The embryo implants into the uterus. State what happens to the fertilised cell for it to become the embryo.

After fertilisation, the fertilised cell, also known as a zygote, begins a process of cell division. This process is called cleavage and it results in an increase in the number of cells, but not their size.

1. The zygote first divides into two cells, then four, then eight, and so on. This mass of cells is called a morula.

2. Around the fourth day after fertilisation, the morula enters the uterus.

3. By the fifth day, the morula has developed into a blastocyst. The blastocyst is a hollow ball of cells with an inner cell mass. The outer cells will become part of the placenta, and the inner cells will form the embryo.

4. The blastocyst begins to implant into the lining of the uterus around the sixth day. This process is completed by the ninth day.

5. The inner cell mass of the blastocyst will continue to differentiate and develop into the embryo. By the end of the eighth week, all major organs and body systems have begun to develop.

6. From this point forward, the developing human is referred to as a fetus until birth.