Sandra I. Perkins
The unit will be broken into five main topics:
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1) The Cell and its Function
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2) Heredity—Inheriting Traits
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3) Animals—Fertilization and Development
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4) Human Development—The Development of the Zygote Into a Fetus
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5) Heredity and Environment—Development of Individuality
Each of these main topics will begin with a list of objectives to be achieved by the student. After the objectives, the concepts to be taught will be discussed with descriptions of the materials to be used at the time as well as any drawings which may be utilized by the teacher or the students.
The Teaching of Biology and Difference to
A Seventh Grade Special Education Class
1) The Cell
Objectives The student will:
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Ðunderstand that cells are the building blocks of all living things
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Ðunderstand the basic parts and function of the cell
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Ðunderstand cells carry out the basic life functions
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Ðunderstand difference between animal and plant cell
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Ðunderstand chromosomes are found within the nucleus
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ÐDNA is found within the chromosomes
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Ðunderstand cell division
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Ðname three one-celled animals
To introduce this unit, a discussion of the scientific method and the microscope will occur so that the student will have an understanding of the processes a scientist goes through in his investigations and a guideline that they will be able to follow as they start to investigate on their own.
In order to find answers to a problem, a scientist uses a method called the scientific method. The five steps to the scientific method are as follows:
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1. Statement—tells about the problem to be investigated
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2. Research-information and observations are made to try to answer the problem
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3. Hypothesis—a possible answer to the question
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4. Experimentation—to test the theory
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5. Theory—the statement which is made to explain the answer which stands up to testing and observation. The microscope is a basic research tool which scientists use to look at objects which are very small, which man cannot see with the naked eye. Anton Leeuwenhoek is credited with making the first microscope from lenses which he ground and polished. He observed living organisms in a drop of pond water.
At this time, the students will be asked to pretend they were Anton looking through the microscope for the first time. How do you think he felt when he observed tiny moving objects in the sample of pond water? After directing them to answer and a discussion of how the microscope should be handled, they will look at their own samples of pond water, make observations and drawings, and describe what they see, and how they felt.
What is a cell? How small is it? Cells were first discovered by Robert Hooke when he looked at cork under the microscope. Scientists continued to study cells of different organisms, plants, and animals and formulated a cell theory. The Cell Theory states that all living things are made up of cells. Cells carry on life functions. Cells produce new cells. The cell is made up of many parts which include the nucleus, cytoplasm, cell membrane. The nucleus controls the life functions of the cell and it controls the reproduction of the cell. The cytoplasm is all the material which is found between the cell membrane and the nucleus. In the cytoplasm are storage spaces called vacuoles. The cell membrane surrounds the cell. Food, oxygen, and wastes pass through the cell membrane. There are different shapes and types of cells. Different cells have different jobs.
An activity for this section involves the student making a cell ‘model’ out of gelatin at home. Before the gelatin hardens, insert a grape or raisin into the center to act as the nucleus. The animal cell model could be used at this time for the students to hold and observe where the parts are located.
Within the nucleus of the cell are chromosomes which are threadlike structures in which DNA is located. DNA controls the development of hereditary traits called genes.
What is the difference between a plant cell and an animal cell? A plant cell contains those parts mentioned earlier as well as chloroplasts and a cell wall. A cell wall surrounds the cell membrane. It protects the cell and helps it to hold it’s shape. The cell wall is made up of hard, non-living material called cellulose. Chloroplasts contain chlorophyll which gives a plant its green color. Vacuoles in a plant cell are larger than those in an animal cell.
Have the students make a chart comparing the differences between plant and animal cells. In the classroom there will also be charts for the students to observe and note differences.
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A Plant Cell Has:
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An Animal Cell Has:
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nucleus
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nucleus
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cytoplasm
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cytoplasm
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cell membrane
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cell membrane
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cell wall
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no cell wall
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large vacuoles
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small vacuoles
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chloroplasts
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no chloroplasts
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A cell reaches a point at which it cannot grow any further. At this point, cell division takes place during which the cell produces a new cell which contains the same information from the original.This process is called mitosis. The nucleus of the cell controls this process. Chromosomes within the nucleus make a copy of themselves then they become short and thick. At this time, the cell membrane disappears. The chromosomes line up in the center of the nucleus. The chromosomes split apart and move towards the opposite ends of the cell.
Part I—The Cell
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At this time, a new membrane begins to form around the chromosomes. The chromosomes then stretch back to their threadlike state, and the two cells separate. What exists now, are two daughter cells which contain the same number of chromosomes is each cell. The two cells are exactly alike. The daughter cells are about half the size of the original parent. How that this has occurred, the cell begins to take in food through their membrane and begin to grow. When the cell reaches a point where it cannot grow any further it will split and divide again in the same manner.
2) Heredity
Objectives The student will understand:
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Ðthe female reproductive cell is the egg
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Ðthe male reproductive cell is the sperm
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Ðgenes are the controllers of hereditary traits
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Ðthe part of the cell which contains genes is the chromosomes
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Ðevery human cell,(except reproductive cell), contains two pairs of twenty-three chromosomes
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Ða reproductive cell contains twenty-three chromosomes
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Ðeach person inherits two genes for a particular trait, one from father, one from mother
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Ðdominant and recessive genes
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Ðevery cell in our bodies contain an identical set of chromosomes from that of the original cell before it began to divide
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Ðour environment influences our inherited traits
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ÐDNA in genes determines what a plant or animal looks like
To interest the students in this new topic of heredity, a question is posed.
“Who do you most look like in your family?”
The teacher can further engage the students in explaining why they answered as they did. The characteristics that the students have mentioned, eye color, hair color, height, etc., are called traits. Traits are those characteristics which are passed from parents to offspring. Heredity is the transmission of traits from generation to generation. Genetics is the science of heredity.
Gregor Mendel was the first scientist to study how traits were inherited, and he founded the science of genetics. His experimentation, and observation of pea plants over generations helped us to understand how traits were inherited.
He crossed pure tall plants with pure short plants. Pure means that the tall plant has two like genes for ‘tallness’, and the short plant has two like genes for ‘shortness’. TT stands for pure tall, and tt stands for pure short. Draw a tall plant and a short plant on the board and label them as mentioned above.Mendel found that when these plants were crossed, the offspring had all tall plants. Each of these plants had one gene for tallness ‘T’, and one gene for shortness,’t’. So each plant had Tt genes. These plants were called hybrids because they had a pair of unlike genes.
At this time use a Punnett Square to diagram how this occurred. At the top put TT, and on the side put tt. Show how when combined we get for sets of Tt.
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Mendel continued to cross the pea plants and he discovered that in a hybrid, having two unlike genes, one gene always showed itself, and the other gene stays hidden. The gene that always shows itself is called dominant. The gene that stays hidden is called recessive.
Referring back to the diagram of the plants that the students drew, ask them, “Which trait of the pea plant was dominant, tallness or shortness?”
Tallness in pea plants is the dominant trait. Whenever pure tall plants are crossed with pure short plants the resulting plants will always be tall.
At this time, it might be helpful to the students to give them some problems about combining traits and telling them which trait is dominant. Dittos using the Punnett square would also be helpful. For example:
One parent is pure for brown hair and the other is pure for blond hair. Brown hair is dominant. What color hair will the offspring have?
(Have the students designate a capital B for brown hair and a small b for blond hair. Complete a Punnetts square. Figure out the ratio of brown hair to blond hair.)
It may take a couple of days for the students to grasp this information. Continue to review that organisms contain two genes for each trait that they have. One gene came from their father and one from their mother. Use diagrams to illustrate this for various traits that the students would like to discuss. Continue to point out that a capital letter stands for dominant, and a small letter stands for recessive.
How do you develop into a girl or boy? Sex chromosomes determine whether a fertilized egg develops into a girl or boy. In males, the sex chromosomes are XY.
In females, the sex chromosomes are XX. When egg cells are produced, each egg receives only one of these sex chromosomes. So female egg cells contain X chromosomes. A male sperm can contain either an X or Y chromosome.
It would be helpful to diagram the possible chromosomes that would be found in a female and male egg cell to show that females can have only X chromosomes in their egg cell, and males can have either an X or Y chromosome in their sperm cells.
If the egg cell is fertilized by a sperm carrying an X, a girl will develop. If the egg is fertilized by sperm carrying a Y chromosome, a boy will develop. At this time it would be helpful to show students the possible combinations using diagrams, or they can try to figure out the combinations using the Punnett Square. Ask the students whether the mother or father determines the sex of the child. All children inherit their sex from their fathers.
Why do we grow to be humans and not a kangaroo, bear or snake? Each fertilized egg contains a set of instructions which tells how the cell should grow. So a human fertilized egg will grow into a human and a chicken egg will grow into a chicken.
Genes, which are found in the chromosomes, are what carries the hereditary information from generation to generation. Genes control how tall we are, the color of our hair, eyes, and skin, and they control the activity that goes on within each cell as it grows. Genes are the reason that people look different from each other. Have the children fill out a chart on hair color, eye color, height, and weight, for all the members of their immediate family. As these characteristics are compared, explain that genes determine the differences that we see among individuals. Remind them that every person inherits two genes for each particular trait. In most cases, the dominant trait will show in the offspring. Sometimes traits combine to produce a mixture of both traits. For example, when blue eyes and brown eyes combine, hazel eye color may result. When two traits combine to form a mixed trait, this is called blending.
Part II—Heredity
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The color of our skin is the result of blending. Have the children look around the room and note how many different colors of skin there are. Because of blending, the amount of melanin that an individual has in his skin is different. More melanin produces darker skin, less melanin produces lighter skin.
Genes are the instructions that are carried from generation to generation that determine heredity and cell activity. These instructions are in a coded form which is determined by DNA. DNA stands for deoxyribonucleic acid.
Each trait that we inherit is made up of a code which is different for every characteristic, job and part of the body which the cell makes up. Refer the class to the model kit of DNA. As the model is demonstrated, discuss the make-up of the structure which looks like a twisted ladder. DNA’s rungs are made up of four nucleotides called adenine, guanine, cytosine, and thymine. Continue the discussion if the students interest remains high on the make-up and coding sequences of DNA.
3) Animals and Development
Objectives The student will understand:
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Ðanimals spend their life struggling to survive
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Ðreproduction is a process which allows survival of the species
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Ðthere are two types of reproduction; asexual and sexual
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Ðfission, budding, and regeneration are types of asexual reproduction
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Ðfertilization can occur internally or externally
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Ðexamples of animals which reproduce asexually
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Ðexamples of animals which have internal/external fertilization
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Ðlife cycles of certain animals
The purpose of this section is to promote an understanding that all animals reproduce differently. Not all animals reproduce through sexual means and have their young born alive or laid in eggs. Most of the students taught at the seventh grade level will have the knowledge that all living things come from other living things of the same kind.
A question to ask to promote interest at the beginning of this section could be “Do all animals reproduce in the same way as others?” Have the students list means of reproducing on the board.
Mention the amoeba to the students and ask how it reproduces. From this point, the discussion can lead to asexual reproduction . During fission, the single cell splits into two cells which look exactly alike. In budding the cell wall pushes out to form a small bud, then the nucleus of the cell moves towards the bud, divides, then the bud breaks away to form a separate cell. When a starfish’s leg is severed, regeneration occurs during which the lost leg grows back. Starfish can also be reproduced into a new starfish from part of its body. This is also called regeneration.
An activity for this section could involve labeling diagrams of different types of asexual reproduction. Observe a yeast cell under a microscope to note budding.
At this point in regular curriculums, the topic turns to sexual reproduction in plants. Plants have been excluded altogether from this unit as the terminology, modes of reproduction can become too complicated for discussion or comparison. The students may begin to transfer or mix up parts, and it can become too confusing. Thus it is recommended that plants and plant reproduction be treated as an entirely separate unit.
What are the reproductive organs in animals who reproduce sexually? A discussion of the reproductive organs and fertilization will occur. Once a zygote is formed, cell division takes place and forms the beginning of the embryo. This rapid cell division is called cleavage, and it continues until a hollow ball of cells is formed. As the embryo develops, one side of the ball begins to grow inward. The hollow ball then becomes two layers, then a third layer develops between the first two layers. The tissues and organs of the organism are formed from these three layers of cells.
Part III—Animals and Development
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Have the students label drawings of these stages. Look at microslides of animal mitosis and the development of a chick from an egg, to further reinforce these concepts.
In most fish and amphibians, fertilization takes place outside of the body and the embryo develops in the water. In most reptiles and birds, fertilization takes place inside the body, and the embryo develops in the egg.
The yolk provides the food for growth. In most mammals, dolphins and whales included, fertilization takes place inside the body, and the embryo develops inside the uterus.
The placenta provides the food for development.
How do insects reproduce and develop? Most insects go through a metamorphosis, or change in form. Have the students name some stages that they have seen for a fly, butterfly, and mosquito. Then put the stages into the appropriate order, using diagrams.
Animals reproduce and develop differently. In order for the young to survive, the parents must care for their young until they are able to function on their own. What would happen if all the parents of one specie of sparrow left their young once they had hatched? Would they survive? Why do some animal babies die when they are born? These questions will promote discussions on what it takes to survive and how different animals have different ways of protecting their species.If an animal dies before reproducing the strong ‘genes’ that allow that particular animal to survive may be lost through many generations.
4) Human Development
Objectives The student will understand:
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Ðparts and functioning of the male and female reproduction system
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The student will understand:
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Ðwhere fertilization occurs
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Ðthe human egg cell is very small because it does not contain any stored food
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Ðcell division continues to occur after fertilization during which the cells differentiate into various tissues and functions
The purpose of this section is to touch on human reproduction. The content of this section will be mainly films, diagrams, and models of the human reproductive organs, and the development of the fetus through the nine months. This will promote a better understanding of what occurs in the mothers womb while she is carrying the fetus. At this time the birth process will not be shown on film, but if the students pose questions about the topic, it will be discussed, or the students will be referred to the resource material.
5) Heredity and Environment—The Development of the Individual
Objectives The student will understand:
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Ðgenes are the means by which offspring have the same characteristics as their parents
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Ðgenes also cause differences among the same members of a species or family
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Ðenvironmental factors produce differences among members of the same family
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Ðtraits that are not brought on by genes, but that develop during the organism’s lifetime are called acquired characteristics
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Ðmutations affect the genes of the sex cells, and cause change
Who are you? What makes you different from your brother or sister, or friend? We learned earlier that we are products of an egg and sperm coming together with genetic information from our mother and from our father. That genetic information combined to give us some traits from our mother and some from our father. Some traits that we have are influenced by both heredity and the environment in which we live. For example, a person could have inherited the gene for tall bone growth, but if that person lives in an environment in which there is a poor diet, which results in a lack of vitamins necessary for bone growth, the bones will not grow appropriately. Some of our behavior is inherited such as our neonatal sucking and rooting reflexes. Other behavior is influenced by both heredity and environment.
Acquired characteristics are those traits that we develop during our lifetime which are not brought on by genes. Foe example, an opera singer’s voice is the result of many years of lessons and practice. Unless the opera singer’s sex cells contain the gene for an operatic voice, the offspring will not inherit it.
When the environment is not right for a trait to develop, the trait will be weak or it will not develop at all. Changes in the environment will not effect the genes but they will determine whether the trait will develop as it should or not.
Sometimes the environment will change. For example, the weather may get colder and remain that way. In order for the species to survive this colder environment, they need to develop new traits. What trait could help you survive if the weather became colder? These traits that are developed to live in the environment are called adaptions.
Mutations are changes which take place in an organism’s gene or chromosome. If it occurs in a sex cell, it will be passed on to the next generation and a new trait may develop. Mutations can help an organism or they can produce a negative effect, such as in mental retardation.
Thus many factors contribute to a person’s individuality. Have the students imagine they were in a different environment, for example, colder or hotter climate. Or have them picture themselves growing up with different parents or in a different town. Have them write about how they would be different from who they are now. Discuss different cultures and their effects on individuality. How would you be different if you were brought up in a tribal village, or Iceland? What effects would the climate, people and their customs have on how you act or what you believe?
