Arrange the following events in correct sequence.A. Formation of zygo…

The correct answer is Option (1) → A, D, B, C

A. Formation of zygote — first. The sperm fertilises the ovum in the ampullary region of the fallopian tube.

D. Formation of morula — second. The zygote divides by mitosis (cleavage) into 2, 4, 8, 16 blastomeres; the embryo with 8–16 blastomeres is the morula.

B. Formation of blastocyst — third. The morula goes on dividing and becomes a blastocyst, with an outer trophoblast and an inner cell mass.

C. Implantation — last. The blastocyst becomes embedded in the endometrium of the uterus.

NCERT Extract:
Fertilisation and Implantation – “… The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus (Figure 2.11) and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula (Figure 2.11e). The morula continues to divide and transforms into blastocyst (Figure 2.11g) as it moves further into the uterus. The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus (Figure 2.11 step H). This is called implantation and it leads to pregnancy.”