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Cell Division
Mitosis and Meiosis
Why Do Cells Divide?
Regrowth- Cells continue to divide to help an
organism or part of an organism grow
Repair- Some tissues must be repaired often
such as the lining of gut, white blood cells, skin
cells with a short lifespan, and cuts, scrapes or
burns of the skin.
Reproduction- Reproduction of the species
How do you become a
multicellular organism if you
started out as just ONE cell?
Cell Division
Cells multiply by dividing!
Cell
Division…
 Through cell division, a
single cell becomes two
cells. Those two cells
divide into four….
The beginning of the cell cycle…
 A cell grows
To full size
Produces structures it needs
 The cell then prepares for division
Cells make a copy of DNA in the nucleus (called
replication)
At the end of replication, the cell has two sets of DNA
that are identical
 The nucleus of the cell divides into two cells
(daughter cells)
A process called mitosis
Cell Cycle
The Cell Cycle in Words (copy this!)
Interphase
Cytokinesis
Cell grows, makes a copy of DNA.
Cell membrane pinches in two;
each daughter cell has same
number of identical
chromosomes.
Prophase
The Cell Cycle
Telophase
Chromosomes stretch out;
new nuclear envelope forms
around chromosomes.
Chromosomes and spindle
fibers form; nuclear envelope
breaks down.
Metaphase
Anaphase
Centromeres split;
chromatids separate and
move to opposite ends.
Chromosomes line up
across the center and
attach to a spindle fiber.
Length of the Cell Cycle
The 5 steps of Mitosis…
Step 1: InterphaseChromosomes are copied (# doubles)
Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome and
its copy (sister chromosome) change to sister
chromatids at end of this phase
The 5 steps of Mitosis…
Step 2: Prophase
Mitosis begins ( cell begins to divide)
Centrioles (or poles) appear and begin to move to
opposite ends of cell
Spindle fibers form between the poles
The 5 steps of Mitosis…
Step 3 Metaphase:
Chromatids (or pairs of chromosomes) attach to the
spindle fibers
The 5 steps of Mitosis…
Step 4 Anaphase
Chromatids (or pairs of chromosomes) separate
and begin to move to opposite ends of the cell
The 5 steps of Mitosis…
Step 5-Telophase:
Two new nuclei form
Chromosomes appear as chromatin (threads rather
than rods)
Mitosis ends
Cytokinesis
At the end of mitosis
Cell membrane moves inward to create two
daughter cells-each with its own nucleus with
identical chromosomes
Mitosis
One More Look at Mitosis
Watch the following clip for more
information on cells
Video Clip (stop clip at definition of Mitosis)
Meiosis
The process by which the number of
chromosomes is reduced by half to form sex
cells (sperms and eggs)
Chromosome pairs separate and are
distributed to two different cells.
The resulting sex cells have only half as many
chromosomes as the other cells in the organism.
Meiosis
 Requires two
divisions of the
nucleus
Meiosis I- (Just
like mitosis)
Meiosis II- two
daughter cells go
through a second
division of the
nucleus. (during
this process, there
is no chromosome
replication)
Meiosis II (after Meiosis I
which is Mitosis)
Meiosis II
(after Mitosis or Meiosis I)
Mitosis and Meiosis
Mitosis
Meiosis
•One division of the nucleus = 2
cells
•Two divisions of the nucleus = 4 cells (sex cells)
•Used for sexual reproduction
•Used for growth and repair
•Before Meiosis begins, Mitosis must first take
place (known as Meiosis I)
Summary:
Summary:
Drawing:
Drawing:
** Copy into spiral notebook (new page) and complete! **
Acrostic Poem
Choose “mitosis” or “meiosis”
Create an acrostic poem
Create an illustration that shows the science
concept using at least 4 colors
Write 3 to 5 sentences explaining how the
horizontal words and terms AND the illustration
represent the vertical word
Cancer is Uncontrolled Mitosis:
•Mitosis must be controlled, otherwise
growth will occur without limit (cancer)
•Mutations in control proteins can cause
cancer
Cancer Cells
Cancer is a disease in which cells grow and divide
uncontrollably, damaging the parts of the body around them.
Cancer
cells are
held
together.
Mutations
A mutation (from Latin word that means change) is any
change in a gene or chromosome.
Can cause a cell to produce an incorrect protein
during protein synthesis.
As a result, the organism’s trait, or phenotype,
may be different from what it normally would
have been.
Results of Mutations
If a mutation occurs in a sex cell, the
mutation can be passed on to an offspring
and affect the offspring’s phenotype.
If a mutation occurs in a body cell, the
mutation will not be passed on to the
organism’s offspring.
Effects of mutations
Introduce change in an organism (genetic
variation)
Can be harmful (reduces the organism’s chance for
survival and reproduction)
Can be helpful (improve an organism’s chance of survival
and reproduction)
Antibiotic resistance in bacteria
Can be neither harmful nor helpful