Transcript Cell Division - Warren County Public Schools

Animal, Plant & Soil Science
Lesson B2-2
Cell Division
Interest Approach
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Ask students if they have ever had a
cut or injury that has healed. Ask
students if they know how their body
created the new cells that healed the
injury. We know that we received half
of our genetic code from each parent.
Ask students if they can explain how
cells can grow, reproduce, and create
reproductive cells.
Objectives
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Define cell theory and examine the
importance of mitosis.
Identify and describe the five stages
of mitosis.
Identify and describe the stages of
meiosis I and II.
Objectives
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Analyze the role of meiosis in
spermatogenesis and oogenesis.
Compare and contrast mitosis and
meiosis.
Terms
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anaphase
centromere
chromatids
cytokinesis
gametes
haploid number
haploid cells
homologous
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interphase
meiosis
metaphase
mitosis
ova
prophase
spermatozoa
telophase
What is cell theory, and why
is mitosis important?
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Cell theory states that cells are the basic
structural unit of all living things.
This theory also states that cells are
created by other living cells through
cellular division.
Mitosis is a sequential process of cell
division.
What is cell theory, and why
is mitosis important?
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At the conclusion of mitosis, what was
formerly one cell becomes two.
This process is repeated over and over
during the life of the organism.
What is cell theory, and why
is mitosis important?
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A. Mitosis is cell division for growth and
repair.
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This process involves the division of cells
that make up the plant body, which consists
of the roots, stem, leaves, and flower parts.
What is cell theory, and why
is mitosis important?
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B. This process is continually occurring.
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It is extremely important because this is how
organisms grow and repair damaged parts.
Without mitosis, plant growth could not
occur.
What are the five stages of
mitosis?
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Mitosis is divided into five stages or
steps.
A. The first stage of mitosis is called
interphase.
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Interphase is thought of as the resting stage
for the cell.
During interphase, the cell is growing and
producing proteins and organelles that will
be needed for division.
What are the five stages of
mitosis?
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B. Prophase, the second
stage, is the stage of
chromosome replication.
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The chromosome contains
the genetic information for
the cell.
What are the five stages of
mitosis?
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C. Metaphase, the
third stage, involves
the chromosomes
(formed in prophase)
moving to the middle
of the cell.
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These chromosomes
line up along the
equator of the cell and
prepare to divide.
What are the five stages of
mitosis?
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D. In the fourth stage,
anaphase, the
chromosomes
separate and move to
opposite sides of the
cell.
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Shortening spindle
fibers separate the
chromosomes.
What are the five stages of
mitosis?
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E. In the final stage,
telophase, the nucleus
reforms and a membrane
appears between each
mass of chromosomes.
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This newly formed membrane divides the
cytoplasm.
Once this stage is completed, the two
separate cells begin to repeat the process.
What are the stages of
meiosis I and II?
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Meiosis occurs in two stages, meiosis I
and meiosis II, with each stage
containing four steps.
A. Meiosis I is very similar to mitosis.
The four steps of meiosis I are:
What are the stages of
meiosis I and II?
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1. In prophase I, thread-like fibers form.
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Homologous, or corresponding,
chromosome pairs are located together and
DNA, which was replicated at the end of
interphase, is present.
What are the stages of
meiosis I and II?
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2. Metaphase I is the step
during which chromosomes
align at the equator of the
cell, with the spindle fibers
attached from the centromere to the
poles of the cell.
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The centromere is the point at which two
chromatids are attached.
Chromatids are strands of identical DNA
that join to form a chromosome.
What are the stages of
meiosis I and II?
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3. In anaphase I, the
centromere does not
duplicate.
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The shortening spindle
fibers pull the paired
chromosomes into two pieces to the poles
of the cell.
This separated chromosome contains half
of the cell’s genetic information.
What are the stages of
meiosis I and II?
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4. The fourth and final step of meiosis I is
telophase I.
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In this step, the chromosomes are still
joined and contain the haploid number, or
half the original chromosome number.
Two daughter cells are produced when the
nucleus reforms.
What are the stages of
meiosis I and II?
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B. After the four steps of
meiosis I, meiosis II begins.
The four steps of meiosis II
are:
1. The first step is prophase II. In this
step, spindle fiber formation begins.
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The main difference between prophase I
and prophase II is that DNA does not
replicate before prophase II.
What are the stages of
meiosis I and II?
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2. Prophase II is followed by metaphase II.
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In metaphase II, chromatids align at the
equator of the cell with spindle fibers
attached.
What are the stages of
meiosis I and II?
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3. The duplication of the centromere
signals the beginning of anaphase II.
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This divides the chromosomes so that each
half is pulled to a pole by the spindle fibers.
What are the stages of
meiosis I and II?
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4. In telophase II, a cell membrane forms
between the developing nuclei.
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Cytokinesis, the division of the cytoplasm,
occurs, and four daughter cells are formed
containing the haploid number of
chromosomes.
What is the role of meiosis in
spermatogenesis and oogenesis?
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Meiosis is the division of cells in the
reproductive process.
A. Haploid cells are cells that are
produced as a result of meiosis.
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These cells have only single chromosomes
rather than a homologous, or matching,
pair.
These cells are known as gametes.
Male gametes are called spermatozoa.
Female gametes are known as ova.
What is the role of meiosis in
spermatogenesis and oogenesis?
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B. Meiosis is a very important and
necessary process.
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During this process, the sex cells for the
organism are produced.
Without these sex cells, the organism could
not reproduce.
If an organism cannot reproduce, the
species will become extinct.
How do the processes of
mitosis and meiosis differ?
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The cellular division processes of mitosis
and meiosis differ in several ways.
A. In mitosis, the division of the mother
cell results in two daughter cells,
whereas in meiosis the division of the
mother cell results in four daughter cells.
B. In mitosis, the mother cell can be
either haploid or diploid, whereas in
meiosis the mother cell is always diploid.
How do the processes of
mitosis and meiosis differ?
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C. In mitosis, the number of
chromosomes remains the same after
division, whereas in meiosis each
daughter cell contains half the original
chromosomes.
D. In mitosis, there is normally no pairing
of homologous chromosomes, whereas
in meiosis there is always pairing of all
homologous chromosomes.
How do the processes of
mitosis and meiosis differ?
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E. In mitosis, there is normally no
exchange of DNA between
chromosomes, whereas in meiosis there
is at least one exchange of DNA per pair
of homologous chromosomes.
F. In mitosis, the centromeres are split
during anaphase, whereas in meiosis the
centromeres do not split until anaphase
II.
How do the processes of
mitosis and meiosis differ?
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G. In mitosis, the daughter cells will be
genetically identical to the mother cell,
whereas in meiosis each daughter cell
contains only half the genetic information
of the mother cell (giving variation in
offspring).
Review
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What is cell theory, and why is mitosis
important?
What are the five stages of mitosis?
What are the stages of meiosis I and
II?
Review
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What is the role of meiosis in
spermatogenesis and oogenesis?
How do the processes of mitosis and
meiosis differ?