module 3

• how are xylem cells produced from cambium (3)

  • cell elongation
  • death of organelles and cytoplasm
  • end walls break down
  • bordered pits form
  • lignification
• how would you improve a sample for light microscopy

  • squash slide for soft samples , allows for more light to be let through
  • wet mount , cover slide applied at a 45 degree angle
  • add stain to slide , allow to air dry , pass through a flame so the specimen will adhere to the slide and take up the stain
• explain the precaution of cutting a shoot underwater

  • prevents air lock
• why Is the fluid mosaic model known as such

  • fluid because phospholipids are free to move
  • mosaic because proteins embedded are different shapes and sizes
• how does the heart make sure the atria has finished contracting before the ventricles contract

  • SAN initiates a wave of excitation causing atrial systole
  • AVN causes slight delay before stimulating bundle of his in the septum
  • bundle of his branch off into purkyne fibres which spread the walls of the ventricles causing them to contact
• examples of source and sinks

  • sources : green leaves and stems , storage organs , food stores in seeds when they germinate
  • sinks : growing roots , meristems which are actively dividing , parts of the plant which are laying down food stores
• describe how a photometer could be used to calculate rate of transpiration

  • use vaseline to ensure airtight
  • dry leaves
  • cut stem underwater so no air enters the xylem
  • measure time for air bubble to move
  • calculate volume of H2O uptake
  • control : temperature , humidity , air movement
• why would you measure rate of transpiration using a photometer instead of measuring water vapour production

  • difficult to differentiate wether its from respiration or transpiration
• similarities between the xylem and phloem

  • both xylem and STE both have no nuclei
  • cells are joined end to end
  • made from more than one cell type
• differences between the xylem and the phloem

  • xylem has a wider lumen , bordered pits and lignin
• how are guard cells adapted to their role

  • thin outer wall , thick inner wall
  • chloroplasts for ATP
• how to guard cells control the opening and closing of the stomata

  • open when guard cells are turgid and closed when they are plasmolysed (low turgor)
• explain why plants are more able to form naturals clones than animals

  • meristematic tissue is totipotent
  • plant cells can rediffrentiate
  • bone marrow cells are multipotent and can only differentiate into blood cells
• why are IPSC's (induced pluripotent stem cells) preferred/not to ESC's (embryonic stem cells)

  • less chance of rejection because they are not from an embryo
  • IPSC's carry a cancer risk
  • stem cells may mutate or still carry the allele for the disease trying to be treated
• how does water move from roots to leaves

  • water enters roots by osmosis
  • water evaporates from mesophyll cell into the air reducing the water potential of the cell
  • water pulled in from adjacent cells along both apoplectic and symplastic pathways
  • adhesion : water forms H bonds with carbohydrates in the xylem vessels
  • cohesion : water molecules form hydrogen bonds between each other
  • capillary action : the process by which water can travel up a narrow tube against the force of gravity
• how is a companion cell adapted to there function

  • many mitochondria , ribosomes
  • plasmodesmata linking then to sieve tube elements
  • transport proteins in plasma membrane
• define transpiration , transpiration stream and pull

  • loss of water by evaporation from leaves
  • water moving in a continuous stream from roots to air surrounding mesophyll
  • water drawn up the xylem to replace the water lost by evaporation
• what does the phloem transport

  • sucrose
  • amino acids