Plant tissues and organs

• Leaves


  • Organs that contain many tissues that work together to perform photosynthesis
• Tissues in leaves


  • Mesophyll
  • Waxy cuticle
  • Upper epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Lower epidermis
  • Stomata
  • Guard cells
• Waxy cuticle


  Makes the leaf waterproof
• Upper epidermis


  Single layer of cells that protects against water loss and is transparent to allow light to pass through
• Palisade mesophyll


  Tightly packed cells with lots of chloroplasts to absorb light for photosynthesis
• Spongy mesophyll


  Spherical cells with lots of air spaces to allow gases to diffuse quickly and a large surface area-to-volume ratio to increase gas exchange
• Stomata


  Tiny openings on the lower surface of the leaf that allow gases to move into and out of the leaf
• Guard cells


  Used to open and close the stomata
• Transpiration


  Water is lost through the stomata by evaporation, pulling water up from the roots through the xylem
• Transpiration


  • Provides water to cells to keep them turgid
  • Provides water to cells for photosynthesis
  • Transports mineral ions to leaves
• Translocation


  Movement of dissolved sugars from the leaves to the rest of the plant through the phloem
• Translocation


  • Moves dissolved sugars made in the leaves during photosynthesis to other parts of the plant for respiration, growth, and glucose storage
• Xylem


  Specialised tissues for one-way transport of water and minerals, made of dead cells joined together with no end walls between them and thick walls stiffened with lignin
• Phloem


  Specialised tissues for two-way transport of water and dissolved sugars, with cells that have end walls with small holes to allow substances to flow through
• Higher temperature


  Increases the rate of transpiration
• Lower humidity


  Increases the rate of transpiration
• More wind


  Increases the rate of transpiration
• Higher light intensity


  Increases the rate of transpiration
• Key terms


  • Photosynthesis
  • Light intensity
  • Stomata
  • Guard cells
  • Temperature
  • Humidity
  • Transpiration
  • Wind speed
  • Translocation
  • Phloem
  • Xylem