Plant Structure and Function: Focus on Leaves

Levels of Organization in Plants

• Plants have different levels of organization, similar to animals:
  • Cells: Similar cells combine to form tissues.
  • Tissues: Different types combine to form organs.
  • Organs: Multiple organs form organ systems.

Structure of a Leaf

• A leaf is an organ that, along with the stem and roots, forms an organ system.
• Function: Transport substances around the plant.
• Leaves are involved in photosynthesis, requiring carbon dioxide and water to produce sugars.

Leaf Anatomy (Cross-section)

1. Stomata

   • Small holes for gas exchange.
   • Found in the lower epidermis.
   • Thousands per leaf.
   • Allow carbon dioxide to diffuse into the leaf.

2. Spongy Mesophyll Tissue

   • Contains air gaps for easy gas diffusion.

3. Palisade Mesophyll Layer

   • Site of most photosynthesis.
   • Packed with chloroplasts.

4. Upper Epidermis

   • Almost transparent cells.
   • Allows sunlight to reach chloroplasts in the palisade cells.

5. Phloem and Xylem

   • Phloem: Transports sugar molecules throughout the plant.
   • Xylem: Transports water from roots to leaves.

6. Waxy Cuticle

   • A thin waterproof lipid layer.
   • Reduces water loss from the leaf's surface.

Water Management in Leaves

• Guard Cells: Control the opening and closing of stomata.
• Water Loss:
  • Water can diffuse out easily through stomata.
  • Stomata open briefly to maximize CO2 intake and minimize water loss.
• Guard Cell Behavior
  • Turgid when hydrated, increasing stomatal opening.
  • Flaccid when dehydrated, closing stomatal gap to conserve water.
  • Sensitive to light, closing at night when photosynthesis isn't needed.

Additional Tissue: Meristem Tissue

• Functions similarly to stem cells in animals.
• Found at growing tips of roots and shoots.
• Can differentiate into various cell types for plant growth.

Additional Resources

• Find more videos, flashcards, and exam materials on the website mentioned (e.g., Cognito). Sign up is free.

Reminder

• Understanding the structure and function of leaves is crucial for grasping plant physiology, especially photosynthesis and water management processes.