question_answer

Assertion : Torsion can be seen in ctenidium. Reason : Ctenidium acts as the respiratory organ.

A) If both the assertion and the reason are true and the reason is a correct explanation of the assertion

B) If both the assertion and reason are true but the reason is not a correct explanation of the assertion 

C) If the assertion is true but the reason is false

D) If both the assertion and reason are false

E) If the assertion is false but reason is true

Correct Answer: B

Solution :

Ctenidium is a monopectinate gill situated on right side of the branchial chamber. Ctenidium helps in respiration by beating of cilia, thus creating water current. Ctenidium is innervated by nerves from the left pleural and supra-intestinal ganglia. This nerve supply indicates that it is actually an organ of the left side but has shifted to the right side during development (torsion). Torsion or twisting is a development of gastropods, which rotates the visceropallium anticlockwise through out  from its initial position, so that mantle cavity with its pallial complex, it brought in front of the body in adult.