Lecture Notes: Plant Structure and Leaf Organization

Levels of Organization in Plants

• Plants, like animals, have different levels of organization:
  • Cells: Basic unit of life.
  • Tissues: Groups of similar cells.
  • Organs: Combination of different tissues.
  • Organ Systems: Combination of multiple organs.

The Leaf as an Organ

• Leaf Structure: A key organ in the plant.
  • Part of an organ system with the stem and roots.
  • Organ system function: Transport of substances around the plant.

Function of Leaves

• Site of Photosynthesis:
  • Requires carbon dioxide and water to produce sugars.
  • Water transported from soil by roots and xylem.
  • Carbon dioxide diffuses from the air through stomata.

Leaf Anatomy

• Epidermis:
  • Lower Epidermis: Contains thousands of stomata (small holes for gas exchange).
  • Upper Epidermis: Transparent for sunlight penetration.
• Spongy Mesophyll:
  • Contains air gaps for easy gas diffusion.
• Palisade Mesophyll:
  • Main site of photosynthesis.
  • Cells packed with chloroplasts.
• Vascular Tissues:
  • Phloem: Carries sugars throughout the plant.
  • Xylem: Transports water from roots to leaves.

Water Loss and Stomata Function

• Waxy Cuticle: Water-proof layer on top of the leaf to minimize water loss.
• Stomata (singular: stoma):
  • Openings controlled by guard cells.
  • Regulate water loss and carbon dioxide intake.
  • Guard cells become turgid (full of water) to open stomata.
  • Become flaccid (lose water) to close stomata and conserve water.
  • Close at night when photosynthesis isn't occurring.

Adaptations of Leaves

• Placement of Stomata:
  • Mostly on the underside of leaves to reduce water evaporation.
• Guard Cells:
  • Sensitive to light; regulate stomata opening according to water availability and light conditions.

Meristem Tissue

• Function: Similar to stem cells in animals.
  • Found at growing tips of roots and shoots.
  • Differentiates into various cell types for plant growth.

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