chapter 9

• need for plant transport systems

  1. size

  2. metabolic demands

  3. SA:V
• dicotyledonous plants


  plants that produce seeds containing two cotyledons, which act as food stores for the developing embryo and form the first leaves when the seed germinates.
• herbaceous dicots


  with soft tissues and a relatively short life cycle
• aborescent dicots


  with hard lignified tissues and a long life cycle
• vascular system in dicots

  xylem and phloem
• what are the xylem and phloem arranged in

  vascular bundles in leaves, stem and roots of herbaceous dicots
• TS stem of young herbaceous plant

  
• TS root of young herbaceous plant

  
• TS dicot leaf

  
• xylem


  plant transport tissue that carries water and minerals from the roots to the other parts of the plant as a result of physical forces.
• what is xylem made up of

  mainly dead cells, they are long hollow structures made by several columns of cells fusing together end to end

  
• what are xylem parenchyma packs

  thick walled tissues surrounding the xylem vessels, storing food and containing tannin deposits
• tannin


  bitter, astringent tasting chemical that protects plant tissues from attack by herbivores
• xylem fibres


  long cells with lignified secondary walls that provide extra mechanical strength but do not transport water
• lignin in xylem vessels

  can form rings, spirals or solid tubes with small unlignified areas called bordered pits
• bordered pits


  where lignification is not complete, leaving gaps in the cell wall and water leaves into other cells of the plant
• phloem


  plant transport tissue that carries the products of photosynthesis (assimilates) to all cells of the plant.
• what does phloem transport

  transports goof in the form or organic solutes around plant from the leaves where they are made by photosynthesis
• what does the phloem supply the plant with


  supplies cells with sugars and amino acids needed for respiration and other synthesis, and these can flow in both ways up and down the plant
• sieve tube elements


  the main cells of the phloem that have a greatly reduced living content and sieve plates between the cells.
• what are sieve tube elements made up of

  made up of cells joined end to end to form a long hollow structure, they are not lignified
• sieve plates


  areas between the cells of the phloem where the walls become perforated giving many gaps and a sieve-like appearance that allows the phloem contents to flow through.
• tonoplast


  vacuole membrane
• companion cells


  the active cells found next to sieve tube elements that supply the phloem vessels with all of their metabolic needs

  
• how do the companion cells link to the sieve tube elements

  plasmodesmata
• companion cell functions

  very active and are 'life support' for STE, which have lost most of their normal cell functions
• what does phloem tissue also contain

  fibres and sclerids, cells with extremely thick cell walls
• turgor pressure / hydrostatic pressure

  result of osmosis in plant cells providing hydrostatic skeleton to support stems and leaves
• what does turgor also drive

  cell expansion
• how does loss of water help a plant

  keep cool
• how are mineral ions and products of photosynthesis transported

  in aqueous solutions throughout the plant
• root hair cells


  cells found just behind the growing tip of a plant root that have long hairlike extensions that greatly increase the surface area available for the absorption of water and minerals from the soil.
• site of exchange surface in plants

  root hair cells
• how are root hair cells adapted to their function

  1. microscopic size - can penetrate easily in soil particles

  2. large SA:V on each hair

  3. thin surface layer - short diffusion/osmosis distance

  4. conc of solutes in cytoplasm maintains gradient
• soil water water potential

  low concentration of dissolved minerals so it has a very high water potential
• cytoplasm and vacoular sap water potential

  contain many different solvents such as sugars, mineral ions and amino acids so the water potential is low, so water moves into cell
• symplast route

  movement of water and solutes through the cytoplasm of cells via plasmodesmata by diffusion.
• symplast route explanation

  water diffuses into the soil making cytoplasm dilute, so it moves from root hair cell into next door cell by osmosis, this is repeated until xylem is reached
• how is steep water potential gradient maintained in symplast route


  when water leaves the root hair cell by osmosis, water potential of cytoplasm falls again so that as much water can move in
• apoplast route


  movement of substances through the cell walls and cell spaces by diffusion and into cytoplasm by active transport.