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The stomatal density of a dicotyledonous plant growing in both Sunny and Shady conditions

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Introduction

CONTENTS Section Page Abstract 2 Plan Proposal 4 Introduction 7 Apparatus 11 Method 12 Results 18 Analysis of Results 20 Discussion of Results 25 Conclusion 28 ABSTRACT This project investigated the stomatal density of a dicotyledonous plant growing in both Sunny and Shady conditions. The stomatal density of a batch of leaves taken from the main branches of the plant was estimated using a light microscope and an eyepiece graticule. Transparent nail varnish was used to obtain replicas of the different adaxial (lower) leaf surfaces by carefully applying it to the same area of the different sample and carefully removing it with the aid of a pair of forceps after drying. The field of view to be used for the stomatal counts was calibrated by placing the stage micrometer on the microscope and counting the calibrations that occupied the graticule scale at magnification X40. The dried nail varnish was viewed under a microscope at magnification X40 and the number of stomata seen in the field of view of the microscope was counted using a hand held tally counter. The counts in the same field of view was repeated twice again and averaged to increase the accuracy in the results. The stomatal density of the adaxial (lower) leaf surfaces of plants found in the sun was found to be higher than the stomatal density on the adaxial (lower) leaf surfaces of plants found in the shade. From the results obtained the average number of stomata seen in the field of view was 39 stomata in the sun and 27 stomata in the shade this thereby supports the above statement. Further evidence of this was given from calculations which indicates that the stomatal density of the adaxial (lower) leaf surfaces of the plant exposed to the sun was approximately 5x105 stomata per square centimeter and the stomatal densities on the adaxial (lower) leaf surfaces of the plants in the shade were approximately 3.4x105 stomata per cm2. ...read more.

Middle

This is so because larger leaves have different stomatal distribution than smaller leaves and this investigation is set out to compare the stomatal density of leaves of the same size in different conditions. The leaves chosen for this investigation were cut from the branches of the plant and placed in a bucket of water. In the laboratory, the surface area of the leaves selected, was determined by placing each leaf on a graph sheet and carefully tracing out its outline. The number of squares on the graph sheet were counted and used to select the leaves suitable for the investigation. Selected leaves used in the experiment ranged from 112 to 116 squares, which is about 15- 20 cm2. SETTING UP THE MICROSCOPE A microscope is an instrument used to view objects that are too small to be seen with the naked eye but visible through a microscope. The microscope enlarges these small objects to sizes that can be visible to the naked eye. The microscope was taken out of the cupboard and placed on the desk. The microscope slides were also taken out and cleaned with a tissue. The slides were then labelled accordingly. The samples taken from the sun were labelled Sunny no 1,2,3,4... and samples from the shade were labelled no 1,2,3,4... The microscope was then plugged into an electrical socket and the slides mounted on it. This therefore led to an orderly arrangement of apparatuses and easier examining of samples. CALIBRATING THE EYE PIECE GRATICULE The eyepiece graticule was calibrated by placing a micrometer on the stage of the light microscope slide and securing it in place with the pair of stage clips. The eyepiece was mounted with the eyepiece graticule in position, and the stage micrometer was brought into focus, and altered such that its initial graduation coincided with the initial mark on the graticule. Counting was done along both scales until a point was reached where there was another coincidence between a graduation mark on the graticule scale and another on the stage micrometer. ...read more.

Conclusion

Accordingly, some trees have developed adaptations, such as fleshy stems, and thickened barks, in order to lower their transpiration rate. These plants in their efforts to retain water have very few stomata on their leaves, if they have any leaves at all. Other trees located in wetlands and marshes have high transpiration rates so will need a high stomatal density to get rid of the excess water vapour. Also, the surface area of the leaves of each different species varies. As the surface area to volume ratio of the leaves increases so does the number of stomata on the leaf. This is because a larger number of stomata will be needed to aid in transpiration from the larger leaves. Most stomata occur in the leaves. In the dorso-ventrally flattened leaves typical at most dicotyledons, stomata are present mainly in the lower epidermis (Taylor et al, 1997). In the experiment performed, it was found out that the stomatal density was highest on the lower epidermis, of leaves exposed to the sun than to leaves found in the shade. The Biological Significance in this experiment is that the knowledge of stomatal distribution can help farmers practice photoperiodism. If they do practice this, their crops will grow better because the leaves in the shade were larger hence will receive more sunlight and will therefore photosynthesise better to produce more glucose which is stored as starch. Experiments to be carried out in the future which may expand on the theories presented should include investigations in which samples of the stomatal traces should be taken from the adaxial(lower) and adaxial(upper) surfaces of the leaves. Also samples should be taken from different types of plants not one type of plant to makes the results more accurate. Conclusion The statistical test carried out on the result obtained rejected the null hypothesis. The alternate hypothesis which was consistent with the observations made was thus accepted. Hence it can be concluded that leaves that are exposed to the sun have a higher stomatal distribution than leaves found in the shade have a higher surface area than leaves exposed to the sun. ...read more.

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