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Why do Cells divide? • Growth of tissue • Cell repair • When you get a cut, where does the “new skin” come from? Cell Growth Rather than increase in size, cells must divide 1. To avoid DNA “overload:” Too many chromosomes would result in mutations 2. Keep exchange of materials through the cell membrane efficient: 3. How fast water, food, and oxygen are transported through the cell membrane depends on size and volume of the cell Surface Area to Volume Ratio • Cells favor a large Surface Area to volume ratio • The larger the surface area to volume ratio, the easier it is for the cell to transport materials in /out of the cell Size of Cells • Are adult and baby cells the same size? • Yes! • If mice cells are transplanted into an Elephant will they get bigger? • It depends, but yes! Controls in Cell Growth • Heart & nerve cells rarely divide once they are mature • Skin & digestive tract cells divide constantly to replace shedding or injured cells • This is programmed by the cell cycle which is controlled by DNA Mitosis • Process in which body cells divide to produce two genetically identical (daughter) cells is known as cell division. • It is asexual reproduction • Somatic Cells are all body cells • The only cells that do not do mitosis are sex cells produced in ovaries and testes. Mitosis terms • • • • • • Body cells have a total of 46 chromosomes They are paired so we have how many pair? 23! We represent 23 PAIRS as 2n If we had a total of only 23 it would be just n We call a total of 23 pairs Diploid, 2n Mitosis -Diagram of Chromosomes WS in packet Mitosis terms-Diagram of key cell terms during mitosis • • • • • • • Chromatin DNA that resembles a ball of yarn Centrioles -microtubules connect to … Centrosomes- region of microtubules Spindle Fibers -connect to chromosomes from Centrioles Poles -regions on end of cell regions. Spindle fibers connect to them Metaphase plate -area where chromosomes line up to divide Cleavage furrow -forms during Telephase. Where cytoplasm divides in the new cells. Pole The Cell Cycle • • There are 3 main stages 1. Interphase, the cell prepares for division. – A. 90% of the cells time is spent in this phase. CELL GROWTH PHASE 1. INTERPHASE http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cy cle_works.html Consists of 3 steps G1-The cell grows, making additional organelles & cytoplasm S-DNA replicates G2-Cell will make anything additional needed for division MITOSIS is Stage 2 and has 4 PHASES http://bcs.whfreeman.com/thelifewire/content/chp09/0902001.html • 2. Mitosis • The cell goes through 4 phases to reproduce a duplicate body cell • The phases are: • Prophase • Metaphase • Anaphase • Telophase Phases of Mitosis Early Prophase Late Prophase Stage 3 CYTOKINESIS • Creation of new cytoplasm that divides the cell into 2 new ones. Plant cell mitosis Animal cell mitosis Uncontrolled Cell Growth Teacher’s Domain Cell folder how cancer grows http://www.pbs.org/wgbh/nova/cancer/grow_flash.html • Cancer is a form of uncontrolled cell growth • The check points that the cell goes through may no longer work • If this occurs, then a tumor may form • It can be non-cancerous which is called benign • Or if it has spread metastasized