A level Biology exam revision resources written by A level Examiners


Embryonic development begins while the fertilized egg is still within the fallopian tube. The developing embryo travels down the tube, reaching the uterus in about a week. As a result of repeated mitotic divisions and some migration of cells, a hollow ball of cells is formed called the blastocyst. Approximately one week after fertilization, the blastocyst embeds itself in the endometrium, a process called implantation. With implantation, pregnancy is established.

The blastocyst will develop into the:

  • baby
  • amnion
  • placenta
  • umbilical cord

and secrete the pregnancy hormone human chorionic gonadotropin (hCG).

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