Biology 2

• Cell division


  Causes division to produce new cells needed for growth and repair. New cells have the same genetic info as the original
• Genetic material in cells

  • Nucleus
  • Chromosome
  • Gene
  • DNA
• Most characteristics are from many genes, not just 1
• Genes that code together for the same characteristics are grouped together on the chromosome
• Karyotype

  46 chromosomes in nucleus of body in 23 pairs. One chromosome in each pair is inherited from the father and one from the mother. Sex cells only have one chromosome from each pair
• Cell division


  1. Mitosis to produce 2 identical daughter cells

  2. Allows growth and development

  3. Asexual reproduction of cells produced by mitosis from cells of parent
• Cell cycle is slower when older and not growing, quickest in child/teen, injured/broken bone, pregnant
• DNA replication


  1. Stage 1 of cell cycle

  2. Form 2 copies of chromosome

  3. Synthesis of new subcellular structures
• Mitosis


  1. Stage 2 of cell cycle

  2. Set of chromosomes is pulled to each end of the dividing nucleus

  3. Nucleus divides
• Cytokinesis


  1. Stage 3 of cell cycle

  2. Cytoplasm and all membrane to form 2 identical daughter cells
• Cell differentiation in animals

  Cells start as unspecialised stem cells and then become the type of cell that is needed. By time baby is born most cells are specialised to carry out a specific function
• In cell differentiation different genes are switched on and off, enabling different cells to have different organelles to carry out their different functions
• Specialised cells produced by mitosis
• Some differentiated cells (e.g. red blood cells) can't divide at all so adult stem cells replace dead or damaged cells
• Cell differentiation in plants

  Plant cells able to differentiate all through their lives. Meristems - mitosis continuously happens here, cells elongate and grow before differentiating. Plant cells don't differentiate until they've reached final position in plant. Differentiation not permanent, cells can move from one area of plant to another and redifferentiate
• Cloning plants


  1. Tissue sample taken from parent plant

  2. Placed in agar containing nutrients

  3. Develops into plantlets

  4. Planted into compost
• Cloning

  Producing identical offspring
• Stem cells in plants

  From plant meristems, can produce large numbers of clones reliably, used to save rare plants from extinction, provide plants for science and horticulture
• Animal stem cells


  Sperm and egg fuse to form zygote which divides to form hollow ball of cells called the embryo. Inner cells are the embryonic stem cells that form all specialised cells of body. Adult stem cells are undifferentiated cells in bone marrow, most differentiated cells divide to replace themselves but some can't - stem cells stay in these tissues for years and only need to differentiate and divide if needed
• Problems with stem cell therapy

  • Embryonic stem cells: come from aborted embryos or spare embryos from fertility clinics, violation of embryo's rights/religious beliefs, slow progress, difficult, expensive, hard to control, may cause cancer if used in treatment
  • Adult stem cells: can carry viruses and transfer virus to patient, may elicit an immune response, patient needs to take immunosuppressant drugs to stop body rejecting new cells
• Future research on stem cells in umbilical cord, tissues/blood of newborn, amniotic fluid surrounding foetus, and stem cells found in biliary duct which produce insulin (trialling use in treatment of diabetic mice)