Studies on Photosynthesis Using the Hill Reaction Report Lab

Studies on Photosynthesis Using the Hill Reaction - Lab Report Example The primary ‘light reaction’ stage requires light and involves the excitation of electrons of the chlorophyll. These electrons then proceed along a series of electron carriers embedded in the thylakoid of the chloroplast resulting in synthesis of ATP in the stroma and the reduction of NADP. The dark reactions of photosynthesis do not directly require light involve the use of ATP and NADPH formed during the light reaction (figure 1) (Berg et al., 553). Hill reaction named after its discoverer Robert Hill (1937) involves the photoreduction of an electron acceptor by the hydrogen atoms of water, along with evolution of oxygen. In laboratory, Hill reaction is demonstrated when isolated and illuminated ‘chloroplasts’ reduce an electron acceptor present with it, and release molecular oxygen: The electron acceptors used in laboratory conditions are not the natural electron acceptors or NADP but instead are artificial electron acceptors (Walker, 109). These artificial electron acceptors intercept the electrons before they reach PS1700. Further they are generally dyes that change color when reduced e.g. DCIP (2,6-dichlorophenolindophenol). Thus Hill reaction can be written as: Thus using the above equation, rate of Hill reaction in isolated protoplasts can be experimentally estimated. The change in absorbance of the dye at 600nm measured under varied conditions of experiment gives the rate of Hill reaction occurring under the preselected set of conditions. Several of the detergents are also known to be inhibitors of photosynthesis such as DCMU [3-(3, 4-dichlorophenyl)-1, 1-dimethylurea], DNP [dinitrophenol] and triton-X etc. Chloroplast was extracted from deveined, washed and blot dried fresh baby spinach leaves. The standard fractionation protocol for extraction of chloroplasts was followed. 50g spinach leaves were homogenized in a pre-chilled blender jar along with buffered isotonic salt solution and antioxidant solution. The homogenate was