5.1.3

Mitosis

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Stages of Mitosis

In mitosis, chromosomes go through interphase, prophase, metaphase, anaphase and telophase in order to produce genetically identical cells.

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Interphase

  • The cell prepares to divide.
  • DNA is replicated by semi-conservative replication. There is now two copies of every chromosome.
  • The organelles are also replicated.
  • More ATP is produced to be used in cell division.
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Prophase

  • The nuclear envelope and the nucleolus break down. Chromosomes are left floating in the cytoplasm.
  • The chromosomes coil more tightly and become shorter and fatter. They can be seen under a light microscope.
  • Small protein bundles called centrioles move to opposite poles of the cell.
  • Microtubules form the mitotic spindle between the centrioles.
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Metaphase

  • The chromosomes line up along the mid-line of the cell.
  • In metaphase, the chromosomes are maximally condensed.
  • They are attached to the spindle by the centromere.
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Anaphase

  • The chromosomes break into two chromatids. The sister chromatids separate at the centromere.
  • The spindles contract and pull the chromatids to each pole of the cell.
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Telophase

  • The chromatids reach the opposite poles and begin to decondense (unravel), becoming chromosomes again.
  • Nuclear envelopes form around the chromosomes so there are now two nuclei.
  • The cytoplasm splits and two daughter cells are formed. The daughter cells are identical to the original cell and to each other.
  • The cell cycle starts again.
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Way to remember the stages:

  • I (interphase).
  • Picked (prophase).
  • My (metaphase).
  • Apples (anaphase).
  • Today (telophase).

Preparation of Stained Squashes of Cells from Root Tips

Only a few cells are able to continue dividing in a multicellular organism. In plants, the growing tips of roots and shoots contain meristem tissue that can divide by mitosis for growth.

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1) Sample preparation

  • Wear gloves and use forceps to handle the tips.
  • Root tips must be sprouting (actively growing).
  • Place into 5 M hydrochloric acid.
  • After 5 minutes, rinse the tips in cold water in a watch glass.
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2) Cut the root tips

  • Using a sharp scalpel, cut root tips that are 2 mm long.
  • Place a root tip onto a microscope slide. Ensure the slide is clean to reduce the chances of artefacts.
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3) Staining

  • Carefully add 2-3 drops of stain and leave for two minutes.
  • Use a mounted needle to spread out the root tips into a thin layer.
  • Place a coverslip over the top of the tips.
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4) Squashing

  • Squash down by applying force to the cover slip. This could be with the flat end of a pencil, or the slide could be covered with a paper towel and pressed.
  • Force must be vertical or the cover slip may break and cause injury.
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5) Viewing the sample

  • Place the slide on the microscope stage using the lowest power lens.
  • Focus the lens on the sample using first the coarse control and then the fine control.
  • Move the slide to see the range of cells. The cells closer to the tip will be those more actively dividing.
  • On a lens power of 400x, it should be possible to clearly see the chromosomes in the dividing cells.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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