Question

By origin brain is
a) Endodermal
b) Peridermal
c) Mesodermal
d) Ectodermal

Answer 1

Hint: A Germ layer is a group of primary layers of cells that forms in the earliest stages of embryonic development. It consists of three layers which form during the process of gastrulation and eventually give rise to the formation of every organ and tissue in the body.

Complete answer:
During the process of gastrulation, zygote transforms into a hollow cluster of cells called blastula and then begins to differentiate with either two or three germ layers: the endoderm, the ectoderm, and the mesoderm.
In the early stage of embryonic life, the cells of zygote form three germ layers across the developing embryo. These layers contribute to the formation of every organ and tissue in the human body during the process of organogenesis.
The ectoderm is the outermost germ layer of the embryo while the endoderm is the innermost layer. Mesoderm, an additional third layer which lies between these two layers: ectoderm and endoderm.
- Ectoderm gradually develops into the brain, spinal cord, peripheral nerves and adrenal medulla. It also forms the epidermis of the cell and gives rise to skin, nails, hair, retina and the lens of the eye.
- Endoderm forms the pharynx, the trachea, the bronchi, the alveoli of the lungs and the alimentary canal including the liver, the pancreas, the stomach and the small intestine.
- Mesoderm is the middle layer of the three germ layers that contribute to the formation of the bones, spleen, cartilage, connective tissues, circulatory and lymphatic system.
Thus, the right option is D.

Note: Robert Remak, a German embryologist, physiologist and neurologist who discovered the origin of cells and three germ layers of the early embryo and named: the ectoderm, the mesoderm, and the endoderm.