Cell Division

• Chromosomes carry genetic information in a molecule called DNA.
• Stem cells are cells that have not undergone differentiation
• Each human body cell contains 46 chromosomes. These can be arranged into 23 pairs.
• What happens in stage 1 of the cell cycle?


  cell grows bigger, DNA replicates, organelles increase in number
• What happens in stage 2 of the cell cycle?

  • chromosomes line up in the middle
  • a set of chromosomes are pulled to each end of the cell
  • 2 nuclear membranes form
  • Nucleus divides
• What happens in stage 3 of the cell cycle?

  cytoplasm and cell membrane divide to form 2 identical daughter cells
• How to find out long a cell stays in a stage?


  length of time = observed number of cells in stage$\div$total number of cells observed
• Prokaryotic cells replicate by binary fission.
• What are advantages of adult stem cells?

  • relatively safe
  • fewer ethical issues
  • reliable
  • treats diseases
  • produces many cells
• What are disadvantages of adult stem cells ?

  • requires a donor/ risk of long wait time
  • can only treat certain diseases
  • painful
  • can be rejected by immune system
• What are disadvantage of embryonic stem cells ?

  • goes against ethical and religious beliefs as potential human life is destroyed
  • risk of viral infections
  • no enough research done
  • found only in embryos
• What are advantages of embryonic stem cells ?

  • can differentiate into any specialised cells - can treat many diseases
  • no donor needed
  • painless