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 diagram showing 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 helping support the plant
• Root hair cells


  Single-celled extensions of epidermis cells in the root that grow between soil particles and 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 with lignin deposition, hollow cells, and one-way movement from roots to leaves
• Transpiration has several functions in plants: transporting mineral ions, providing water to keep cells turgid, providing water for 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 wind speed or temperature and repeat
• As temperature increases, the rate of transpiration also increases
• As wind speed increases, the rate of transpiration also increases
• Transpiration stream


  • Water molecules are attracted to each other by cohesion, creating a continuous column of water up the plant
  • Transpiration produces a tension or 'pull' on the water in the xylem vessels by the leaves
• Wilting


  When more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, causing the plant to collapse
• Translocation


  The transport of sucrose and amino acids in the phloem, from regions of production to regions of storage or use
• Comparison between Xylem and Phloem Tissue

  • Xylem
  • Phloem