all cells arise from other cells

• how do eukaryotic cells replicate

  by mitosis/meiosis
• when does dna replication occur

  during interphase
• what are the 3 stages of the cell cycle and explain them

  -interphase, longest stage of cell cycle it’s when organelles double, the cell grows and then dna replicates

  -nuclear division, either mitosis or meiosis, creating 2 identical diploid cells or 4 genetically diff haploid cells mitosis creates cells with identical dna for growth and repair whereas meiosis creates gametes

  -cytokinesis, final stage, it is the division of cytoplasm to create new cells
• describe mitosis and what is the 4 key stages of mitosis

  prophase metaphase anaphase telophase

  one round of division

  genetically identical cells are made

  diploid cells made

  for growth and repair e.g clonal expansion of b cells
• what happens in prophase

  chromosomes condense and become visible

  nucleolus disappears

  in animal cells centrioles (which create spindle fibres) separate and move to opposite poles of cell plants have spindle fibres but no centrioles
• what happens in metaphase


  chromosomes align along equator of cell

  the spindle fibres released from poles attach to the centromere and chromatid
• what happens in anaphase

  spindle fibres pull centromere and chromatids towards opposite poles of cell

  this causes centromere to divide in 2 and the individual chromatids are pulled to each opposite pole

  this stage requires energy in form of atp
• what happens in telophase


  chromosomes are now at each pole of cell and become longer and thinner again

  the spindle fibres disintegrate and nucleus starts to reform

  final stage in cell cycle is when cytoplasm splits in 2 to create the 2 new genetically identical cells
• how is mitotic index calculated

  number of cells in mitosis in field of view/the total number of cells in view
• how are tumours formed

  -mutations in dna can lead to uncontrolled cell division

  -tumour formed if this results in mass of abnormal cells
• describe the 2 types of tumours

  -malignant tumour: cancerous, can spread

  -beningn tumour: non-cancerous
• suggest how cancer treatments control rate of cell division

  -some disrupt spindle fibre activity/formation

  so chromatids can be separated to oppposite poles

  -some prevents dna replication during interphase

  so cant make 2 copies of each chromosome
• describe how prokaryotic cells replicate

  -by binary fission

  1-replication of dna

  2-replication of plasmids

  3-division of cytoplasm to produce 2 daughter cells
• how do viruses replicate

  viruses do not undergo cell division as they are non-living

  1-attachment proteins attach to complementary receptors on host cell

  2-inject viral nucleic acid into host cell

  3-infected host cell replicates virus particles
• Define the term mutagenic agent.


  (A factor that) increases (the rate of) mutations;