Cell division, stem cells

• Stem cell


  Undifferentiated cell that can differentiate into one or more specialised cell types
• Adult stem cells


  Stem cells from adults that can only differentiate into certain specialised cells
• Where adult stem cells are found

  Bone marrow
• Embryonic stem cells


  Stem cells from embryos that can differentiate into any specialised cell
• Where embryonic stem cells are found

  Early human embryos (usually from spare embryos from fertility clinics)
• Therapeutic cloning


  Patient's cells are used to create an early embryo clone of themselves - stem cells from the embryo can then be used to treat the patient's medical conditions
• Advantages of therapeutic cloning

  • Stem cells from the embryo are not rejected when transplanted because they have the same genes as the patient
  • Fewer ethical issues as obtained from adults who can consent to their use
• Advantages of using adult stem cells

  • Fewer ethical issues as obtained from adults who can consent to their use
• Disadvantages of using adult stem cells

  • Can take a long time for a suitable donor to be found
  • Can only differentiate into some specialised cell types, so treat fewer diseases
• Advantages of using embryonic stem cells

  • Can differentiate into any specialised cell, so can be used to treat many diseases
  • Easier to obtain as they are found in spare embryos from fertility clinics
• Disadvantages of using embryonic stem cells

  • Ethical issues surrounding their use, as every embryo is a potential life
  • Potential risks involved with treatments, such as transfer of viral infections
• Plant meristems


  Area where rapid cell division occurs in the tips of roots and shoots
• Advantages of using plant meristems to clone plants

  • Rare species can be cloned to protect them from extinction
  • Plants with special features (e.g, disease resistance) can be cloned to produce many copies
• Disadvantages of using plant meristems to clone plants

  • No genetic variation, so, for example, an entire cloned crop could be destroyed by a disease
• Cell division by mitosis

  Body cells divide to form two identical daughter cells
• Purpose of mitosis


  Growth and repair of cells, and asexual reproduction
• First stage of the cell cycle

  Cell grows bigger, chromosomes duplicate, number of sub-cellular structures (eg, ribosomes and mitochondria) increases
• Mitosis


  One set of chromosomes is pulled to each end of the cell and the nucleus divides
• Third stage of the cell cycle

  The cytoplasm and cell membrane divide, forming two identical daughter cells