Notes on Mitosis Cell Division
1. Cells don’t get bigger and bigger as an organism grows. If a cell did it would die because it would not
be able to get enough materials in or out of the cell membrane.
2. Cell division allows cells to grow by increasing the total number of cells in an organism.
3. In cell division, one cell divides into two daughter cells. Each daughter cell is identical to the other
and to the parent cell.
4. All cells in your body reproduce this way except for your brain cells (they don’t reproduce) and your
sex cells (they do meiosis).
5. Cell division happens in the series of steps listed below. The sentence helps you remember the order.
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STEP 1: INTERPHASE – chromosomes are copied
a. In ANIMAL cells, two objects called centrioles show up outside the nucleus (their job is
to make the plant fibers for the spindle)
b. Chromosomes make EXACT copies of themselves, doubling the normal number
STEP 2: PROPHASE – mitosis begins now
a. Cell division is now called mitosis. Mitosis – process in which the nucleus of a cell divides
into two new nuclei and two new daughter cells begin to form
b. In ANIMAL cells, the two centrioles begin to move to opposite ends of the cell
forming a mesh-like spindle between them. The spindle acts as a “bridge” between the
opposite ends of the cell and is where the chromosomes will attach.
c. In PLANT cells, a spindle forms but without the help of the centrioles – the plant can
make plant fibers on its own
d. The nuclear membrane begins to break down and the nucleolus disappears
STEP 3: METAPHASE – chromosomes attach to the spindle
a. Chromosomes attach to the middle of the mesh-like spindle that runs the length of the cell
STEP 4: ANAPHASE – chromosomes begin to separate
a. Chromosomes separate from each other and begin to move to opposite ends of the cell
b. The cell membrane begins to lengthen and make the cell longer.
STEP 5: TELOPHASE – two new nuclei form
a. A nuclear membrane reforms around each set of chromosomes once they reach the ends of
the cell. The nucleolus reappears inside each newly formed nucleus.
c. The cell continues to lengthen and the cell membrane begins to pinch together in the middle.
d. The spindle and the centrioles (in the animal cell) begin to disappear.
e. Mitosis is complete.
STEP 6: CYTOKINESIS – two identical daughter cells form
a. Cytoplasm in the cell divides into two nearly equal parts when the cell membrane pinches
inward to form a figure 8 (the sides touch in the middle and two cells are now made).
b. Each part of the cytoplasm has a nucleus with identical chromosomes.
c. Cell membrane forms and two new daughter cells are made.
d. In PLANT cells, a cell wall also forms around each new daughter cell.