Describe how a zygote develops into a full-term fetus, noting the characteristics of the three stages of prenatal development.

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The Answer is The answer should include the following information: The three stages of prenatal development are the germinal period, the embryonic period, and the fetal period. The germinal period is the first two weeks of prenatal development. During this period, the single-celled fertilized egg (the "zygote") undergoes rapid cell division and implants in the wall of the mother's uterus. By the end of the germinal period, the zygote has become a cluster of cells called the embryo. The embryonic period extends through week 8 and is a time of rapid growth, intensive cell differentiation and formation of the major organs and systems of the body. At this stage the embryo is contained in the fluid-filled amniotic sac and depends on the umbilical cord for nourishment, oxygen, and water as well as the removal of carbon dioxide and wastes. The placenta acts as a filter to prevent many harmful substances in the mother's blood from reaching the embryo. By the end of the embryonic period, the embryo has grown from the size of the head of a pin to over an inch in length, weighing about an ounce. Although its head accounts for about half of its body size, the embryo now looks distinctly human. The fetal period extends from the beginning of the third month onward. During this stage, the body systems grow and reach maturity in preparation for birth. By the end of the third month the fetus can move its arms, legs, mouth, and head and is capable of reflexive responses. During the fourth month the mother can feel the fetus moving (termed "quickening"), and the fetus begins to have distinct sleep-wake cycles and periods of activity. During the sixth month the fetus' brain becomes similar to that of a newborn baby. During the final two months, the fetus will double in weight and gain three to four pounds of body fat, which will help with temperature regulation after birth.

Describe How a Zygote Develops into a Full-Term Fetus, Noting