Which one of the following statements is totally wrong about the occurrence of notochord, while the other three are correct?
- It is present only in larval tail in ascidian.
- It is replaced by a vertebral column in adult frog.
- It is absent throughout life in humans from the very beginning.
- It is present throughout life in Amphioxus.
Answer
(3) It is absent throughout life in humans from the very beginning.
Solution
As per NCERT, all chordates possess a notochord at some stage of life.
⇒ Urochordata (ascidians): notochord present only in the larval tail.
⇒ Cephalochordata ( Amphioxus): notochord extends from head to tail and persists throughout life.
⇒ Vertebrata (frog, humans): notochord present in the embryonic stage and replaced by a cartilaginous or bony vertebral column in the adult.
∴ In humans the notochord is present in the embryo, so the statement that it is absent from the very beginning is totally wrong.
Answer: (3)