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CELL DIVISION Process by which cells multiply & divide HOW OFTEN DO CELLS DIVIDE? • Rate determined by function & environment – Skin, blood, digestive tract divide on regular basis – Heart & nerve cells rarely multiple/divide after initial formation REGULATING CELL GROWTH • Cells grow in number, NOT in size – Smaller cells more efficient – Easier take in nutrients & get rid of wastes • multiply & divide until they touch one another – Form solid layer – division stops PROBLEMS W/ CELL GROWTH • Uncontrolled cell growth – Cells continue to multiply & divide even when touching another cell – Form mass of cells/tissue called tumor • Cause of Cancer STRUCTURES • Chromatin – mass genetic material • Chromosome – X-shaped structure contains DNA • Chromatid – each ½ of chromosome • Centromere – center chromosome; holds chromatids together STRUCTURES • Centrioles – proteins in cytoplasm (form cytoskeleton) • Spindle fibers – threads attach to centromere & move chromosomes around the cell TYPES OF CELL DIVISION • MITOSIS – Division of somatic cells • body cell • Bone, blood, skin – Diploid cells (46) • 2 sets chromosomes – Produces 2 identical cells • MEIOSIS – Division of gametes • Reproductive cells • Egg & sperm – Haploid cells (23) • 1 set of chromosomes – Produces 4 different cells CELL CYCLE • INTERPHASE – Longest phase – Replication occurs • Chromosomes duplicate – Appearance • Chromosomes not visible • Mass threads called “chromatin” MITOSIS • PROPHASE - (PAIRING) – Chromosomes pair – Nuclear membrane begins to dissolve MITOSIS • METAPHASE – (middle) – Chromosomes lined up in middle cell – Nuclear membrane completely dissolved MITOSIS • ANAPHASE – (apart) – Centromere splits – Chromosomes move opposite sides of cell MITOSIS • TELOPHASE – (two) – Cell membrane pinches together – Nuclear membrane returns • Plants – Cell wall prevents cell pinching together – Form “cell plate” separates two cells CELL CYCLE • CYTOKINESIS – – – – Cyto – cytoplasm Kinesis – movement “cytoplasm splits” 2 identical copies of original cell CELL CYCLE PLANTS vs. ANIMALS Interphase PLANTS vs. ANIMALS Prophase PLANTS vs. ANIMALS Metaphase PLANTS vs. ANIMALS Anaphase PLANTS vs. ANIMALS Telophase