Question: 148: 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 vertebral column in the adult vertebrates.
In the light of the above statements, choose the most appropriate answer from the option given below :
(1) (A) is correct but (R) is not correct
(2) (A) is not correct but (R) is correct
(3) Both (A) and (R) are correct and (R) is the correct explanation of (A)
(4) Both (A) and (R) are correct but (R) is not the correct explanation of (A)
Answer: Option (3)
Explanation:
Chordates are characterized by the presence of a notochord at some stage of their life cycle.
Vertebrates are a subphylum of chordates in which the notochord is replaced by
a vertebral column during development.
Hence, all vertebrates belong to the phylum Chordata.
However, some chordates like urochordates and cephalochordates possess a notochord but do not develop a vertebral column.
Therefore, all chordates are not vertebrates.
The reason correctly explains why vertebrates form a distinct group within chordates.
Thus, both the Assertion and the Reason are correct,
and the Reason is the correct explanation of the Assertion.