transport in plants

• why do plants need transport system and what to do they move

  • all living things need to take substances from and return waste to the environment
  • water and minerals from the roots up to the leaves
  • sugars from the leaves to the rest of the plants
• do plants require a high or low metabolic demand

  plants require low metabolic demand, they don't need to take o2 around
• outline the movement of water through a plant

  • mineral ions are absorbed by active transport, because of the high [] water moves in by via osmosis down a [] gradient
  • root hair cell has high SA has mitochondria to provide ATP for the active transport
  • water can move through via any pathway but mainly apoplast
  • more active transport of mineral ions into vascular bundle and water follows via osmosis
  • root pressure is high pushes up the stem towards the leaf
• what are the 3 ways that water can move through - cell to cell

  • apoplast - moving through the cell walls
  • symplast - inside the cell and has to cross the plasma membrane or via plasmodesmata
  • vacuolar - like symplast but through the vacuole
• casparian strip

  • rings around all the cells blocks and impermeable and made out of suberin, it blocks the apoplast pathway forces the water into the other pathways
• movement of water through the root

  • cross section of a root - X shape for the xylem and the small seed looking things are the phloem (starfish)
  • around the vascular bundle is a special sheath of cells called endodermis which contains the casparian strip
  • endodermis active cells - mitochondria
  • underneath the endodermis there are meristems underneath called pericycle
• xylem

  • dead cells
  • lignin impregnates the cell wall making it water proof and strength
  • lignin thickening causes patterns to prevents the vessel from being to rigid and allows some flexibility of the stem or branch - spiral , annular (rings) or reticulate (network of broken rings), full (boarded pits) allow lateral movement some water move out to supply other parts
  • cells fuse end to end to form continuous tube
• what is cohesion and adhesion - capillary action

  • force that attracts water molecules together
  • how water molecules stick to the walls of the xylem
  • allows the water to move up the tube
  • at the top of the leaf water is evaporating which pulls the water up from the lower end of the xylem because of adhesion water molecules like crawl up the walls
• cross section of a stem

  • looks like an orange, includes the pith
  • very outer layer = sclerenchyma
  • outer side of the vascular bundle = phloem
  • middle - cambium
  • inner - xylem
• leaf structure

  • waxy cuticle - stops water loss
  • upper epidermis - transparent layer , letting light through
  • palisade mesophyll - chloroplasts tightly packed closer to the incoming light as vacuole pushes it towards the surface
  • spongy mesophyll - air spaces
  • vascular bundle - xylem - larger and phloem which is smaller
  • stomata - controlled by guard cells
• water moves out the xylem, water moves from cell to cell

  • evaporation of water from the surface of the cell into the air space = water vapour
  • diffuses out of the stomata
• transpiration - is the loss of water though evaporation

  • measured by a potometer measures the water uptake of a plant
  • the same cutting is needed and several different times to compare transpiration rates in different settings
  • sharp knife and cut underwater to prevent any air bubbles
  • seal the newly cut shoot into the potometer, keeping it underwater as you do so
  • track how fair the bubble moves and record the distance it moves and plot a graph
• what are the factors effecting transpiration

  • wind increases it
  • temp increases it
  • light increases it
  • humidity decreases it
• xerophytes plants example

  • cactus, marram grass
  • cactus don't have leaves to minimise water loss
  • marram grass - rolled leaf - traps water vapour
  • thick waxy cuticle
• hydrophytes - water loving plants

  • stomata are on the upper surface to maximises gas exchange
  • air spaces - cause the leaf to float - buoyancy allows oxygen to diffuse down the stem and to the roots
• what are the adaptations of the phloem

  • living cells, most contents have been cleared out, cytoplasm that is left
  • leaves room for mass flow
  • sieve plate between cells
• what do the companion cells do

  • next to the phloem
  • help load(source)and unload sugar into the phloem and out of the phloem
  • H+ is pumped to the cell wall from the cytoplasm as there [H] at the cell wall, creating a gradient via carrier protein uses ATP = ADP + pi
  • H+ comes back in via co transport of H+ and sucrose together
  • sucrose moves into phloem, water follows via osmosis from the xylem
  • high hydrostatic pressure
  • sink = active unloading - increases the water potential
  • water into the phloem at the source and water out at the sink = mass flow