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7th Science Chapter 10.1
Cell Division and Mitosis
Cell Division
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All of us are made of trillions of cells
Many organisms begin as one cell
that divides and becomes two and
eventually 4-8-16 and so on
Many celled organisms (like us)
grow because cell division increases
the total number of cells
Cell Division
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Everyday billions of red blood cells
wear out and are replaced.
Cell division is important to one
celled organisms as well – its how
they reproduce themselves.
Cell Cycle
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A living organisms life cycle
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1. organisms formation
2. growth and development
3. death
Cell Cycle
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The cell cycle is a series of events
that take place from one cell
division to the next.
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Cell cycles are not the same for all
cells.
In humans, cells needed for repair,
replacement, or growth, like skin
and bone cells, constantly repeat
the cycle.
Interphase
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Most of the life of a eukaryotic cell
(cell with a nucleus) is spent in
interphase, which is a period of
growth.
An actively dividing cell, such as a
skin cell, copies its heredity material
and prepares for cell division during
interphase.
Interphase
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Before the cell divides, a copy of the
heredity material must be made so
that each of the two new cells will
have a complete copy.
After interphase, cell division
begins.
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The nucleus divides and then
cytoplasm separates to form two new
cells.
Mitosis
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Mitosis – process in which the
nucleus divides in cells to form two
identical nuclei.
Mitosis is a series of phases or
steps.
Mitosis
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Steps of Mitosis
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1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
Mitosis
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Chromosome – structure in the
nucleus that contains heredity
material.
During interphase, chromosomes
duplicate and when the nucleus is
ready to divide each duplicated
chromosome coils tightly into two
thickened, identical strands called
chromatids.
Prophase
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The nucleus and nucleolus
disintegrate
Two small structures called
centrioles begin moving to opposite
ends of the cell.
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Between the centrioles, threadlike
spindle fibers begin to stretch across
the cell.
Plant cells also form spindle fibers but
do not have centrioles.
Metaphase
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Pairs of chromatids line up across
the center of the cell
Centrioles are attached to spindle
fibers and they continue to move to
opposite ends of the cell and stretch
the spindle fibers.
Anaphase
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The chromatids break at the
centromere and begin to separate.
The centrioles continue to move to
opposite ends pulling the
chromosomes farther apart
The separated chromatids are now
called chromosomes.
Telophase
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Spindle fibers disappear
Chromosomes begin to uncoil
New nucleus forms
Cytoplasm starts to divide
End of Mitosis
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After the nucleus has divided, the
cytoplasm separates and two new
cells are formed.
During cytoplasm division in plant
cells, a cell plate forms and in
animal cells the cell membrane
pinches in the middle.
Mitosis
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The biggest thing to remember
about mitosis is that the nucleus
divides and it produces two new
nuclei.
Every cell in your body, except
reproductive cells, has a nucleus
with 46 chromosomes.
Mitosis
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Each of the trillions of cells in your
body, except reproductive cells, has
a copy of the same heredity
material.
Cell division allows growth and
replaces warn out or damaged cells
We are larger and have more cells
than a baby because of cell division.
Mitosis
• We are larger and have more cells
than a baby because of cell division
• When you cut yourself, your wound
heals because of cell division.
Reproduction
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There are two types of
reproduction, sexual and asexual
Sexual reproduction requires two
organisms and asexual requires one
organism
Asexual Reproduction – a new
organism is produced from one
organism.
Asexual Reproduction
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The new organism will have
heredity material that is identical to
the parent.
Organisms with eukaryotic cells,
asexually reproduce by cell division.
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Ex. – sweet potato growing in water
Reproduction
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Remember mitosis divides the
nucleus, so bacteria is without a
nucleus so they reproduce asexually
by fission.
Budding – type of asexual
reproduction, where a new
organism will begin to grow from
the body of a parent.
Reproduction
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When a bud becomes large enough, it
will break off and live on its own.
Regineration – is the process that
uses cell division to regrow body
parts.
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Ex. – sponges, planaria, sea stars