Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Rigor mortis is caused by the breakdown of the glycogen of the muscle into lactic acid.
Reason (R) : It is a sign of freshness.
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:

Always check if the "Reason" answers the question "Why?" for the "Assertion."
Here, the physical biochemical cause of rigor (glycogen/ATP depletion) is entirely unrelated to its utility as a freshness indicator, meaning (R) is not the explanation of (A).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Rigor mortis is a key post-mortem physical change in fish, characterized by the stiffening of the body muscles shortly after death.
Understanding the biochemical changes behind rigor mortis is essential for assessing fish freshness and optimizing processing times.

Step 2: Detailed Explanation:
Let us analyze the Assertion and Reason statements:
- Assertion (A): Post-mortem biochemical changes begin with anaerobic glycolysis.
Because the circulatory system stops delivering oxygen, muscle cells convert glycogen into lactic acid to produce ATP.
This accumulation of lactic acid lowers the muscle pH.
As glycogen is depleted and ATP levels fall, actin and myosin filaments bind together permanently to form actomyosin, causing the muscles to stiffen.
Thus, the post-mortem breakdown of glycogen into lactic acid, which runs parallel to ATP depletion, is a primary driver of the biochemical changes leading to rigor mortis.
Therefore, Assertion (A) is considered true in the context of post-mortem biochemistry.
- Reason (R): A fish in rigor mortis (or pre-rigor) indicates that it has been harvested recently and has not undergone bacterial or enzymatic decay.
Thus, the presence of rigor mortis is a highly reliable physical indicator of excellent freshness.
Therefore, Reason (R) is also true.
However, the fact that rigor mortis is a sign of freshness (R) does not explain the biological mechanism of how muscle glycogen breakdown causes muscle stiffening (A).
Because they are independent true statements where the Reason does not explain the biochemical cause of the Assertion, Option (B) is the correct choice.

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