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Chapter 8-2: Cell Reproduction Cell Reproduction 1 cell makes 2 identical cells Ex: make new skin cells when you get cut Chromosomes Contain DNA Carry out genetic material Chromatin—relaxed form of chromosomes Each chromosome 2 halves (sister chromatids) Held together by a centromere Chromosomes cont… Cell Cycle Sequence of growth and division in the cell Interphase First phase of the cell cycle Busiest phase of the cell cycle G1=First part of interphase Cell grows Interphase cont… S phase Second part of interphase Cell copies its chromosomes 46 to 92 Interphase cont… G2 phase Third and last part of interphase Cell copies all the other organelles Mitosis Last 4 phases of the cell cycle Dividing the nucleus of the cell Prophase Second phase of the cell cycle First and longest phase of mitosis Prophase cont… Chromatin becomes chromosomes Prophase cont… Nuclear envelope and nucleolus disappear Prophase cont… Centrioles (found only in animals) move to opposite ends of the cell Prophase cont… Spindle fibers grow out of centrioles Looks like string/rope Metaphase Phase 3 of the cell cycle Spindle fiber attaches to chromosomes at centromere Chromosomes line up in the middle of the cell Anaphase Phase 4 of the cell cycle Centromeres break apart Chromatids (each half of the chromosome) move to opposite ends of the cell Pulled apart by centrioles and spindle Telophase Phase 5 of the cell cycle Chromatids unwind into chromatin Spindle fibers and centrioles disappear Nucleolus and nuclear envelope reappear Cytokinesis Last step before cell divides Division of the cytoplasm 1—2—4—8—16 In Animals Plasma membrane pinches in to form two new cells Cytokinesis cont… In plants Cell plate forms between two cells Levels of Organization Atoms Molecules Cells Tissues---group of cells that perform same function (Ex: Smooth muscle) Organs—groups of tissues (Ex: Stomach) Organ systems—several organs that work together (Ex: Digestive system) Organism—all the organ systems together (Ex: Humans)