transport in plants

• vascular bundles

  -roots, leaves, stems

  -plant equivalent of blood vessels

  -xylem, phloem, cambium
• each part of a plant takes care of its own gas exchange- stomata in the leaves, lenticels- stems
• plants respire at much lower rates than animals- less metabolically active. only during photosynthesis is a large volume of oxygen needed
• leaves have a large surface area to volume ratio- broad and thin
• stomata

  -pores on underside of the leaf

  -allow carbon dioxide to diffuse in and oxygen and water vapour out

  -stomal pore- surrounded by 2 guard cells- control opening and closing of the pore

  -reduces water loss by evaporation

  -stomata tend to be open in the day for photosynthesis and closed at night- may be reversed in hot conditions.
• lenticels


  -lens shaped pores

  -pathway for direct exchange of gases between internal tissues and atmosphere through bark (dead tissue)- otherwise impermeable to gases
• monocots

  -seed embryo has one cotyledon (first leaf)

  -major leaf veins are parallel
• dicot

  -seed embryo has 2 cotyledons

  -major leaf veins are more branched
• vascular tissues- leaf

  -xylem is inside of mid- rib and is on top of the phloem

  -phloem is outside of mid-rib and is underneath the xylem
• xylem

  -can carry water and minerals from roots to very top of the plant
• xylem- lignin

  -long thin walls- lignin waterproofs the walls of the cells

  -as a result the cells die and end walls and contents decay- long column of dead cells

  -lignin thickening- patterns in cell walls- spiral- annular (rings) or reticulate (network of broken rings)

  -pores called pits- allow water to leave 1 vessel and pass into another
• xylem- tracheids

  -structural elements

  -thickening- adds strength
• xylem- parenchyma


  -basic unspecialised packing tissue of plant body

  -cells may store food (starch) and provide support when turgid

  -intracellular air spaces aid diffusion of gases through the plant body- pinth (inner cortex)
• xylem- narrow

  -effective capillary action as chain doesn't break easily
• xylem- dead cells

  -continous column
• xylem- pits

  -allow lateral (sideways) movement
• xylem- lignin

  -prevents collapse- provides water proofing
• xylem- gaps in lignin

  -allows stretch and bending
• xylem- flow of water isn't impeded

  -no cell contents

  -no end walls
• phloem

  transports sugars from one end of the plant to another- up or down. consists of 2 types of cells- sieve tube elements and companion cells
• phloem- sieve tubes

  -not true cells- no nucleus and very little cytoplasm

  -line up end to end- carry sucrose

  -sucrose is dissolved in water- sap

  -contains cross walls at intervals- pores- allow sap to flow

  -cross walls called sieve plates and tubes are called sieve tubes
• phloem- companion cells

  -inbetween sieve tubes- small cells

  -large nucleus and dense cytoplasm- numerous mitochondria- produce ATP

  -carry out metabolic processes needed by sieve tube elements

  -cytoplasm of companion cells and sieve tube elements are linked through many plasmodesmata
• phloem- few cell contents

  -flow of sap isn't impeded
• phloem- many mitochondria in companion cells

  -provide ATP for active processes- loading of sucrose into sieve tubes
• phloem- many ribosomes in companion cells

  -metabolically active cell- many proteins made
• phloem- plasmodesmata between cells

  -allow communication and flow of minerals between cells