Stomatal Density Lab Report PDF

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Stomatal Density Lab Report...

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Jane Doe Form & Function Thursdays AM 10/24/19 Plant Physiology Lab Report Purpose and Predictions The purpose of this experiment was to predict if the leaf of a callery pear tree, Pyrus Calleryana, would have an effect on leaf production when examining old versus new leaves. We hypothesized that the older leaves would have a lower stomatal density and the younger leaves would have a higher stomatal density. Materials and Methods This experiment was conducted using the leaves of a callery pear tree, Pyrus Calleryana . Stomatal density was analyzed on these leaves using new and old production times. The manipulated variables were the age of the leaf, therefore, stomatal density was calculated by counting the number of stomata per surface area of the leaf. Leaves were calculated on a callery tree based off of leave production time. The older leaves were browning and starting to wither. While the new leaves were slightly smaller bright green with no signs of browning. The independent variable in our experiment was age while the dependent variable was stomatal density. Our initial step was to collect a total of four leaves; two young leaves and two old leaves. Next, came the leaf peel technique where a thin layer of clear nail polish was painted on a small surface of the leaf. After wee allowed the painted leaf to dry and then adhered a piece of tape long enough to cover the painted surface. The tape was firmly pressed to the leaf to ensure a smooth peel. Once the tape was peeled with an impression of the stomata density, it was then adhered to a slide and viewed under a microscope to see the

individual stomatas. The process above was done a total of five times per leaf for both the old and new leaves. The leaf peeling was done multiple times per leaf to account for variation in stomatal density at different areas of a single leaf. To understand out data in a holistic way, a t-test was used to analyze the relationship between stomatal density in older leaves compared to newer leaves based on the stomatal densities collected in the experiment. Results There was no statistical difference found in the age of the callery pear leaves (t18=1.86, p=0.08; Fig. 1). There stomatal density of callery pear leaves(n=10), Pyrus calleryana , was unable to be determined by the leaves’ production time.The younger leaves had a slightly higher stomatal density compared to older leaves.

Figure 1. Comparison of stomatal density of callery pear leaves in older (n=10) or newer (n=10). Data shown as mean ± SD.

Figure 2. This is an image of stomata under a callery pear leaf using 100x microscope magnification with a lense area of 0.47mm2 . Discussion According to the results of the data the older callery pear leaves have a higher stomatal density compared to newer callery pear leaves. Our hypothesis was rendered null because we the stomatal density would be lower in the old callery pear leaves compared to newer leaves. However, our results do support the second hypothesis that leaves located in areas with high sun exposure had higher stomatal density compared to leaves located in an area with little sun exposure. Stomata are tiny pores found on the epidermis of the leaf and their main role is gas exchange between the leaf and the environment. The development of stomata on the leaves of a plant is determined by the interaction between different genes and environmental factors. According to our data, the time production of callery pear leaves showed inconclusive results in relation to stomatal density. This can be due to the fact that there is a relationship between

stomatal density and environmental factors such as temperature changes and light intensity. Which the collected plants in this experiment definitely faced as they were at two different ages of young and old. Research has shown that stomatal densities are controlled by environmental conditions during leaf development, but are fixed after the leaf matures (Schlüter U., Muschak M., Berger D., Altmann T. et. al., 2003). This relates to our data because older leaves contained a more stomata because they are fully grown. While the stomata on younger leaves are growing as the leaf matures, thus the stomata measure was lower when compared to older leaves. A possible confounding variable could be not knowing the specific age of the plants. Though they are young and old, some leaves could have been close in age than others. This could have skewed the data because the recorded young leaves could have a higher stomatal density because it is reaching maturity. Determining the age of plants is difficult, especially given the time frame, so we accounted for this by taking into consideration the size and color of the leaves when categorizing them into a young or old callery pear leaf. It is important to note that while collecting our callery pear leaves the older leaves seemed to be at the outer ends of the branches. While younger leaves were collected towards the tree trunk. Our data showed that at a higher sunlight exposure stomatal density is greater (older leaves) and at a lower sunlight exposure the stomatal density is low. Both light intensity and carbon dioxide concentration have been shown to influence the frequency at which stomata develop on the leaves of plants (Casson S, Gray JE, 2008). Plants can respond to changes in environmental conditions by changing their stomatal frequency. Recent research has shown that signals from older leaves can influence the development of stomata on the younger leaves (Miyazawa S, Livingston NJ, Turpin DH., 2006). Furthermore, if the environmental conditions

to which the older leaves are exposed change, then the younger leaves can increase or decrease their stomatal density; this physiological adaptation can help the plant cope with the changing environment. According to research done by Jennifer McElwain, the number of stomata per square inch of leaf surface can reveal different aspects of the atmosphere in which that plant lived (McElwain, 2019). This research is very important, especially when it comes to climate change, we must think about how our current atmosphere affect plant life compared to the atmosphere in past eras. When stomatal density is low means that the levels of CO2 in the atmosphere is high, and when CO2 levels are low it means that stomatal density on leaves are high. Researchers use stomata as indicators of carbon dioxide levels at different points in Earth's history (McElwain, 2019). Studying how modern plants respond to these environments helps biologists understand how long extinct plants were affected by their environments. With CO2 levels rising in our  atmosphere today that means stomatal densities are decreasing which is concerning. This is why this research is so important, because understanding the past can aid us in fixing our future to avoid plants from going extinct.

Literature Cited Casson S, Gray JE. Influence of environmental factors on stomatal development. New Phytol 2008;178:9-23. McElwain J. Understanding Evolution. The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California. 2019 Miyazawa S, Livingston NJ, Turpin DH. Stomatal development in new leaves is related to the stomatal conductance of mature leaves in poplar (Populus trichordata x P deltoids). J Exp Bot 2006;57:373-80. Schlüter U, Muschak M, Berger D, Altmann T. Photosynthetic performance of Arabidopsis mutant with elevated stomatal density under different light regimes. J Exp Bot 2003;54:867-74....