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Cell Division: Cell Division: why? cells wear out & must be replaced organisms grow & so need more cells when? cells have different life spans Cell type Cell life span Stomach lining cells Sperm cells Platelets Skin epidermal cells days weeks Lymphocytes Red blood cells months Macrophages Pancreas cells Bone Cells years Cell Cycle: The process of a cell growing and preparing for cell division Phases of the Cell Cycle: G1 - (Growth Phase 1) cell grows larger cell organelles duplicate S - (Synthesis Phase) the DNA is duplicated G2 – (Growth Phase 2) the DNA is checked for errors cell is prepared for division M – Phase Mitosis a process to separate the DNA packaged in chromosomes into two identical cells Terms chromatin a mixture of DNA and proteins found in the interphase nucleus chromosome condensed chromatin chromatid one arm of a double-stranded chromosome centromere a structure that holds two sister chromatids together single-stranded chromosome a chromatid after it has been separated from its sister chromatid chromosome centromere chromatids Summary of the Phases of Mitosis: Prophase prepare Metaphase middle Anaphase separate Telophase finish Interphase between Prophase cell membrane cytoplasm 1. Chromosomes condense & become visible 2. Nuclear membrane breaks down 3. Spindle fibres connect the two centrioles 4. Centrioles separate & move to each pole of cell Metaphase 1. the centrioles are at the poles 2. the spindle fibres pull the centromeres into line 3. the double-stranded chromosomes align at the cell equator 4. the centromeres now divide Anaphase 1. the spindle fibres contract & pull the centromeres to the poles 2. the chromatids of the double-stranded chromosomes now separate 3. Now called single-stranded chromosomes they are pulled to opposite poles Telophase 1. the nuclear membrane reforms 2. the ss chromosomes now uncoil and will disappear Cytokinesis 3. The cell membrane pinches inward 4. The result is the separation of genetic material into two identical parts Interphase 1. The chromatin is uncoiled 2. The nuclear membrane is fully intact 3. Two almost identical cells are produced 4. The cell now starts to go through G1, S and G2 again Problems with mitosis What if a cell does not stop dividing? cancer Why is this a problem? cancer takes away things from normal cells cancer takes space cancer takes blood this means oxygen and nutrients Now let’s look at mitosis under the microscope After we learn some things about microscpes key parts of a microscope ocular lens course adjustment fine adjustment objective lens slide stage Rules for microscopes when on high power only use the fine adjustment to focus on low power, focus down and away from the objective lens with the course adjustment always use two hands to carry a microscope and do not swing it these microscopes are parafocal and so once they are in focus on low power, little adjustment is needed on medium or high power only move a slide on or off a microscope with it on low power Onion root tip Cells undergo mitosis in this section of the root tip