Explain chemiosmotic theory with suitable diagram.

Explanation

Chemiosmotic theory was proposed by P-Mitchell (1966). According to this theory electrons are transported along the membrane through PS I and PS II and connected by Cytochrome `b_6-f` complex. The flow of electrical current is due to difference in electrochemical potential of protons across the membrane. Splitting of water molecule takes place inside the membrane. Protons or `H^+` ions accumulate within the lumen of the thylakoid (`H^+` increase 1000 to 2000 times). As a result. Proton concentration is increased inside the thylakoid lumen. These protons move across the membrane because the primary acceptor of electron is located outside the membrane. Protons in stroma less in number and creates a proton gradient. This gradient is broken down due to the movement of proton across the membrane to the stroma through CFo of the ATP synthase enzyme. The proton motive force created inside the lumen of thylakoid or chemical gradient of `H^+` ion across the membrane stimulates ATP generation.

The evolution of one oxygen molecule (4 electron required) requires 8 quanta of light. `C_3` plants utilize 3 ATPs and 2 DPH + `H^+` to evolve one Oxygen molecule. To evolve 6 molecules of Oxygen 18 ATPs and 12 DPH + `H^+` are utilised. `C_4` plants utilise 5 ATPs and 2 DPH + `H^+` to evolve one oxygen molecule. To evolve 6 molecules of Oxygen 30 ATPs and 12 DPH + `H^+` are utilised.