plant transport

• why do plants require a transport system

  • high metabolic demand
  • small SA:V ratio
  • diffusion distance too long so cannot rely on diffusion alone
• phloem

  transports dissolved assimilates
• xylem

  transports water and mineral ions
• herbaceous dicotyledonous plants 


  flowering plants with a characteristic distribution of vascular tissue throughout the plant
• parts of a root

  • root hair cell
  • root cortex
  • endodermis
  • medulla
  • vascular bundle
  • xylem
  • phloem
• parts of a stem

  • collenchyma
  • sclerenchyma
  • parenchyma
  • vascular bundle
  • phloem
  • meristem cambium
  • xylem
• parts of a leaf

  • branches of veins
  • midrib
  • xylem
  • phloem
• meristem in roots


  • layer inside endodermis
  • pericycle
  • divide to form new roots
• meristem in stem 


  • cambium
  • divide to form new xylem and phloem
• collenchyma

  provides structural support
• parenchyma 


  stores nutrients and starch in the middle
• sclerenchyma

  provides structural support
• endodermis 


  • surrounds vascular bundle in the roots
  • role in transporting water from root cortex to medulla into xylem
• xylem consist of

  • vessel to transport water and mineral ions
  • fibres to support the plant
  • parenchyma cells which act as storage
  • dead plant cells stacked end on end leaving a long continuous hollow column for water to move
• structure of xylem

  • lumen
  • lignified cell wall
  • non lignified bordered pits
  • spiral lignin
  • surrounded by parenchyma
• reasons for lignification

  • waterproof to reduce lateral flow of water
  • spiral lignin for flexibility
  • strength and support to prevent xylem collapsing
  • adhesion helps move water up the xylem
• reason for non lignified bordered pits

  bordered pits align to allow water to move laterally between incase of a blockage
• symplast pathway

  water moves through living parts of cells and cytoplasm of neighboroughing cells by osmosis
• neighbouring cells are connected by

  plasmosdesmata
• apoplast pathway

  water passes between or through non living parts of cells, the cells walls avoiding cell membranes by mass flow
• endodermis 


  layer of cells before medulla and xylem
• movement of water into root hair cell

  • mineral ions are absorbed from the soil by active transport
  • lowering water potential of cytoplasm
  • water enters root hair cell by osmosis as water potential gradient is formed
• movement of water across root

  • water moves across root cortex via symplast pathway
  • some water moves across cell walls via apoplast pathway
• what happened when water reaches the endodermis

  • apoplast pathway is blocked by casparian strip
  • forcing water into symplast pathway
  • cell membrane of the endodermis contains transport proteins which actively pump mineral ions into the medulla and xylem
  • lowering water potential in medulla
  • water moves from root cortex into medulla by osmosis
  • finally moving into xylem
• what happenes when water enters xylem

  • water enters xylem increasing hydrostatic pressure at the bottom
• transpiration stream

  movement of water up the xylem vessel from the roots, up the stem, to the leaves
• how does water move up the xylem

  • water vapour diffuses out of leaves reducing hydrostatic pressure at the top of xylem
  • creating a pressure gradient and tension
  • water moves down the pressure gradient by mass flow
• mass flow

  bulk movement of a substance due to a pressure gradient
• how does cohesion and tension aid transpiration

  • water evaporates from leaves
  • creating tension pulling a column of water up into the leaf
  • water is cohesive due to hydrogen bonds
  • allowing water to be polled up in a column
• how does adhesion aid transpiration

  • water molecules are attracted to walls of xylem vessels
  • causing adhesion which helps pull water up the xylem
  • by capillary action
• transpiration

  loss of water vapour down a water vapour potential gradient from aerial parts of a plant
• process of transpiration

  • water enters leaves via xylem vessels
  • water moves by osmosis to spongy mesophyll cells
  • water evaporates from cell walls of spongy mesophyll into air spaces of the leaf
  • water diffuses out of open stomata down a water potential gradient
• why is transpiration important

  • inevitable consequence of gas exchange
  • stomata open to allow CO2 in and O2 out for photosynthesis
  • essential for production of glucose in plants
• factors effecting transpiration rate

  • high light intensity increases transpiration
  • high temperatures increases transpiration
  • low humidity increases transpiration
  • high wind speed increases transpiration
  • high surface area increases transpiration
• potometer

  measures the rate of transpiration by measuring rate of water uptake
• precautions when setting up a potometer

  • set up under water to ensure no air gets inside
  • add vaseline to ensure potometer is air tight
  • cut shoot at an angle to increase surface area
  • use a capillary tube to measure distance air bubble moves
  • dry leaves to maintain water potential gradient
• volume equation

  volume =
• rate equation

  rate = volume / time
• xerophyte 


  • plant adapted to living in dry conditions
  • adapted to reduce transpiration
  • e.g. cacti and marram grass
• cacti adaptations

  • thick waxy cuticle on epidermis to be waterproof to reduce water lost
  • spines instead of leaves to reduce surface area
  • close stomata during hottest times of the day