B2-Cell division

• Mitosis


  The process by which a cell divides into two or more cells
• Cell cycle


  The series of events that a cell goes through from the time it is formed until it divides into two cells
• Body cells contain 23 pairs of chromosomes
• Gametes have chromosomes that are not paired
• Chromosome


  Structures in the nucleus that carry genetic information
• Chromosomes carry a large number of genes that determine many of our features
• Animals and plants contain a very large number of cells
• Cell cycle including mitosis


  1. DNA replication

  2. Mitosis

  3. Cytoplasm and cell membrane division
• Mitosis


  • Copies one cell into two identical cells
  • Essential for growth and development of multicellular organisms
  • Takes place when an organism repairs itself
  • Happens during asexual reproduction
• Stem cell


  An undifferentiated cell which can give rise to more cells of the same type and can differentiate into other types of cells
• Fertilization


  1. Sperm cell joins with ovum

  2. Fertilized ovum undergoes mitosis

  3. Forms a ball of cells called an embryo

  4. Cells continue to undergo mitosis

  5. Cells begin to form specialized cells
• Differentiation


  The process where cells specialize
• Embryonic stem cells


  Undifferentiated cells in the early stage embryo that can differentiate into any type of body cell
• Adult stem cells


  Stem cells found in adult organisms that cannot differentiate into any other type of cell
• Adult stem cells


  • Bone marrow stem cells that differentiate into blood cells
• Bone marrow transplant


  1. Patient's bone marrow is destroyed

  2. Patient receives transplant of donor bone marrow

  3. Stem cells divide and form new bone marrow

  4. Stem cells differentiate and form blood cells
• Problems with bone marrow transplants


  • Donor must be compatible
  • Risk of viruses being passed from donor to patient
• Therapeutic cloning


  1. Embryo is produced with same genes as patient

  2. Stem cells from embryo can be transplanted into patient without rejection

  3. Stem cells can differentiate to replace malfunctioning cells
• Therapeutic cloning could be useful for a range of medical conditions
• Some people have ethical or religious objections to therapeutic cloning
• Plant stem cells


  • Found in meristem tissue at root tips and buds
  • Can differentiate into any type of plant tissue
• Using plant stem cells


  1. Clone rare plants to prevent extinction

  2. Produce cloned crop plants resistant to diseases