829 Words Oct 19th, 2014 4 Pages
Practical 2: Photosynthesis

Introduction: Photosynthesis is a vital process in plants as carbon dioxide is used to form sugars and other complex compounds for growth. There are two basic processes in photosynthesis: light-dependent and light-independent. Light-dependent process, a temperature-independent reaction where light energy is absorbed by the photosynthetic pigments and transformed into chemical energy which is used for water, splitting into oxygen molecule, proton (H+) for driving ATP during phosphorylation, and electron (e-) which is being passed down the electron transport chain to yield NADPH. Light–independent, temperature-dependent reaction occurs to form carbohydrate and water molecule by the assimilation
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At time zero (minutes), absorbance was recorded for all treatments immediately after addition of DCPIP and mixing of contents. Immediately following the time zero reading, tube 2 was wrapped in aluminium foil and tubes 6 and 7 were wrapped with red and green lanterns paper respectively. Tubes 1-7 were capped then placed horizontally on ice in a huge container, under lights. At thirteen minute intervals, readings of absorbance were taken for all treatments, except for the dark tube which was kept wrapped in foil for 90 minutes, after which its absorbance was measured.


In Tube 2 (Dark), the initial absorbance is higher than that at 90 minutes which does not match my prediction, where the absorbance should have no difference. This difference may cause by some electrons produced from light-dependent reaction that are left behind in the silverbeet leaves before the tube is covered by aluminium foil. Therefore, the remained electrons inside the tube reduce DCPIP during the time intervals. Tube 3 (Light) shows a gradually decreasing trend which meets my prediction. Under the exposure of light, light-dependent reaction is able to be conducted by silverbeet chlorophyll, thus more electrons being produced which reduce DCPIP. Hence, the higher the rate of DCPIP turns into colourless. Only a slight change in the absorbance of Tube 4 (Boiled) over 90 minutes period as chloroplast consists of chlorophyll-protein

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