Question

State the requirements for chemiosmosis.

Answer 1

Chemiosmosis is the movement of ions down an electrochemical gradient across a semipermeable membrane bound structure. Ions will move across a membrane from areas of high concentration to areas of low concentration because chemiosmosis is a type of diffusion. Ions move in order to balance the electric charge across a membrane.

Complete Answer:
Chemiosmosis, also known as the chemiosmotic hypothesis, is a process that occurs in plants and explains how ATP is synthesised in plant cells to produce glucose via the Calvin cycle or the Krebs cycle.
Chemiosmosis involves the movement of ions across a selectively permeable membrane. Ions travel down an electrochemical gradient. Dr. Peter Mitchell discovered this process in 1961.
A proton gradient, a membrane, a proton pump, and an ATP synthase enzyme that is responsible for the synthesis of ATP that must be used in the Calvin cycle are all required for chemiosmosis to occur.
Many factors contribute to the formation of a proton gradient, including electron transport, water splitting, and the NADP reductase enzyme. These aid in the accumulation of protons within the thylakoid lumen.
Water splitting produces oxygen gas and protons. Because water molecules are split on the inner side of the membrane, oxygen gas escapes as a byproduct of photosynthesis, and protons of hydrogen ions accumulate within the lumen of the thylakoids.
Protons from the stroma are transported across the membrane into the lumen of the thylakoid as electrons move through the photosystems. This occurs when an electron's primary acceptor transfers its electron to a H carrier, causing this molecule to remove a proton from the stroma while transporting an electron.
The NADP reductase enzyme is found on the stroma side of the membrane. Protons are required for the reduction of NADP^{+} to NADPH^{+}] H^{+}. These protons are also taken out of the stroma.
As a result, all of these factors contribute to the formation of a proton gradient in which the stroma lacks protons while the lumen of the thylakoids has an excess of protons.
When this gradient is broken down, enough energy is released to synthesise ATP.
The ATP synthase enzyme is made up of two parts: F_{0} and F_{1}. The F_{0} is embedded in the thylakoid membrane and forms a transmembrane channel that allows protons to diffuse across the membrane.
It is the breakdown of the proton gradient that causes a conformational change.
When the proton gradient is broken, the ATP synthase's F$1$ particle undergoes a conformational change, causing the enzyme to synthesise several molecules of energy-packed ATP.

Note:
During photosynthesis, protons accumulate on the inside of the membrane closest to the lumen in chloroplasts, whereas during respiration, protons accumulate on the outside of the membrane closest to the lumen in mitochondria.