Tuesday, September 24, 2019
PHOTOSYNTHESIS Essay Example | Topics and Well Written Essays - 1000 words
PHOTOSYNTHESIS - Essay Example The learner should also explain the source of the electrons that are transported in the light reaction of the light dependent reaction of photosynthesis. Introduction Photosynthesis takes place in plants which have chlorophyll, in some algae and some bacteria. Photosynthesis needs chlorophyll-the green coloring pigment found in the chloroplasts. The process takes place in two phases: the light dependent reaction and the light independent reaction. The light-dependent reaction takes place in the thykaloid membranes while the light independent reaction takes place in the stroma of chloroplast. At this phase light is taken up by chlorophyll molecules and transferred to electrons of a water molecule. This energy causes the water molecules to split releasing an oxygen atom and two hydrogen atoms. The electrons carry energy which used in the synthesis of high energy molecules like ATP and NADPH2. 2H2O + 3 ADP + NADP +3Pi = O2 +3ATP + NADPH2                Light energy is needed in the process. ... This can be done if the thykaloid membranes (sites for light reaction) and the stroma (site for carbon fixation) are uncoupled or separated by cell fractionation. Using the isolated thykaloids, the light reactions will proceed without carbon fixation if light is present. It is an in-vintro type of reaction. DCPIP is used in Hill’s reaction to be the electron acceptor to accept the electrons after water molecules are split. It is blue in when oxidized state and colorless when in the reduced state. DCPIP (oxidized) + 2e = DCPIP (reduced) (Blue)                                    (Colorless) This way the electron transport rate in the Hill’s reaction can be accounted for spectrophotometrically on a 620 nm wavelength by the change in absorbance of DCPIP as it accepts electrons by the conversion of water molecules in the chain. The rate of electron transport is a function of light intensity. Method Hill’s reaction was used to show how photosynthesis occurs in two distinct reactions. It also shows the role of light in photosynthesis which is shown by the difference in the readings of the spectrophotometer between tubes 3 and 4 where tube 3 is placed in the presence of light and tube 4 in the dark. Also boiling the solution destroys the chloroplasts in it, thus there is no observable change in absorption. This shows there was little or no photosynthetic reaction taking place. Ice cold solutions were used to stop any reactions that could have affected or altered the results in the Hill’s reaction in the electron transport chain. The reaction conditions were light to produce the needed energy, carbon dioxide and water which is broken down to
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