Lab 7 - Kayla Jeeter BIO 111 Lab 7 Photosynthesis Abstract...

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  • BIOL 111
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Kayla Jeeter BIO 111 October 28, 2015 Lab 7: Photosynthesis Abstract: During this lab, we did three key experiments that showed us (1) the effect of light intensity on photosynthesis, (2) the effect of light wavelength on photosynthesis, and (3) the activity of photosynthetic pigments. Introduction: In the first experiment of this lab, we observed how light intensity affects the process of photosynthesis. Light wavelength and light intensity both affect the rate of photochemical reactions (Tonna Harris-Haller, 2015). Oxygen is released as a by-product of these reactions, therefore, it is possible to measure the amount of oxygen produced, thus determining the rate of photosynthesis. Furthermore, it is possible to measure the effect of light intensity on electron transport by substituting NADPH with DPIP, which we did in our experiment. When DPIP is oxidized, it is blue, but after it accepts electrons, DPIPH2 is reduced and becomes clear. It is possible to measure the effect of light intensity because the rate of color change depends on the rate of excitation of the chlorophyll molecules. The more clear (greater the reduction), the more absorbance the solution will have. Our hypothesis was that the tube closest to the light would have the greatest absorbance. Our null hypothesis was that all the tubes would have the same amount of absorbance. Our dependent variable was the amount of absorbance and our independent variable was the light treatment the test tube got. In the second experiment in this lab, we observed how different light wavelengths inhibit or prohibit photosynthetic action. The light used in photosynthesis requires a specific wavelength for the pigments in chloroplast to absorb it. White light includes all the wavelengths of light, but on the other hand, some objects contain pigments that selectively reflect or transmit some wavelengths and absorbs other wavelengths. That is why we see color (Tonna Harris-Haller, 2015) Red and Blue, wavelengths are the most effective wavelengths that promote photosynthesis (more so red though). In order to chart the effectiveness of different wavelengths of light on photosynthesis, an action spectrum is used. In our experiment, we developed an action spectrum by observing the production of oxygen, which can tell us the photosynthetic activity. In order to observe this, we used spinach leaf disks aspirated in sodium bicarbonate. The leaf disks float when photosynthetic activity fills the intercellular spaces with oxygen, and sink when aspirated. Therefore, the faster the rate of photosynthesis, the faster the leaf will float (Tonna Harris-Haller, 2015). Our hypothesis was that the beaker in the red light box would have the most photosynthetic activity, or the most leaves floating. Our null hypothesis was that none of the leaves in any of the beakers would float. Our dependent variable was the number of leaves floating at the end of 30 minutes, and our independent variable was the color of light each beaker was exposed to. Our positive control variable was the white light and our negative control

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