Photosynthesis is a food making process for algae and plants. The photosynthesis process rate varies from different wavelengths and intensities of light. This lab will evaluate the optimal wavelengths and degrees of intensity during photosynthesis when chloroplast is exposed to light. The mixtures of DCPIP with water, PO4 buffer, and chloroplast will be prepared in a number of cuvettes. The cuvettes were tested individually at different wavelengths and intensities to find the optimal rate of photosynthesis by using a spectrophotometer, measuring the greatest change in absorbance. From this experiment, two data charts and four graphs were obtained. The hypothesis was set from graphs obtained in this lab, and the optimal reaction rate was found at a wavelength of 650 nm and an intensity of 50 uEinsteins/m^2/sec. Introduction
Every species on earth needs some kind of energy sources in order to survive. In animal cells, the mitochondria produce ATP from cellular respiration. However, the plant cells have a different type of center that produces energy- chloroplasts. The main process of photosynthesis is the absorption of light by the pigments. The light energy absorbed is first transferred by exited electrons to reaction centers. Part of the light energy is stored in ATP and NADPH through a series of electron carriers. ATP and NADPH are the energy currency, which are further used for CO2 fixation and photorespiration. (Plant Ecophysiology, 1996). The lab experiment deals with wavelength and intensity, which are the two most important variables in the photosynthesis process. Being easily found in the leaves, chloroplasts are located in plant cells. The photosynthesis process takes place inside the chloroplasts, which are stacked in thylakoids called grana. The area between the thylakoids and the inner membrane is called the stroma (Campbell, 2002). The light reactions of photosynthesis take place in the thylakoid while the Calvin cycle occurs in the stroma. The chemical equation for photosynthesis is shown below. 6CO2 + 12H2O( light energy ( C6H12O6 + 6O2 + 6H2O
During the day, plant-cells consume carbon dioxide, water, and light energy to form carbohydrates, oxygen, and water. At night, photosynthesis stops and plant-cells consume oxygen as animal cells (The Life of Plants, 2002). Through reducing NADP+ into NADPH and producing ATP by the addition of a phosphate group to ADP, the light reactions alter light energy to chemical energy. The Calvin Cycle then yields light reactions- NADPH and ATP along with CO2 to produce carbohydrates (Campbell, 2002). Due to its dependence on the products of light reactions, the Calvin Cycle, which indirectly accepts light energy, only occurs in the day light. Chlorophyll is the photosynthetic pigments on the thylakoids.
In this lab, we measured the amount of light absorbed from each experimental cuvette with a spectrophotometer, which varies over time due to the relations with DCPIP- the artificial electron acceptor. As DCPIP is reduced, the amount of absorption will decrease and the sample will become colorless. This was the demonstration made by Robert Hill in 1938, known as "The Hill Reaction" (Advanced Biology, 2000). The study of Emerson and his associates at the University of Illinois in the 1940s found that the most effective light for photosynthesis in chlorella were red from 650 nm to 680 nm and blue from 400 nm to 460 nm, which were the strongest absorbed colors by chlorophyll (Light-Harvesting Antennas in Photosynthesis, 2003). The reaction rate of photosynthesis varies with light intensity, and as the light intensity increases the reaction rate also increases only up to a certain point (Advanced Biology for You, 2001). From the given information, the hypothesis was that the optimal reaction rate was expected to be at the wavelength near 450 nm and 650 nm. Also, for the optimal reaction rate for different intensities should be at 50 uEinsteins/m^2/sec. Materials...
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