148.Given below are two statements: one is labelled as Assertion A and another one is labelled as
Reason R
Assertion A: Within a few hours after an animal is killedrigor mortis sets in with a contraction of muscle
fibres and an increasing toughness of the meat.
Reason R: The loss of glycogen and disappearance of ATP from the muscles are observed in freshly
killed animals.
In light of the above statementschoose the correct answer from the options below:
(a) A is false but R is true
(b) A is true but R is false
(c) Both A and R is true and R is NOT the correct explanation of A
(d) Both A and R is true and R is the correct explanation of A

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What Happens After an Animal is Killed? The Process of Rigor Mortis

Rigor mortis is a well-known phenomenon that occurs after an animal dies, causing muscle stiffness and increasing meat toughness. But what causes this? To understand rigor mortis and its relationship with ATP depletion, we need to break down the processes involved.

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Understanding Rigor Mortis and Muscle Contraction

Assertion A: “Within a few hours after an animal is killed, rigor mortis sets in with a contraction of muscle fibers and an increasing toughness of the meat.”

• True: After death, muscle cells stop receiving oxygen and nutrients, leading to the depletion of ATP (adenosine triphosphate), which is needed for muscle relaxation. In the absence of ATP, muscles cannot relax, causing them to contract. This leads to stiffness in the muscles, known as rigor mortis. As rigor mortis progresses, meat becomes tougher, as muscle fibers remain contracted.

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The Role of Glycogen and ATP in Muscle Function

Reason R: “The loss of glycogen and disappearance of ATP from the muscles are observed in freshly killed animals.”

• True: When an animal dies, the oxygen supply to its muscles is cut off. ATP, the primary energy source for muscle function, is produced through aerobic respiration, which ceases immediately after death. As ATP is consumed, the muscle cells begin to use up glycogen reserves to produce small amounts of ATP anaerobically (without oxygen). Eventually, glycogen stores run out, and ATP is depleted, which is a key contributor to rigor mortis.

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The Connection: Explanation of Rigor Mortis

Conclusion:

• Both Assertion A and Reason R are true.

• Reason R provides an accurate explanation for Assertion A. The loss of ATP and glycogen in the muscles after death causes the muscle fibers to contract and leads to the increasing toughness of the meat, which is observed as rigor mortis.

Therefore, the correct answer is:

(d) Both A and R are true and R is the correct explanation of A