Question

Which one of the following statements with regard to embryonic development in humans is correct?

• A. Cleavage divisions bring about considerable increase in the mass of protoplasm.
• B. In the second cleavage division, one of the two blastomeres usually divides a little sooner than the second.
• C. With more cleavage divisions, the resultant blastomeres become larger and larger.
• D. Cleavage division results in a hollow ball of cells called morula.

Answer 1

The correct option is B In the second cleavage division, one of the two blastomeres usually divides a little sooner than the second.

Cleavage is a series of mitotic cell divisions that increase the number of cells but does not change the size of the original mass.

During embryonic development of human, in the second cleavage division, one of the two blastomeres usually divides a little sooner then the second.

Interphase in cleavage divisions is short and does not involve growth so that the resulting blastomeres become smaller and smaller as their number increases.

Cleavage division results in a hollow ball of cells called blastocyst. A morula is distinct from a blastocyst in that a morula (3-4 days post fertilization) is an 8 cell mass in a spherical shape whereas a blastocyst (4-5 days post fertilization) has a cavity inside the zona pellucida along with an inner cell mass.

Therefore, the correct answer is option B.