Which one of the following is wrong statement?

Options

A. Anabaena and Nostoc are capable of fixing nitrogen in free-living state also
B. Root nodule forming nitrogen fixers live as aerobes under free-living conditions
C. Phosphorus is a constituent of cell membranes, certain nucleic acids and all proteins
D. Nitrosomonas and Nitrobacter are chemoautotrophs

Answer

To determine which statement is incorrect among the provided options, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- Statement: "Anabena and Nostoc are capable of fixing nitrogen in free living state."
- Explanation: Anabena and Nostoc are types of cyanobacteria (often referred to as blue-green algae) that can fix atmospheric nitrogen. They possess specialized cells called heterocysts that facilitate this process.
- Conclusion: This statement is **correct**.

2. **Analyze the Second Statement:**
- Statement: "Root nodule formation nitrogen fixer leaves as aerobes under free living conditions."
- Explanation: This statement refers to nitrogen-fixing bacteria like Rhizobium, which form symbiotic relationships with the roots of leguminous plants. These bacteria are indeed aerobes and can fix nitrogen in root nodules.
- Conclusion: This statement is **correct**.

3. **Analyze the Third Statement:**
- Statement: "Phosphorus is a constituent of the cell membrane, certain nucleic acids and all proteins."
- Explanation: Phosphorus is indeed a component of cell membranes (in the form of phospholipids) and nucleic acids (as phosphate groups). However, phosphorus is **not** a component of all proteins; proteins are primarily made of amino acids which contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur, but not phosphorus.
- Conclusion: This statement is **incorrect**.

4. **Analyze the Fourth Statement:**
- Statement: "Nitrosomonas and Nitrovector are chemoautotrophs."
- Explanation: Nitrosomonas and Nitrobacter are indeed chemoautotrophic bacteria that obtain energy by oxidizing inorganic nitrogen compounds. This statement is correct.
- Conclusion: This statement is **correct**.

### Final Conclusion:
Based on the analysis, the **incorrect statement** is the third one: "Phosphorus is a constituent of the cell membrane, certain nucleic acids and all proteins."