Question

The literal meaning of “gastrulation” is-
A) Formation of primary germ layers
B) formation of a gut
C) Morphogenetic movement
D) Commencement of organogenesis

Answer 1

Hint: Gastrulation means the changes which occur during the growth of an embryo. It is the process during embryonic development, where the embryo changes from a blastula with a single layer of cell to a multi-layer of cells known as cells of gastrula. Gastrulation termed as blastula in folding itself to divide into two or more layers of cells. Gastrula has 3 layers- ectoderm, mesoderm and endoderm.

Complete answer:
Option A formation of primary germ layers- As we discussed that blastula folds itself and divides to form multi-layer this is known as blastulation. Gastrulation is the formation of primary or three types of germ layers in the developing embryo. In which the embryo shows distinct features, the primary germ layers are- outer-ectoderm, middle-mesoderm, inner-endoderm. Gastrulation takes place after cleavage formation and blastula and it is followed by organogenesis (the formation of different types of organ from germ layers).
So, option A is correct.
Option B formation of gut- The gut tube is arising from gastrointestinal tract during the process of gastrulation from the endoderm and it extends from buccopharyngeal cavity to cloacal membrane. The gut is derived from the primitive gut tube from the yolk sac during the fourth week of embryo development. The glands associated with the digestive tract are- liver, pancreas which are derived from endoderm. Gut has three parts- foregut, midgut, hindgut.
So, option B is not correct
Option C Morphogenetic movement- the movement of cells in the early embryo that changes the shape of differentiating cells or tissues are known as morphogenetic movements. During gastrulation cells move from one position to another position. The cells establish a particular form which are involved in organ formation. There are different types of morphogenetic movements such as- gastrulation, invagination, ingression, involution, epiboly etc. Morphogenetic hormones promote growth and also cell differentiation which helps in organogenesis.
So, option C is not correct.
Option D Commencement of organogenesis- organogenesis is the phase where the gastrulation period is over and it continues in formation of organs from germ lining till adulthood. As we discussed the germ layers and evolution of organs from these germ layers, basically it forms the internal organs. The cells of each germinal layer undergo differentiation where the cells get more specialized and developed into organs. The endoderm is the inner germ layer of embryo which gives rise to gastrointestinal and respiratory organs by epithelial lining. Like- liver, lungs and pancreas. Mesoderm the middle layer gives rise to- heart, kidney, blood, muscles, connective tissues. Ectoderm the outer layer gives rise to- epidermis of skin, brain and the nervous system.
So, option D is not correct.

So the correct answer is Option A.

Note:
The development of an offspring to embryo comprises various developing stages. Starting from fertilization, formation of zygote to embryo cells differentiation and neurulation and organogenesis. After the birth stem cells are preserved which derives from the mother's womb.