Cell Division

• Chromosomes

  • nucleus of a cell contains chromosomes made of DNA
  • Each chromosome carries hundreds to thousands of genes
  • different genes contain the code to make different proteins
  • In body cells chromosomes are found in pairs, one coming from each parent
• Mitosis and the Cell Cycle

    Cells go through a series of changes involving growth and division, called the cell cycle.

    One of the stages is mitosis, when the cell divides into two identical cells.

    Before a cell can divide, it needs to grow and increase the number of sub-cellular structures, such as ribosomes and mitochondria.

    The DNA then replicates to form two copies of each chromosome.
• During mitosis:

  1. One set of chromosomes is pulled to each end of the cell.
  2. The nucleus divides.
  3. The cytoplasm and cell membranes divide to form two identical cells.
• Stem Cells

  • Some cells are undifferentiated - they have not yet become specialised.
  •  They can divide to make different types of cells.They are called stem cells.
  • Stem cells are found in human embryos, in the umbilical cord of a new born baby, and in some organs and tissues.
  • Stem cells from human embryos are called embryonic stem cells and can make all types of cells.
  • Adult stem cells are found in some organs and tissues, e.g. bone marrow.
• Stem cells

  Cells that may be very useful in treating conditions where cells are damaged or not working properly
• Conditions stem cells may be useful for

  • Diabetes
  • Paralysis
• Therapeutic cloning


  A cloned embryo of the patient may be made and used as a source of stem cells
• Stem cells from cloned embryos

  • They will not be rejected by the patient's body, so they could be very useful in treating the patient
• Disadvantages of using stem cells from cloned embryos

  • Risks, such as the transfer of viral infection
  • Religious objections
• Meristems


  Special areas in plants where stem cells are found
• Meristems


  • Allow plants to make new cells for growth
• Cloning plants using stem cells

  The stem cells can be used to produce clones of plants quickly
• Reasons for cloning plants using stem cells

  • Rare species can be cloned to protect them from extinction