Transcript 7th Science Chapter 10.1

7th Science Chapter 10.1
Cell Division and Mitosis
Cell Division
• 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
• 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
• A living organisms life cycle
– 1. organisms formation
– 2. growth and development
– 3. death
Cell Cycle
• The cell cycle is a series of events that
take place from one cell division to the
next.
– Cell cycles are not the same for all
cells.
– Ex. – Bean plant cells take about 19
hours to complete and an animals
embryo cell completes its cycle in
less than 20 minutes.
Cell Cycle
• In humans, cells needed for repair,
replacement, or growth, like skin and
bone cells, constantly repeat the cycle.
Interphase
• 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
• 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.
– The nucleus divides and then
cytoplasm separates to form two new
cells.
Mitosis
• Mitosis – process in which the nucleus
divides in cells to form two identical
nuclei.
• Mitosis is a series of phases or steps.
Mitosis
• Steps of Mitosis
– 1. Prophase
– 2. Metaphase
– 3. Anaphase
– 4. Telophase
Mitosis
• 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
• The nucleus and nucleolus disintegrate
• Two small structures called centrioles
begin moving to opposite ends of the
cell.
– Between the centrioles, threadlike
spindle fibers begin to stretch across
the cell.
– Plant cells also form spindle fibers
but do not have centrioles.
Metaphase
• 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
• 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
•
•
•
•
Spindle fibers disappear
Chromosomes begin to uncoil
New nucleus forms
Cytoplasm starts to divide
End of Mitosis
• 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
• The biggest thing to remember about
mitosis is that the nucleus divides and
it produces two new nuclei.
• Every cell in your body, except sex
cells, has a nucleus with 46
chromosomes.
Mitosis
• Each of the trillions of cells in your
body, except sex 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
• When you cut yourself, your wound
heals because of cell division.
Reproduction
• 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
• The new organism will have heredity
material that is identical to the parent.
• Organisms with eukaryotic cells,
asexually reproduce by cell division.
– Ex. – sweet potato growing in water
Reproduction
• 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
– 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.
– Ex. – sponges, planaria, sea stars