B2- cell division

• How many chromosomes in each human body cell

  23 pairs
• What is the purpose of mitosis

  Growth, development and repair
• What is the cell cycle

  Process from when the cell s generated to the time it goes through mitosis
• What is the alternative name for the division stage of mitosis

  Cytokinesis
• Cell cycle stages

  Cell growth

  DNA synthesis - chromosomes Double stranded

  Further growth - dna checked for errors

  Mitosis

  Cytoplasm separates - two cells formed

  Temporary rest period or cell stops dividing
• Mitosis stages

  cell begins to divide

  DNA replicates to form two copies of each chromosome

  Nuclear membrane breaks down and chromosomes collect at centre of cell

  One set of chromosomes is pulled to each and of the cell and the haploid nucleus divides

  The cytoplasm and cell membrane divide to form two identical daughter cells
• What are stem cells

  • cells that is undifferentiated
  • Cells collected at early stages of development are embryonic
• where can adult stem cells be collected from

  brain

  eyes

  heart

  bone marrow

  skin

  muscle
• problems with adult stem cells

  can only differentiate into related cell types

  bone marrow can only differentiate into blood cells (red blood cells, white blood cells, platelets) and immune system cells
• Bone marrow transplant stages

  Leukaemia is a cancer of the bone marrow

  Patients existing bone marrow is destroyed by radiation

  Patient receives a transplant of bone marrow from a donor

  Stem cells in bone marrow undergo mitosis and form new bone marrow

  Also differentiate and form blood cells
• Problems with bone marrow transplant

  • donor has to be compatible with patient or white blood cells produced could attack patients body
  • Risk of viruses can be passed from donor to patient
• therapeutic cloning

  Embryo produced with same genes of patient

  Stem cells from embryo can be transplanted into the patient without being rejected by the immune system

  Once inside the stem cells can differentiate to replace cells which have stopped functioning

  
  

  useful for a range of medical conditions (diabetes or paralysis)

  
  

  ethical or religious objections
• Where are stem cells found in plants

  Roots and buds contain meristem tissue

  Meristem stem cells can differentiate into any type of plant tissue, at any point in the life of the plant
• What are meristem cells used for

  To clone a rare plant to stop it going extinct

  Produced clone crop plants for farmers
• Examples of cells that can be replaced with stem cells

  Diabetes - damage to pancreas cells which produce insulin

  Paralysis - damage to nerve cells

  Sickle cell anaemia - misshapen red blood cells
• process of extracting embryonic cells

  extract embryonic stem cells from early embryos

  Grow them in a laboratory

  Stimulate them to differentiate into any type of specialised cell

  Replace faulty cell of patient
• Drawbacks of using embryonic stem cells

  Requires embryonic stem cell

  -Limited supply

  Rejection

  -different genomes

  -immune system may reject stem cels

  -tries to destroy foreign cells

  -can give medication to suppress immune system
• Risks of stem cells

  Risk of infection being carried

  Tumours may develop- cellls may divide rapidly when transplanted and develop to tumor and cancer
• Ethical objection to embryonic stem cells

  • embryonic stem cells are usually unwanted from fertility clinics which otherwise would have been destroyed
  • However have the potential to be human life
  • Existing human life > rights of embryos
• importance of mitosis

  • growth - increasing cell number in multicellular organisms
  • repair - replacing damaged or dead cells
  • asexual reproduction- bacteria, hydra or plants