Which one of the following statements is totally wrong about the occurrence of notochord, while the other three are correct? [2011M]a)It is present only in larval tail in Ascidiansb)It is replaced by a vertebral column in adult frogc)It is absent throughout life in humans from the very beginningd)It is present throughout life in AmphioxusCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

Answer

Phylum chordata is fundamentally characterised by the presence of notochord,a dorsal hollow nerve chord, and pharyngeal gill slits.
in ascidia notochord is present only in larval tail.
in subphyllum of vertebrata during embryonic life it is replaced by cartilaginous or bony vrrtbral collumn in the adult.
in amphioxus(branchiostoma or lancelet)it is present throughout their life. so option c is correct.

Answer

Explanation:

The notochord is a flexible, rod-like structure that provides support and serves as the precursor to the vertebral column in chordates. It is an important characteristic of chordates and is present in various stages of their life cycle.

Statement a: It is present only in larval tail in Ascidians
Correct. Ascidians are primitive chordates, also known as sea squirts. They have a notochord present only in their larval stage, which helps in swimming. However, the notochord degenerates and disappears as they undergo metamorphosis into the adult form.

Statement b: It is replaced by a vertebral column in adult frog
Correct. Frogs belong to the class Amphibia and undergo metamorphosis from tadpole to adult. During this process, the notochord is replaced by a vertebral column composed of vertebrae. The vertebral column provides better support and flexibility for the adult frog's locomotion.

Statement c: It is absent throughout life in humans from the very beginning
Incorrect. The notochord is present in humans during early embryonic development. It plays a crucial role in the formation of the axial skeleton and serves as a scaffold around which the vertebrae develop. However, during later stages of development, the notochord is replaced by the vertebral column.

Statement d: It is present throughout life in Amphioxus
Correct. Amphioxus, also known as lancelets, are primitive marine chordates. They retain the notochord throughout their entire life. The notochord provides support and flexibility for their body, as they lack a well-developed vertebral column.

Therefore, the totally wrong statement about the occurrence of the notochord is option c, which states that it is absent throughout life in humans from the very beginning.

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