cell division

• what are chromosomes?


  thread-like structures made of DNA and proteins that carry genetic information

  they are normally found in pairs
• what happens during the 1st stage of the cell cycle?

  -cell grows bigger; sub-cellular structures increase such as the ribosomes and mitochondria

  -DNA replicates (chromosomes are duplicated)
• what happens during the 2nd stage of the cell cycle? (mitosis )


  -a complete set of chromosomes is pulled to either end of the cell

  -the nucleus divides to form 2 nuclei
• what happens during the 3rd stage of the cell cycle?

  cytoplasm and cell membrane divide to form TWO genetically identical daughter cells
• what is the purpose of mitosis?

  -growth and repair of cells

  -asexual reproduction
• what is a stem cell?

  and undifferentiated cell that can differentiate into ONE or MORE specialised cell types
• what are adult stem cells?

  -stem cells from adults that can only differentiate into certain specialised cell types

  -they are found in the bone marrow
• what are embryonic stem cells?

  -stem cells from embryos that can differentiate into any specialised cell

  -they are found in early human embryos
• what are plant meristems?


  area where rapid cell division occurs in the tips of roots and shoots of a plant
• what is therapeutic cloning?

  patient's cells are used to create an early embryo clone of themselves - stem cells from the embryo can then be used to treat medical conditions
• give one advantage of therapeutic cloning:

  stem cells from the embryo won't be rejected when transplanted because they have the same genes as the patient
• give two disadvantages of therapeutic cloning:

  -ethical issues surrounding their use, as embryo's are a potential life

  -potential risks involving the treatment, such as transfer of viral infections
• give two advantages of using plant meristems to clone plants:

  -rare species can be cloned to protect from extinction

  -crop plants with special features such as disease resistance can be cloned to produce many copies
• give one disadvantage of using plant meristems to clone plants:

  no genetic variation; e.g. an entire cropped clone could be destroyed by a disease