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Density of Stomata and desiccation rates

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DENSITY OF STOMATA AND DESICCATION RATES Since the investigation is to study and experiment with one of the factors that effect the amount of water lost from a leaf, it is important to describe the structure of the leaf. Enlarged portion of leaf The structure of a leaf The function of the leaf is pertinent to its structure. A leaf usually consists of the following parts: - Petiole - the narrow stalk of the leaf attaching it to the stem. Lamina - the photosynthetic part of the leaf. Mid-rib and veins - consist of many tiny tubes which convey water into the leaf and carry food from it Epidermis - the outermost layer of cells of a plant. This layer is one cell thick. Waxy cuticle - covers the epidermis and reduces water loss. The lower epidermis consists mainly of stomata. Stomata are pores, which lead to an extensive system of air spaces between the cells of the leaf. The spaces allow diffusion of gases in and out of the cell. Before deciding on which variable to vary it is essential to establish all the factors both environmental and structural influencing water loss from leaves. This is to ensure that during experimentation the other factors are constant or are controlled. Environmental factors 1. Wind velocity Movement of the air surrounding the leaf removes the surface of moist air formed around the leaf. ...read more.


> Intensity of light - All the leaves will be put near the same source or absence of light; the lab has fluorescent tube lights, which are all switched off at the same time. > Temperature - the experiment is carried out indoors where thermostatic heating is present. A thermometer will also be placed near the experiment to ensure constancy. The experiment will not be carried out near any direct heat or cold. > The structural factors are impossible to control however relevant observations will be taken into account. ___________________ Most of the water is lost through stomata therefore transpiration rate is related to the stomatal density. The hypothesis to be tested is: AS STOMATAL DENSITY INCREASES THE RATE OF DESICCATION WILL INCREASE. APPARATUS AND MATERIALS Justification for apparatus use and method The apparatus used for such an experiment is basic. However the main piece apparatus used to measure the rate of desiccation has to be verified. There are two main methods: > using a potometer which measures the rate of water absorption by the leaf > using a top pan balance which measures the loss in weight as the loss in water The weight loss method is the preferred method because it is easier to administer. Rather than use one leaf to measure water loss several should be used so a significant water loss is measured. ...read more.


Repeat steps 17 - 20 for the remaining fifty-three leaves. 22. Record the results in the table below. SURFACE AREA (cm2) TYPE 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 TOTAL 23. Cut a piece of string about 10cm long and weight it. 24. Use the string to tie eight of the nine leaves together using the petioles and reweigh. 25. Deduct the result to step 23 from step 24. 26. Repeat steps 23 -25 for the other 5 types of leaves. 27. Hang the leaf lines up in the conditions described. 28. Reweigh every 2 hours. For the whole day. The control 1. The ninth leaf of each type should be weighed individually. 2. Then covered in nail polish and left to dry 3. Then reweigh 4. Reweigh every 2 hours. Because it is the control no weight loss should be experienced. The total leaf surface area of the eight leaves should then be used to calculate the water loss per m2. This can be done using the below calculation: (10000/TOTAL SURFACE AREA) * AVERAGE WATER LOSS. Having done this, quantitative results have to be calculated by calculating the average % mass loss. Graphs will be plotted and the gradients calculated. The results can be tabulated below: STOMATAL DENSITY WATER LOSS The Rank Spearman test will be undertaken to test the results to see if they match the hypothesis. _________________________________________________ ...read more.

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