Question

The rolling of endodermal and mesodermal cells from the surface of embryo into its interior is called as
(A) Ingression
(B) Invagination
(C) Involution
(D) Inversion

Answer 1

Hint: The fusion of male and female gametes results in the formation of embryos and the process is called fertilization. Blastula is the first stage of embryogenesis. It is a spherical, hollow, one-called thick structure. Blastula is known as ‘pre-embryo’. Blastula forms a multilayered structure which is called gastrula.

Complete Answer:
- The rolling of endodermal and mesodermal cells from the surface of the embryo into its interior is called involution.
- The process of development of embryos after fusion of gametes or after fertilization is called embryogenesis. Embryogenesis involves the process and cell growth, cell division, cell differentiation and cell death. The various involved in animal embryogenesis are gastrulation. Early nervous system formation and organogenesis.
- The process of formation of gastrula form blastula is called gastrulation. Gastrulation is preceded by organogenesis. Gastrula comprises their germ layers that led to the development of organs in late embryo stapes.

The three germs layers are ectoderm, mesoderm and endoderm.
- The outermost layer is ectoderm. It involves information about the skin, brain and spinal card.
- The middle layer takes part in the formation of connective tissue, muscles, cartilage etc. this is called mesoderm.
- The innermost layer is called endoderm and it differentiate into basic primitive gel. During gastrulation, many morphogenetic movements occur such as ingression, Invagination, involution and inversion.

The process in which cells leave the epithelial sheet and become freely migrating mesenchyme cells as ingression. The inward bending of the epithelial sheet is invagitation. The inward rolling of the epithelial sheet is called involution.

Therefore, from the above explanation the correct option is (C) Involution.

Note: Blastula does not involve movement of cells whereas in gastrulation, there is morphogenetic movement of cells masses. Blastula is formed by slow mitotic division of blastula whereas blastula is formed by rapid mitotic division of zygote.