Question

Given below are two statements
Statement I: Photsynthetic bacteria do not contain PS-I
Statement II: Photsynthetic bacteria do not contain PS-II
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct, but Statement II is incorrect
• D. Statement I is incorrect, but Statement II is correct

Hint:

Anoxygenic photosynthetic bacteria have only one photosystem. They lack a true, water-splitting Photosystem II (PS-II), which is why they do not produce oxygen during photosynthesis.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Photosynthetic bacteria include both oxygenic phototrophs (like cyanobacteria) and anoxygenic phototrophs (such as purple bacteria and green sulfur bacteria).
Anoxygenic photosynthetic bacteria utilize a simpler photosynthetic apparatus that does not produce oxygen.

Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement I: This statement asserts that photosynthetic bacteria do not contain Photosystem I (PS-I).
Anoxygenic photosynthetic bacteria contain only a single photosystem.
In green sulfur bacteria and heliobacteria, this single photosystem is a Type-I reaction center, which is structurally and functionally homologous to eukaryotic Photosystem I (PS-I).
Therefore, they contain a PS-I-like apparatus. Thus, Statement I is incorrect.
- Statement II: This statement asserts that photosynthetic bacteria do not contain Photosystem II (PS-II).
Anoxygenic photosynthetic bacteria utilize either a Type-I or a Type-II reaction center, but they never possess both.
Crucially, they completely lack a functional Photosystem II (PS-II) identical to that found in plants and cyanobacteria, which is responsible for the photolysis of water.
They cannot split water and instead use alternative electron donors like $H_2S$ or organic compounds. Thus, Statement II is correct.
Therefore, Statement I is incorrect, but Statement II is correct.

Step 3: Final Answer
The correct option is (D).