1. Unit 6

3. Chapter 20 The Beginning of The Life Cycle

5. When these layers are being formed, a thin membrane called the amniotic sac, surrounds the developing embryo. In the sac, the fluid acts as a shock absorber that protects from the temperature changes and bumps. Placenta – A blood-rich tissue developed from an outer layer of cells from the embryo and tissues from the mother. Umbilical Cord – A tube through which nutrients and oxygen pass from the mother’s blood into the embryo’s blood. The umbilical cord’s blood vessels carry waste products from the embryo, where they diffuse into the mother’s blood. The embryo grows rapidly in length and weight during the first six weeks of pregnancy. At eight weeks the embryo measures at 1½ inches in length. Fetus – The name by which the embryo is known from the end of the eighth week until birth.

13. Chapter 21 Adolescence- A time of change

19. Chapter 22 The Life Cycle Continues