. However, after several re-painting of the leaf I did manage to get an epidermis impression. To stop this from happening in the further investigations you could do an epidermis peel, this is were the epidermis is removed directly from the leaf and looked at under the microscope. 1 Emma Cheney: A-level bio coursework (TG: JXL) ...read more.

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