Adaptations gas exchange plants

• Cuticle


  A waxy transparent layer that allows light to pass through to the photosynthetic palisade mesophyll below but reduces water lost by evaporation through the top surface of the leaf
• Upper epidermis


  • Transparent for light to easily penetrate to photosynthetic layers
• Palisade mesophyll


  • Main photosynthetic layer packed with chloroplasts
• Spongy mesophyll


  • Surrounded by air spaces for easy diffusion of gases
• Vascular bundle


  • Contains xylem (carrying water from roots), phloem (to carry sucrose to other parts of the plant) and bundle sheath parenchyma
• Stomata


  The stomatal pores allow the exchange of gases down a concentration gradient
• Gas exchange through stomata

  Gases diffuse through intracellular spaces to and from the photosynthetic cells where they dissolve in the cell lining and diffuse into the cells
• Guard cells


  Open and close the stomata, the closing of the stomata during the night reduces water loss
• Opening and closing of stomata

  1. Open: Turgid guard cells bend due to thickened inner walls opening the stomatal pore

  2. Closed: Flaccid guard cells meet in the middle, closing the stomatal pore
• Mechanism for opening stomata

  1. In light, chloroplasts in guard cells photosynthesise and produce ATP

  2. The ATP is used for the active transport of potassium ions into guard cells

  3. Starch is converted to malate

  4. Malate and potassium ions lower water potential of guard cells and water is drawn in by osmosis

  5. Uneven thickening of guard cell inner walls causes them to bend as they swell, opening the stomatal pore
• When there is no light

  The opposite occurs, closing the pore
• Leaves adapted for photosynthesis

  • Large surface area and orientate perpendicular to the sun for maximum light absorption
  • Thin with a transparent cuticle and upper epidermis for light to penetrate into the leaf and also for efficient diffusion of gases from the stomata, up through the gas spaces to the photosynthetic layers
  • Palisade cells packed with chloroplasts: cells are densely stacked with long axes perpendicular to leaf surface