mitosis

Question 1

when is mitosis necessary

Answer 1

• when daughter cells have to be genetically identical (growth, replacement, repair of tissues in multicellular organisms)
• asexual reproduction

Question 2

what happens before mitosis in interphase

Answer 2

• DNA replicated
• each DNA molecule is converted into 2 identical DNA molecules called chromatids
• chromatids are joined at the centromere
• DNA combines with histones (proteins) to form a dense complex called chromatin

Question 3

prophase

Answer 3

• chromatin fibres (complex made of proteins, RNA,DNA) coils, condenses to form chromosomes which take up stain to become visible under light microscopes
• nucleolus disappears
• nuclear membrane breaks down
• microtubules form spindle-shaped structures linking poles
• fibres forming spindle necessary to move chromosomes into correct positions
• centrioles(bundles of protein that form spindle) migrate to poles
• spindle fibres attach to centromeres and move chromosomes to centre

Question 4

metaphase

Answer 4

• chromosomes are moved by spindle fibres to form the metaphase plate in the centre

Question 5

anaphase

Answer 5

• centromeres holding the pairs of chromatids divide
• chromatids separated and pulled to opposite poles by shortening spindle fibres
• ‘V’ shape due to being dragged through liquid cytosol

Question 6

telophase

Answer 6

• chromatids reached poles and are now called chromosomes
• 2 new sets of chromosomes assemble at each pole
• nuclear envelope reforms around them
• chromosomes uncoil, nucleolus is formed
• cytokinesis begins

Question 7

cytokinesis in animal cells

Answer 7

• cleavage furrow forms in middle of the cell
• cell surface membrane is pulled inwards by the cytoskeleton until it fuses in the middle

Question 8

cytokinesis in plant cells

Answer 8

• vesicles from Golgi apparatus assemble in the same place where the metaphase plate was formed
• vesicles fuse with each other and the cell surface membrane, dividing cell into 2
• new sections of cell wall form along sections of cell membrane