CBSE Class 11-science Answered

Hi Archana,

• Chemiosmotic hypothesis explains the mechanism of ATP synthesis in the thylakoids of chloroplast.
• In photosynthesis, the synthesis of ATP is linked to the development of a proton gradient across the cell membrane.
• The protons that are produced by the splitting of water are accumulated inside the membrane of thylakoids.
• As the electron moves through the photosystems, protons are transported across the membrane.
• NADP reductase enzyme located on the stroma side of the membrane, along with the electrons from the acceptor, removes H⁺ from the stroma during reduction of NADPH and H⁺.
• This creates proton gradients across the thylakoid membrane as well as a measurable decrease in pH of the lumen.
• The enzyme ATPase has a channel that allows diffusion of protons back to the stroma across the membrane. 
• This releases energy to activate ATPase enzyme that catalyses the formation of ATP and provides energy for the process.