Stem Cells (OCR A level biology)

• Stem cells

  Undifferentiated cells capable of differentiating into most cell types. They can undergo cell division continuously and are a source of new cells for growth, tissue repair and development. All cells in animals and plants begin as stem cells.
• What happens once a cell has become specialised?

  It enters the Go phase of the cell cycle.
• Why must stem cell division be controlled?

  If there's a lack of division, tissues can't be replaced quickly enough. If there is too much division, this can lead to masses of cells eg. tumours.
• Stem cell potency


  Stem cell's ability to differentiate into different cell types.
• Topipotent


  Can differentiate into any type of cell. eg. zygote and the first 8 or 16 cells formed from mitosis, extra embryonic tissues eg. amniote.
• Pluripotent


  Can form all tissue types (not whole organisms) eg. early embryo
• Multipotent


  Can form a range of cells within a certain type of tissue. eg. hematopoietic stem cells in bone marrow.
• Replacing red blood cells


  All blood cells are derived from stem cells in the bone marrow. Due to the lack of organelles, erythrocytes only last 120 days so are constantly replaced
• Replacing white blood cells

  Neutrophils only live for 6 hours and are essential for the functioning of the immune system. Up to 1.6 billion are replaced for kg of body mass per hour.
• Sources of animal stem cells

  Embryonic stem cells and tissue (adult) stem cells
• Embryonic stem cells


  Topipotent but become pluripotent after 7 days.
• Tissue stem cells


  Multipotent. They are present throughout life and are found in specific areas eg. bone marrow.
• Sources of plant stem cells

  Meristematic tissue, vascular cambium
• Meristematic tissue


  Found wherever plant is growing eg. roots and shoots
• Vascular cambium


  Sandwiched between the xylem and phloem, allowing vascular tissue to grow throughout plants' life.
• Uses of stem cells- heart disease

  Heart attacks damage the heart, usually irreparably. Stem cells are used to repair damage. This has been tried experimentally with some success.
• Uses of stem cells- type 1 diabetes

  Their immune system destroys insulin producing cells (beta cells). Injecting stem cells has been done experimentally with some success.
• Uses of stem cells- Parkinson's disease


  The symptoms are caused by the death of dopamine producing cells in the brain. There is currently no cure- drugs can only slow the development. There is research into stem cells being used as a cure.
• Uses of stem cells- Alzheimer's disease


  Brain cells are destroyed as a result of a build up of proteins. Currently drugs can only alleviate the symptoms.
• Uses of stem cells- Macular degeneration


  Causes severe vision impairment. There are currently no treatments but trials are looking positive.
• Uses of stem cells- birth defects


  These are structural changes present at birth. This has been successfully treated in mice using stem cells.
• Uses of stem cells- spinal injuries


  Stem cells has restored some movements to the hind limbs of rats.
• Where do the embryos come from?

  Embryos left over from fertility treatments. Now scientists can create embryos just for use in the lab. Currently the embryo is destroyed in the process but technology is being developed to allow the removal without destroying the embryo.
• Ethical issues

  Religion, moral objections (believe it's murder), who owns the genetic material being used for research? This is slowing down research into stem cell treatments.
• Solutions to the ethical issues

  Umbilical cord stem cells- only multipotent/some pluripotent. Reprogramming adult stem cells- induced pluripotent stem cells (iPSCs)