Question

Explain the specific process creates the high concentration of protons inside the thylakoid membranes?

• Here is an example of an answer that is not acceptable because it is too broad : active transport or proton pumping.
• You need to explain the molecular process and energy transfers that are used to build the high concentration of protons inside the thylakoid membrane lumen,

Answer 1

Photosynthesis in the process of formation of sugar in the presence of Sunlight and chlorophyll molecules by using atmospheric carbon dioxide. This process is atmospheric carbon dioxide which is an abiotic source of carbon into biotic source of carbon in the form of glucose in the biomass of plants.

It is divided into two stages. The first stage is light dependent reaction which occurs in the presence of sunlight in thylakoid membrane of chloroplast and the second stage is dark reaction of Calvin cycle or light independent reaction which take place in the stroma of cell. Dark reaction can take place in the absence of presence of light but is dependent upon the product of light reactions.

During light reaction, light is absorbed by photosystem 2 (P700) which causes photolysis of water and release of oxygen as gas and excitation of electrons released by the photolysis of water. This results in the entry of electron into electron transport chain taking place in thylakoid membrane. In electron transport chain, electrons are transported from one electron carrier to the other. All the electron Carriers are arranged in increasing order of their electrochemical potential. As the electrochemical potential increases, the affinity of an electron carrier for electron also increases. The electrons pass from PS2 to cytochrome b6f complex and than to PS1 (P680). Ultimately the electrons are accepted by NADP+, primary electron acceptor, to form NAPDH which is a high energy electron carrier. When electrons are transported from one electron carrier to another, protons are pumped from the lumen of thylakoid to the stroma of chloroplast. This results in an increase in the acidity of stroma and differential concentration of protons across thylakoid membrane. This leads to the formation of proton gradient or electrochemical gradient across the membrane. The electrochemical energy stored in Proton gradient is used by ATP synthase enzyme for the synthesis of ATP.

Hence light reaction begin with the photolysis of water and results in the evolution of Oxygen and formation of ATP and NADPH.

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