Question

Match the following and choose the correct answer

A	Zona hatching	(i)	mitotic division of the zygote
B	Trophoblast	(ii)	embedding of the blastocyst in the endometrium
C	Cleavage	(iii)	blastocyst releasing from zona pellucida
D	Implantation	(iv)	outer layer of blastocyst attached to the endometrium

• A. A- (iii), B-(i), C-(ii), D-(iv)
  
• B. A- (iii), B-(iv), C-(i), D-(ii)
• C. A- (ii), B-(i), C-(iii), D-(iv)
  
• D. A- (ii), B-(iv), C-(iii), D-(i)
  

Answer 1

The correct option is B A- (iii), B-(iv), C-(i), D-(ii)

Cleavage is a special type of mitosis that occurs in the zygote where the actual size of the zygote remains the same but the number of blastomere cells keeps on increasing. These divisions result in 2, 4, 8, 16 celled stages of embryos. The stem cells in the embryo are called blastomeres. The stage which undergoes implantation is blastocyst. An embryo before implantation needs to be free from the zona pellucida. Zona pellucida is a thick transparent membrane surrounding a mammalian ovum before implantation. So the process of hatching out of embryo from the zona pellucida is called zona hatching.
Attachment of the blastocyst to the uterine wall and getting embedded by the cells of the endometrium is called implantation. Blastomeres in the blastocyst are arranged in two layers, the outer or peripheral layer and the inner layer. Blastomeres arranged in the periphery, which finally attach to the endometrium of the uterus is called the trophoblast. A group of totipotent cells attached to the peripheral trophoblast cells in the blastocyst is called inner cell mass.