Final answer:
The zygote undergoes a type of cell division called mitosis to produce many identical cells through a process known as cleavage, leading to the formation of a morula and then a blastocyst.
Step-by-step explanation:
After fertilization, the zygote divides by a type of cell division called mitosis to produce many cells that are identical to itself. These early mitotic divisions are known as cleavage. Cleavage division results in an increase in the number of cells, forming a multicellular structure without increasing the overall mass of the organism. The process of cleavage leads to the formation of a solid ball of cells called a morula, which eventually becomes a blastocyst with a distinct inner cell mass and a fluid-filled cavity.
The development of multicellular organisms begins with this single-celled zygote, which undergoes rapid cell division, cleavage, to form the blastula. This series of divisions continues several times as the embryo travels towards the uterus, eventually leading to the differentiation of cells and the formation of the blastocyst. The cleavage cell divisions are crucial for the early development of the embryo and do not contribute to an increase in the total volume of the conceptus.