Question 2

The morula sinking into the tissue of the uterine wall and being deposited there. It erodes the tissue as it goes, and this is the end of the journey that began at fertilisation.

The fusion of a sperm cell with an ovum is fertilisation itself, and the release of the ovum from the ovary is ovulation — the two events before it. The fertilised ovum is the zygote; it becomes the morula by dividing as it travels down the tube.