Question

In which of the following the notochord is present only in the embryonic stage?
A. Vertebrates
B. Some chordates
C. All chordates
D. Non-chordates

Answer 1

Hint:
-The notochord is a midline structure that is present in all the members of chordates.
-It is the beginning of the formation of the backbone.
-It is present from the head to the tail of the organism and in between the digestive tube and nerve cord.

Complete answer: As fertilization occurs, there will be formation of a zygote.
This is followed by cell division and formation of a single-layered blastula.
This single-layered blastula develops into gastrula which is made up of three layers of cells - ectoderm, mesoderm and endoderm.
The mesoderm is responsible for the development of the notochord, skeletal system and muscular system.
The word vertebrate is derived from vertebrae, the bone which forms the spinal cord. All the members of vertebrates contain a notochord during the embryonic stage which is later replaced by a bony vertebral column. Notochord serves as a major skeletal component in the developing embryo.
The notochord is present in the embryonic stage of all chordate members. They are even present in the adult stage of some cephalochordates.
Non- chordates are organisms which do not have a notochord. This phylum consists of a small group of worms.
Vertebrates have a notochord present only in the embryonic stage.
So, the correct answer is “Option A”.

Note: The notochord in the case of chordate embryos acts like the vertebral column of the adult. This serves as the initial stage for the development of a complete skeletal vertebral column. The presence of nerve cord and pharyngeal gill slits are also other distinctive features of chordates.