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Cell Growth and Division
Mrs. Nell’s Life Science Class
Cells
• Your body cells are constantly growing, dividing, and dying.
This is true for animal cells and plant cells. Most of the life of
any cell is spent in a period of growth and development
called interphase. Cells in your body that no longer divide
(like nerve and muscle cells) are always in interphase.
Mitosis
Cells divide in two steps. First, the nucleus of the cell divides, and
then the cytoplasm divides. Mitosis is the process in which the
nucleus divides to form two identical nuclei. Each of the two nuclei
contains the same number and type of chromosomes as the original.
Steps of Animal Mitosis
Stage 1: Interphase
• Nucleus can be clearly seen.
• Chromosomes (structures in the
nucleus that contain DNA) cannot
be seen but are actively copying
themselves.
• When the cell is ready to divide
the chromosomes become visible.
They are thick and double
stranded and are held together
at a region called a centromere.
Steps of Animal Mitosis
Stage 2: Prophase
• Chromosomes can now be
clearly seen.
• Nucleolus and nuclear
membrane fade and
disappear.
• Centrioles (cylinder shaped
organelles found in the
nucleus of a cell) move to
opposite ends of the cell.
• Between the centrioles,
spindle fibers begin to stretch
across the cell.
Steps of Animal Mitosis
Stage 3: Metaphase
• Double-stranded
chromosomes line up
across the center of the
cell.
• Each centromere attaches
to a spindle fiber.
Steps of Animal Mitosis
Stage 4: Anaphase
• Centromeres divide.
• Two strands of each
chromosome separate.
• Separate strands move away
from each other toward
opposite ends of the cell.
(Each ‘daughter cell’ now has
an identical set of genes)
Steps of Animal Mitosis
Stage 5: Telophase
• Centrioles and spindle
fibers start to disappear.
• Chromosomes stretch
out and become harder
to see.
• Nuclear membrane
forms around each
mass of chromosomes.
• New nucleolus appears
in each new nucleus.
Cell Division- Animal Cells
• Once the nucleus has divided, the cytoplasm also
separates and two whole new cells are formed.
• In animal cells, the cytoplasm pinches in to form the new
cells, then the cycle starts all over again.
Cell Division- Plant Cells
• Plant cells have rigid cell walls
and do not pinch apart as
animal cells do.
• In plant cells a cell plate forms
between the two new nuclei.
New cell walls form along the
cell plate.
• Plant cells do not have
centrioles, but they do have
spindle fibers during mitosis.
Results of Mitosis
• Remember- mitosis is the
division of a nucleus.
• Mitosis produces two new
nuclei that have the same
number of chromosomes as
the original nucleus (human
body cells have 46
chromosomes… new body
cells will have 46
chromosomes as well).
Websites to See on Mitosis
http://highered.mcgraw-hill.com/sites/0073031216/student_view0/exercise13/mitosis_movie.html
Websites to See on Mitosis
Asexual Reproduction
• Your body forms two types of cells- body cells and sex
cells.
• Sex cells are the egg or sperm in the reproductive
organs.
• In asexual reproduction new organisms are produced
from one parent.
• Offspring produced by asexual reproduction have DNA
identical to the DNA of the parent organism.
Examples of Asexual Reproduction
Planaria regenerating
Yeast budding
Hydra budding
Budding: asexual reproduction in which a new organism grows from the body
of the parent organism
Regeneration: asexual reproduction in which an organism repairs damaged or
lost body parts
Fission: asexual reproduction in which organism divides into two equal parts
Examples of Asexual Reproduction (II)
Newt limb regeneration
Sponge regeneration
Bacteria fission
Strawberry plant runner
Sea star regeneration
Spider plant runner
Sexual Reproduction and Meiosis
• In sexual reproduction a new organism is
produced when sex cells from two parents
combine.
• The sex cell from the male parent is called the
sperm.
• The sex cell from the female parent is called the
egg.
• Meiosis is the process of nuclear division that
produces sex cells (takes place in reproductive
organs of both plants and animals).
Importance of Sex Cells
• Human sex cells have 23 chromosomes, not 23 pairs of
chromosomes. Sex cells are haploid (contain only one chromosome
from each pair).
• A cell that has two of every kind of chromosome is diploid. Body cells
which have 23 pairs of chromosomes are diploid.
Fertilization
• The joining of an egg and a
sperm is called
fertilization.
• The cell that forms in
fertilization is called a
zygote.
• A zygote has 46
chromosomes and is,
therefore, diploid.
Meiosis
• In meiosis there are two divisions of the nucleus,
meiosis I and meiosis II.
Meiosis I
• Prophase I
• double-stranded
chromosomes and spindle
fibers appear.
• Nuclear membrane and
nucleolus disappear.
• Like chromosomes come
together in matching pairs.
Meiosis I
• Metaphase I
• Pairs of chromosomes line
up in the center of the cell.
• Centromeres attach to
spindle fibers.
Meiosis I
• Anaphase I
• Double-stranded
chromosomes separate.
• Chromosomes are pulled
to opposite ends of the
cell.
Meiosis I
• Telophase I
• Cytoplasm divides and
two cells form.
• Each chromosome is still
double-stranded.
Meiosis II
• Prophase II
• Double-stranded
chromosomes and
spindle fibers reappear
in each new cell.
Meiosis II
• Metaphase II
• Double-stranded
chromosomes move to
center of cell.
• Centromeres attach to
spindle fibers.
Meiosis II
• Anaphase II
• Centromere divides.
• Two strands of each
chromosome separate
and move to opposite
ends of the cell.
Meiosis II
• Telophase II
• Spindle fibers disappear.
• Nuclear membrane forms
around the chromosomes at
each end of the cell.
• Each nucleus contains half the
number of chromosomes that
were in the original nucleus.
(23 single-stranded
chromosomes for human body
cells).
End Product
Comparing Mitosis and Meiosis
Feature
Mitosis
Meiosis
What type of cell
Body cell
Sex cell
Beginning cell
Diploid
Diploid
Number of cells
produced
Two
Four
End-product cell
Diploid
Haploid
Number of
chromosomes
produced
Same as parent- 46
Half the parent cell
number- 23
Image Bibliography
http://sylva.for.ulaval.ca/foret/mitose/interpro.jpeg
http://www.bmb.psu.edu/courses/biotc489/notes/prophase.jpg
http://www2.marianopolis.edu/BIO-NYA/cell%20_division/anaphase.jpg
http://virtual.yosemite.cc.ca.us/randerson/Lynn's%20Bioslides/88.jpg
http://www.bmb.psu.edu/courses/biotc489/notes/telophas.jpg
http://www.microscopy-uk.org.uk/mag/imgaug99/whole.jpg
http://bio.winona.msus.edu/berg/IMAGES/cytokinP.gif
http://ad2004.com/Biblecodes/matimages/Chromosome1.gif
http://www3.ac-clermont.fr/10-15/ressources/sciences/experimentation/regeneration.jpg
http://www.evzonemusic.com/sponges.jpg
http://zom.free.fr/images/sea/sea_star.JPG
http://www.karlloren.com/biopsy/images/TEM-Fission_rod.jpg
http://strawberry.ifas.ufl.edu/runnering%20plant%202.jpg
http://www.vetmed.iastate.edu/departments/vdpam/swine/basics/anatomy/repro/labels/AI%20sperm%20normal%20label.JPG
http://cgee.hamline.edu/see/crs_and_concept/cycle_ovum.jpg
http://imiloa.wcc.hawaii.edu/krupp/BIOL101/present/lectur14/img005.jpg
http://sprott.physics.wisc.edu/pickover/zygote.jpg
http://genetics.gsk.com/graphics/meiosis.gif
http://mil.citrus.cc.ca.us/cat2courses/bio104/ChapterNotes/images/ch9/0171cl.jpg