GRADE: Eighth

CONTENT STANDARD: Life Science

CONTENT TOPIC: Regulation and Behavior

CONCEPT: The continuation of a species is maintained through heredity.

CONTENT OBJECTIVE: 8F2.00 To understand growth and development

INSTRUCTIONAL OBJECTIVES: The learner will:

2.01 describe the major stages in the development of the embryo.
2.02 explain sex determination in humans.
2.03 list the stages in the human life cycle.
2.04 give the ages at which humans usually reach major developmental stages in their lives.
1.05 list environmental factors that influence human traits.
1.06 graph the average growth rate in males and females.

I. Main developmental stages
II. Sex determination
III. Human life cycle stages
IV. Environmental factors influencing human traits
V. Average growth rates

TN COMPONENT OF SCIENCE: Process of Science

TN GOAL:

To enable students to demonstrate the processes of science by posing questions and investigating phenomena through language, methods and instruments of science.

1.3 COLLECTING DATA - The acquiring, recording, arranging and storing of information must be performed in a complete, accurate, concise and user-friendly manner.

1.3a Data are collected using the senses, instrumentation, and a variety of other technologies.

BENCHMARK: The reading and interpretation of measuring instruments are necessary in determining length, volume, weight, elapsed time, rates, and temperature.

1.3b Data should be appropriate, accurate, and free of bias.

BENCHMARK: The larger a scientific sampling is, the more likely it is to represent the whole.

BENCHMARK: Information may be acquired from a variety of sources such as reference books, computer disks and databases, and back issues of periodicals.

TIME REQUIRED:

Two 45 minute instructional periods

Books and articles including references to genetics and traits which are hereditary

Adolescence, chromosomes, development, hormones, fetus, heredity, maturity, metamorphosis, puberty

Humans begin life as a single cell. We change from an embryo to a fetus with many physical changes occurring during the nine month gestation period. Sex of the organism is determined by the chromosome combination that is supplied by the father. After birth, the person undergoes the developmental stages of infancy, childhood, adolescence, adulthood, and older adulthood. Environment, as well as heredity, influences the expression of traits in an individual. People grow at different rates; however, growth rate is at its highest levels during the first two years of life and adolescence. Most people stop growing between the ages of 18 and 30.

Animals begin as one fertilized egg. It then divides to form a tiny ball of cells which after entering the uterus, becomes attached to its lining. An organism is known as an embryo while in its first stages of development. The stomach, brain, heart, liver, eyes, and ears have formed during the first month. At this stage of development the embryo has a mass of 0.02 grams. During the second month arms, legs, fingers, toes, lips, eyelids, muscle, and bone form. The embryo doubles in size and has a mass of 1.0 gram. At the beginning of the third month the embryo is called a fetus. A fetus is an embryo that has all of its body systems. The fetus begins to kick, bend, and turn. By the fourth month. At this stage of development, the fetus is 160 millimeters and has a mass of 100 grams. During the second three months, the fetus grows larger and the organs develop further. by the end of the fourth month the heartbeat can be heard. By the end of the sixth month the fetus is about 32 cm long and weight about 700 grams. The fetus grows longer and gains a great deal of weight during the final three months. By the end of the ninth month the fetus is fully developed, weighs about 3 kg, and is about 45 cm long. The fetus turns itself into a head-down position and it is ready to be born.

Sex determination of an unborn child is decided at the instant of fertilization, and it is the father's sperm cell that is the determining factor. Every egg that a woman produces is female in the sense that it contains an X, or a female, sex chromosome. In a man, half of the sperm cells carry an X chromosome, while the other half carry a Y, which is the male sex chromosome. If an X sperm fertilizes the X egg, the result is a fertilized egg with a combination of XX chromosomes that will produce a girl. If the Y sperm fertilizes the egg, the result is a fertilized egg that has one X chromosome and one Y chromosome, and will produce a boy. The type of sperm that penetrates the egg is randomly determined. There have been roughly equal numbers of X- and Y-bearing sperm in the males studied. Sperm are formed from primary germ cells that contain both an X and a Y chromosome. When these cells divide to form two sperm, one sperm receives the X and the other receives the Y chromosome. (Discuss the kings throughout history who have divorced wives for producing only female heirs.)

The stages of life after birth are infancy, childhood, adolescence, adulthood, and older adulthood. During the first year of life, infants grow several centimeters, learn how to crawl and walk, and may triple their birth weight. During childhood, the ages of two to twelve, a vast amount of growing and physical changes occur. Children develop a vocabulary, learn to talk in sentences, feed themselves, dress themselves, read, write, cooperate with others, lose baby teeth, etc., while in this stage of development. A child's weight doubles during childhood.

Rapid physical changes occur during adolescence. Adolescence begins between the ages of 11 to 14. During this stage young people usually experience a growth spurt and grow taller and gain weight. Males begin to produce sperm, and females release an egg cell about every 28 days in the adolescent stage of development.

Adulthood occurs between the ages of 18 and 21 when physical growth is complete. From the late teens to the late twenties coordination and muscle development reaches its highest point. Physical strength and reaction time decrease after age 30. Hearing, agility, physical strength, and eye sight tend to decrease during older adulthood. The American people are living longer and living active lives into their seventies and eighties.

There is an influence, other than heredity, that controls the expression of traits. This influence is the environment of the organism. The environment of an organism includes all the substances, forces, and other organisms that it comes into contact with during its life time. For example, you may have genes for tallness, however, if you do not eat well and get enough rest, you may not grow properly. (Discuss the results of a pregnant woman using drugs and alcohol.)

From birth to adulthood, body proportions change rapidly. A baby's head measures about one-fourth the length of its body. The head is only one-eighth the person's height in an adult. In humans, the sequence of growth - head, trunk, arms, legs - govern the baby's control over his body as well as physical development. According to research, boys and girls grow most rapidly during the first two years of their lives. Growth rate is much slower until the individual reaches the adolescent period. Adolescent boys usually show this spurt of growth between the ages 12 and 17 years. This gain in height often ranges from 4 inches to 12 inches. This spurt of growth in girls usually begins two years earlier than in boys, and their growth rate is somewhat less than that of boys. Most people stop growing some time between the ages of 18 and 30. A person is usually tallest about the age of 20. When a person stops growing in height, he begins to shrink due to a thinning of the pads of cartilage that grow between the bones of the backbone.

(The following activities are suggested.)

1. Fruit Fly Metamorphosis. Insects develop through a series of stages. Each stage has a form very different from the others. Metamorphosis is development by radical change.

Materials: fruit flies, banana, hand lens, quart jar, cheesecloth, rubber band

1. Have students place a piece of a ripe banana in an open quart jar and leave it in a warm place for several days. If fruit flies are around, you will soon see them flying in the jar. You can purchase fruit flies from a biological supply company if you prefer. Place a piece of cheesecloth over the jar opening and keep it in place with a rubber band. Keep a record of the date the flies were secured in the bottle. Have students observe their activities with a hand lens. The females will lay fertilized eggs in a day or two. Remove the adult flies and cover the jar with cheesecloth after the larvae hatch. Watch for the pupal stage when the insect becomes inactive with a hard shell. Keep a record of the dates and changes until the adult fruit flies emerge. Fruit flies have been used in genetic research because they reproduce quickly in large numbers, have a simple diet, and take up little space. Some inherited characteristics that can be studied are eye color and shape, wing size and shape, and body color.

2. Have students make posters using labeled snapshots or photographs of themselves from infancy through adolescence. What changes can students detect other than size?

3. Growth Patterns: Measure the heights of 10 students in your class. Measure 10 students in each grade K - 7. Record the age and sex of each person you measure. Organize the measurements into age groups 5 - 14. Find the average height for males and females of each age group. Draw a bar graph to show the average heights of people in the age groups you measured. Allow one color to represent females and another color to represent males. Show a color key in the corner of the graph. Graph the average height of the males and females in each age group. To obtain your measurements have the person you measure stand against the wall. Use a piece of masking tape to mark the spot where the person's head touches the wall. Measure the distance from the tape to the floor.

4. Purchase tadpoles from a biological supply company. Have students observe and record by drawing the tadpoles as they undergo metamorphosis. Note: Adding the hormone thyroxine to the water with the larvae speeds up metamorphosis.

Life begins for humans as one fertilized egg. Fertilization and development of an embryo occur inside the body of a female. The stages of development of the unborn child are embryo and fetus. An embryo undergoes a series of cell division and development to form a fetus. The embryo is called a fetus at two months. The sex of the child is determined by the father's chromosomes. After birth the stages of life are infancy, childhood, adolescence, adulthood, and older adulthood.

Some human traits are the result of environment rather than heredity. For example, facial characteristics and mental ability can be different due to a mother consuming large amounts of alcohol during pregnancy. Growth rate is greatest during the first two years of life and during adolescence.

adolescence - a period of growth and change in a person between the ages of nine and eighteen.

chromosomes - microscopic rod-shaped cells which carry the genes that convey heredity characteristics and are constant in number for each species.

development - a change in form or appearance.

hormones - chemicals that help regulate body activities such as growth, development, and reproduction.

fetus - an embryo after it has developed into the shape of its species.

heredity - the passing of traits from parent to offspring.

maturity - full development of body and mind.

metamorphosis - changes that some animals go through as they develop fro- eggs to adult.

puberty - the time when a human is first able to reproduce.

This is the time this file has been accessed since 04/04/98.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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