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Cell division.

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Presentation on theme: "Cell division."— Presentation transcript:

1 Cell division

2 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

3 As cells increase in size, the surface area-to-volume ratio decreases.

4 This holds true for any cell shape!

5 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

6 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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8 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.

9 The Cell cycle The cell cycle has 3 parts: Interphase, Mitosis, and Cytokinesis Mitosis has 4 phases.

10 The steps MITOSIS Interphase Prophase Metaphase Anaphase Telophase
Cytokineseis – division of the cytoplasm MITOSIS I – PMAT – C for short

11 interphase Centrioles Duplicated DNA Cell Membrane Nucleus

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14 PROPHASE Fragments of nuclear membrane

15 METAPHASE Mitotic Spindle

16 anaphase Daughter chromosomes

17 telophase

18 Cytokinesis – animal cells
Cleavage furrow

19 Cytokinesis in a human kidney cell

20 Cytokinesis – plant cells
Instead of “pinching”, a cell plate forms which separates the two new nuclei This cell plate becomes a new cell wall

21 Cell plate formation

22 The Cell Cycle

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