Cell
Division
Topic
Mitotic division produces cells for growth and repair, and meiotic division
produces gametes.
Introduction
Mitotic cell division occurs in all living things. Unicellular organisms
undergo binary fission, a type of mitotic cell division that creates
offspring. Multicellular organisms rely on mitosis to create new cells for
growth and repair. All of the cells produced in mitosis are clones of the
parent cell. Mitosis occurs in the somatic, or body cells, of these living
things. In humans, for example, skin constantly replaces lost cells
through the process of mitosis.
Sexually reproducing organisms have special organs in which cells undergo
meiosis. Unlike mitosis, meiosis yields cells that are not exactly like the
parent cell. Daughter cells created in meiosis contain only half the original
number of chromosomes. These cells act as gametes, or reproductive
cells, for the multicellular organism. Females produce egg cells through
meiosis and males produce sperm. During fertilization, an egg and sperm
unite, resulting in a zygote that has the same number of chromosomes as
their parent cells (see Figure 1). In this activity, you will explore and
compare the phases of mitosis and meiosis.
is
tos
mi
fertil
iza
tio
n
zygote
gametes
adult
m eio sis
Figure 1
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CELL DIVISION
2
Time Required
55 minutes
Materials
✒ access to the Internet
✒ colored pencils
✒ science notebook
Safety Note
Please review and follow the safety guidelines.
Procedure
1.
Before mitosis begins, a cell makes copies of its chromosomes.
The cell then undergoes division in four stages: prophase,
metaphase, anaphase, and telophase. Use the Internet to
determine what happens in each phase of mitosis. In your science
notebook, write a description of each phase.
2. Figure 2 shows an interphase cell and a prophase cell with two
chromosomes, each of which is replicated. Copy the figure in your
nucleus
spindle
fibers
interphase
chromatids
centriole
prophase
Figure 2
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CELL DIVISION
3
science notebook. Use colored pencils to complete the drawing by
adding cells in the remaining phases of mitosis. Include
chromosomes, centrioles, spindle fibers, and cell membranes.
3. Meiosis also begins with prophase. However, in meiosis, a cell
undergoes two cell divisions. As a result, a meiotic cell moves from
interphase to prophase I, metaphase I, anaphase I, telophase I,
prophase II, metaphase II, anaphase II, telophase II. Use the
Internet to determine what happens in each phase of meiosis. In
your science notebook, write a description of each phase.
4. In your science notebook, use colored pencils to draw the phases
of meiosis for a cell that has two replicated chromosomes.
5. Copy the Venn diagram in figure 3 into your science notebook,
making it large enough to write on. Compare your drawings of
mitosis and meiosis. Use these drawings to help you complete the
Venn diagram. Under “mitosis,” list three facts about mitosis that
are different from meiosis. Under “both,” write three similarities of
these two events. Under “meiosis,” write three facts about meiosis
that are different from mitosis.
mitosis
both
meiosis
Figure 3
Analysis
1.
How many daughter cells are produced during mitosis? How many
are produced in meiosis?
2. A human somatic cell contains 46 chromosomes. How many
chromosomes are in each daughter cell after mitosis? How many
chromosomes are in each daughter cell after meiosis?
3. What is the purpose of each type of cell division?
4. Why must the chromosome number be reduced by half in meiosis?
5. What is the function of the mitotic spindle? When does it appear?
When does it disappear?
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CELL DIVISION
4
What’s Going On?
A cell spends most of its life in interphase, a period of
growth. Near the end of interphase, the cell makes copies of
its chromosomes. A set of replicated chromosomes, or sister
chromatids, is held together by a centromere. During
prophase, the nuclear membrane begins to disappear.
Centrioles produce the mitotic spindle, fibers that attach to
and move the chromosomes. In metaphase, the spindle
fibers move the chromosomes into the middle of the cell.
During anaphase, the spindle fibers contract and pull apart
the pairs of sister chromatids. Telophase begins when the
chromatids have reached opposite ends of the cell. After the
nuclear material is divided, the cell undergoes cytokinesis to
divide its cytoplasm. Mitosis yields two cells that have the
same number of chromosomes as the parent cell.
In meiosis, prophase I is similar to prophase in mitosis: the
nuclear membrane disappears and centrioles form the
mitotic spindle. However, an important event occurs that
does not take place in mitosis. Homologs, matching
chromosomes from each parent, come together and swap
pieces of DNA in the process of synapsis. Because of
synapsis, meiosis produces daughter cells with a high degree
of genetic variation. In metaphase I, pairs of homologous
chromosomes line up in the center of the cell. These pairs
are pulled apart in anaphase I and make their way to the
opposite poles of the cell in telophase I. After cytokinesis,
the resulting two cells undergo another round of division.
When meiosis II ends, there are four cells, each containing
only half as many chromosomes as the original cell.
Want To Know More?
See Our Findings.
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OUR FINDINGS
5.1 CELL DIVISION
Suggestion for class discussion: Remind students of old
cuts and scrapes that have removed skin from the knees. Ask students
where the new skin came from to heal those wounds. Elicit from the
class the concept that new skin, tissue for repair, comes from mitosis of
existing skin cells.
Teacher notes: Some good Websites include:
•
http://www.biolessons.com/lessonplans/mitosisandmeiosis/ has
some interactive animations of the two types of cell division
•
http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main
.html, an interactive meiosis tutorial
•
http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/
cell_cycle.html, an onion root tip activity showing mitotic cells
•
http://www.cellsalive.com, an interactive tutorial on cell division
Analysis
1. 2, 4
2. 46, 23
3. Mitosis produces cells for growth and repair. Meiosis produces
gametes.
4. The chromosome number must be reduced by half so that when
egg and sperm fuse, the zygote will have the correct number of
chromosomes.
5. The mitotic spindle moves chromosomes during cell division. It
appears in prophase and disappears after telophase.
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SAFETY PRECAUTIONS
Review Before Starting Any Experiment
Each experiment includes special safety precautions that are relevant to
that particular project. These do not include all the basic safety
precautions that are necessary whenever you are working on a scientific
experiment. For this reason, it is absolutely necessary that you read and
remain mindful of the General Safety Precautions that follow this note.
Experimental science can be dangerous, and good laboratory procedure
always includes following basic safety rules. Things can happen very
quickly while you are performing an experiment. Materials can spill, break,
or even catch fire. There will be no time after the fact to protect yourself.
Always prepare for unexpected dangers by following the basic safety
guidelines during the entire experiment, whether or not something seems
dangerous to you at a given moment.
We have been quite sparing in prescribing safety precautions for the
individual experiments. For one reason, we want you to take very seriously
every safety precaution that is printed in this book. If you see it written
here, you can be sure that it is here because it is absolutely critical.
Read the safety precautions here and at the beginning of each experiment
before performing each lab activity. It is difficult to remember a long set of
general rules. By rereading these general precautions every time you set
up an experiment, you will be reminding yourself that lab safety is critically
important. In addition, use your good judgment and pay close attention
when performing potentially dangerous procedures. Just because the
book does not say “Be careful with hot liquids” or “Don’t cut yourself with
a knife” does not mean that you can be careless when boiling water or
using knives. Notes in the text are special precautions to which you must
pay special attention.
GENERAL SAFETY PRECAUTIONS
Accidents caused by carelessness, haste, insufficient knowledge, or
taking an unnecessary risk can be avoided by practicing safety
procedures and being alert while conducting experiments. Be sure to
check the individual experiments in this book for additional safety
regulations and adult supervision requirements. Anytime you are working
with an electrical current, it becomes possible to shock yourself on
exposed wires. If you will be working in a lab, do not work alone. When
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SAFETY PRECAUTIONS
2
you are working off-site, keep in groups with a minimum of three students
per group, and follow school rules and state legal requirements for the
number of supervisors required. Ask an adult supervisor with basic
training in first aid to carry a small first-aid kit. Make sure everyone knows
where this person will be during the experiment.
PREPARING
• Clear all surfaces before beginning experiments.
• Read the instructions before you start.
• Know the hazards of the experiments and anticipate dangers.
PROTECTING YOURSELF
• Follow the directions step by step.
• Do only one experiment at a time.
• Locate exits, fire blanket and extinguisher, master gas and electricity
shut-offs, eyewash, and first-aid kit.
• Make sure there is adequate ventilation.
• Do not horseplay.
• Keep floor and workspace neat, clean, and dry.
• Clean up spills immediately.
• If glassware breaks, do not clean it up by yourself; ask for teacher
assistance.
• Tie back long hair.
• Never eat, drink, or smoke in the laboratory or workspace.
• Do not eat or drink any substances tested unless expressly permitted
to do so by a knowledgeable adult.
USING EQUIPMENT WITH CARE
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Set up apparatus far from the edge of the desk.
Use knives or other sharp, pointed instruments with care.
Pull plugs, not cards, when removing electrical plugs.
Clean glassware before and after use.
Check glassware for scratches, cracks, and sharp edges.
Let your teacher know about broken glassware immediately.
Do no use reflected sunlight to illuminate your microscope.
Do not touch metal conductors.
Use alcohol-filled thermometers, not mercury-filled thermometers.
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SAFETY PRECAUTIONS
3
USING CHEMICALS
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Never taste or inhale chemicals
Label all bottles and apparatus containing chemicals
Read labels carefully.
Avoid chemical contact with skin and eyes (wear safety glasses, lab
apron, and gloves).
• Do not touch chemical solutions.
• Wash hands before and after using solutions.
• Wipe up spills thoroughly.
HEATING SUBSTANCES
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Wear safety glasses, apron, and gloves when boiling water.
Keep your face away from test tubes and beakers.
Use test tubes, beakers, and other glassware made of Pyrex™ glass.
Never leave apparatus unattended.
Use safety tongs and heat-resistant gloves.
If your laboratory does not have heat-proof workbenches, put your
Bunsen burner on a heat-proof mat before lighting it.
Take care when lighting your Bunsen burner; light it with the airhole
closed, and use a Bunsen burner lighter rather than wooden matches.
Turn off hot plates, Bunsen burners, and gas when you are done.
Keep flammable substances away from flames and other sources of
heat.
Have a fire extinguisher on hand.
FINISHING UP
• Thoroughly clean your work area and any glassware used.
• Wash your hands.
• Be careful not to return chemicals or contaminated reagents to the
wrong containers.
• Do not dispose of materials in the sink unless instructed to do so.
• Clean up all residues and put in proper containers for disposal.
• Dispose of all chemicals according to all local, state, and federal laws.
BE SAFETY CONSCIOUS AT ALL TIMES!
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