CONCEPT: The cell is the basic unit of living things.
CONTENT OBJECTIVE: 75212.00 To understand the mechanics of cellular
division
INSTRUCTIONAL OBJECTIVES: the learner will:
2.01 recognize the importance of cell division to organisms.
2.02 compare cell division in prokaryotic and eucaryotic cell.
2.03 identify the stages of mitosis.
2.04 recognize meiosis in reproductive calls.
A. reproduction in unicellular organisms
B. regeneration
C. healing and repairing process
D. growth
II. Types of cell division
A. Fission in prokaryotic cells
B. Mitosis in eucaryotic cells
1. Stages of Mitosis
a. prophase
b. metaphase
c. anaphase
d. telophase
C. Meiosis in reproductive cells
TN COMPONENT OF SCIENCE: Unifying Concepts of Society
TN GOAL:
To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical and earth/space sciences.
TN THEME:
2.2 FORM AND FUNCTION - Form may determine the function of a
material or a system, and function may alter form.
TN STANDARD(S):
2.2a - How an object functions is related to its form.
BENCHMARKS: Specialized structures perform specific functions.
All objects in the universe are affected by the gravitational forces.
There are different forms of energy such as heat, mechanical, chemical,
electrical, nuclear, and light.
The flow of energy has an impact of geological, biological and environmental
conditions.
CLASSROOM CONNECTOR
TIME REQUIRED: approximately 2-3 instructional periods
This lesson addresses Instructional Objective 2.01.
SET:
Every multicellular organism begins life as a single cell. By the time
you were born you were made of many trillions of cells. Where do these
cells come from? (According to the cell theory, every cell comes from another
cell.) Human cells are not the only kind of cells that make more of its
own kind. All organisms both multicellular and unicellular make new cells
by a similar process of cell division. Each cell is able to form new cells
just like itself.
INSTRUCTION:
In unicellular organisms, cell division is the way these organisms
reproduce. The cell divides producing a duplicate of itself.
In multicellular organisms, cell division has several functions.
One of these functions is regeneration. In regeneration, parts of organisms
that have been damaged grow back or are replaced. For example, a starfish
can grow a new arm if one is cut off. Do you know of any other animals
that can replace lost parts? (Some lizards can grow new tails, some species
of worms can grow back a lost part, salamanders can grow new legs, crayfish
can grow new claws, etc.) A free-living flatworm called a planarian has
an amazing ability of regeneration.
Another function of cell division is the healing of wounds which
in a way is a type of regeneration. Whenever you have a cut or scrape on
your skin, you can see the healing take place over a period of time. While
the wound heals, new cells are made to replace the destroyed and damaged
cells. The new cells are formed by cell division.
A fourth important result of cell division is the growing process. After
a cell divides, both new cells grow and divide to form more new cells.
Some cells can divide every few hours. (Using chalkboard or overhead projector,
show how number of cells can increase.)
As the number of cells increase in an organism so does its size.
ACTIVE PARTICIPATION:
1. Have students determine the number of cells formed from a single
cell in 24 hours if division occurs every two hours. (2048 cells in 24
hrs)
2. Use either planarian or tubifex worm to demonstrate regeneration.
REGENERATION USING TUBIFEX WORMS
Materials:
several tubifex worms (which may be obtained in aquarium store or biological
supply company); clean single edge razor blade; several petri dishes or
other small glass or plastic dish; water; microscope (optional)
Procedure:
1. Cut each worm as shown and separate the sections into individual
dishes.
2. Add a small amount of water to each dish.
3. Maintain at room temperature for three weeks.
4. Replace water that evaporates.
Observations:
Regeneration of worms takes approximately two to three weeks.
KEY QUESTION:
Why is regeneration an advantage to an organism? (The organism survives
body .)
KEY QUESTION:
Where does regeneration occur in your body? (Skin or bone)
REGENERATION IN PLANARIA
Materials:
planarian may be obtained from a biological supply company; several
petri dishes; single edge razor blade; microscope; microscope slide; water;
tooth pick; Epsom salts
Procedure:
1. Put a planarian in a culture dish and add a few crystals of Epsom
salts. In a few minutes the worm will be anesthetized.
2. Transfer the planarian to a drop of water on a glass slide with a
toothpick.
3. Cut the planarians in several different ways according to the diagrams.
4. Transfer each piece to a separate dish.
5. Add fresh water and put the dishes in a dark place.
6. Observe the animals daily, changing water as you do so.
7. Record any changes by description or drawing.
KEY QUESTION:
Which sections regenerated most quickly?
CLOSURE:
We have learned that cell division is an important process in all organisms.
Take a sheet of paper and write down the four important functions of cell
division in organisms. (reproduction, regeneration, healing, and growing)
Let students compare answers and then summarize what happens in each one.
This lesson addresses instructional objectives 2.02, 2.03, and 2.04
SET:
We have learned that cell division is the way a cell reproduces. How
does this occur? (A cell divides to Form two new identical cells.) Biologists
know that there are different ways that cells reproduce. This is determined
by the way the nuclear material is arranged in the cells.
INSTRUCTION:
One kind of cell has its nuclear material spread throughout the cytoplasm
in whole cell. These kind of cells are called prokaryotic cells. These
cells are found only in the unicellular organisms in the kingdom Monera.
Bacteria and blue-green algae are examples of these kinds of cells.
The prokaryotic cells reproduce simply by dividing in half. This process
is called fission. Before fission begins, the nuclear material doubles.
During fission the cytoplasm and nuclear material of the cell divides in
half to form two new cells of the same size. Each new cell has the same
amount as the original cell. In some bacterial cells, fission can occur
as often as every 20 minutes under the right conditions.
Most other unicellular organisms such as paramecium can reproduce by
fission also.
The other kind of cell has a membrane separating the nucleus from the
rest of the cytoplasm. These cells are called eucaryotic cells. Animals
and plants are made of eucaryotic cells.
The dividing of a eucaryotic cell is referred to as a cell division
called mitosis. Cell division can be broken down into four stages. The
division is a continuous process, but in order to study mitosis we will
look at some major things which happen in each stage. We will not note
every change that occurs in each stage, but you should be aware that there
are other activities involved.
Pass out drawing of cells for students to label during discussion.
The first stage is called prophase. During this stage, rod-shaped strands.
Chromosomes are made of protein and a certain number of chromosomes in
all its cells. The number 78, a cat has 32, a rose has 14. This is a very
important chromosomes not only appear, but they double in number. disappears.
the chromosomes in the nucleus appears as chemical called DNA. Each
living thing has a of chromosomes in our cells is 46. A dog has number
for each organism.
During prophase the Also during this time, the nuclear membrane
The second stage of mitosis is called metaphase. During this stage,
the chromosomes line up in the center of the cell.
The third stage is called anaphase. The chromosomes divide in half and
move to each side of the cell.
After this the final stage called telophase occurs. A nuclear membrane
forms around each set of chromosomes. The cell membrane forms around each
nucleus and then the two cells split apart. The two new cells are identical
- each has the same number of chromosomes that the cell had before it divided.
The new cells will grow and perform the activities that keep it alive
time called interphase since the cell is not dividing.
Mitosis occurs in all cells of an organism's body except in the reproductive
cells where another type of cell division occurs. This type of cell division
is called MEIOSIS. In meiosis each cell ends up with exactly one-half the
number of chromosomes that it originally had. Human cells have 46 chromosomes
so if meiosis occurs, the new cells will have how many chromosomes? (23
- 1/2 of 46.) If a frog has 26 chromosomes, how many chromosomes will be
in the reproductive cells? (13 - 1/2 of 26.)
The process of meiosis is similar to mitosis; however, in meiosis there
are two divisions of cells instead of one. The first division of cells
is mitosis with the number of chromosomes staying the same.
In the second division, each of the two new cells divide again, but
the number of chromosomes does not change during this division. This results
in the new cells having one-half the number of chromosomes.
Meiosis is often called reduction division because the new cells have
half the normal number of chromosomes.
DIAGRAM OF MEIOSIS
First Division
Second Division
This diagram does not show all steps - just the results of meiosis.
ACTIVE PARTICIPATION:
(1. Students can view prepared slides of prokaryotic and eucaryotic
cells. They will make drawings of each and describe the difference between
each.
2. Students label drawing of stages of mitosis.
3. Students examine prepared slides of onion root tip under microscope.
Locate the cells in the different stages of mitosis.)
CLOSURE:
We have studied three ways that cell division occurs. Which kind of
cell division occurs in prokaryotic cells? (Fission) The cell simply divides
in half. What kind of cell division occurs in eucaryotic cells?
(Mitosis) What happens to the number of chromosomes during mitosis?
(The two new cells have the same number as the original cell.) A third
kind of cell division is called meiosis. It occurs only in what kind of
cells? (Reproductive) What happens to the number of chromosomes during
meiosis? (Reduced by 1/2)
ENRICHMENT:
(Have students find number of chromosomes in other organisms.)
Hemiler. Focus on Life Science. Charles E. Merrill Publishing Company,
1984.
GLOSSARY:
chromosomes - rod-shaped bodies that appear in cell during mitosis
eucaryotic cells - a cell that has a well defined cell
nucleus fission - a kind of asexual reproduction that takes place when
cells divide
meiosis - cell division in which sex cells having half the number of
chromosomes are produced mitosis - process in which a cell divides to form
two identical cells
prokaryotic cells - a cell that has its nuclear material spread throughout
the cell
regeneration - replacing of lost parts
DIAGRAM OF MITOSIS
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