Question

Choose the correct answers from the alternatives given.
In implantation, which of the following burrows into the endometrium

• A. Zygote
• B. Blastocyst
• C. Gastrula
• D. Morula

Answer 1

The correct option is B Blastocyst

After fertilisation, a two cells embryo/zygote is formed. It enters into the cleavage stage. As cleavage proceeds, the ovum has 16 cells, called as a morula. Morula consists of an inner and outer cell mass. The outer cell mass gives rise to Trophoblast. This morula keeps on dividing and forms blastocyst which have a cavity called blastocoel. By this time the embryo has travelled down the uterine tube and is prevented from sticking to the epithelium by zona pelluciada. During this period embryo receives nutrition from the substances stored within the worm. By the time a blastocyst is formed embryo needs additional sources of nutrition. This nutrition is received, when the blastocyst sticks to the uterine endometrium and gets implanted in it.

So the correct option is ' Blastocyst '.