The mother's blood does not mix with the embryo's blood. Substances are exchanged through the placenta by diffusion. Food and oxygen from the mother's blood pass through the placenta to the embryo. The developing fetus does not breathe within the uterus, but instead it uses the placenta. After nine months the baby is ready to be born.
Birth is easier if the baby's head presents itself first into the vagina.
Happening hints For your test you should be able to Say what happens at puberty. Explain the processes involved in human reproduction. Outline the menstrual cycle. Describe the role of the placenta. Cervix Neck of uterus that extends into the vagina.