AIIMS 2007 Zoology Respiratory System Assertion Reason Question

To tackle this question regarding the assertion and reason related to the ctenidium and torsion in the context of zoology, let's break down the components.

Explanation of the Assertion and Reason

1. Assertion (A): Torsion can be seen in ctenidium.

   • Torsion refers to a developmental process in certain mollusks, where the body twists during larval development. This results in a 180-degree twist of the body, bringing the anus and mantle cavity to the front of the animal. Torsion primarily occurs in gastropods, a class of mollusks that includes snails and slugs.
   • The ctenidium is a specialized gill-like structure found in some aquatic mollusks, primarily bivalves and some gastropods. It plays a crucial role in respiration and feeding.

2. Reason (R): Ctenidium acts as the respiratory organ.

   • This statement is true; ctenidia are indeed gill structures that facilitate gas exchange in aquatic organisms. They allow for the uptake of oxygen and the expulsion of carbon dioxide, functioning in respiration.

Correct Answer Justification: B

• Both the assertion (A) and the reason (R) are true. However, the reason is not the correct explanation for the assertion.
  • Torsion is a developmental process that occurs in some mollusks, and while it is related to the anatomy of these organisms, it is not directly caused by the function of the ctenidium as a respiratory organ. Therefore, the assertion and reason are true, but the reason does not explain the assertion.

Why Other Options are Incorrect

• Option A: If both assertion and reason are true and reason is the correct explanation of assertion.

  • This option is incorrect because, although both statements are true, the reason does not explain the assertion. Torsion is a developmental process, and the function of ctenidia as respiratory organs is separate from this process.

• Option C: If assertion is true but reason is false.

  • This option is incorrect because both the assertion and the reason are true. The assertion about torsion is accurate, and the reason regarding ctenidia being respiratory organs is also correct.

• Option D: If both assertion and reason are false.

  • This option is also incorrect as both statements are true.

Summary

In summary, the correct answer is B: both the assertion regarding torsion and the reason regarding ctenidia are true, but the reason does not correctly explain the assertion. This distinction is important in understanding the relationship between anatomical structures and their functions in the context of mollusk physiology.