Question

What was Robert Hill's experiment with photosynthesis? State and explain it.

Answer 1

Hint: Plants produce food by the process of photosynthesis. It is a well-known fact for a long period of time. But, the specific cells responsible for photosynthesis were widely unknown till Robert Hill experimented and found the exact cell organelles. The experiments Robert Hill carried out then are now popularly known as Robert Hill's experiment on photosynthesis.
Complete step-by-step answer:

- In his experiment, Robert Hill isolated the chloroplasts of the Stellaria plant. Then he proceeded to place the isolated chloroplasts in illuminated water having the presence of suitable hydrogen acceptors like ferricyanides and chromates. Now, in the absence of carbon dioxide, he found out that oxygen was liberated by the chloroplasts.
- In his experiment, he found out that ferricyanide was reduced to ferrocyanide and the molecules of water, was simultaneously oxidized into oxygen molecule.
- The finding of Hill that isolated chloroplasts can make oxygen without fixing carbon dioxide gave rise to the conclusion that light and dark reactions in plats occur at different sites within the cell.
- Hill's finding was, that the actual origin of oxygen in the process of photosynthesis is water and not carbon dioxide as was believed previously. These observations were enough for Hill to conclude that oxygen is released only during the light-dependent steps of photosynthesis.
- Robert Hill also discovered Hill reagents.
- These reagents are artificial electron acceptors that participate in the light reaction and change color when reduced in the experiment.
- Dichlorophenolindophenol (DCPIP) is an example of a hill reagent. These dyes made it possible to find out the electron transport chains during the process of photosynthesis.

Note: In the light-dependent step(Hill reaction), oxygen is a by-product, and the solar energy or light energy of the sun is converted to the chemical energy of reduced co-enzymes.