Transport

• Diffusion

  Movement of substances from high [] to low [] until equilibrium is reached
• Passive transport


  • Moving down the concentration gradient (higher [] → lower [])
  • No energy required
• Active transport

  • Moving against the concentration gradient (lower [] → higher [])
  • Energy required
  • Used to move nutrients/minerals that cannot move freely across cell membrane
• Osmosis


  Diffusion of H2O molecules
• Concentration gradient

  Differences in [solute] between 2 areas
• Transpiration

  H2O evaporates through the stomata caused by dry air, wind, heat<|Transpiration = loss of water = negative pressure = tension H2O in xylem = water moving from roots to stem
• Cohesion-Tension model: Transport in Xylem

  1. Water moves from roots to leaves roots contain higher [nutrients] than soil

  2. H2O enters roots via osmosis into xylem

  3. Xylem tissues bring water from roots to stem

  4. Xylem transports H2O & minerals to leaves 90% of water that reaches leaves evaporates through stomata
• Source vs. sink


  • Sources: regions sucrose enters sieve tube elements e.g. palisade & spongy mesophyll of leaves
  • Sinks: regions where sucrose is used/stored e.g. flowers, fruits
• Translocation

  Transport of sucrose/organic molecules through phloem to areas of growth, metabolism, or storage<|Food molecules flow through sieve tube elements<|Translocation moves sucrose from source to sink
• Pressure-flow model: Phloem

  1. Sucrose pumped from source cells to phloem

  2. H2O moves to phloem due to increase of [sucrose]<|Internal pressure builds up at the source end of sieve tube<|Pressure gradient between sources and sinks pushes sucrose to sinks<|Sucrose moves to sink
• Entering root: root to dermal tissue to root hair with increased surface area to cortex made of parenchyma cells that store water, minerals etc. to endodermis made of endodermal cells surrounded by casparian strip thus passing through plasma membrane and cytoplasm to vascular system
• less water = less pressure
• transpirational pull is when water gets pulled up to the leaves via cohesion which is when the attraction of water molecules creates an unbroken water column and is very strong so it is negative pressure
• less pressure = more tension on water
• source ex: leaves