Question

Given below are two statements, one is labelled as Assertion (A) and other labelled as Reason (R).
• [Assertion (A):] Phytoplasma do not have cell wall and motility. 
• [Reason (R):] Phytoplasma colonize phloem. 
In light of the above statements, choose the correct answer from the options given below. 
 

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Because phytoplasmas lack a cell wall, they are completely resistant to penicillin-type antibiotics (which target cell wall synthesis).
However, they are highly sensitive to tetracyclines, which inhibit protein synthesis.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Phytoplasmas are specialized, insect-transmitted bacteria that cause various diseases in plants, such as little leaf, phyllody, and witches' broom.
They belong to the class Mollicutes and have unique structural and ecological characteristics.

Step 3: Detailed Explanation:
Let us evaluate the Assertion and Reason statements:
- Assertion (A) is true: Phytoplasmas are pleomorphic (variable in shape) because they lack a rigid peptidoglycan cell wall.
Instead, they are enclosed only by a triple-layered cytoplasmic membrane.
They also lack flagella and are completely non-motile.
- Reason (R) is true: Phytoplasmas are phloem-limited plant pathogens.
They reside and multiply within the nutrient-rich sieve tube elements of the plant's phloem tissue.
They are transported systemically through the phloem and are transmitted between plants by sap-sucking insect vectors, such as leafhoppers.
- Evaluating the connection: The Reason explains the ecological niche of phytoplasmas within the host plant's vascular tissue.
However, their lack of a cell wall is an evolutionary trait of the class Mollicutes, not a consequence of colonizing the phloem.
Therefore, both statements are true, but (R) is not the correct explanation of (A).

Step 4: Final Answer:
Both (A) and (R) are true, but (R) is not the correct explanation of (A), matching Option (B).