2.6.2(mitosis)

Describe 3 ways in which mitosis is significant

1. Asexual reproduction

2. Growth

3. Tissue repair

Give 4 examples of where mitosis is used in Asexual reproduction

• Single-celled organisms use mitosis to divide to produce new individuals (such as yeast, Amoeba and paramecium)

• Some plants use mitosis to form new plantlets other ends of stolons(runners) such as strawberries

• Some animals use Mitosis to asexually reproduce if there are no males

• Aphids may sometimes produce eggs that do not need fertilising using mitosis

What are the stages of mitosis

• PMAT:

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

Describe what happens during the Prophase

• The identical sister chromatids, now shorten and thicken as the DNA supercoils(Chromosomes condense)

• The nuclear envelope breaks down

• The centriole in animal cells divides and the 2 new daughter centrioles move to opposite poles of the cell

• Cytoskeleton protein(tubulin) threads from a spindle between these centrioles.

Describe what happens during the metaphase

• The sister chromatids attach to the spindle fibred at the equator region of the cell

• They attach by their centromeres

Describe what happens during the anaphase

• The centromere of each pair of chromatids splits

• Motor proteins, walking along the tubulin fibres, pull each sister chromatid of a pair, in opposite direction, towards opposite poles

• Because their centromere goes first, the chromatids, now called chromosomes assume a V shape

Describe what happens during the Telophase

• The separated chromosomes reach the poles

• A new nuclear envelope forms around each set of chromosomes

• The cell now contains 2 nuclei each genetically identical to each other and to the parent cell from which they arose

State where the centriole in the animal cells is normally found

• Within a region of cells called the centrosome

State what organelle forms the tubulin threads in plants

• The cytoplasm

Describe Cytokinesis in animal cells and plant cells

• Animal cells:

  • The plasma membrane folds inwards and forms a cleavage and the cells begin to separate at the periphery of the cell and moves inwards until 2 new identical daughter cells are formed

• Plant cells:

  • An end plate forms where the equator of the spindle was, and new plasma membrane and cellulose cell-wall material are laid down on each side along this end plate

  • Starts at he centre and grows outwards until 2 new identical daughter cells are formed