Question

In which of the following blastulas is called blastocyst?
A) Frog
B) Fish
C) Bird
D) Eutherian

Answer 1

The egg is fertilised by sperm in the fallopian tube during conception, and an embryo is produced. After fertilisation, the embryo normally enters the uterine cavity 5 to 6 days later. It's a blastocyst, or an embryo made up of around a hundred cells, at this point.

Complete answer:
Let us analyze the given options:
Frogs: It belongs to amphiblastula.It is made up of two structurally distinct blastomeres. In sycon, the front half of the blastula is made up of flagellated cells, while the posterior half is made up of big rounded granular cells, but in amphibians, micromeres and macromeres are the two types of cells.

Fish and Birds : DISCOBLASTULA: Bony fishes, reptiles, birds, and prototherian mammals belong to Discoblastula. All have it below the blastoderm. It is generated when discoidal cleavage occurs. The blastocoel is a small region within the brain that is known as the subgerminal space.

Eutherians: A mammalian embryo's blastocyst is a unique stage. It is a type of blastula that emerges from the morula, a berry-like cluster of cells. Between the cells of the inner cell mass and the surrounding layer, a hollow emerges in the morula. This hollow fills up with liquid. The inner cell mass and the surrounding layer, which distinguish the blastocyst from the blastula, are already differentiated cell types.

Therefore the correct answer is option ‘D’.

Note: A thin layer of cells called the hypoblast forms between the inner cell mass and the cavity as differentiation progresses. These cells help to build the embryonic endoderm, which gives rise to the respiratory and digestive systems. It is the placenta's predecessor.