This chapter:

• states that human bodies are designed to make babies.

• points out that human bodies are made up of about 100 trillion cells and composed of tissues and organs.

• notes that sexual reproduction allows two individuals to provide DNA to create new beings that are different from their parents.

This chapter:

• introduces a man and a woman expecting a baby.

• states that men produce sperm from puberty on, but all of a female's eggs are made when a fetus.

• explains ovulation.

• notes that an egg has all components to start life except DNA from sperm, and a few hours after being released, the egg will die if it does not join with a sperm.

• discusses human sexual chemistry and the physical aspects of it.

This chapter:

• states that the acidic nature of the vagina kills sperm that don't travel quickly enough through it.

• tells that even in healthy men, up to about 60 percent of the sperm are imperfect.

• explains that woman's body controls whether or not a healthy sperm reaches an egg and successfully fertilizes it.

• states what happens to the cervix during ovulation, describes the sperms' journey into a fallopian tube, and notes how sperm fertilizes the egg.

This chapter:

• states that sperm and egg join to create a viable embryo, but more than 50 percent of all fertilized eggs don't develop.

• explains that after the sperm enters the egg, meiosis is completed.

• discusses the process of how the cells, now called a blastocyst, move toward and attach to the mother's uterine lining.

This chapter:

• explains that when the blastocyst is the size of a poppy seed, cells organize into an embryo.

• discusses gastrulation, a process in which three different layers of cells develop, and different organs develop from each layer.

• tells that at four and one-half weeks, the embryo is about 1/5 in. long.

• summarizes that all organs develop from the same cell with 46 chromosomes, but cells in different organs do not look alike because different genes are activated in different cell types causing different proteins to be made.

This chapter:

• notes that one pair of chromosomes among 23 determine the sex—XX for female and XY for male.

• explains that late in the sixth week, a chain of chemical reactions occur turning on some genes and off others.

• presents how the journey becomes a fetus.

• tells that at six months, the fetus is 400 times larger than at two months.

This chapter:

• explains that in a growing fetus a few crucial events are still occurring, including fat being laid down in the brain.

• describes the role of the placenta.

• outlines how different body organs develop.

This chapter:

• notes that by the third trimester, all organ systems are in place.

• describes how fat is laid down in the brain, and how a fatty covering called myelin surrounds nerve cells.

• explains the brain's need for nourishment during the final trimester.

• shows the birth of the developed fetus, and explains how dangerous human births were, particularly before C-sections were possible.