Question

Given below are four statements $(i)-(iv)$ regarding embryonic development in humans.
(i) Cleavage divisions bring about considerable increase in the mass of protoplasm.
(ii) With more cleavage divisions, the resultant blastomeres become smaller and smaller.
(iii) The blastomeres in the blastocyst are arranged into two layers, trophoblast and endometrium.
(iv) Cleavage divisions result in a solid ball of cells called morula.
Which of the above two statements are correct?

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

Answer 1

Answer: (B)

Cleavage is a series of rapid mitotic divisions of the zygote, characterised by absence of growth in daughter cells, which converts a single celled zygote into a multicellular structure called blastocyst. It starts in the Fallopian tube and is holoblastic. Interphase in cleavage division is short and don not involve growth so that the resulting blastomeres become smaller in size as their number increases. During cleavage, at 8-16 celled stage, a solid ball of cells called morula (as it look like mulberry) is formed. In cleavage, there is increased mobility of protoplasm. The blastomeres in the blastocyst get arranged into outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. So, the correct answer is '(ii) and (iv)'.