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Cell division
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Why do cells need to divide?
The cell membrane is permeable to some substances (semi-permeable) and all nutrients and wastes must pass through it As cells grow (increased volume), the number of organelles increases – so they require more supplies: nutrients and oxygen As the cell gets bigger, the volume increases faster than the surface area of the membrane
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As cells increase in size, the surface area-to-volume ratio decreases.
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This holds true for any cell shape!
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At a certain size, there is not enough surface area for nutrients/wastes to cross that is required by the cell So a cell divides into smaller cells in order to allow enough surface area to suit its needs
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Functions of cell division
Growth – multi-cellular organisms can get larger Repair – help organisms heal (e.g.cut or broken bone) Reproduce – so organisms can produce offspring
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A cell cannot just break in two!
Why? There is only one nucleus! Which is not always in the middle of the cell The contents (chromosomes / DNA) are not organized for easy division Cell Division includes a multistep process called MITOSIS. The 1 cell before it divides is called the parent cell. The 2 new cells are called daughter cells.
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The Cell cycle The cell cycle has 3 parts: Interphase, Mitosis, and Cytokinesis Mitosis has 4 phases.
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The steps MITOSIS Interphase Prophase Metaphase Anaphase Telophase
Cytokineseis – division of the cytoplasm MITOSIS I – PMAT – C for short
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interphase Centrioles Duplicated DNA Cell Membrane Nucleus
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PROPHASE Fragments of nuclear membrane
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METAPHASE Mitotic Spindle
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anaphase Daughter chromosomes
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telophase
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Cytokinesis – animal cells
Cleavage furrow
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Cytokinesis in a human kidney cell
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Cytokinesis – plant cells
Instead of “pinching”, a cell plate forms which separates the two new nuclei This cell plate becomes a new cell wall
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Cell plate formation
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The Cell Cycle
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