Question

Assertion (A): It is necessary to know the life history of an ascidian to consider it a chordate.
Reason (R): Ascidians exhibit retrogressive metamorphosis in which larval stages are in a degenerated condition.

• 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:

Ascidians are chordates due to their larval features. The adult is degenerate—not the larva.

Answer 1

The Correct Option is C

- Assertion (A) is true: Ascidians (e.g., sea squirts) are classified as chordates based on features like notochord, dorsal nerve cord, and pharyngeal slits—which are present only during their larval stage. Thus, studying their life history is essential to identify them as chordates.
- Reason (R) is false: Retrogressive metamorphosis in ascidians involves a transformation where the larval stage is well-developed and motile, showing all chordate features. During metamorphosis, the adult becomes sessile and loses most chordate characteristics. Therefore, it's the adult that is degenerated, not the larva.
Hence, A is correct but R is incorrect.

Answer 2

Assertion (A): It is necessary to know the life history of an ascidian to consider it a chordate.
Reason (R): Ascidians exhibit retrogressive metamorphosis in which larval stages are in a degenerated condition.

The assertion (A) is true because ascidians, also called sea squirts, show the typical chordate features such as a notochord, dorsal nerve cord, and post-anal tail only during their larval stage. The adult ascidian lacks many of these chordate characteristics. Therefore, to classify ascidians as chordates, it is essential to study their life history and larval form, where these features are evident.

However, the reason (R) is false. Retrogressive metamorphosis in ascidians means that the larval stage is the well-developed, active stage possessing chordate features, while the adult stage is simpler or degenerated. Hence, the larval stages are not degenerated but actually more complex and chordate-like compared to the adult stage.

Thus, the correct understanding is that the larval stages retain the chordate characteristics, and the adult undergoes retrogressive metamorphosis, losing some of these features.