Question

Assertion: In morula stage, cells divide without increase in size.
Reason: Zona pellucida remains undivided till cleavage is complete.
a) Both assertion and reason are correct and reason is the correct explanation for assertion
b) Both assertion and reason are correct, but reason is not the correct explanation for assertion
c) Assertion is correct but reason is incorrect
d) Assertion is incorrect but reason is correct

Answer 1

In the stage of human embryonic development, Morula stage occurs in the first week following fertilization. Morula is produced by a series of cleavage divisions of the early embryo. It starts to form with a single-celled zygote up to the stage of 16 cells.

Complete answer:
Morula is an early stage of embryonic development that happens after fertilization. Zygote undergoes a rapid series of mitotic cell divisions called cleavage within 24 hours after fertilization and produces two daughter cells called blastomeres.
By three to four days, several divisions occur to form equally sized blastomeres in a solid ball contained within the zona pellucida. The formation of embryos consisting of a solid mass of sixteen to thirty-two cells is called a morula stage. The embryo at this stage appears like a "mulberry" and it is known as morula.
Though the number of cells in this morula stage is increased, the cleavage division of cells takes place without any increase in the size / growth of cells. It becomes a solid mass of cells and is covered by Zona pellucida. It is a transparent non cellular glycoprotein layer which is found in the eggs of mammals. The cells contained in Zona pellucida remain undivided till the cleavage is complete.
Thus, the right option is B.

Note: Assisted Reproductive Technology (ART) includes assisted reproductive fertility treatments to address infertility with the help of IVF - ET, ZIFT, GIFT, and FET. In such medical treatments, one of the earliest prenatal diagnostic tests will be carried out at the morula stage in order to remove the single cell (blastomere) or to culture the embryo under biopsy technique.