Chloroplasts and Photosynthesis

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Chloroplasts and Photosynthesis

(Laboratory Report)

Zhanerke Yermekkyzy

BC Group: 5B

Date of submission: 17.04.2018

Introduction

Photosynthesis consists of two main groups of reactions: light-dependent, which harness the sunlight energy and the Calvin cycle, which fixes carbon dioxide and synthesizes organic molecules using that energy.

Light reactions of photosynthesis are the result of a series of oxidation-reduction reactions and require the presence of a terminal electron acceptor. Normally such an acceptor is NADP, which plays an important role in the oxidation of water.

Photons are absorbed at photosystems I and II during the light reactions. They excite electrons in each photosystem’s reaction center. Transferring the electrons to the primary electron acceptor, they then go through an ETC. Finally, NADP⁺ is being reduced to NADPH by these electrons. The overall equilibrium reaction that goes within a chloroplast is (Karp, 2010):

Electrons obtained during the splitting of water enter the photosystem II, where they absorb light energy, and then enter the electron transport chain of photosynthesis (ETC). These high-energy electrons are used to restore NADP. Thus, solar energy is converted into chemical energy by restoring NADPH to NADPH.

In nature, NADPH then provides electrons and H⁺ for the light-independent reactions.  

Direct observation of the electrons movement is difficult, however, it could be studied by adding an artificial electron acceptor in the chloroplasts. In this laboratory practical the 2,6-dichlorophenolindophenol (DCPIP) will be used to show the movement of electrons through its color change. It has a blue color in the oxidized state, but became colorless when it is reduced. The Hill reaction:

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