2.2

• Differentiation


  The process by which unspecialised cells become specialised to carry out specific functions
• Differentiation in animal cells

  • Cells become specialised very early in life
  • Different types of specialised cells have different sub-cellular structures to carry out specific functions
  • Most specialised cells can divide by mitosis but only form the same type of cell
  • Some differentiated cells cannot divide at all and are replaced by stem cells
  • Nerve cells do not divide once differentiated and are not replaced by stem cells
• Differentiation in plant cells

  • Undifferentiated cells are formed at active regions of the stems and roots (meristems)
  • Cells elongate and grow before finally differentiating
  • Plant cells can redifferentiate and become a different type of cell even after initial differentiation
• In a mature animal, little or no growth takes place. Cell division is almost entirely restricted to repair and replacement of damaged cells, and each differentiated cell type divides only to make more of the same cells.
• Cloning


  Producing identical offspring
• Producing plant clones


  1. Take a piece of leaf tissue

  2. Cells become unspecialised and undergo mitosis many times

  3. Each undifferentiated cell produces more cells by mitosis

  4. Cells then differentiate to form tissues like xylem, phloem, photosynthetic cells, and root hair cells to form a new plant identical to the original
• It is difficult to clone animals because most animal cells differentiate permanently early in embryo development and cannot change back.
• Artificial animal clones can only be made by cloning embryos, although adult cells can be used to make an embryo.
• Cells produced by mitosis are genetically identical to the parent cell.
• An adult human is around 37.2 trillion (3.72 x 10^13) cells bigger than the original fertilised ovum.