3.3 - Plant Transport

• Why do plants need transport systems?

  To transport Water, Carbon Dioxide, Oxygen, Minerals, Organic Nutrients as they have a high basal metabolic rate.
• Why is it hard for plants to transport substances?

  Large plant so a Low Surface Area:Volume ratio
• What are plant transport vessels called?

  Vascular System
• Label the Root TS

  1 - Xylem

  A) Xylem

  B) Phloem

  C) Epidermis

  
• What are pericycle cells?

  Inside of the vascular bundle and contain meristematic cells
• Label the Stem TS diagram below:

  Label

  A) Epidermis

  B) Phloem

  C) Xylem

  
• Why is the vascular bundle arranged around the stem?

  Provides mechanical support/strength and flexibility to withstand pressure
• What is cambium?

  A layer of meristematic cells between xylem and phloem
• Label the Leaf TS:

  Label:

  A) Xylem

  B) Phloem

  C) Epidermis

  
• Describe the arrangement of the vascular bundle in leaves

  They form the midrib, the xylem is on top of the phloem
• What does the Xylem transport?

  Dissolved mineral ions and water
• `Describe the location of Xylem Vessels

  They are surrounded by thick-walled parenchyma containing tannin deposits
• What is tannin?

  A bitter chemical that protects plant tissues from herbivores eating it
• Describe the pattern of lignin deposits

  Spiral, annular (in rings) and reticulate (broken rings)
• Why is lignin deposited reticulately?

  To allow the plant to be flexible
• Why does the xylem have lignified cell walls?


  Strength to withstand hydrostatic pressure
• Why does the Xylem have pits in the wall?

  So water can move laterally
• Why are there no end plates in the xylem vessel

  Mass flow of water and so capillary action continues
• Why does the Xylem have a small vessel diameter

  Assists with capillary action
• Why does the xylem not have a cytoplasm?

  Mass flow is not stopped
• What is a tracheid?

  Long and tapered lignified cell
• What does the Phloem transport?

  Organic Compounds (assimilates)
• In what direction does the xylem transport water?


  Upwards only
• In what direction does the phloem transport assimilates?


  Sources to sinks (any direction)
• Which vessel involves a form of active transport?

  Phloem in translocation
• Features of Sieve Tube Elements

  Sieve plates with pores, Cellulose cell wall, No large organelles, Thin cytoplasm
• Why does the sieve tube have no large organelles

  Maximises space for translocation
• Describe the features of Companion cells

  Large Organelles present, Transport proteins in membrane, Many Mitochondria, Plasmodesmata
• What type of cell is a xylem vessel

  Hollow dead and lignified
• Why does a plant need water?

  Turgor pressure for support, Cell expansion of roots, Cooling, Mineral ion transport, photosynthesis
• Describe the adaptations of the root hair cell

  Small, large surface area to volume ratio, thin surface layer, high concentration of solutes
• What is the symplastic pathway?


  Water moves through cells and a continuous cytoplasm. Goes through plasmodesmata
• What is the apoplastic pathway?


  Between the cell walls, water travels.
• What is the function of the Casparian strip?


  A waterproof layer made up of suberin forcing water to go through cells which are selectively permeable filtering out harmful substances
• What is water potential?


  The potential energy of water (always moves from high to low)
• What is cohesion?


  Hydrogen bonding in water causing water molecules to be attracted to each other
• What is adhesion?


  Water being attracted to its surroundings
• Describe the transpiration stream

  • Water molecules evaporate from the surface of mesophyll cells
  • Loss of water lowers water potential so water moves in
  • Adhesion and cohesion result in capillary action through the transpiration pull
• How does light affect transpiration?


  Increasing light increases the number of open stomata, increasing the water vapour diffusion rate.
• How does temperature affect transpiration?

  • Increases water's kinetic energy so more evaporation
  • Decreases the humidity of surrounding air so better water potential gradient