Transport in plants

• Xylem


  Transport water and minerals from the roots to the stem and leaves
• Phloem

  Transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
• Vascular bundles

  Groups of xylem and phloem vessels arranged throughout the root, stem and leaves
• Xylem is always on the inside and phloem is always on the outside in a cross-section of a root, stem or leaf
• Xylem cells

  • Lose their top and bottom walls to form a continuous tube
  • Essentially dead, without cell contents, to allow free passage of water
  • Outer walls are thickened with lignin, strengthening the tubes and supporting the plant
• Root hair cells

  Single-celled extensions of epidermis cells in the root that absorb water and minerals from the soil
• Pathway of water into and across a root

  Root hair cell → Root cortex cells → Xylem → Leaf mesophyll cells
• Placing a plant (like celery) into a beaker of water with a stain added can show the pathway of water uptake
• Transpiration


  The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
• Xylem


  • Adapted to transport water and mineral ions from roots to leaves
  • Lignin is deposited in the cell walls causing the cells to die and become hollow
  • Cells join end-to-end to form a continuous tube
  • Lignin strengthens the plant to withstand water movement pressure
  • Movement is only from roots to leaves
• Transpiration has several functions in plants: transporting mineral ions, providing water for cells and photosynthesis, and keeping the leaves cool
• Investigating the effect of temperature & wind speed on transpiration rate

  1. Cut a shoot underwater and place in tube

  2. Dry the leaves

  3. Allow plant to adapt to new environment for 5 minutes

  4. Record start and end location of air bubble

  5. Change temperature or wind speed and repeat