Cell division

• Chromosome


  A structure in the nucleus of a cell that carries a large number of genes made of DNA molecules
• Gene


  A section of DNA that codes for a specific protein
• DNA


  The molecule that carries the genetic instructions for the development and functioning of living organisms
• Chromosomes are made of DNA molecules
• Cell


  The basic unit of life, which can exist as an independent unit or as part of a multicellular organism
• Nucleus


  The control centre of a cell, containing the chromosomes
• In normal body cells, the chromosomes are normally found in pairs
• Stem cell


  An undifferentiated cell that can develop into one or more types of specialised cell
• Types of stem cells

  • Adult stem cells
  • Embryonic stem cells
• Adult stem cells


  • Can only differentiate to form certain types of cells
  • Found in specific parts of the body in adults and children, e.g. bone marrow
• Embryonic stem cells


  • Can differentiate into any type of specialised cell in the body
  • Obtained from early human embryos, often from fertility clinics
• Meristem


  Regions in the roots and shoots of plants where stem cells are found
• Cell cycle


  1. Cell grows bigger

  2. DNA replicates (chromosomes are duplicated)

  3. Increase in number of sub-cellular structures, such as ribosomes and mitochondria

  4. A complete set of chromosomes is pulled to each end of the cell

  5. The nucleus divides to form two nuclei
• Mitosis


  A type of cell division that produces two identical daughter cells
• Therapeutic cloning


  The process of creating a cloned early embryo from a patient's own cells, and using stem cells from this embryo for medical treatments and growing new organs
• Cloned plants are genetically identical, so a whole crop is at risk of being destroyed by a single disease or genetic defect
• Therapeutic cloning has fewer ethical issues as the stem cells are obtained from the patient's own cells
• Therapeutic cloning may be possible to grow whole replacement organs