Chloroplasts and Photosynthesis

Chloroplasts and Photosynthesis

(CW3: Laboratory Report)

Zhanerke Yermekkyzy

BC Group: 5B

Word count: 1165

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.

During the light reactions, the water molecule is split into protons, electrons, and an oxygen atom and photons are absorbed at photosystems I and II (Reece et al. 2009, 114).

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. The overall equilibrium reaction that goes within a chloroplast is (Karp 2010, 148):

Resulting NADPH acts as a reducing agent in the process of incorporation of carbon dioxide to organic compounds, providing electrons and H⁺ for the light-independent reactions.

Direct observation of the electrons movement is difficult to perform; 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. Electrons released during light reactions will reduce DCPIP, making it transparent and thus indicating the movement of electrons. The Hill reaction may be summarized as follows (Karp 2010, 153):