Question

Describe how the zygote gets fixed to the uterus wall after fertilisation.

Answer 1

After fertilisation, the zygote travels along the oviduct towards the uterus while undergoing repeated mitotic divisions called cleavage.

1. The zygote divides into 2, 4 and then more cells. The cells formed are called blastomeres.
2. A compact ball of cells, called the morula, forms.
3. Fluid collects within the morula, turning it into a hollow structure called the blastocyst. It has an inner cell mass, which develops into the embryo, and an outer layer of cells called the trophoblast.
4. The blastocyst reaches the uterus, where the endometrium has been prepared and thickened. The trophoblast attaches to and becomes embedded in the uterine lining, usually about 6–7 days after fertilisation.

This attachment and embedding of the blastocyst in the uterine wall is called implantation. It establishes the early connection between the developing embryo and the mother.