Gas exchange

• Explain how the leaves of dicotyledonous plants are adapted for gas exchange

  1. Many stomata (high density)

  2. Large surface area for gas exchange (when opened by guard cells)

  3. Spongy mesophyll contains air spaces

  4. Large surface area for gas exchange
• Thin short diffusion distance
• Leaf cross-section


  • Waxy cuticle
  • Upper epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Closed stomata
  • Open stomata
• Stomata allow vapour out
• Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

  1. Thicker waxy cuticle

  2. Cuticle increases diffusion distance so less evaporation

  3. Sunken stomata in pits/rolled leaves/hairs trap water vapour/protect stomata from wind

  4. Reduced water potential gradient between leaf and air

  5. Less evaporation

  6. Spines/needles reduce surface area to volume ratio
• Xerophyte plant


  • Adapted to live in very dry conditions
  • e.g. Cacti and mangrove
• Describe the gross structure of the human gas exchange system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli (air sacs)
  • Capillary network surrounding alveoli
  • Lungs
• The main function of the endocrine system is to secrete hormones into the bloodstream, which then travel throughout the body.
• Leaves of dicotyledonous plants

  • Many stomata (high density)
  • Large surface area for gas exchange (when opened by guard cells)
• Spongy mesophyll


  • Contains air spaces
  • Large surface area for gases to diffuse through
• Leaf cross-section


  • Thin
  • Short diffusion distance
• Leaf cross-section layers


  • Waxy cuticle
  • Upper epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Lower epidermis
• Gas exchange in leaves

  1. Closed stomata

  2. Open stomata

  3. Water vapour OUT, O2/CO2 IN
• Xerophytic plants


  • Thicker waxy cuticle
  • Sunken stomata in pits/rolled leaves/hairs
  • Spines/needles
  • Hairs
• Structural adaptations in xerophytes

  • Increases diffusion distance so less evaporation
  • Trap water vapour/protect stomata from wind
  • Reduces surface area to volume ratio
• Structural adaptations in xerophytes


  • Reduces water potential gradient between leaf and air
  • So less evaporation