Ch. 19 The Beginning of the Life Cycle

1. Ch. 19 The Beginning of the Life Cycle

2. The _________ is the basic unit of structure and function in living things. Our bodies are made up of trillions of cells, which most all can reproduce and repair themselves. • Levels of Organization in Multicellular Organisms • *________ - the most basic unit of structure and function in a living organism. • *________ – a group of cells that perform a similar function. • *________ – a group of tissues that perform a specific job. • *________________ – a group of organs that work together to perform a common function. • *_______________ – a group of organ systems working together.

3. The union of a male sperm cell and a female egg cell (ovum) is called ________________ or _______________. The resulting fertilized egg cell is called a ______________. • Fertilization occurs in the _____________________. The zygote then travels to the __________________. By the time it reaches the uterus, the zygote has divided many times to form a cluster of cells with a hollow center called a _____________________. • This cluster of cells attaches itself to the wall of the uterus in a process called _________________________. After implantation, the cluster of cells is known as an ___________________. After about the eighth week of development, it is called a ____________.

4. The cells of the embryo continue to divide, forming three layers of tissues that will later become body systems: One layer becomes the respiratory and digestive systems; one layer develops into bones, muscles, blood vessels, and skin; one layer becomes the nervous system, sense organs, and mouth. • Also, a thin membrane called the ______________________ develops outside the embryo. It serves to protect and insulate the embryo.

5. Cells from the embryo along with tissue from the mother develops into the ___________________ ( a thick blood-rich tissue that lines the walls of the uterus during pregnancy and nourishes the embryo). The embryo is connected to the placenta by the _______________________. This is how the embryo receives nourishment, as well as rids itself of wastes. • After 36 – 40 weeks of development, which is broken up into 3 month periods called trimesters, the baby is ready to be born. The baby’s head usually moves to the lower part of the uterus, causing the uterine muscles to contract. The closer the baby is to being born, the more regular, stronger, and closer together these contractions are.

6. These stronger contractions induce labor( the final stage of pregnancy in which the uterus contracts and pushes the baby out of the mother’s body). There are three stages of labor a female goes through: 1) dilation – stretching of the cervix; 2) passage through the birth canal; 3) afterbirth – the placenta is pushed out of the uterus.

7. Heredity is the passing of characteristics from parents to offspring. Heredity begins in chromosomes, which are tiny structures within the nuclei of cells. Chromosomes carry the codes for inherited traits. Most cells in our bodies contain 46 chromosomes arranged in 23 pairs. Sex cells (sperm & egg) only have 23 chromosomes so that when sperm and egg unite the resulting zygote will have 46 chromosomes, 23 from each parent. • Genes (the basic units of heredity) are small sections of chromosomes that control hereditary characteristics by carrying codes for specific traits. Genes also occur in pairs. One gene from each pair is inherited from each parent. We have thousands of genes in every cell of our bodies.

8. Heredity involves a chemical compound called DNA (deoxyribonucleic acid). Chemical compounds, called bases, make up the structure of DNA. The arrangement of the bases along each DNA molecule differs. Because several thousand pairs of bases are in each gene, countless numbers of arrangements are possible. • The order of the bases is called the genetic code. Our cells use the genetic code to make proteins. Different kinds of proteins will result in various traits. Everyone’s DNA is unique (unless they have an identical twin).

9. Of the 46 chromosomes in a zygote, 2 are specialized sex chromosomes. In females these 2 look exactly alike and are called X chromosomes. In males, one is shorter and does not match the other. The smaller one is the Y chromosome. Our sex cells (sperm & egg) contain only one sex chromosome, not two. Sperm cells may contain an X or Y, while an egg cell contains only an X. If the egg is fertilized by a sperm cell carrying an X chromosome, the combination is XX and the baby is a girl. If the sperm cell is carrying a Y chromosome, the combination is XY and the baby is a boy. • *Determination of sex is based on the father’s sperm.

10. Gene pairs are responsible for human traits. Some genes are dominant, and others are recessive. The traits of dominant genes usually appear in offspring whenever they are present. The traits of recessive genes usually appear only when dominant genes are not present. • Sometimes the genes that an individual inherits contain a mutation in the base sequence of the genetic code. This mutation could result in a genetic disorder (disorder caused partly or completely by a defect in genes). Some genetic disorders are apparent at birth, while some do not show up until later in life.

11. Common Human Genetic Disorders • 1. ________________________ • 2. ___________________________ • 3. ________________________ • 4. ___________________________ • 5. ________________________ Identifying Genetic Disorders • Amniocentesis – removal of fluid from the amniotic sac with a syringe. Doctors can examine the chromosomes in fetal cells taken from the amniotic fluid for genetic abnormalities or to determine the age or gender of the fetus. Usually performed 16 – 20 weeks after fertilization.

12. Chorionic villi sampling (CVS) – a small piece of membrane is removed from the chorion, a layer of tissue that develops into the placenta. Usually performed around 8th week. • Erik Erickson’s theory of human development consists of eight stages, each characterized by developmental tasks (events that need to happen in order for a person to continue growing toward becoming a mature, healthy adult). Success in each stage is dependent on an individual’s experiences during that stage.

13. Stage 1 – ______________________ – birth to 1 year • * Developmental task – to develop trust – an infant is completely dependent on others to provide for him/her and must be able to trust others to do so. • Stage 2 – _____________________________ – 1 to 3 years • * Developmental task – to develop the ability to do tasks for oneself – learns to walk, talk, feed himself/herself; begins to desire independence. • Stage 3 – _____________________________ – 4 to 6 years • * Developmental task – to develop responsibility, take initiative – initiates play activities rather than always following the lead of others; models adult behavior; learn to control impulses. • Stage 4 – _____________________________ – 7 to 12 years • * Developmental task – to develop an interest in performing activities – child completes transition from home to school; develop skills in reading, writing, and math; learn appropriate role in society and develop a conscience.

14. Stage 5 – Puberty – between 12 and 18 years • Stage 6 – Young adulthood – 19 to 40 years • Stage 7 – Middle adulthood – 40 to 65 years • Stage 8 – Late adulthood – 65 years to death