Organising plants

• Leaves


  Organs that contain many tissues that work together to perform photosynthesis
• Waxy cuticle


  • Makes the leaf waterproof
• Upper epidermis


  • Single layer of cells
  • Protects against water loss
  • Transparent to allow light to pass through
• Palisade mesophyll


  • Tightly packed cells
  • Lots of chloroplasts to absorb light for photosynthesis
• Guard cells


  • Control the opening and closing of the stomata
• Stomata


  • Air spaces
  • Allow gases to diffuse quickly
• Spongy mesophyll


  • Spherical cells
  • Lots of air spaces to allow gases to diffuse quickly
  • Large surface area-to-volume ratio to increase gas exchange
• Lower epidermis


  • Tiny openings that allow gases to move into and out of the leaf
• Stomata


  • Tiny openings in the undersides of leaves that reduce water loss through evaporation
  • Control gas exchange and water loss from leaves
• Stomata opening and closing

  1. Guard cells become turgid, cell wall on inner surface is thick so it cannot stretch as much as outer surface, guard cells curve away from each other to open stomata

  2. Guard cells become flaccid, stomata close
• Factors affecting transpiration rate

  • Higher temperature increases transpiration rate
  • Lower humidity increases transpiration rate
  • More wind increases transpiration rate
  • Higher light intensity increases transpiration rate
• Transpiration


  Water lost through stomata by evaporation, pulls water up from roots through xylem
• Translocation


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


  • One-way transport of water and minerals
  • Made of dead cells, joined with no end walls
  • Thick walls stiffened with lignin
• Phloem


  • Transport of water and dissolved sugars in both directions
  • Cells have end walls with small holes to allow substances to flow through
• Root hair cells


  • Increase absorption of water and mineral ions into root by increasing surface area
  • Contain lots of mitochondria to provide energy for active transport of mineral ions