Biology Cell division and stem cells

• Genetic information


  Found in the nucleus of each body cell
• Chromosome


  A linear arrangement of genes
• Chromosomes


  • Normally found in pairs in the nucleus
• In humans, there are 46 chromosomes in each body cell (normally found as 23 pairs)
• Gene


  A section of DNA located on chromosomes, also normally found in pairs in the nucleus
• DNA


  The chemical that genes and chromosomes are made up of
• Genes


  Control specific characteristics in the body
• Mitosis


  One type of cell division
• Mitosis

  1. All the chromosomes and genes in the mother cell are copied

  2. The cell divides to produce two daughter cells
• Daughter cells from mitosis

  • Genetically identical to each other, and to the mother cell
  • The number of chromosomes stays the same
• If mitosis is uncontrolled


  Cancer can occur
• Purpose of mitosis


  When an organism grows, replaces worn out cells, or repairs damaged cells
• Meiosis


  A second type of cell division
• Meiosis


  Takes place to produce gametes
• Gametes


  • Sperm
  • Eggs (in animals)
  • Pollen
  • Eggs (in flowering plants)
• Meiosis


  1. All the chromosomes and genes in the mother cell are copied

  2. The cell divides twice to form four gametes

  3. Each gamete has half the number of chromosomes of the original mother cell
• All gametes are genetically different from each other - they show variation
• Stem cell


  An undifferentiated cell that can develop into a specialised cell
• Stem cells


  • Could be used to replace cells that have been damaged or destroyed
  • For example, cases of spinal cord or brain injury which have led to paralysis
• Meristem


  Regions in plants where stem cells are found
• Meristem cells


  • Can differentiate to produce all types of plant cells at any time during the life of the plant
  • The main meristems are close to the tip of the shoot, and the tip of the root
• Embryonic stem cells


  Can differentiate into a wider range of cell types
• Best source of embryonic stem cells


  Five-day-old embryo
• Embryonic stem cells are often unused embryos from IVF treatment
• Many people object to the use of embryos in this way


  A potential life (the embryo) is destroyed
• Adult stem cells


  Can be taken from several areas of the body, such as the bone marrow
• Benefits of using your own stem cells


  • No rejection
  • No need to find a donor
  • No need for tissue typing
• Main disadvantage of adult stem cells


  They will differentiate into a narrower range of cell types