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

Assertion (A):

All vertebrates are chordates but all chordates are not vertebrates.

Reason (R):

Notochord is replaced by a vertebral column in the adult vertebrates.

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

Correct Answer: 2)

Concept:

• Chordates are a group of animals having a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits.
• Phylum Chordata is divided into three subphyla: Urochordata or Tunicata, Cephalochordata, and Vertebrata.
• Vertebrates are chordates in which the notochord is replaced by a bony vertebral column. ​

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Statement I: All vertebrates are chordates, but all chordates are not vertebrates.

This statement is true, in vertebrate notochord is replaced by a vertebral column. The notochord is present in the embryonic stage and the adult stage, it is replaced by a bony vertebral column. So, all vertebrates are chordates, but all chordates are not vertebrates

Statement II: A notochord is replaced by a vertebral column in adult vertebrates.

This statement is true, the notochord is a cartilaginous rod that is found in the embryonic stage in vertebrates, and later, it gets replaced by a bony vertebral column. That is why they are known as vertebrates.

So, the correct answer is 2.