GRADE: Seventh

CONTENT STANDARD: Life Science

CONTENT TOPIC: Living Systems

CONCEPT: The cell is the basic unit of living things.

CONTENT OBJECTIVE: 7D1.00 To understand the basic structure and function of plant and animal cells

INSTRUCTIONAL OBJECTIVES: The learner will

1.01 learn the parts of a light microscope.
1.02 learn proper procedures for using a microscope.
1.03 define cell.
1.04 state cell theory.
1.05 describe basic function of cell parts.
1.06 compare animal and plant cells.
1.07 describe cellular activities.
1.08 describe ways cells are organized.

Labeling, taking notes, making observations, using the microscope, making comparisons and recording data, drawing conclusion, using the library

I. Basic instruction on use of light microscope
A. History
B. Kinds of microscope
C. Parts of light microscope and their functions
1. eyepiece
2. low power objective
3. high power objective
4. coarse adjustment knob
5. fine adjustment knob
6. arm
7. base
8. diaphragm
9. stage
10. clips
11. light source (lamp or mirror)
II. Define Cell
III. Cell Theory
IV. Animal Cell
A. Describe basic structure and function
1. cell membrane
2. protoplasm
3. nucleus
4. nucleus membrane
5. vacuole
6. mitochondria
7. endoplasmic reticulum
8. ribosomes
V. Plant Cell
A. Review parts of an animal cell
B. Additional structures in plant cells not in animal cell
1. cell wall
2. chloroplasts
VI. Cellular Activities
A. Movement of material
B. Chemical reactions
VII. Cellular Organization
A. Unicellular Organisms
B. Multicellular Organisms
1. cell specialization to form tissues
2. tissues form organs
3. organs form systems

TN COMPONENT OF SCIENCE: Habits of Mind

TN GOAL:

To enable students to demonstrate ways of thinking and acting inherent in the practice of science; and to exhibit an awareness of the historical and cultural contributions to the enterprise of science.

3. 1 HISTORICAL & CULTURAL PERSPECTIVE - The knowledge and processes of science have evolved over time as an approximation of truth within cultural contexts.

3.1b Individual initiative and vision create changes in science.

BENCHMARK Scientists around the world have made significant contributions to the body of scientific knowledge.

3.1f Progress in science depends heavily on societal events, and the course of history often depends on scientific and technological developments.

BENCHMARK Inventions have enhanced our abilities to study science.

TIME REQUIRED:

Minimum of 1 week (time determined by number of student activities incorporated into lessons)

Drawing of microscope to pass out to students, microscopes, glass slides, cover slips, water, newsprint, colored thread, toothpicks, iodine, Elodea leaf, air-freshened in spray can

Cell, diffusion, enzymes, multicellular, osmosis, plasmolysis, semi-permeable, unicellular

This classroom connector addresses Instructional Objectives 1. 01 and 1. 02.

Inventions often lead scientists to make discoveries. One of the most important discoveries in life science was the microscope. What is the purpose of a microscope? (Magnification) Why do you think this was such an important discovery? (pause) In order to see one-celled organisms as well as small multicellular organisms, the ability to use the microscopic correctly is very important.

It is not known who really invented the first microscope; however, there are indications that some type of magnifying instrument as used about 100 A. D. Magnifying glasses were probably not used extensively until the thirteenth century. Leonardo da Vinci (1452-1519) an Italian painter and architect stressed the use of lenses in studying small objects. The early microscopes are commonly called "flea microscopes" because a flea was a commonly studied specimen.

Anton van Leeuenhoek (1632-1723), a Dutch scientist developed a simple microscope about 1673. Robert Hooke (1635-1703) is given credit for using the term cell to describe what he observed while looking at a thin slice of cork under the microscope. There has been much scientific progress in the development of the microscope.

The most powerful of the microscopes today is the electron microscope. It has the ability to magnify on object over 100,000 times by the use of a beam of electrons. This type of microscope first came into use during the 1950s.

The type of microscope we will be studying is called the light microscope. The most powerful light microscope can magnify up to 2000X. Light microscopes work by the use of light and lens. In order to properly use the microscope we will first learn to identify the main parts of the microscope; then we will learn the correct procedure for using the microscope.

(Pass out the drawing of the microscope. The students will label while the teacher discusses each part. ) The eyepiece is the part of the microscope one looks through. There is a lens in the eyepiece which usually has a magnifying power of 10X. The other lens is located in a part called the objective. Usually there are two objectives - the high power objective and the low power objective. The magnifying power of the objectives can be found by looking on the side of each objective.

While viewing an object through a microscope you are actually looking through 2 lens - the eyepiece and the objective. To know what the total magnification would be use the following formula:

power of power of Total

eyepiece lens times objective lens equals Magnification

10x 10 =100X

(Ask students to figure what the Total magnification is when using the high power objective if the magnifying power of the objective is 43X. )

Eyepiece X Objective = Total Magnification

10X43=430X

The two knobs are used for focusing. What does focus mean? (To make clearer) The larger knob is called the coarse adjustment knob and the small knob is called the fine adjustment knob.

The arm and base are used to carry the microscope. Correctly pick up a microscope by the arm with the other hand under the base.

To view a specimen always place it on a glass slide. The glass slide is placed on the stage and the 2 clips hold it in place. The diaphragm is under the stage and it controls the amount of light needed to view a specimen. The light source for the light microscope is either an electric lamp which is built in or a mirror which uses reflected light.

Now that you know the parts of a microscope, the next step is to learn the correct procedure for using a light microscope.

1. Place the microscope on a flat surface with the arm toward your body.

2. The low power objective should be in place and close to the stage.

3. The diaphragm should be wide open.

4. Either turn on lamp or look through eyepiece and adjust the mirror to let in the greatest amount of light. The circle of light is called the field of vision.

5. Place glass slide in center of stage and secure with clips.

6. Look in eyepiece and slowly turn the coarse adjustment knob toward body to focus.

7. Make adjustment with diaphragm if needed.

8. To view with high magnification - turn the high power until it clicks in place.

9. Focus only with the fine adjustment knob.

10. Before putting the microscope away, always turn the low power objective into place and raise it about 2 or 3 centimeters above the stage.

(Students will practice using the microscope.

Materials: Small newsprint, colored thread, strand of hair, glass slide, cover slip, dropper, water.

Make wet mount slide by putting one drop of water in center of glass slide. Next place object to be viewed in drop of water and gently place cover slip on top.

Students should view under low and high power.

Dry the glass slide after each use. )

We have learned the parts of a light microscope and how to properly use a microscope. (Using either a microscope or transparency, point out the parts and have the students identify each part). Why is knowing how to use a microscope important? (Many organisms or parts of organisms cannot be seen without being magnified. )

This classroom connector addresses Instructional Objects 1. 03, 1. 04, 1. 05, and 1. 06.

A brick wall made of many smaller parts. What are these parts? (Bricks) Of what is a mosaic made? (small tiles) Matter is made of atoms. Can you think of something that is made of small parts put together? (Answers will vary. ) Scientists have made many observations about living things and all are found to be made of smaller parts called cells.

You remember that Robert Hooke first named the compartments of cork "cells". Cells are the basic unit of structure or the building blocks of all living things. After many years of observing and studying information about cells, a cell theory was formed. This theory states:

1. All living things are made of cells.

2. All functions of living things are carried on in cells.

3. Living cells come from other living cells.

This theory is so important because it applies to all living things. Every time people observe organisms with a microscope they see cells. These observations support the cell theory

The study of the cell has been enhanced by the improvement of the microscope. Scientists have observed cells and the parts of the cell. (Using a transparency or chalkboard label a drawing of the cell as each part is discussed )

We will first study the parts of the animal cell. The cell is held together by the cell membrane. It acts as a covering for the cell. The cell membrane controls movements of materials into and out of the cell. It is thick enough to keep the materials of a cell inside, yet it is thin enough to allow certain materials to pass into or out of the cell. We say the cell membrane is semi-permeable meaning certain substances can pass through while others cannot.

The inside of the cell is filled with a jelly-like material called protoplasm. This is the living material" of the cell which is composed of water, salts, and organic compounds.

The dark area of the protoplasm near the center is the nucleus. The nucleus controls all the activities of the cell. The rest of the protoplasm outside the nucleus is called cytoplasm. The nucleus is separated from the cytoplasm by a thin covering called the nuclear membrane. It controls the movement of materials into and out of the nucleus.

The electron microscope made it possible to see tiny tube-like structures that form a network of canals inside the cells. These are called the endoplasmic reticulum (ER). They extend from the nuclear membrane to the cell membrane Scientist- believe that materials are moved through these tubelike structures.

While studying the ER, scientists discovered little bumps on some. These bumps are called ribosomes. This is where proteins are made in the cell.

The mitochondria are rod-shaped structures known as the "powerhouse" of the cell. These are involved with the storing and releasing of energy. Some cells have vacuoles. These may sometimes appear as air bubbles. The vacuoles are storage areas for water, food, and wastes.

All these parts may be found in plant cells as well as animal cells. In addition, plants cells have some structures not found in animal cells. Two of these structures are a cell wall and chloroplast. A cell wall is a non-living outer layer that surrounds the cell membrane. Chloroplast are tiny compartments in the cell that contain the green chemical called chlorophyll. Why does a plant need chlorophyll? (To make food)

Please label the drawing of the microscope

(1. Students should label cell parts on the drawing when each part is discussed )

2. Microscopic comparison of plant and animal cells

a. Place 1 drop of water in center of glass slide

b. Using the wide end of a flat toothpick, gently rub the inside of the cheek

c. Stir the end of the toothpick in the water

d. Place 1 drop of iodine in water (Explain that cells are transparent so iodine stains the cell so it can be easily seen.)

e. Gently place cover slip

f. View under low and high power

g. Draw a cheek cell

h. Label the nucleus, cytoplasm, cell membrane

i. Remove leaf from tip of Elodea plant and make wet mount slide

j. View under low and high power.

k. Draw an Elodea cell

l. Label cell, wall, cytoplasm, and chloroplast

Compare the two cells and record any difference you notice (Check that the cheek cell is oval, while Elodea is rectangular. Cytoplasm in Elodea cell is moving and does not move in cheek cell )

We have learned that the cell is the basic unit of structure in all living things. Many scientists support the cell theory. Why is this so important? (All living things are made of cells ) Let us review the parts of the cell. (Students should tell the name of the cell parts as the teacher points to each part )

(Students may make report about the scientific contributions related to the cell made by:

1. Robert Hooke

2. Matthias Scheiden

3. Theodore Schwann

4. Rudolf Vichow

5. Marcelloo Malpighi

6. Anton Van Leeuenhoek

7. Robert Brown

8. Edmund B. Wilson)

SET:

We have learned about some of the parts of a cell, and their function in the cell. Cells need certain substances to carry on the activities that keep them alive. Today, we will learn about some of these activities and how the cell get these substances. What part of the cell allows materials to move in and out? (Cell membrane)

In order to study how substances move in and out of cells, you need to know something about how molecules move from place to place. One way of moving is called diffusion. What does diffusion mean? (To spread out)

Please watch me closely as I do this demonstration

(1. Show diffusion by spraying air-freshened in a corner of the room. Instruct students to raise hand when they smell odor. Have students to observe and describe the sequence which hands are raised. (Those closest to odor should raise hands first - then gradually all will detect odor.)

2. Show diffusion between two liquids. Take a beaker of water and add a few drops of food coloring. Do Not Stir. See how long it takes for the water to become colored.

3. Demonstrate how a solid when dissolved in a liquid will diffuse. Take a beaker of water and add a small amount of either of the following: instant coffee, copper sulfate, or potassium permanganate. Again see how long it takes for the color of the water to change.)

A good way to describe diffusion is the moving of molecules from a place where they are concentrated close together to a place where they are less concentrated or farther apart. When molecules are spread out evenly diffusion seems to stop.

Water is very important to all living things because a large percentage of a cell is water. So the movement of water into and out of a cell by diffusion through a membrane is common. This special kind of diffusion is called osmosis. Like other kinds of diffusion, osmosis keeps going until the concentration of water on one side of the cell membrane is the same as on the other side. Many substances will dissolve in water. Water can diffuse through the cell membrane carrying dissolved materials into and out of the cell. This is why water is so very important to cells.

Please watch closely during this demonstration involving osmosis

(1. Fill a plastic sandwich bag approximately 1/2 full with starch solution and tie with a rubber band or twist tie.

2. Place a bag in a beaker filled with iodine solution

3. After one hour (or 24 hours) examine the plastic bag

4. Starch inside the bag is no blue-black. Liquid out-side has not changed color.

5. Ask students which solution diffused through the plastic membrane. (iodine solution moved into starch solution because starch changed colors. Starch did not move across the plastic membrane because iodine did not change color.) The plastic bag can be compared to the cell membrane. It is semi-permeable. This means that some material can move through the cell membrane while other substances cannot (iodine will cause the starch to change color when the two substances come into contact with one another.)

Prepare 1% starch solutions

boil 1 liter of water

mix 1/2 teaspoon corn starch with enough cold water to form a paste pour paste into boiling water and stir for two to three minutes.

Prepare Iodine solution: Mix 10 grams potassium iodine or 2 grams of iodine into 1 liter of water )

Diffusion of water into a cell by osmosis builds up the pressure in the cell which is called osmotic pressure. This pushes outward on the cell membrane and gives the cell shape. Too much movement of water into a cell could increase the pressure causing the cell to burst. Loss of water by the cell can cause it to shrink and become limp. This is called plasmolysis and can cause a cell to die. Example - What does a plant look like when it needs water? (Limp and hanging) How does it look after receiving water? (Straight)

Place thin strips of raw carrot in containers of fresh water and in salt water for a few hours. Have students observe the difference in flexibility (Carrot in salt water will become more flexible due to water loss, while the carrot in fresh water remains stiff.)

In some cases molecules pass through a cell membrane in a direction different from diffusion. The molecules go from an area of less concentration to greater concentration. For this type of movement, the use of energy by the cell is needed. Biologists do not fully understand how this happens. It is called active transport.

Next we will look at some activities that occur inside the cell. Many chemical changes occur inside a cell - these are the changes that keep the cell alive and enable it to grow.

Energy is obtained from food by chemical changes. When food combines with oxygen the result is that energy is released. To prevent energy from being lost, cells have a substance that can trap, store, and release energy. This chemical is called adenosine triphosphate - ATP. Chemical changes in the mitochondria of the cell involve the storing and releasing of energy in the cell

Chemical changes are regulated by substances called enzymes. It has been estimated that there are a thousand different enzymes in a cell. Enzymes are made in the cell according to the life code. Each species of organism has a different life code. For every chemical change there is an enzyme that controls that change. Enzymes are kinds of proteins. The ribosomes are the location where proteins are manufactured by the cell, which are the results of chemical reactions.

In plant cells, the manufacturing of food is the result of a series of chemical changes. This happens in the chloroplasts of the plant cells.

We have discussed some of the activities that occur in the cell. You should begin to realize that the cell is the center of activity in an organism. There are many more activities that occur in the cell, but we have discussed only a few. List as many different activities as you can recall that occur in the cell (pause, then review answers)

Match the words with the correct definitions:

1. diffusion	A. chemical involved with energy
2. osmosis	B. shrinking of cell caused by loss of water
3. ATP	C. movement of molecules from an area of great concentration to an area of less concentration
4. active transport	D. movement of molecules through a membrane requiring energy
5. semi-permeable	E. substance that controls a chemical change
6. plasmolysis	F. describes how cell membrane will allow certain substances to move in and out of the cell, while others cannot
7. enzymes	G. diffusion through a membrane

1. Research how protein is made in a cell, describing role of DNA, RNA and ribosomes

2. Describe in greater detail the role of ATP in a cell

This classroom connector addresses Instructional Objective 1.08.

We know that all living things are made of cells. What is a cell? (Basic unit of structure or building blocks of all living things) We have studied about some of the activities that occur in the cell to keep it alive. No matter what size the organism - the center of activity for any type of organism is the cell

Some organisms are only one cell in size and they are called unicellular organisms. Do you know what some of these unicellular organisms are? (Answers will vary - some may say the kingdoms Protist, Monera, and, some Fungi or some may name specific organisms such as amoeba, paramecium, bacteria, yeast, etc.) The chemical changes and activities we have discussed keep these unicellular organisms alive.

There are organisms which are composed of many cells, and these are referred to as multicellular organisms. What are some examples of multicellular organisms? (All animals, plants, and most fungi or students may give specific organisms. )

There are several levels of organization found in the multicellular organisms. These organisms are generally made of many different kinds of cells - each having a special job to perform. When similar cells group together to perform a special job the result is the forming of TISSUES. Each tissue in a multicellular organism contains similar specialized cells.

When tissues work together to perform a specific life activity the result is the formation of ORGANS. An organ is a structure that performs one or more life activity for an organism to keep it alive.

When two or more organs work together to carry on a certain life activity, the formation of a SYSTEM has occurred. Many multicellular organisms have bodies composed of several systems which all work together.

Some multicellular organisms are not highly developed For example sponges have different kinds of cells, but the cells are not clearly arranged into tissues. The coelenterates, jellyfish, have different kinds of cells that clearly form different tissues. These are considered to be very simple organisms. The more complex the organisms become - the more organs and systems. What are some systems in our bodies? (Nervous, circulatory, digestive etc.) What are the organs that make up these systems? Answers will depend on the systems named.

We have studied the levels of organization that we find in organisms. We can divide organisms into two groups based on the number of cells in their body - unicellular and multicellular. Describe the difference between these two. (Unicellular means being composed of only one cell while multicellular means being composed of more than one cell.)

How many levels of development do we find in the multicellular organisms? (Four - cellular, tissue, organ, systems). Are all organisms at the same level of development? (No) Give examples. (Sponges on cellular level, jellyfish on tissue level, humans on system level.)

(Students will fill in the ladder with levels of development beginning with the simplest level and moving up the ladder with the more complex levels.)

SYSTEMS

ORGAN

TISSUE

CELL

cell - basic unit of structure in all living things (building blocks)

diffusion - to move from area of great concentration to area of less concentration, to spread out

enzymes - chemicals that regulates chemical changes

multicellular - made of more than one cell

osmosis - diffusion through a membrane

plasmolysis - shrinking of a cell caused by loss of water in cytoplasm

semi-permeable - material which will allow certain substances to pass through

unicellular - made of only one cell

This is the time this file has been accessed since 04/02/98.

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

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