biology, B3

• Cell division by mitosis


  • Important for the growth and repair of replacement of skin cells
  • Used for asexual reproduction
• Cell cycle stages


  1. Stage 1: Cell grows bigger, DNA replicates (chromosomes duplicated), increase in number of sub-cellular structures

  2. Stage 2 (mitosis): A complete set of chromosomes is pulled to each end of the cell, the nucleus divides to form two nuclei

  3. Stage 3: Cytoplasm and cell membrane divide to form two identical daughter cells
• a stem cell is an undifferentiated cell that can divide to produce more cells of the same type of specialised cell
• stem cells can be cloned to produce a large number of identical cells
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
  • Plant meristem
• Adult stem cells


  • Found in specific parts of the body in adults and children, for example bone marrow
  • Can only differentiate into certain types of cells, for example stem cells in bone marrow can only differentiate into types of blood cells
• Embryonic stem cells


  • Found in early human embryos
  • Can differentiate into any type of specialised cell in the body, for example a nerve cell or a muscle cell
  • Often taken from spare embryos from fertility clinics
• Plant meristem


  • Found in the roots and shoots of plants
  • Can differentiate into all cell types, they can be used to create clones of whole plants
• Therapeutic cloning


  Cells from a patient's own body are used to create a cloned early embryo of themselves, and stem cells from this embryo can be used for medical treatments and growing new organs. These stem cells have the same genes as the patient, so are less likely to be rejected when transplanted.