leaves

• Functions of the Leaf

  • Photosynthesis
  • Gas Exchange
• Photosynthesis


  Conversion of light energy into chemical energy (glucose) using chlorophyll and other pigments, from carbon dioxide and water
• Gas Exchange


  Stomata facilitate the intake of CO2 for photosynthesis and the release of O2 during respiration
• Transpiration


  Loss of water vapor through stomata, crucial for nutrient uptake and cooling
• Leaf Adaptations - Xerophytes (Desert Plants)

  • Thick, reduced leaves minimize water loss
  • Stomata open only at night to conserve water
  • Thick waxy layer (cuticle) prevents water loss
• Leaf Adaptations - Floating Leaves (Lily Pads)

  • Stomata primarily on upper epidermis
• Leaf Adaptations - Submerged Leaves (Algae)

  • Lack stomata due to submerged environment
• Leaf Adaptations - Conifers

  • Needle-like leaves with thick, waxy cuticles
  • Evergreen adaptation for continuous photosynthesis
  • Sunken stomata reduce water loss
• Types of Leaves

  • Broad
  • Narrow
  • Needle-like
• Simple leaves


  Single blade per petiole
• Compound leaves


  Divided into smaller leaflets but originate from single axillary bud
• Types of Compound Leaves

  • Pinnately compound - leaflets in pairs along extension of petiole
  • Palmately compound - leaflets attached at same point at end of petiole
• Leaf Attachment

  • Alternate
  • Opposite
  • Whorled
• Venation

  • Parallel - monocot
  • Netted - dicot
  • Pinnate - One primary vein, included within enlarged midrib
  • Palmate - several primary veins fan out from base of blade
• Phyllotaxy


  • Alternate - leaves attached alternately in spiral along stem, one leaf per node
  • Opposite - two leaves arise form opposite node
  • Whorled - 3+ leaves occur at a node
• Tissues in Leaf Blade (Dicot)

  • Dorsiventral (palisade and spongy mesophyll layers)
  • Upper and lower epidermis with cuticle
  • Vascular bundles (xylem and phloem)
  • Guard Cells: Regulate stomatal opening and closing
  • Trichomes: Hair-like structures reduce water loss and protect from predators
• Stomata


  Pores primarily on lower epidermis<|>Control gas exchange and water loss<|>Responsive to light, moisture, and temperature changes
• Monocot vs. Eudicot Leaves

  • Monocots: Narrow, parallel venation
  • Eudicots: Broad, netted venation
• Specialized or Modified Leaves

  • Cotyledons: Seed leaves containing stored food
  • Colored Bracts: Attract pollinators
  • Insect-Trapping Leaves: Modified for prey capture
  • Tendrils and Spines: Adaptations for climbing and defense
  • Storage Leaves: Succulent adaptations for water retention
• Leaf Abscission

  Shedding in response to seasonal changes<|>Involves the formation of an abscission layer and cork cells
• Economic Importance of Leaves

  • Food: Cabbage, lettuce, herbs
  • Dyes and Fibers: Henna, abaca, jute
  • Medicinal Uses: Digitalis from foxglove