Question

Assertion (A): Adult gastropods are asymmetrical though they are included in phylum Mollusca.
Reason (R): Symmetry of organism is determined in early developmental stages but not in adults.

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is not the correct explanation of A
• C. A is correct but R is incorrect
• D. A is incorrect but R is correct

Hint:

Gastropod asymmetry is due to torsion, not the timing of developmental symmetry.

Answer 1

The Correct Option is C

- Assertion (A) is correct: Adult gastropods, such as snails, undergo a developmental process called torsion, which leads to asymmetry in the adult form. This is a characteristic feature of this class in phylum Mollusca.
- Reason (R) is incorrect: While it's true that some aspects of body structure are established early in development, symmetry itself is initially bilateral in molluscs, and the asymmetry in gastropods is due to a specific later-stage developmental process (torsion), not simply general developmental timing. Hence, A is true but R is not.

Answer 2

Assertion (A): Adult gastropods are asymmetrical though they are included in phylum Mollusca.
Reason (R): Symmetry of organism is determined in early developmental stages but not in adults.

Explanation:
The assertion is true. Adult gastropods (such as snails) are indeed asymmetrical. Although phylum Mollusca is generally characterized by bilateral symmetry, gastropods undergo a unique process during development called torsion. This process results in the twisting of the body, leading to asymmetry in the adult stage.

However, the reason is incorrect. The symmetry of an organism is primarily defined by its adult form, not just by the early developmental stages. In the case of gastropods, they initially develop with bilateral symmetry, but due to torsion, their adult form becomes asymmetrical. Thus, the early stage symmetry does not determine the final symmetrical condition of the adult organism in this case.

Correct Answer: Assertion is correct but Reason is incorrect