Cell Division

• A stem cell is an undifferentiated cell that can differentiate into one or more specialised cell types.
• Adult stem cells are stem cells from adults that can only differentiate into certain specialised cells.
• Adult stem cells can be found in bone marrow.
• Embryonic stem cells are stem cells from embryos that can differentiate into any specialised cell.
• Embryonic stem cells are found in early human embryos (usually from spare embryos from fertility clinics).
• Therapeutic cloning is when patient's cells are used to create an early embryo clone of themselves - stem cells from the embryo can then be used to treat the patient's medical conditions.
• Therapeutic cloning is good because stem cells from the embryo are not rejected when transplanted because they have the same genes as the patient.
• Adult stem cells are good because there are fewer ethical issues as obtained from adults who can consent to their use.
• Disadvantages of using adult stem cells:

  Can take a long time for a suitable donor to be found.

  Can only differentiate into some specialised cell types, so treat fewer diseases.
• Advantages of using embryonic stem cells:

  Can differentiate into any specialised cell, so can be used to treat many diseases.

  Easier to obtain as they are found in spare embryos from fertility clinics.
• Disadvantages of using embryonic stem cells:

  Ethical issues surrounding their use, as every embryo is a potential life.

  Potential risks involved with treatments, such as transfer of viral infections.
• Plant meristems are an area where rapid cell division occurs in the tips of roots and shoots.
• Advantages of using plant meristems to clone plants:

  Rare species can be cloned to protect them from extinction.

  Plants with special features (e.g. disease resistance) can be cloned to produce many copies.
• A disadvantage of using plant meristems to clone plants is there will be no genetic variation, so, for example, an entire cloned crop could be destroyed by a disease.
• Mitosis is a type of cell division where body cells divide to form two identical daughter cells.
• The purpose of mitosis is growth and repair of cells and asexual reproduction.
• In the first stage of the cell cycle, the cells grows bigger, chromosomes duplicate, number of sub-cellular structures (e.g. ribosomes and mitochondria) increases.
• During mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides.
• During the third stage of the cell cycle, the cytoplasm and cell membrane divide, forming two identical daughter cells.