Question

Which statements correctly describe Mycoplasma?
1. They lack a cell wall.
2. They can survive without oxygen.
3. They are the smallest known free-living organisms.
4. Their cell membrane contains sterols.

• A. 1, 3, 4
• B. 2 and 4
• C. 1, 2, 3
• D. 1, 2, 3, 4

Hint:

Mycoplasmas are pathogenic in both plants and animals.
Remember that because they completely lack a cell wall, they are unaffected by antibiotics like penicillin, which target cell wall synthesis.
Instead, they are treated with antibiotics that inhibit protein synthesis (such as tetracyclines or macrolides).

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
This question is from "Biological Classification" in the NCERT Class 11 biology curriculum, specifically focusing on the kingdom Monera and the unique characteristics of the genus Mycoplasma.
We need to evaluate the four given statements to determine which ones are correct.

Step 2: Key Concept or Approach:
Mycoplasmas are a group of atypical, extremely small, wall-less prokaryotic microorganisms.
Because they lack a cell wall, they exhibit unique physical and biochemical properties that distinguish them from standard bacteria.

Step 3: Detailed Explanation:

• Let us analyze each of the four statements:
-

Statement 1: They lack a cell wall. This is correct. Mycoplasmas completely lack a cell wall, which makes them pleomorphic (capable of changing shape) and naturally resistant to beta-lactam antibiotics (like penicillin) that work by inhibiting cell wall synthesis.
-

Statement 2: They can survive without oxygen. This is correct. Mycoplasmas are facultative anaerobes, meaning they can grow and survive in both aerobic and anaerobic conditions.
-

Statement 3: They are the smallest known free-living organisms. This is correct. They have an extremely small size, typically ranging from $0.1$ to $0.3\ \mu\text{m}$ in diameter, and can pass through standard bacterial filters.
-

Statement 4: Their cell membrane contains sterols. This is correct. Unlike almost all other bacteria, which lack sterols in their membranes, Mycoplasmas actively incorporate sterols (like cholesterol) into their plasma membranes to provide rigidity, structural stability, and osmotic protection in the absence of a cell wall.

• Since all four statements are scientifically accurate, the correct option must include all of them.



Step 4: Final Answer:
All statements (1, 2, 3, 4) correctly describe Mycoplasma, which corresponds to option (D).