Question

Which of the following is true about all notochords?
A) Present in all adult chordates
B) Present in all echinoderms
C) Present in chordates during embryological development
D) Always a vestigial organ in chordates
E) Part of the nervous system of all vertebrates

Answer 1

Hint: The notochord is very important in embryonic development. It is a midline dorsal structure fairly firm and rod-like, serving as a kind of support or guidance for the developing embryo.

Complete answer:
Chordates are not to be confused with vertebrates. The notochord is an important part of the development of a higher nervous system that includes the brain and spinal cord. When the spinal cord is then encased in a vertebral column, the organism is a vertebrate. Chordates can be vertebrate and invertebrate.
The notochord forms during embryonic development on the dorsal side. All chordates go through this process during embryogenesis. Option C is the correct answer.
If the adult chordate belongs to class vertebrate, the notochord is replaced by a bony spinal column. Therefore option A is incorrect.
Echinoderms are not chordates at all; they do not have a notochord even though they are considered to be very close to hemichordates and chordates. Option B is incorrect.
The notochord does not remain as a vestigial organ. It is a more primitive structure to protect the nervous system, in higher animals it is replaced by a vertebral column. Option D is incorrect.
Since it is missing from higher vertebrates, it cannot be a part of the nervous system; therefore option E is also incorrect.

Hence the correct answer is OPTION(C)

Note: All vertebrates are chordates, but not all chordates are vertebrates. Having a notochord is evolutionarily one step further to developing a vertebral column made of bony and cartilaginous vertebra, culminating with the skull at one end.