6.2 Leaf Structure

Leaf Structure & Adaptations for Photosynthesis

• Function of Leaves: Plant organs that carry out photosynthesis.
• Structural Adaptations:
  • Large Surface Area: Maximizes light absorption.
  • Thin Structure: Facilitates efficient movement of gases between leaf cells and surrounding air.
  • Gas Diffusion: Thin leaves enable rapid diffusion of gases like CO2.

Identifying Leaf Structures in a Dicotyledonous Plant

• Dicotyledonous Plants: A group of flowering plants with specific leaf structures.
• Key Leaf Structures:
  • Cuticle: Transparent, fatty layer on the upper surface.
  • Stomata: Pores for gas and water vapor diffusion.
  • Guard Cells: Surround stomata; capable of shape change to open or close stomata.
  • Spongy Mesophyll: Layer with photosynthesizing cells and air spaces.
  • Palisade Mesophyll: Tightly packed column-shaped cells with chloroplasts.
  • Vascular Bundles: Include xylem and phloem.
  • Xylem: Transports water.
  • Phloem: Transports sucrose and amino acids.
  • Upper and Lower Epidermis: Layers of thin cells on leaf surfaces.

Functions and Adaptations of Leaf Structures

• Waxy Cuticle:
  • Protects leaf and reduces water loss by evaporation.
  • Allows light to pass through.
• Stomata:
  • Allow CO2 to diffuse into leaf.
  • Enable O2 and water vapor to diffuse out.
• Guard Cells:
  • Control stomata opening to reduce water loss.
• Spongy Mesophyll:
  • Conducts photosynthesis and facilitates gas movement.
• Palisade Mesophyll:
  • Maximizes photosynthesis by packing many cells under leaf surface.
• Vascular Bundle:
  • Transports water and nutrients essential for photosynthesis.
• Xylem:
  • Provides water for photosynthesis and maintains transpiration stream.
• Phloem:
  • Moves photosynthesis products to other plant parts.
• Upper Epidermis:
  • Allows light penetration to photosynthetic cells.
• Lower Epidermis:
  • Facilitates gas exchange via stomata and guard cells.