Question

The experiments helped researchers in understanding of photosynthesis in plants is

• A. Joseph Priestley's experiments
• B. Jan Ingenhousz's experiments
• C. C B van Neil's experiments
• D. T W Engleman's experiments

Hint:

Remember:
C.B. van Niel used purple sulfur bacteria to prove that oxygen released during photosynthesis comes from \( \text{H}_2\text{O} \) and not from \( \text{CO}_2 \).
This was a major milestone in understanding the biochemistry of photosynthesis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The historical elucidation of the biochemical equation of photosynthesis involved several key experimental milestones over more than two centuries.
These experiments established the roles of light, carbon dioxide, water, and chlorophyll in the synthesis of carbohydrates and the release of oxygen.

Step 2: Detailed Explanation:
Let us review the historical contributions of each scientist:
1. C.B. van Niel's Experiments (C): Cornelius van Niel conducted key experiments using purple and green sulfur bacteria.
He demonstrated that photosynthesis is essentially a light-dependent redox reaction, where hydrogen from an oxidizable compound reduces carbon dioxide to organic matter:
\[ 2\text{H}_2\text{A} + \text{CO}_2 \xrightarrow{\text{Light}} 2\text{A} + \text{CH}_2\text{O} + \text{H}_2\text{O} \] For oxygenic plants, the electron donor is water (\( \text{H}_2\text{O} \)), which is oxidized to release oxygen (\( \text{O}_2 \)).
For sulfur bacteria, the electron donor is hydrogen sulfide (\( \text{H}_2\text{S} \)), yielding elemental sulfur (\( \text{S} \)) instead of oxygen.
This work demonstrated that the oxygen released during plant photosynthesis comes from water (\( \text{H}_2\text{O} \)), not from carbon dioxide (\( \text{CO}_2 \)), which was later confirmed using the stable isotope \( ^{18}\text{O} \).
2. Joseph Priestley (A): In 1770, Priestley showed that plants restore oxygen to air that has been depleted by burning candles or breathing mice.
3. Jan Ingenhousz (B): Ingenhousz showed that sunlight is essential for this restoration process, and that only the green parts of plants release oxygen.
4. T.W. Engelmann (D): Engelmann used a prism to split light and show that red and blue wavelengths are most effective for photosynthesis, creating the first action spectrum.
Among these, C.B. van Niel's formulation provided the foundational biochemical framework for our modern molecular understanding of photosynthesis.

Step 3: Final Answer:
C.B. van Niel's experiments provided the key conceptual breakthrough in understanding the redox nature of photosynthesis, corresponding to option (C).