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Explanation for the Correct Answer (ii) and (iii)
1. Introduction
The phylum Chordata is characterized by the presence of a notochord, a dorsal hollow nerve cord, pharyngeal gill slits, and a post-anal tail (at least in some stage of development). Here, we assess each statement to identify which ones correctly describe Chordata.
2. Evaluating Statement (i)
Statement (i): "In Urochordata notochord extends from head to tail and it is present throughout their life."
In urochordates (also called tunicates), the notochord is found only in the larval stage and is typically restricted to the tail region. During metamorphosis into the adult form, the notochord is reduced or lost. Thus, the notion that it extends from head to tail and remains throughout their life is incorrect.
3. Evaluating Statement (ii)
Statement (ii): "In Vertebrata notochord is present during the embryonic period only."
This statement is correct. In vertebrates, the notochord is replaced by the vertebral column (spine) during embryonic development, so it is only present in the embryo.
4. Evaluating Statement (iii)
Statement (iii): "Central nervous system is dorsal and hollow."
This is another hallmark feature of chordates. The spinal cord (in vertebrates) and nerve cord in other chordates is indeed dorsal (toward the back) and hollow (forming a tubular structure). Thus, statement (iii) is correct.
5. Evaluating Statement (iv)
Statement (iv): "Chordata is divided into 3 subphyla: Hemichordata, Tunicata, and Cephalochordata."
Hemichordata is recognized as a separate phylum, not a subphylum of Chordata. The three subphyla of Chordata are Urochordata (sometimes called Tunicata), Cephalochordata, and Vertebrata. Hence, the mention of Hemichordata as a subphylum is incorrect.
6. Conclusion
Based on the above evaluations:
Statement (ii) is correct.
Statement (iii) is correct.
Statements (i) and (iv) are not correct descriptions.
Therefore, the correct answer is (ii) and (iii).
