Photosynthesis is a redox reaction which requires carbon dioxide, water and light to produce water and a 6-carbon sugar. The process of photosynthesis consists of two parts, a light reaction and a light-independent reaction. The method of changing light energy into chemical energy for the formation of NADPH and ATP is done through the light reactions. Light independent reactions use carbon dioxide and the products of light reactions (ATP and NADPH) to form compounds such as glucose. The rate of photosynthesis can be determined indirect by the indicator DCPIP. When reduced this indicator changes from blue to a colorless solution. When light is absorbed, water is oxidized and the excited electrons are transferred for the process of reducing NADP+ to NADPH. This transfer is done via the electron transport chain. DCPIP is able to capture the electrons that are transferred through the electron transport chain which will cause the color intensity of the indicator solution to decrease. The decrease in intensity of the indicator correlates to an increased rate of photosynthetic activity. Varied light intensities can alter the photosynthetic capability of chloroplasts. As light intensity increases, it is apparent that the rate of photosynthesis begins to decrease until a certain level of light saturation. If the intensity extends over a certain tolerance level, photo inhibition occurs. The light used for photosynthesis requires a specific wavelength for the pigments in chloroplast to absorb it. Light independent reactions occur in the stoma of the chloroplast whereas the light reactions occur in chloroplasts that sit on the thylakoid membrane. White light is comprised of all the colors in the spectrum where each of these colors contains different energy; hence they are all of different wavelengths. Since pigments only absorb certain wavelengths within the visible spectrum, the others are transmitted or reflected. Blue and red light tend to contribute to the highest rates of photosynthesis whereas green and yellow result in the lowest rates. The purpose of the experiment was to investigate photosynthetic electron transport, using isolated chloroplast from silver beet leaves. Red light tend to contribute to the highest rates of photosynthesis whereas green result in the lowest rates. The faster the rate of photosynthesis, the faster the dye will lose color and the more rapid is the decrease in absorbance. METHOD
TABLE 1: EXPERIMENTAL DESIGN FOR THE ELECTRON TRANSPORT CHAIN.
ACHLOROPLAST SUSPENSION (ML)22.214.171.124-126.96.36.199
BBUFFERED SOLUTION (ML)188.8.131.52.184.108.40.206
C BOILED CHLOROPLAST SUSPENSION (ML)---1.5--- D0.01M DCMU (ML)----0.10--
[ADD THIS LAST]-0.200.200.200.200.200.20
Treatment/ Tube PREDICTIONS
DARK: Tube 2The rate of change of color of dye is low. The solution will not turn colorless. LIGHT: Tube 3The dye turns colorless fast
Tube 4The dye does not turn colorless because the chloroplast is destroyed hence photosynthesis does not occur. DCMU: Tube 5The dye does not turn colorless.
Tube 6The dye does turn colorless.
Tube 7The dye does not turn colorless.
Seven spectrophotometer tubes were numbered and solutions A-D were added according to the volumes 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, tube 2 was wrapped in foil and tube 6 and 7 were placed into larger tubes covered...