Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): All vertebrates are chordates but all chordates are not vertebrates
Reason (R): Notochord is replaced by the vertebral column in the adult vertebrates.

In the light of the above statements, choose the most appropriate answer from the options given below:

• 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 not correct
• D. (A) is not correct but (R) is correct

Answer 1

The Correct Option is A

The given statements are related to the classification of chordates and vertebrates. To determine the correctness and relationship between the Assertion (A) and the Reason (R), we need to analyze each statement: 
Assertion (A): "All vertebrates are chordates but all chordates are not vertebrates." 
Reason (R): "Notochord is replaced by the vertebral column in the adult vertebrates." 

Explanation: 

The phylum Chordata includes all animals that have, at some stage of their lives, a notochord, a hollow dorsal nerve cord, and pharyngeal slits. Vertebrates are a subgroup of chordates that, during their development, replace the notochord with a more complex and rigid vertebral column (backbone). Therefore, all vertebrates belong to the broader phylum Chordata, but not all chordates develop a vertebral column; some retain the notochord throughout their life (e.g., lancelets and tunicates).

• The Assertion (A) is correct because it accurately describes the hierarchical classification of chordates and vertebrates.
• The Reason (R) correctly explains a critical characteristic of vertebrates: the development of the vertebral column replacing the notochord.

Given these points, both Assertion (A) and Reason (R) are correct, and Reason (R) effectively explains why not all chordates are vertebrates, affirming that the vertebral column development is the distinguishing factor.

Conclusion: Both (A) and (R) are correct and (R) is the correct explanation of (A).