Lab+4-+Photosynthesis

__Purpose:__ The purpose of this lab was to understand the different pigments present in plant cell chloroplasts and what the cell needs to go through photosynthesis. Learn how to calculate Rf values, and understand why the rate of photosynthesis varies under different conditions. __Summary:__ To examine the pigments used in photosynthesis, we separated pigments out of a spinach leaf. A line of pigment was drawn across the chromatography paper with a quarter. The end of the paper was then dipped in a buffer solution, allowing the water to wick up the paper and drag the pigment with it. The orange pigment (carotene) ran the furthest up the paper. The next band was the yellow (xanophyll) followed by olive colored (chlorophyll b) and then bright green pigment (chlorophyll a). This means that the carotene was the most soluble, then the xanophyll, then the chlorophyll b, and chlorophyll a.

To examine the effects of light and chloroplasts, various cuvettes were filled with chloroplasts and DPIP that had been exposed to light or darkness, and boiled or not boiled. The DPIP served as an electron carrier to simulate photosynthesis. The cuvettes were then put in a spectrometer were we tested to see how much of the DPIP was reduced. Boiling the chloroplasts killed the chloroplasts, and the chloroplasts exposed to darkness did not have enough ATP or NADPH to carryout photosynthesis. Therefore the cuvette exposed to light and with unboiled chloroplasts reduced the greatest amount of DPIP.

__Conclusion:__ The function of DPIP in this experiment was to act as an electron carrier. DPIP "replaces" NADPH found in chloroplasts. We used a spectrophotometer to measure the percent of light transmitted which could be used to determine the amount of photosynthesis occurring. Cuvette 1 functions as a control. Cuvette 2, the unboiled and dark sample, demonstrated unharmed chloroplasts without electron excitement. Cuvette 3, the unboiled and light sample, demonstrated unharmed chloroplasts with electron excitement. Cuvette 4, the boiled and light sample, demonstrated electron excitement with denatured chloroplasts. Cuvette 5, the no chloroplasts and light sample, demonstrated absence of chloroplasts with electron excitement. The darkness reduces the amount of electrons excited which reduces the reduction of DPIP. In increased temperatures, the proteins in the chloroplasts are denatured so DPIP is not reduced. The difference in the percentage of transmittance between the live chloroplasts that were incubated in the light and those that were kept in the dark can be explained by the limited amount of excited electrons reducing the amount of time the process can continue. In the presence of light, the process can continue without restraints.

__Valid:__ The results are valid because plants can't go through photosynthesis without chloroplasts and sunlight and therefore couldn't survive without them. Also, the DPIP clearly changed color when photosynthesis was occurring.