Haematopoiesis occurs in several locations in the embryo, at different stages during development.  

1) Describe when and where haematopoiesis occurs in the body, including the location, the cell types involved, and the time during embryonic/fetal and post-natal development.  (8 marks)

2) To ensure the process of implantation is successful, what key changes occur in the embryo, and in the endometrium?  (5 marks)

3) What is the role of the yolk sac during embryogenesis in humans?  (2 marks)