Question

Which one of the following is derived from ectoderm?
a. Enamel of teeth
b. Dentine
c. Skull
d. Axial skeleton

Answer 1

Hint: Ectoderm layer is differentiated into many parts. Ectoderm mesenchyme is one of them. The layer of teeth is formed from one of its parts. The formation of skull and axial skeleton occurs by the process of endochondral ossification. Tooth germ forms the dentine.

Complete answer:
Ectoderm is the most exterior of the three germ layers in the early embryo. Mesoderm is the middle layer while endoderm is the innermost layer of the cell. The outer layer of the germ cells differentiates to form ectoderm. It is differentiated into some types of tissues that are epithelial tissues of the nervous tissue, tooth, enamel, and the skin. The inner lining of the mouth, anus, nostrils, sweat glands, hairs and nails are formed by ectoderm. Endoderm layer also derived to form other types of epithelium.

It can be divided into four parts: the external ectoderm, the neural plate, neural crest and neurogenic placodes. Neuroectoderm consists of neural plate and neural crest.

The ectoderm and ectoderm mesenchyme (which is a neural crest derivative) forms the layer of teeth. The ectodermal components form the enamel of teeth. Dentine, pulp, cementum are all derived from the ectomesenchyme.

Hence, the correct answer is option (A).

Note: Formation of ectoderm was first observed in amphibians and fish. During the formation of the blastula, two layers are formed: the animal hemisphere and the vegetal hemisphere. The animal hemisphere develops into ectoderm. Cell division occurs in the cells and forms various layers in the cell. The process of neurulation and organogenesis involves the process of cell differentiation. Ectoderm layers have clinical significance that is Ectodermal dysplasia.