Question

What happens in cells of embryo during cleavage?
A. Decrease in cytoplasm
B. Increase in cytoplasm and decrease in nuclear material
C. Decrease in both
D. Both remains constant

Answer 1

The process by which an embryo develops into a foetus is known as embryogenesis. It all starts when an ovum and sperm get together and fertilize each other. Fertilization results in the formation of a zygote. In animals, the zygote divides numerous times without considerable growth or cellular differentiation, resulting in the creation of an embryo. Each species goes through different stages during embryo development.

Complete answer:
Option A: The zygote undergoes cleavage shortly after fertilization, which is a sequence of rapid mitotic divisions with no interval of growth between each cell cycle, resulting in a drop in cytoplasm content.
So, option A is correct.
Option B: Cleavage is the process of cell division that results in a cluster of cells that is the same size as the initial zygote.
So, option B is incorrect.
Option C: Cleavage is distinct from other types of cell division in that it increases the number of cells and nuclear mass while leaving the cytoplasm unchanged. This means that each consecutive subdivision reduces the amount of cytoplasm in each daughter's cell by nearly half.
Hence option C is incorrect.
Option D: Shortly after fertilization, the zygote experiences cleavage, which is a series of rapid mitotic divisions with no growth delay between each cell cycle, resulting in a decrease in cytoplasm content.
So, option D is incorrect.

Hence, Option A is the correct answer.

Note:
Fertilization is the process of combining gametes to form a new creature. The process in animals involves sperm fusing with an ovum, which leads to the creation of an embryo. Cleavage is the process of cell division that results in a cluster of cells that is the same size as the initial zygote. The morula becomes a blastula when the seventh cleavage produces $128$ cells. During gastrulation, cells travel to the blastula's core, where they divide into two (in diploblastic animals) or three (in triploblastic animals) germ layers. Organogenesis begins when the different germ layers have been defined.