Plant Tissues, Organs and Systems

• Epidermal tissue


  • Covers the entire plant
  • Has a waxy cuticle which helps reduce water loss from the leaf surface
• Palisade mesophyll tissue


  • Contains lots of chloroplasts which allows photosynthesis to progress at a rapid rate
• Spongy mesophyll tissue


  • Has lots of air spaces which allow gases (including oxygen and carbon dioxide) to diffuse in and out
• Xylem


  • Made up of dead cells which form a continuous hollow tube - allows the movement of water and mineral ions from the roots to the leaves
  • Strengthened by lignin - makes the vessel strong and waterproof
  • Has bordered pits - allow minerals to be transported to specific places
• Phloem


  • Made up of elongated living cells
  • Cells have sieve plates that connect them together - cell sap can move through plates into other cells
  • Sieve tube cells have few organelles to allow the efficient transport of substances
• Meristem tissue


  • Made up of stem cells which can differentiate into many different cell types, allowing the plant to grow
• Tissues in the leaf organ

  • Epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Xylem
  • Phloem
  • Guard cells
• Guard cells


  Control the opening and closing of the stomata, according to the water content of the plant
• Stomata


  • Allow the control of gaseous exchange and water loss from the leaf
  • More stomata on the base of the leaf - minimises water loss as this side is cooler and shaded
  • Have guard cells which control their opening and closing
• Root hair cells


  • Allow the uptake of water and mineral ions from the soil
  • Large surface area - maximises rate of absorption
  • Contain lots of mitochondria -- release energy for active transport of mineral ions
• Translocation


  The movement of dissolved sugars from the leaves to other parts of the plant
• Transpiration


  The evaporation of water vapour from the surface of a plant
• How transpiration works


  1. Water evaporates from the leaf surface via the stomata

  2. Water molecules cohere together - more water is pulled up the xylem in an unbroken column

  3. More water is taken up from the soil - creating a continuous transpiration stream
• Increasing temperature


  Increases the rate of transpiration
• Increasing relative humidity


  Decreases the rate of transpiration
• Increasing wind speed/air movement

  Increases the rate of transpiration
• Increasing light intensity


  Increases the rate of transpiration