Lecture Notes: Structure and Function of a Leaf

Overview of Plant Organization

• Levels of Organization
  • Cells combine to form tissues
  • Tissues combine to form organs
  • Organs combine to form organ systems
• Leaf as an Organ
  • Forms an organ system with stem and roots
  • Main function is the transport of substances

Structure of a Leaf

• Leaf Cross-Section
  • Examined from top to bottom

Function of Leaves

• Site of Photosynthesis
  • Requires carbon dioxide and water to make sugars
  • Water: Transported to leaves by roots and xylem
  • Carbon Dioxide: Diffuses directly into the leaf

Leaf Structures and Functions

• Stomata
  • Small holes for gas exchange
  • Found on lower epidermis
• Spongy Mesophyll Tissue
  • Contains air gaps for gas diffusion
• Palisade Mesophyll Layer
  • Main site of photosynthesis
  • Packed with chloroplasts
• Upper Epidermis
  • Transparent for sunlight penetration
• Phloem
  • Transports sugar molecules

Water Management in Leaves

• Xylem and Phloem
  • Xylem brings water up from the roots
  • Phloem carries sugars
• Waxy Cuticle
  • Reduces water loss from the top
• Stomata Regulation
  • Balance between carbon dioxide absorption and water loss
  • Guard cells control stomata opening
    • Turgid Guard Cells: Open stomata when water is abundant
    • Flaccid Guard Cells: Close stomata to conserve water
  • Light sensitivity helps regulate opening and closing

Adaptations in Leaves

• Stomata Location
  • Mostly on the underside to reduce water evaporation
• Guard Cells and Light
  • Close at night to conserve resources

Additional Tissue: Meristem

• Meristem Tissue
  • Plant stem cells found at root and shoot tips
  • Differentiate into various cell types

Additional Resources

• Links to videos on:
  • Stem Cells
  • Root Hair Cells and their function in active transport

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