Mitosis Section 9-2

What is it? The stage of the cell cycle during which the cell’s nucleus and nuclear material divide.

Why does is it occur? For an organism to grow larger To replace damaged cells As a means of reproducing in asexual organisms

How does it occur? It has 4 stages Prophase Metaphase Anaphase Telophase

Prophase Chromatin coils into visible chromosomes Nuclear membrane & nucleolus disappear Centrioles migrate to poles Spindle fibers begin to form between poles **Longest phase

Metaphase Chromosomes attach to spindle fibers at their centromeres Chromosomes line up across the equator of the cell

Anaphase Microtubules of the spindle shorten This separates the sister chromatids at their centromeres and moves them to opposite poles

Telophase Chromosomes arrive at the poles of the cell Chromosomes relax (unwind) Two new nuclear membranes form Nucleoli reappear Spindle breaks down

Cytokinesis What? When? Why? How? The division of the cytoplasm Following mitosis Why? To finish dividing the cells, to form two new cells How? It differs in plants and animals

Cytokinesis In Animals In Plants Microfilaments pinch in and form a cleavage furrow, which cut the cytoplasm into two A rigid cell plate is laid down between the two new nuclei Cell walls then form on either side of the cell plate

How does mitosis look? Mitosis Animation