Photosynthesis is the conversion of solar energy into chemical energy in order to synthesize organic compounds necessary for plant life. The light reactions occur in the thylakoids of chloroplasts in spinach leaves. Inside the thylakoids are pigment molecules that capture and absorb light, initiating the process of making NADPH and ATP required for carbohydrate production in the dark reactions. The rate of photosynthesis is affected by changes in wavelength of light and light intensity. Spectrophotometry was used in my experiment to monitor these changes by measuring the amount of light absorbed by the chloroplasts after being subjected to these altering factors over time. This data was then translated into rates of photosynthesis.
[...] I tested the photosynthesis rate of chloroplasts in four different wavelengths as shown in Figure and at four different light intensities as shown in Figure 2. This required eight cuvettes of experimental solution to be made consisting of 2.5 mL DCPIP mL of water mL of phosphate buffer, and 0.2 mL of suspended chloroplasts which I did not add to each cuvette until commencing with the absorbance readings of the experiment. I suspended the chloroplasts by blending about 50 g of deveined spinach leaves and 200 mL of 0.5 M sucrose to disrupt the structure of the leaves. [...]
[...] Mathis, P Photosynthetic Reaction Centers. Pp.75-76 in Light as an Energy Source and Information Carrier in Plant Physiology. Jennings, ed. Plenum Press, New York. Vliet, K A Lab Manual for Integrated Principles of Biology Part II BSC2011L Fourth Edition. Pearson Custom Publishing. Boston, Massachusetts. Figure 1. Absorbance as a result of differences in Wavelengths; Orange bars represent 450 nm with rr= red bars exhibit 545 nm with rr= pink bars indicate 650 nm with rr= and blue bars correspond to 750 nm with rr= [...]
[...] The P700 pigment molecule, with a maximum wavelength absorbance of 700 nm, in PS II absorbs light energy as well and releases electrons to acceptors which transfer the electrons to NADP+. This movement of electrons causes the hydrogen protons from PS I and NADP+, which now is rich in electrons, to produce NADPH (Campbell and Reece 2005, Vliet 2008). The products of the light reactions, ATP and NADPH, are then used by the dark reactions, also called the Calvin Cycle, which occur in the stroma. [...]
[...] I was able to just observe the light reactions because the rate of the dark reactions is directly dependent on the rate of the light reactions resulting in the rates of the light reactions and photosynthesis to be equal. I assessed the effects of two changing factors on the rate of photosynthesis, the wavelength of light and light intensity (Vliet 2008). Some wavelengths of light are better absorbed by pigment molecules than others resulting in varying rates of photosynthesis. The main two types of pigment molecules in plants that absorb the most light are chlorophyll a and chlorophyll b. [...]
[...] The rates of photosynthesis were of higher value in the light intensity portion of the experiment because in the wavelength potion, the pigment molecules were restricted to absorbing only one wavelength when they, along with other accessory pigments, can absorb light over a broad range of wavelengths at the same time. Contrarily, the light intensity experiment involved a source of white light which expanded the whole spectrum of light wavelengths. Based on previously conducted similar experiments the graph of the reaction rates in response to wavelength should have shown the influence of the absorption spectrum of chlorophylls a and which it did. [...]
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