BIO1011 PRAC PHOTOSYNTHESIS.docx - 1 Kiara Corso An...

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1 Kiara Corso An investigation on the light dependent electron transport using DCPIP Introduction: Photosynthesis is the process which allows plants to produce glucose (oxygen is a by- product) from carbon dioxide and water. This provides energy for the plant to grow and reproduce. Light energy is absorbed by chloroplasts, these chloroplasts become excited and split water into oxygen molecules, releasing ATP. This ATP is used in the electron transport chain between photosystem I and II. These photosystems produce electrons which power light independent reactions which produces glucose. When there are low amounts of light energy there is a “decreased rate of electron flow through the electron transport chain” (Boardman 1977), therefore decreasing the rate of photosynthesis. The aim is to investigate the effects of different treatments on the electron transport in chloroplasts. It was hypothesised that chloroplasts exposed to no light, chloroplasts that were boiled and chloroplasts with DCMU will have a low rate of electron transport, shown by slowly decreasing absorbance. Chloroplasts with exposed to red wavelengths and white light will have high rates of electron transport, displayed by low absorbance which rapidly decrease. Those chloroplasts exposed to green wavelengths will have a low rate of electron transport displayed by high absorbency. Method: Seven spectrophotometer tubes were numbered, and solutions A-D were added according to the volumes shown in Table 1. Tube 1 was capped and inverted several times. The spectrophotometer was calibrated using tube 1, which contained chloroplasts and sucrose only, as the blank, to ensure that any changes in absorbance for the other treatments could be attributed to the reduction of the dye DCPIP. At time zero (mins), absorbance was recorded for all treatments immediately after addition of DCPIP and mixing of contents. Immediately following the time zero reading, all tubes (1-7) were placed in larger plastic tubes; tube 2 in a

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