Effect of Wavelength and Light Intensity on the Reaction of Photosynthesis

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Abstract :

The purpose of the experiment was to determine the wavelength and light intensity effect on the reaction rate of photosynthesis. Photosynthesis is the conversion of light energy to chemical energy in the form of organic compounds. There are two phases in photosynthesis, the light reaction and dark reaction. The following experiment tested only the light reaction. Photosynthesis takes place on the chloroplast, and the chloroplast contains chlorophyll pigments which absorb light energy. Pigments are particular to different wavelengths. The following experiment helped determined the fastest photosynthetic reaction rate from wavelength ranging from 450, 545, 650, and 750 nm, and intensities 3, 7, 15, 35, and 150 uEinsteins/m^2/sec. The products from the light reaction are needed for the dark reaction. Therefore the light reaction rate determines the photosynthetic reaction rate. Experiment Data showed that at 650 nm and a light intensity of 35 m2/sec was a peak. The peak represented the highest points of absorbance. at those points. The absorbance determines was an optimum. Biological concepts of light absorbance support the experimental results. The wavelength at 650 nm is energetically stable and it would be able to efficiently deliver energy for the transfer of electrons. While with higher light intensities the chlorophyll readily absorbs light and photosynthetic rate increases.

Introduction
This research is important because it helped determine at which wavelength of light and at which light intensity the chloroplast would generate the fastest photosynthetic reaction rate of photosynthesis. Photosynthesis takes place on chloroplasts. Chloroplasts are powered by the sun to transform light energy into chemical energy of ATP and NADPH. Photosynthesis is the biological conversion of light energy to chemical bond energy that is stored in the form of organic compounds (Falkowski, pg 1). The reaction of photosynthesis works as follows: 6 molecules of carbon dioxide + 12 molecules of water + photons combine to produce 1 molecule of glucose and 6 molecules of oxygen. Furthermore, the reaction of photosynthesis is divided into 2 phases, the light reaction and the dark reaction. The light reaction determines the rate of the dark reaction because the byproducts of the light reaction are needed in the dark reaction (lab manual). Therefore, the light rate of reaction will determine the overall reaction rate of photosynthesis. In the experiment, the light reaction was tested. There are several limiting factors on the photosynthetic rate of reaction. For purposes of this experiment, however, only light intensity and wavelength were measured. Light is an electromagnetic radiation that changes the energy state of atoms or molecules. The entire range of radiation is known as the electromagnetic spectrum. The most important segment is the radiation of visible light, which ranges from 380 nm to 750 nm (Campbell pg186). Substances that absorb visible light are called pigments. Different pigments are characteristic of different wavelength. Radiation from light emits wavelengths, which is the distance between the crest of electromagnetic waves. The shorter the wavelength, the greater the energy of each photon of that light. The chlorophyll molecules of chloroplasts absorb the wavelengths of violet-blue at 450nm and red light at 650nm and transmits green light. Violet-blue and red light are the most effective colors that conduct photosynthesis. This is why, leaves appear green. By using a spectrophotometer, one is able to measure the ability of a pigment to absorb various wavelengths. Photosynthesis begins when pigment chlorophyll absorbs one photon (light) from the sun and loses one electron. As light is absorbed, a light reaction occurs. In photosynthesis, the light absorbed is used to alter the electronic structure of pigment molecules. Then an electron can be physically transferred from electron donor to...
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