B6 - organisation in plants

• Palisade mesophyll


  • Single layer of transparent cells allow light to pass through
  • Cells secrete a waxy substance that makes leaves waterproof
  • Tightly packed cells with lots of chloroplasts to absorb much light as possible for photosynthesis
• Spongy mesophyll


  • Air spaces increase the surface area and allow gases to diffuse quickly
• Guard cells


  Control the opening and closing of the stomata
• Xylem


  Transport water and mineral ions from the roots to the rest of the plant
• Xylem

  • Made of dead cells
  • No end wall between cells
  • Walls strengthened by a chemical called lignin to withstand the pressure of the water
• Phloem


  Transport dissolved sugars from the leaves to other parts of the plant for respiration, growth, and storage
• Translocation

  Movement of water from the roots to the leaves through the xylem
• Transpiration

  Movement of water from the roots to the leaves through the xylem
• Purpose of transpiration

  • Provide water to keep cells turgid
  • Provide water to cells for photosynthesis
  • Transport mineral ions to leaves
• Factors affecting rate of transpiration

  • Temperature
  • Light intensity
  • Humidity
  • Wind speed
• Higher temperatures

  Increase the rate of transpiration
• Higher levels of humidity


  Decrease the rate of transpiration
• Increased light intensity


  Stomata open wider to let more carbon dioxide into the leaf for photosynthesis
• Function of stomata


  Allow diffusion of gases into and out of the plant
• Location of most stomata

  Underside of leaves
• Advantage of having many stomata on underside of leaves


  Reduces the amount of water loss through evaporation