Question

Consider the following statements:
Assertion (A): In cockroach, 6th abdominal ganglion is the largest ganglion.
Reason (R): It is formed by the fusion of ganglia of 7-10 abdominal segments.
The correct answer is

• A. Both (A) and (R) are true, (R) is the correct explanation of (A)
• B. Both (A) and (R) are true, (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:

Total ganglia in cockroach ventral nerve cord = 9 (3 Thoracic + 6 Abdominal).

Answer 1

The Correct Option is A

Step 1: Analyze the Nervous System:
The cockroach has a ventral nerve cord with segmental ganglia:

• Thorax: 3 ganglia (T1, T2, T3).
• Abdomen: 6 ganglia (A1 to A6).

Step 2: Explain the 6th Ganglion:
The first 5 abdominal ganglia correspond to the first 5 abdominal segments. However, the last ganglion (the 6th one), located in the 7th segment, is a compound ganglion. It is formed by the fusion of the neuromeres of the 7th, 8th, 9th, and 10th abdominal segments. Because it represents the fusion of multiple ganglia, it is physically the largest among the abdominal ganglia.
Step 3: Conclusion:
The Assertion is true (it is the largest). The Reason is true (formed by fusion) and correctly explains \why it is the largest.