B2-Cell division

• Chromosomes


  Structures in the nucleus of a cell that contain the instructions for making proteins and new cells
• In human body cells the chromosomes are normally found in pairs
• The karyotype diagram shows the 23 chromosome pairs for a female human
• DNA


  Coiled strands that make up the chromosomes
• Gene


  A section of DNA that codes for a specific protein or characteristic
• Humans have around 24,000 genes and there are up to 2,000 genes in one human chromosome
• Cell division - Mitosis and the cell cycle

  1. Growth

  2. DNA synthesis

  3. Mitosis
• Mitosis occurs during growth and to repair or replace damaged cells
• Asexual reproduction occurs by mitosis in both plants and simple animals
• Stem cells


  Undifferentiated cells within an organism that can produce other stem cells and differentiate into many different types of cells
• Types of human stem cells

  • Embryo stem cells
  • Adult stem cells
• Embryos produced by therapeutic cloning have the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body
• There are risks of using stem cells such as transfer of viral infections
• Some people have objections to stem cell use for ethical and religious reasons
• In the UK, scientists can use embryos formed during fertility treatment for research, but only under very strict guidelines
• Plant stem cells


  Undifferentiated cells in structures called meristems that can then specialise into different cell types
• Uses of plant stem cells

  • Cloning rare species to protect from extinction
  • Cloning crop plants with special features such as disease resistance
• Crop plants that can be cloned

  • Potatoes
  • Strawberries
  • Dates