Question

During cleavage, what is true about cells?
a. Nucleocytoplasmic ratio remains unchanged
b. Size does not increase
c. There is less consumption of oxygen
d. The division is like meiosis

Answer 1

The development of organisms begins from a single celled zygote. The zygote undergoes rapid cell division to form the blastula. The division is usually rapid and it’s termed as cleavage. When cleavage has produced over hundred cells, the embryo is then called a blastula. There are different types of cleavage including determinate, indeterminate, holoblastic, meroblastic etc. Cleavage of cells is a very important process, the absence of which can cause polyspermy (i.e., multiple sperm fertilize the same egg).

Complete explanation:
Option A nucleocytoplasmic ratio remains unchanged: In cleavage there is an increase in number of cells and nuclear mass without increase in the cytoplasmic mass. With each subdivision, there is only half the cytoplasm in each daughter cell than before that division, and hence the ratio of nuclear to cytoplasmic mass increases.
Option A is incorrect.
Option B size does not increase: There is no growth in the blastomeres during cleavage. The total size and volume of the embryo does not increase.
Option B is correct.
Option C there is less consumption of oxygen: When the egg undergoes cleavage, there is rapid consumption of oxygen. Hence, this option cannot be correct.
Option C is incorrect.
Option D the division is like meiosis: The process of cleavage happens through repeated mitotic divisions. These divisions result in blastomeres. Meiosis is a type of cell division that occurs only to produce gametes and plant spores. Cleavage is not a meiotic division.
Option D is incorrect.

So, the correct answer is option B. Size does not increase.

Note:
The blastula gives rise to blastocyst in the next stage of development. The cells in the blastula arrange in two layers namely the inner cell mass and the trophoblast (outer layer). The inner cell mass also called the embryoblast will go on to form the embryo. It consists of embryonic stem cells that will differentiate into the different cell types as required by the organism. The trophoblast becomes a large part of the placenta and provides nutrients to the embryo.