Correct Option
The correct option is 2 only
Explanation
Photosynthesis is the physicochemical process by which plants, algae, and certain bacteria use light energy to drive the synthesis of organic compounds. In oxygenic photosynthesis, water serves as the electron donor, and oxygen is released as a byproduct.
Statement-wise Analysis
- Statement 1 is Incorrect: The oxygen evolved during photosynthesis arises from the oxidation of water (photolysis). This process occurs in the thylakoid membrane of chloroplasts, specifically associated with Photosystem II. Water molecules are split into hydrogen ions ($H^+$), electrons ($e^-$), and molecular oxygen ($O_2$).
- Statement 2 is Correct: Not all autotrophs produce sulphur. While photosynthetic sulphur bacteria (e.g., purple and green sulphur bacteria) use hydrogen sulphide ($H_2S$) as a hydrogen donor and deposit sulphur instead of evolving oxygen, higher plants, cyanobacteria, and algae perform oxygenic photosynthesis where oxygen is produced. Therefore, oxygen evolution is not "always" replaced by sulphur production.
- Statement 3 is Incorrect: Oxygen is not derived from carbon dioxide. Experimental evidence provided by Cornelius van Niel and later confirmed using radioisotopic techniques ($O^{18}$) demonstrated that the oxygen released comes exclusively from water ($H_2O$). The oxygen atoms present in carbon dioxide ($CO_2$) are incorporated into the carbohydrate (glucose) molecules and water produced during the process.
Key Takeaway
Key Takeaway: In oxygenic photosynthesis, the oxygen evolved is a product of the photolysis of water, whereas the carbon and oxygen found in glucose are derived from carbon dioxide.