Question

Notochord is
a. Solid
b. Hollow
c. Lacunate
d. Partially solid and partially hollow

Answer 1

In chordates, notochord appears as the skeletal support. It is present throughout the life of chordates. It is formed by the mesoderm and composed of glycoproteins and collagen fibers. It leads to the vertebra in higher vertebrates. It also serves as the source of midline signals.

Complete answer:
The phylum chordata contains the notochord. The notochord is the primitive form of the backbone. It is formed from the mesoderm cells which condense and become rigid. The stiff tissues are present in the notochord which provide the skeletal support of the organism. It is formed of the cartilage which makes it flexible. It lies in the anteroposterior axis. It is formed by the process of notogenesis from the epiblasts.

It is primarily composed of the core of glycoprotein, covered by a sheath of the collagen fibers which wound into two opposing helices. The vacuolated, turgid cells store the glycoproteins. The thickening and thinning is determined by the angle between the fibers. It does not contain gaps in between.

The most important function of the notochord is that it provides directional signals to surrounding tissue during development. It acts as a vertebral precursor. The transient notochord structures develop into the embryos of the modern vertebrates. It also plays an important role in the development of the central nervous system.

From the above information we know that the notochord is solid.
Hence, the correct answer is option (A).

Note: It is found for the lifetime in the lancelets but in tunicates the notochord is only present at the larval stage. Notochord is absent in the adult tunicates. In vertebrates, it develops into the vertebral column and becomes vertebra. In amphibians and fishes, the notochord develops into the hypochord through the secretion of vascular endothelial growth factor. In humans, presence of the notochord may cause pathologic conditions.