Photosynthesis Lab Report

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The Effects of Light Intensity, Light Wavelength, and the Activity of Pigments on the Rate of Photosynthesis By Rachel Whaley 3/23/15 Yumna Zahid Biology 111, Section 537 Abstract Photosynthesis converts carbon dioxide, water, and light energy into chemical energy (glucose) and oxygen, and serves as the foundation for most food webs. The distance chloroplasts were from a light source was varied and a spectrophotometer measured the rate of photosynthesis in the first experiment. Light intensity and the rate of photosynthesis were directly related. In the second experiment, spinach leaf disks were aspirated, exposed to different colored lights, and floating leaf disks showed which light wavelengths were the most effective for photosynthesis.…show more content…
Photochemical reactions occur in the thylakoid membranes of chloroplasts where different chlorophyll pigments are contained in photosystems I and II (Campbell 2011). Light energy is absorbed in these photosystems, electrons are excited and passed down an electron transport chain to the next photosystem after being trapped by a primary electron acceptor, ATP and oxygen are generated, electrons pass to a terminal electron acceptor, and eventually electrons reduce the final electron acceptor (NADP+) (Harris-Haller…show more content…
The objective was to determine the relationship between light intensity and the rate of photosynthesis. My hypothesis was that the rate of photosynthesis would be the lowest for the dark tube and the highest for the tube closest to the light source (24 cm). The rate of photosynthesis was measured using the spectrophotometer by recording the absorbance values of each of the tubes. The lower the absorbance values, the higher the rate of photosynthesis. This occurred because as electrons were absorbed by the acceptor DPIP as a result of photosynthesis occurring, the color changed from blue (higher absorbance values and little/no photosynthesis occurring) to clear (lower absorbance values and more photosynthesis occurring). Pigments selectively absorb and reflect different wavelengths of light; the reflected wavelengths determine the color of the object (Campbell 2011). Chlorophyll pigments play a role in passing on electrons to the electron acceptors and absorb certain wavelengths (which are useful to complete photosynthesis) while they reflect others (which are not able to be used to excite electrons for photosynthesis) (Campbell

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