why do cells need to divide?
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Why do cells need to divide?. How do cells divide? What needs to happen to make an exact copy of this cell? . Does an organism grow because its cells get larger or because it increases the number of cells? What limits the size that a cell can reach? - PowerPoint PPT PresentationTRANSCRIPT
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Why do cells need to divide?
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How do cells divide? What needs to happen to make an exact copy of this cell?
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• Does an organism grow because its cells get larger or because it increases the number of cells?
• What limits the size that a cell can reach?• How does the surface area change when a large cell
divides into smaller cells that have the same total volume?
• Are cells dividing all the time?• Do all cells divide at the same rate?• What must duplicate/replicate before a cell divides?
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Types of Reproduction
• Asexual Reproduction
– Cloning of an individual cell
– Produce genetically identical offspring
– Occurs in bacteria, body cells
• Sexual Reproduction– Occurs when two
reproductive cells join– Make genetically diverse
cells since the offspring get traits from both parents
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VocabularyChromatin- long strand of
DNAChromatid- each strand of a
duplicated chromosomeCentromere- the area where
two chromatids are joined. Splits during anaphase.
Kinetochore- a protein on chromosomes where spindle fibers attach.
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Centrioles- tiny structures in the cytoplasm of animal cells that help organize the spindles. (2 centrioles =centrosome)
Spindle fiber- a fanlike microtubule structure that helps separate the chromatids
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• Spindle- a fanlike microtubule structure that helps separate the chromatids -composed of centrioles and spindle fibers
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Cell Cycle- Interphase• G1 – Cell Growth-increase in
size, routine functions (longest)
• S – DNA replication- Synthesis of new DNA/ chromosomes replicated
• G2- Preparing for Cell Division- replication of organelles, microtubules and other molecules for cell division
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M Phase (minutes to days)
• Mitosis– Prophase– Metaphase– Anaphase– Telophase
Pro=beforeMeta=afterAna=backTelo= end
• Cytokinesis– Division of the
cytoplasm and organelles
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Mitosis- phases
• Prophase– Chromosomes become
visible (coil)– nuclear membrane
dissolves – Spindle forms– Nucleolus disappears
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Prophase
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Metaphase
• Chromosomes line up along the equator
• Spindle fibers connect centromeres (of chromatids) to opposite poles
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Anaphase
• Centromeres divide• Chromosomes move
toward opposite poles– Each Sr. Chromatid is
pulled toward opposite pole
• Spindle fibers shorten
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Telophase
• Reverse of Prophase• Nuclear membrane
forms at each pole• Chromosomes uncoil• Spindle fibers dissolve• Cytokinesis begins
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Cytokinesis
• Cytoplasm divided in half
• Cell membrane pinched by a belt of protein threads or contractile ring
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Plant vs Animal Cell Division
Animals• Centrioles• Pinching or cleavage of cell
membrane
BothEqual sized offspring cellsIdentical copy of original cell’s
chromosomes
Plants• No centrioles• Vesicles fuse forming a cell
plate• A new cell wall forms on
either side of the cell plate
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Animal and Plant Cell Division
• http://iknow.net/cell_div_education.html
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• Prophase- a “pro” is #1• Metaphase- “M” middle• Anaphase- Away• Telephase – Two nuclei
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• http://glencoe.mcgraw-hill.com/sites/dl/free/0078802849/164155/00053413.html
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