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lab report - Effects of Light Intensity and Various...

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Effects of Light Intensity and Various Compounds on Photosynthetic Electron Transport and CO 2 Fixation Author: Sarah Akhtar Lab Partner: Hava Rubin Wednesday, BIOL 006
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Abstract In this experiment, the effect of several compounds, including iodoacetamide, DCMU, and uncoupler, on photosynthetic electron transport in thylakoids and CO 2 fixation in intact algae cells was examined. An oxygen polarograph was used to measure photosynthetic electron transport and CO 2 fixation. A thylakoid prep was found to be functional before and after the trial. The effect of various light intensities on the rate of whole chain and PSI electron transport was measured in the presence and absence of uncoupler. At low light intensities, no photosynthetic electron transport occured. A positive linear relationship was observed between light intensity and the rate of photosynthetic electron transport. When uncoupler was added, the rate of electron transport increased. For the whole chain reaction with uncoupler and PSI reaction without uncoupler, the rate of electron transport reached saturation. The maximum rate in terms of electrons in the PSI reaction was greater than the maximum rate in the whole chain reaction which means the rate limiting step is in PSII. The effect of uncoupler, iodoacetamide, and DCMU on carbon fixation was measured in algae cells. Uncoupler and iodoacetamide slowed down the rate of carbon fixation. DCMU decreased the rate of carbon fixation to nearly zero. Uncoupler, iodoacetamide, and DCMU were added to thylakoids sequentially. Uncoupler increased the rate of photosynthetic electron transport. Iodoacetamide had no effect on the rate of photosynthetic electron transport. DCMU decreased the rate of photosynthetic electron transport. 2
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Introduction Plant cells produce energy through a biochemical process known as photosynthesis that occurs in chloroplasts. The process of photosynthesis can be divided into two interdependent reactions: Photosynthetic Electron Transport (PET), which requires light, and the Calvin Cycle, which does not require light. Photosynthetic Electron Transport is responsible for reducing NADP+ to NADPH. The components of the PET chain are located in the membranes of thylakoids, sac-like structures in the chloroplast. The electron transport chain contains two chlorophyll molecules, P680 (Photosystem II) and P700 (Photosystem I) which use light energy from the sun to excite electrons to higher energy states. Electrons are first excited to a higher energy state by Photosystem II (PSII) and are then donated down a series of complexes to Photosystem I (PSI) where light energy is used to re-excite the electrons. The Calvin Cycle uses ATP (made from the pH gradient across the thylakoid membrane in a process called photophosphorylation) and NADPH made from PET to fix six CO 2 molecules into a sugar to be used by the cell for energy. In this experiment, the effect of light intensity and uncoupler methylamine (MA) on the
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lab report - Effects of Light Intensity and Various...

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