1. The Beginning of the Life Cycle
Chapter 17
The Beginning of the Life Cycle

2. Lesson 1
The developing fetus and the mother need special care during pregnancy to ensure the health of the baby and mother.
The life cycle starts with fertilization, aka conception.
Fertilization – the union of a male sperm cell and a female egg.
The cell that results is called a zygote.

3. Lesson 1 Continued The very beginning:
Only one sperm can fertilize an egg
As the zygote travels down the fallopian tube toward the uterus, it divides many times
About 6 days after fertilization, the zygote burrows into the lining of the uterus
Implantation – process by which the zygote attaches to the uterine wall
After about two weeks the zygote becomes an embryo.
Embryo – cluster of cells that develops between the third and eighth week of pregnancy

4. Lesson 1 Continued The embryo becomes a fetus after about eight weeks.
Fetus – group of developing cells
The embryo forms three layers of tissue:
One layer becomes the respiratory and digestive systems
A second layer develops into muscles, bones, and blood vessels
A third layer forms the nervous system, sense organs, skin, and mouth

6. Lesson 1 Continued
The amniotic sac is a thin, fluid –filled membrane that surrounds and protects the developing embryo.
The umbilical cord is a ropelike structure that connects the fetus with the mother’s placenta.
The placenta is thick, blood-rich tissue that lines the walls of the uterus and nourishes the embryo.

8. Lesson 1 Continued The growing embryo:
0-2 weeks – spinal cord grows, brain, ears, and arms begin to from, heart begins to beat
3-8 weeks – 1 inch long at 8 weeks – mouth, nostrils, eyelids, hands, fingers, feet, and toes begin to form, nervous and cardiovascular system are functional
9-14 weeks – develops a human profile, sex organs, eyelids, fingernails, and toenails develop, by week 12 can make crying motions and may suck its thumb

9. Lesson 1 Continued
15-20 weeks – blink its eyes, more active, body begins to grow, growth of the head slows and limbs reach full proportion, eyebrows and eyelashes develop
21-28 weeks – can hear conversations, regular cycle of waking and sleeping, weight increases rapidly, 12 inches long and weighs a little more than a pound, may survive if born after 24 weeks with special medical care
29-40 weeks – uses all five senses, passes water from the bladder, some dream during the eighth and ninth months, 266 days after conception the baby weighs 6.9 pounds and is ready to be born

11. Lesson 1 Continued Multiple births:
Identical twins – single zygote splits into two separate embryos; identical traits and the same gender
Fraternal twins – two eggs are released and are fertilized by two different sperm; can be different genders
Prenatal care – steps that a pregnant female can take to provide for her own health and the health of her baby

12. Lesson 1 Continued
Females at a healthy weight before becoming pregnant can gain between 25 and 35 pounds during pregnancy.
Expectant mothers should avoid tobacco, alcohol, drugs, and environmental hazards.
Fetal alcohol syndrome – group of alcohol-related birth defects that includes both mental and physical problems

13. Lesson 1 Continued Complications of pregnancy: Cesarean delivery
Premature birth
Miscarriage – before twentieth week
Gestational hypertension – high blood pressure may occur after the twentieth week; a severe form is preeclampsia
Ectopic pregnancy – zygote implants in the fallopian tube, abdomen, ovary, or cervix

14. Lesson 1 Continued Childbirth:
Labor – muscle contractions in the uterus become regular and stronger this cause the cervix to dilate and widen
Delivery – cervix is fully dilated, baby passes from through the birth canal and emerges from the mother’s body
Afterbirth – contractions will continue until the placenta is pushed from the mother’s body

16. Lesson 2
Certain traits, such as eye and hair color, come from both parents.
Heredity is the passing of physical traits from parents to their children.
Chromosomes – thread-like structures found within the nucleus of a cell that carry the codes for inherited traits
Genes – basic units of heredity
DNA – chemical unit that makes up chromosomes

17. Lesson 2 Continued Human cells contain 46 chromosomes, or 23 pairs.
Egg and sperm cells have half that number – 23 chromosomes.
Egg – Sperm – 23 = Zygote – 46 chromosomes.
Some genes are dominant and some are recessive.
Females have only X chromosomes therefore egg cells only have an X chromosome.
Sperm contain either an X or a Y chromosome, thus the sperm from the male determine the gender of the child.

18. Lesson 2 Continued Genetic disorders are caused by defects in genes.
Amniocentesis – procedure in which some of the amniotic fluid is removed and tested for genetic disorders
Common genetic disorders:
Sickle cell anemia – red blood cells have a sickle shape and clump together
Tay-Sachs disease – destruction of the nervous system
Cystic fibrosis – mucus clogs many organs
Down syndrome – varying degrees of mental retardation
Hemophilia – failure of blood to clot

19. Lesson 2 Continued
Chorionic villi sampling – another method used to test for genetic disorders
Gene therapy – process of inserting normal genes into human cells to correct genetic disorders

20. Lesson 3
Developmental tasks – events that need to happen in order for a person to continue growing toward becoming a healthy, mature adult
Childhood:
Birth to 12 months:
Opens and closes hands
Associates sounds with objects
Imitates new word sounds
May walk a few steps
Experiences the five basic emotions
Forms strong attachment to parents
Begins to smile
Wants companionship
Begins experiencing stranger anxiety
Shows strong likes and dislikes

21. Lesson 3 Continued Early childhood: Ages 1-3 Walks well
Picks up objects
Throws ball overhead
Draws recognizable pictures
Shows defiance and disagreement
Behaves affectionately
Wants to help
Begins to be bothered by fears
Desires approval
Bosses other children
Takes part in group activities

22. Lesson 3 Continued Middle childhood: Ages 4-6: Dresses and undresses
Uses eating utensils
Becomes more independent
Eager to explore
Craves praise and approval
Self-confidence grows
Begins forming friendships
Becomes more outgoing and talkative
Respects others’ belongings
May want to things their way

23. Lesson 3 Continued Late childhood: Ages 7-12: Puberty may begin
Sensitivity about body image may begin
Sense of self
Recognizes unique personality traits
Sense of competence
Becomes aware of the dangers in the world
Deeper friendships develop
Relationships with parents change
Begins facing moral decisions
Peer pressure becomes stronger

24. Lesson 3 Continued
Autonomy – confidence that a person can control his or her own body, impulses, and environment
Children need many different types of health screenings to make sure they do not fall behind because of something that could slow their development.
Hearing
Vision