Plant Transport

• Vascular tissue = term used to describe xylem and phloem vessels
• Stele of plant helps resist vertical stress and anchors the plant in the soil
• In dicotyledon stem, xylem provides flexible support and resist bending the stem
• What plants transport and why:

  • water - for transport of other solutes, cooling via evaporation, photosynthesis
  • nitrates - to synthesise amino acid, nucleic acids (ATP)
  • magnesium - chlorophyll, phosphates (synthesis ATP + phospholipids), calcium (strength in cell wall)
• Root hair cells in plants have a very large surface area, allowing more water to enter via osmosis down a water potential gradient
• The soil solution, a dilute solution of mineral ions, has a higher water potential than the vacuole, creating a water potential gradient for diffusion to occur
• When there is low water potential in the soil, water needs to be transported via active transport through carrier proteins using energy in the form of ATP
• High mineral ion concentration is transported across a cell membrane by facilitated diffusion through channel or carrier proteins down the concentration gradient
• From root hair to xylem:

  • apoplast pathway - water + solutes travel through the cell wall -> once it hits the casparian strip, it diffuses into the cytoplasm and continues travelling in the symplast pathway
  • symplast pathway - water + solutes travel through cytoplasm and plasmodesmata
  • vacuolar pathway - water + solutes travel through vacuolar, cytoplasm and plasmodesmata
• Casparian strip - made of Suberin and is impermeable to water (hydrophobic)
• From endodermis, water moves into the xylem via osmosis down a water potential gradient
• From endodermis, mineral ions are actively transported using ATP into xylem which lowers the water potential in the xylem -> water moves in by osmosis down a water potential gradient