Question

Which one of the following statements is correct about morula in humans?

• A. It has more cytoplasm and more DNA than an uncleaved zygote.
• B. It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA.
• C. It has far less cytoplasm as well as less DNA than in an uncleaved zygote.
• D. It has more or less equal quantity of cytoplasm and DNA as in uncleaved zygote.

Answer 1

The correct option is B It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA.

At about 30 to 36 hours of fertilisation, the zygote moves through the isthmus of oviduct to uterus and divides mitotically by a process called cleavage which results into two smaller cells called blastomeres. A second cleavage occurs which results in the formation of 4 cells. Cleavage continues to occur and results in a solid ball of cells i.e. morula having 16 cells (occasionally 32).

Since the divisions are mitotic, therefore the size of morula is same as that of zygote because with each cleavage division, number of cells increases but their size decreases. Due to mitotic divisions, content of cytoplasm of morula is same as that of zygote but DNA content is increased as each cell has its own DNA.

So, the correct answer is 'It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA'.