Download A. Why is cell division important?

Table of Contents
Chapter: Cell Reproduction
Section 1: Cell Division and Mitosis
Section 2: Sexual Reproduction
and Meiosis
Section 3: DNA
Cell Division and Mitosis
1
A. Why is cell division important?
1. Many organisms start as just one cell.
That cell divides and becomes two, two
become four, four become eight, an so on.
2. Many-celled
organisms, including
you, grow because
cell division
increases the total
number of cells in an
organism.
Cell Division and Mitosis
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A. Why is cell division important?
3. Even after growth stops, cell division is still
important. Because the cells in your body
wear out and are replaced.
For example, your bone marrow produced
about six million red blood cells for wear out
red blood cells in your body.
4. Cell division is important to one-celled
organisms, too—it’s how they reproduce
themselves.
Cell Division and Mitosis
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B. The Cell Cycle
1. A living organism has a live cycle.
A life cycle begins
with the organism’s
formation, is
followed by growth
and development,
and finally ends in
death.
Individual cells also
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have life cycles.
Cell Division and Mitosis
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B. The Cell Cycle
2. The cell cycle is a series of events that takes
place from one cell division to the next.
3. The time is taken to complete a cell cycle is
not the same in all cells.
Cell Division and Mitosis
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C. What is the longest part of the
cell cycle?
1. For cells that have a nucleus, the longest part
of the cell cycle is a period of growth and
development called interphase.
2. Cells in your body that no longer divide,
such as nerve and muscle cells, are always
in interphase.
3. An actively dividing cell, such as a skin cell,
copies its hereditary material and prepares
for cell division during interphase.
Cell Division and Mitosis
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D. Interphase
1. Before a cell divides, a copy of the hereditary
material must be made so that each of the two
new cells will get a complete copy.
2. Each cell needs a complete set of hereditary
material to carry out life functions.
3. After interphase, cell
division begins. The
nucleus divides, and
then cytoplasm
separates to form two
new cells.
Cell Division and Mitosis
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E. Mitosis
1. Mitosis (mi TOH sus) is the process in which
the nucleus divides to form two identical
nuclei. Each new nucleus also is identical to
the original nucleus.
2. Mitosis is described as a series of phases, or
steps. The steps of mitosis in order are
named prophase, metaphase, anaphase, and
telophase.
Cell Division and Mitosis
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F. Steps of Mitosis
1. A chromosome is a structure in the nucleus
that contains hereditary material. During
interphase, each chromosome duplicates.
Cell Division and Mitosis
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F. Steps of Mitosis
2. When the nucleus is ready to divide, each
duplicated chromosome coils tightly into two
thickened, identical
strands called chromatids.
Cell Division and Mitosis
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F. Steps of Mitosis
3. During prophase, the chromatid pairs can
be seen. The nuclear membrane breaks apart.
Two small structures called centrioles (SEN
tree olz) move to opposite ends of the cell.
4. Between the centrioles,
threadlike spindle fibers begin
to stretch across the cell.
5. Animal cells have centrioles,
but plant cells do not.
Cell Division and Mitosis
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F. Steps of Mitosis
6. In metaphase, the pairs of chromatids line
up across the center of the cell.
The centromere of
each pair usually
becomes attached to
two spindle fibers—
one from each side
of the cell.
Cell Division and Mitosis
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F. Steps of Mitosis
7. In anaphase, each centromere divides. The
spindle fibers become shorter, and each
chromatid separates from its partner.
8. The separated
chromatids begin to
move to opposite ends
of the cell. They are
now called
chromosomes.
Cell Division and Mitosis
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F. Steps of Mitosis
9. The final step of
mitosis is telophase.
During telophase, the
spindle fibers start to
disappear. The
chromosomes start to
uncoil, and a new
nucleus forms.
Cell Division and Mitosis
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G. Division of the Cytoplasm
1. For most cells, after the nucleus has
divided, the cytoplasm separates and two
new cells are formed.
2. In animal cells, the cell
membrane pinches in
the middle, like a
balloon with a string
tightened around it, and
the cytoplasm divides.
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Cell Division and Mitosis
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G. Division of the Cytoplasm
3. In plant cells, the appearance of a cell plate
tells you that the cytoplasm is being divided.
4. New cell walls form along the cell plate,
and new cell membranes develop inside the
cell walls.
5. Following division of the cytoplasm, most
new cells begin the period of growth, or
interphase, again.
Cell Division and Mitosis
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G. Results of Mitosis
1. Every cell in your
body, except sex cells,
has a nucleus with 46
chromosomes—23
pairs.
2. Each of the trillions of
cells in your body,
except sex cells, has a
copy of the same
hereditary material.
Cell Division and Mitosis
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G. Results of Mitosis
3. Cell division allows growth and replaces
worn out or damaged cells.
4. If you cut yourself, the wound heals because
cell division replaces damaged cells.
5. Another way some organisms use cell
division is to produce new organisms.
Cell Division and Mitosis
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I. Asexual Reproduction
1. Reproduction is the process by which an
organism produces others of its same kind.
2. Among living organisms, there are two types
of reproduction—sexual and asexual.
3. Sexual reproduction usually requires two
organisms.
Cell Division and Mitosis
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I. Asexual Reproduction
4. In asexual reproduction,
a new organism
(sometimes more than
one) is produced from one
organism.
5. The new organism will
have hereditary material
identical to the hereditary
material of the parent
organism.
Cell Division and Mitosis
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J. Cellular Asexual Reproduction
1. Organisms with eukaryotic cells asexually
reproduce by cell division.
2. However, bacteria do not have a nucleus so
they can’t use mitosis. Instead, bacteria
reproduce asexually by fission.
3. During fission, an organism whose cells do
not contain a nucleus copies its genetic
material and then divides into two identical
organisms.
Cell Division and Mitosis
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K. Budding and Regeneration
1. Budding is a type of asexual reproduction
made possible because of cell division.
2. When the bud on the adult becomes large
enough, it breaks away to live on its own.
Cell Division and Mitosis
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Budding and Regeneration
3. Some organisms can regrow damaged or lost
body parts.
4. Regeneration is the process that uses cell
division to regrow body parts.
5. Sponges, planaria, sea
stars, and some other
organisms can use
regeneration for asexual
reproduction.
Section Check
1
Question 1
Many-celled organisms grow by _______.
Section Check
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Question 2
What is the longest part of the cell cycle?
Section Check
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Question 3
_______ is the process in which the nucleus
divides to form two identical nuclei.
End of Chapter Summary File