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B2 Cell Division (Stem Cells (Plant Stem Cells (Clones of the mature plant…

- - - - from embryos
      - can differentiate into all types of body cells
      - an egg and sperm fuse to form a zygote
        
        this single cell divides into a ball of cells - the embryo
        
        inner layers of embryo are the stem cells
    - - from bone marrow
      - can differente into limited types of cells
        
        to replace cells that can't divide
      - small no. found in different body tissues
  - - - cells formed can be used to treat conditions
        
        Paralysis/ Spinal Chord Injury
        
        differentiating into new nerve cells
        
        Macular Degeneration
        
        restore lost vision in eye
        
        differentiating into light-sensitive cells in retina
        
        Diabetes
        
        producing cells sensitive to blood sugar and can produce insulin
        
        stem cells from tubes connecting liver and pancreas to small intestine
        
        Organs
        
        to be used in transplant surgery
        
        Infertility
        
        producing sperm/egg cells
        
        Dementia
        
        differentiating into nerve cells
        
        damaged bone and cartilage
        
        heart damage after heart attack
      - development of an embryo cloned from patient
        
        stem cells can be made to differentiate into many types of cells
        
        stem cells won't be rejected by patient
        
        cells genetically identical
  - - - prevent extinction of rare plant
      - produce genetically identical plants for scientific research
        
        removes unwanted variables
      - horticulture
        
        producing large no. of plants for sale
      - agriculture
        
        produce large no. of crop plants
        
        produce crop plants with special features
        
        disease resistant
  - - - too much money wasted on stem cell research (social and ethical)
    - - come from aborted embryos or spare embryos from fertility treatment
        
        embryo cannot give permission (ethical)
        
        interference with reproduction (religious)
        
        hard to control/ differentiate
        
        risk of cancer
        
        they divide rapidly
      - using embryonic stem cells found in the umbilical cord blood of babies or amniotic fluid of the fetus
        
        could overcome ethical objections
    - - could transmit viruses
      - trigger immune responses/ rejection
        
        if donor is unrelated
        
        take immunosuppressant drugs
      - painful so deters donors
- - - - chromosomes carry genes (made of DNA) which determine our features
      - in each pair, one chromosome is inherited from each parent
  - - - DNA replicates
        
        makes two copies of each chromosome
        
        the chromosome and the copy remain attached (X shape)
      - the longest stage
      - cells grow bigger
      - replicates sub-cellular structures
    - - one set of chromosomes is pulled to each end of the dividing cell
      - the nucleus divides
    - - the cytoplasm and the cell membrane divide
      - two identical cells formed
    - - depends on cell type and stage of life of the organism
        
        in embryos, cycle is very short as baby develops
        
        in adults cell cycle slows down
        
        but cells such as hair follicles, skin, blood and digestive system lining continue to replace itself
- - - - they can only divide by mitosis to form the same specialised cell
        
        cells mainly divide for repair and replacement
      - some cells can't divide
        
        red blood cell, skin cell
        
        replaced by adult stem cells
        
        nerve cells cannot be repaired or replaced
    - - different sub-cellular structures for different functions
      - some genes have been switched on and others off
  - - - due to cell enlargement and cell division
    - - as cells grow, divide and develop, they differentiate (become specialised)
      - in early embryo development, cells are unspecialised stem cells
        
        they can become any type of cell needed
  - - - undifferentiated (stem) cells found in the apical meristem
        
        mitosis takes place in the zone of cell division continuously
        
        cells then elongate in zone of elongation
        
        cells then differentiate in zone of differentiation
        
        meristem is the active region in stem and roots
        
        plants keep growing all through their lives at these growing points
      - cells do not differentiate until they are in their final position in the plant
      - differentiation is not permanent
        
        plant cells can redifferentiate to form a different cell type
  - - - easy to clone
      - cells can become unspecialised
        
        divide by mitosis
        
        then redifferentiate into various plant cells
      - new plant is identical to original plant
    - - difficult to clone
      - cells differentiate permanently in embryo development
      - cloning embryos
        
        adult stem cells can make an embryo