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Why do cells divide?  Growth  Repair  Replace dead cells.

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Presentation on theme: "Why do cells divide?  Growth  Repair  Replace dead cells."— Presentation transcript:

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2 Why do cells divide?  Growth  Repair  Replace dead cells

3 What cells divide often?  Skin  Stomach lining  Red Blood cells  Embryo  Plant roots  Hair  Nails

4 What cells rarely/never divide?  Nervous System  Liver

5 Why do we age?  Eventually cells stop being replaced  “Apoptosis”  Cell death  “We die because out cells die.”  William R. Clark

6 “C” Terms  Chromosomes  Long threads of genetic material  Found in nucleus  Chromatid  One side of a duplicated chromosome

7 “C” Terms  Centromere  Structures that hold sister chromatids together  NOTE  2 sister chromatids = 1 duplicated chromosome

8 “C” Terms  Chromatin  DNA tnagled around a histone (a protein)  Condensed chromatin = chromosome

9 Huh? B. Chromatin A. DNA histone C. Duplicated chromosome

10 “C” Terms  Centrioles  Small protein bodies  In cytoplasm  Animal cells only

11 Cell Division in a Nutshell  Before:  Chromosome duplicates = 2 sister chromatids  During:  Sister chromatids separate  After:  2 “daughter” cells  Genetically identical

12 Cell Cycle  Mitotic phase  10%  Interphase  90%

13 Interphase  Made up of three phases:  G 1, S, G 2  What happens?  Things necessary to divide

14 Interphase  G 1 Phase  Cell Growth  8-10 hours  S Phase  DNA replication  Chromosome replication  6-8 hours  G 2 Phase  More Cell Growth  Centriole replication  4-6 hours

15 Mitotic Phase  Mitosis  Division of nucleus (chromosomes)  Occurs after interphase  Cytokinesis  Division of cytoplasm  Creates 2 daughter cells  Occurs at the end of mitosis

16 Mitosis Phases  Interphase  Prophase  Prometaphase  Metaphase  Anaphase  Telophase

17 Task  Draw a diagram of mitosis  Label 6 phases & give each a short description

18 Interphase  “Resting Phase”  Cell NOT dividing  Precedes mitosis  Prepares cell for division  How?

19 Early Prophase  Centrioles:  Make spindle fibres  Move towards opposite plates  Chromosomes now visible

20 Late Prophase  Centrioles reach poles  Nuclear membrane (envelope) & nucleolus start to disappear

21 Metaphase  Spindle fibres attach to centromeres  Duplicate chromosomes line up at equator  Guided by spindle fibers

22 Anaphase  Spindle fibers retract  Pull sister chromatids apart  Towards opposite polls

23 Telophase  Chromatin reappears  Nuclear membrane & nucleolus reappear  Cytokinesis occurs  Result  Two daughter cells

24 What phases do you see? A D B C

25 Cytokinesis  Why would it occur differently in animal and plant cells?  Plant cells have a rigid cell wall!

26 Cytokinesis Animal Cells Plant Cells  Cell membrane pinches inward  Creates cleavagefurrow  Think:  Pull a string around a balloon  Cell Plate forms between two new nuclei  Becomes cell wall

27 Cytokinesis

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29 Plant vs. Animal – Another Difference?  Centrioles not present in plant cells  What makes spindle fibers in plant cells?  Form from cytoskeleton

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32 Concept Map


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