Question

Blastopore occurs in-
A) Gastrula
B) Blastula
C) Blastocoel
D) Morula

Answer 1

Blastopore is an opening that can be observed while embryogenesis. It forms openings in animals such as the mouth and/or anus.

Complete answer:
To understand the terms of this question, let us have a look at embryogenesis. Formation and development of human embryos is referred to as human embryogenesis or human embryonic development. It can be understood through following stages-

1. Fertilization- A sperm (male gamete) and the ovum (female gamete) fuse together to form a zygote, this process is known as fertilization or syngamy.
2. Cleavage, Blastulation and implantation- After fertilization, the zygote undergoes cleavage where it multiplies to form a cluster of cells of same size which are called blastomeres (2, 4, 8, 16 celled stages). Blastomeres form a compact cell mass known as morula. The morula further divides to form a blastocyst. The blastocyst is implanted into the uterine wall where the blastomeres are arranged into an outer layer called trophoblast enclosing the inner cell mass. Trophoblast layer and endometrium connect to form placenta. The trophoblast layer gets attached to the endometrium and the inner cell mass gets differentiated as embryoblast which polarises at one end. The polarization leads to formation of a cavity called blastocoel. The inner cell mass gives rise to pre-embryo, yolk sac, allantois and amnion. At the beginning of the second week, 2 main layers of bilaminar germ disc are formed which are called hypoblast and epiblast.

Gastrulation- Formation of the primitive streak by epiblast which establishes the bilateral symmetry marks the beginning of gastrulation which takes place in the third week. A specific head to tail and front to back orientation can be observed from this stage onwards. A neural plate is formed which later forms the nervous system. Gastrulation marks the formation of the blastopore. Blastopore is an opening directed into the archenteron.
4) Somitogenesis and histogenesis.
6) Organogenesis- Most of the major organ systems are formed by the end of the first trimester (12 weeks). The formed foetus grows into a full grown baby which takes around 9 months to form fully. It gets delivered during parturition.

Therefore the correct answer is A. Gastrula.

Note: Blastopore occurs in amnions. The blastopore does not open into the blastocoel, it represents a different opening which pushes the existing surfaces of the blastula together.