Question

Write short notes on Hill Reaction.

Answer 1

Hint: Robert Hill recognized as Robin Hill, was a British plant biochemist who, in 1939, showed the 'Hill reaction' of photosynthesis, demonstrating that oxygen is produced during the light involving steps of photosynthesis. He has made important contributions to the creation of the Z-scheme of oxygenic photosynthesis.

Complete Answer:
- A reaction, identified by Robert Hill in 1939, wherein the separated chloroplasts emit oxygen and hydrogen if activated in the presence of oxidising agents. Release of oxygen from isolated illuminated chloroplasts as sufficient electron acceptors are added to the ambient water.
- Robert Hill's reaction was discovered in 1939. Electron acceptors replace NADP$^+$, the normal acceptor of light-dependent photosynthesis reactions. In 1937, Robert Hill demonstrated that in the absence of carbon dioxide, isolated chloroplasts could produce oxygen. His discovery was one of the first hints that the cause of the electrons in the light reactions was probably space.
- He provided an artificial electron receiver. The artificial electron receiver intercepts the electrons. The mechanism of plant photosynthesis is carried out entirely inside the chloroplasts.
- Around 1940 Hill observed that green particles from broken cells could create oxygen from water in the presence of light and a chemical compound, such as ferric oxalate, capable of acting as an electron acceptor. This process is referred to as the Hill Reaction.
- It is possible to incorporate an artificial electron acceptor into a light reaction, such as a pigment that changes colour as it is reduced. They are known as Hill Reagents. These dyes allowed the discovery of transport chains of electrons during photosynthesis.

Note: During photosynthesis, the NADP natural electron acceptor is reduced to NADPH in chloroplasts. The light-dependent redox reaction occurs prior to the light-independent photosynthesis reaction.