Question

Two formative movements that take place during gastrulation are
A. Involution and invagination
B. Epiboly and emboly
C. Invagination and ingression
D. Ingression and delamination

Answer 1

Gastrulation is a process where the embryo gets changed from single layered blastula into multilayered gastrula during the embryonic development.

Complete answer:
First of all, you should know what gastrulation is. Gastrulation is a phase of embryonic development in most animals where the blastula which is single layered gets reorganised into a multilayered structure called gastrula. This process takes place after cleavage and after the formation of the blastula.
There are three germ layers of gastrula in triploblastic organisms which are ectoderm, mesoderm and endoderm. But in diploblastic organisms, there is presence of only ectoderm and endoderm.
There are five movements which occurs during gastrulation which are-
Involution, Invagination, Ingression, Delamination and Epiboly.
But the formative movements that take place during gastrulation are Epiboly and Emboly.

Option A - Involution and Invagination.
It is an incorrect option since these are movements of gastrulation but not formative movements and therefore this option gets eliminated.

Option B - Epiboly and Emboly.
This is the correct option since epiboly is movement of cells which occurs in early embryos at the same time as gastrulation whereas emboly is formation of gastrula from blastula by invagination of germ layers. Therefore, this option is correct as these are the formative movements which take place during gastrulation.

Option C - Invagination and ingression.
It is an incorrect option since these are movements of gastrulation but not formative movements and therefore this option gets eliminated.

Option D - Ingression and delamination.
It is an incorrect option since these are movements of gastrulation but not formative movements and therefore this option gets eliminated.

Hence, the correct answer is option (B).

Note: Epiboly is the movement of cells in the early embryo when gastrulation is taking place. Emboly is formation of gastrula from blastula by invagination of germ layers and during emboli there is migration of three germ layers which occurs in blastocoel. These are the formative movements as there is formation of gastrula from blastula during gastrulation.