Light and Dark Reaction Discussion

Topics: Photosynthesis, Leaf, Carbohydrate Pages: 2 (563 words) Published: April 16, 2013
Photosynthesis is a process of converting light energy into chemical energy and storing in the bonds of sugar. Photosynthesis takes place in the plant leaves. In the leaves, there are mesophyll cells that have chloroplasts, where the photosynthesis occurs. During experiment, two leaves were tested for the presence and localization of starch. One leaf was a light-grown plant with mask, and the other was a dark-grown plant with mask. Both leaves were soaked in iodine solution and then rinsed in order to observe the pattern of staining.

According to the result, the light-grown leaf’s masked areas had no blue-black coloration and the unmasked area turned blue-black in color. The blue-black coloration of the leaf indicated the presence of starch. The light-grown leaf’s unmasked areas turned blue-black because the leaf have been performing photosynthesis and producing starch (Photosynthesis, n.d.). Photosynthesis involves both light-dependent stage and light-independent stage. The light-grown had been growing in bright light for several hours and it performed both photosynthesis stages. In light-dependent stage, water is photolyzed by the light into Hydrogen and oxygen. Hydrogen enters the second stage and oxygen became a by-product. Then, in independent stage, and enzyme catalyse the reduction of carbon dioxide by hydrogen, forming a carbohydrate, which is glucose. Glucose can be translocated in the dorm of fructose or sucrose or stored as starch in granules. To put it simply, carbon dioxide and water molecules form glucose and oxygen with light energy, and the overall equation for photosynthesis is (Testing a leaf, n.d.); 6CO2 + 6H2O  C6H12O6 + 6O2

That was why the unmasked area turned to blue-black. It was because those areas contain starch and iodine stains the starch by binding onto the starch (UCSB ScienceLine, n.d.). As for the unstained masked area, the masked leaf areas did not turn to blue-black because of lack of light for photosynthesis to...
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