B2 - Cell division

• Chromosome


  Structure in the nucleus of cells that carries genetic information
• Gene


  Small packet of information that controls a characteristic, or part of a characteristic, of the body
• DNA


  Unique molecule that makes up chromosomes
• Cell cycle


  1. Stage 1: Replication of DNA to form two copies of each chromosome and synthesis of new sub-cellular structures

  2. Stage 2: Mitosis (nucleus divides)

  3. Stage 3: Cell divides in two
• Cell division by mitosis produces two identical cells
• Cell division by mitosis is important for growth, repair, and development of multicellular organisms
• As an adult, cell death and mitosis keep more or less in balance


  When you get very old, mitosis slows down and you show the typical signs of ageing
• Growth


  Permanent increase in size as a result of cell division or cell enlargement
• Differentiation


  Process where cells become specialised to carry out a particular job
• In early development, animal and plant cells are unspecialised and can become any type of cell
• Differentiation in animal cells

  • Many types of cells become specialised very early in life
  • Specialised cells can only form the same type of cell
  • Some differentiated cells cannot divide at all
• Differentiation in plant cells

  • Most plant cells can differentiate throughout their lives
  • Undifferentiated cells are formed at active regions of the stems and roots (meristems)
  • Plant cells can redifferentiate if moved to a different part of the plant
• Producing identical offspring is known as cloning
• It is difficult to clone animals because most animal cells differentiate permanently early in embryo development
• Stem cells are undifferentiated cells that can give rise to many more cells of the same type
• Embryonic stem cells differentiate to form all the specialised cells of the body
• Adult stem cells remain in the body even when you are an adult
• Stem cell therapy may be used to treat medical conditions by replacing damaged or diseased cells
• Stem cells


  Undifferentiated cells that can give rise to many more cells of the same type
• Embryonic stem cells


  Inner cells of the embryo that differentiate to form all of the specialised cells of the body
• Adult stem cells


  Undifferentiated cells of an organism that can give rise to many more cells of the same type
• Sources of stem cells

  • Egg and sperm cell fusion
  • Bone marrow
  • Blood
  • Brain
  • Muscle
  • Liver
• Stem cells


  • Some tissues cannot replace damaged cells, so stem cells stay in these tissues and start dividing to replace the different types of damaged cell when needed
• In 1998, two scientists managed to culture human embryonic stem cells, capable of forming other types of cell</b>
• Scientists hope that the embryonic stem cells can be encouraged to grow into almost any different type of cell needed in the body
• Scientists have used nerve cells grown from embryonic stem cells to restore some movement to the legs of paralysed rats
• In 2010, the first trials testing the safety of injecting nerve cells grown from embryonic stem cells into the spinal cords of paralysed human patients were carried out
• In 2014, doctors transplanted embryonic stem cells into the eyes of people going blind as a result of macular degeneration
• Scientists are also using different types of stem cells to try and grow cells that are sensitive to blood sugar levels and produce the hormone insulin to help treat people with diabetes
• Scientists hope that stem cells may help overcome human infertility in the future
• Potential benefits of using stem cells

  • Treat paralysis
  • Treat diabetes
  • Treat heart disease
  • Treat blindness
  • Grow new organs
• Therapeutic cloning


  Using cells from an adult to produce a cloned early embryo of themselves to provide a source of perfectly matched embryonic stem cells
• Scientists have discovered stem cells in some of the tubes that connect the liver and the pancreas to the small intestine, and have managed to make these cells turn into the special insulin-producing cells in the pancreas that are so important for controlling blood sugar
• Scientists have transplanted these modified stem cells into diabetic mice, which worked to control the blood sugar levels
• In the UK, stem cell research is being carried out into potential therapies to treat spinal cord injuries, diabetes, heart damage, blindness, and damaged bone and cartilage
• Problems with embryonic stem cells

  • Ethical concerns about using a potential human being as a source of cells
  • Slow, difficult, expensive, and hard to control progress in developing therapies
  • Potential to cause cancer if used to treat patients
• Problems with adult stem cells

  • Risk of being infected with viruses and transferring infections to patients
  • Potential immune response if used to treat another unrelated person
• Scientists are finding ways of growing adult stem cells, although so far they have only managed to develop them into a limited range of cell types
• Adult stem cells avoid the controversial use of embryonic tissue and have been used successfully to treat some forms of heart disease and to grow some new organs such as tracheas
• Scientists have discovered stem cells in the umbilical cord blood of newborn babies and even in the amniotic fluid that surrounds the fetus as it grows, which may help to overcome some of the ethical concerns about the use of embryonic stem cells