Determining Photosynthetic Activity in Plants Using Different Wavelengths of Light and Pigmentation

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Determining Photosynthetic Activity in Plants Using Different Wavelengths of Light and Pigmentation

The roles played by light and pigmentation in photosynthesis were examined in the geranium and Coleus plant. In addition, the separation of certain pigments based on their molecular structure was also examined, with the use of paper chromatography. When different leaves of the geranium plant which were exposed to different wavelengths of light, photosynthesis proved to be most actively present in those exposed to blue and red wavelengths of light. These wavelengths aid in the production of starch in the leaves which is an essential indicator of photosynthetic activity, hence, the use of the I2KI solution to test for the presence of starch in the leaves. With the use of paper chromatography, the results showed that the most polar molecule or pigment was chlorophyll b since it traveled the least up the polar paper since it was so attracted to it. The least polar pigment was Carotene which traveled the farthest up the paper since it was most attracted to the non polar solvent. When the multicolored Coleus leaf was tested for starch using the I2KI solution, the data suggested that the areas which had most chlorophyll, contained the most starch therefore, also having the most photosynthetic activity.

In plants, light energy is converted to chemical energy that is stored in sugar and other organic molecules in a process known as photosynthesis. (Campbell, 2009) Compounds such as water and carbon dioxide go through a series of steps to be converted into glucose (which is the main source of energy for all cells) and the oxygen that we breathe. Photosynthesis can be summarized into this basic chemical equation: 6H2O (water) + 6CO (carbon dioxide) 6O2 (oxygen) + C6H12O6 (glucose) + H2O In plants, chlorophyll is a pigment that absorbs light energy and also give plants their green color. In photosynthesis, the colors that are transmitted by plants are usually the wavelengths of light that are not absorbed. For instance, plants absorb blue and red wavelengths of lights, therefore these colors are not shown in plants. On the other hand, plants tend to reflect or transmit green wavelengths, thus, their characteristic green color. A germanium plant was used to determine different levels of photosynthetic activity in plants based on certain wavelengths of light that are absorbed and the amount of glucose that is produced by the plant. Using a red, blue, green and black filter paper for a different on the germanium plant, we hypothesized that glucose would be most evident in the leaves covered with the red filter paper and the blue filter paper (with the use of the I2KI solution which is used to test the presence of starch by deviating from its light amber color to a black or dark purple) since they would allow the plant to transmit their respective colors and allow for the process of photosynthesis and the production of glucose.

Chlorophyll is not the only pigment present in plants. The multicolored leaf of the Coleus plant is known for its variety of pigments. The upper green portions of the leaf are known to house chlorophyll but the dark purple part of the leaf consists of both chlorophyll and another pigment known as Anthocyanins which are water soluble pigments and do not contribute to photosynthesis. The pink portion of the leaf only contains Anthocyanins and the white or yellowish part of the leaf contains no pigments at all. In this experiment, we hypothesized that the I2KI test for glucose on the leaf would test positive for only the parts of the leaf that contain chlorophyll, that is only the green and dark purple portions of the leaf are capable of photosynthesis.

Molecules that have partial positive and negative charges are known as polar and molecules that have no partial charges are know as non polar. Polar substances tend to dissolve in other polar substances and non polar substances...
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