Chapter 7: Transport in Plants

Introduction

• Focus shifts from biomolecular stuff to big systems (organisms).
• Transport in plants focuses on dicots only.

Plant Anatomy (Part 1A)

Plant Organs

• Leaves
• Stem
• Roots

Key Structures

• Xylem and Phloem: Positions and details vary for different plant types.

Detailed Examination of Plant Organs

Root

• Sections: Transverse & Longitudinal
• Anatomy (Transverse Section):
  • Epidermis with root hairs (cytoplasmic extensions, part of epidermal cells)
  • Cortex between epidermis and endodermis
  • Xylem in the middle, surrounded by phloem and pericycle
• Anatomy (Longitudinal Section):
  • Root cap and root hairs present

Stem

• Sections: Transverse & Longitudinal
• Anatomy (Transverse Section):
  • Epidermis on the outside
  • No endodermis; vascular bundles forming a circle
  • Xylem on inner layer, phloem on outer layer
  • Cortex outside vascular bundles, pith in the middle (storage)

Leaf

• Sections: Transverse
• Anatomy:
  • Mid-rib (transverse section focus)
  • Palisade mesophyll, spongy mesophyll
  • Upper & lower epidermis, with stomata and guard cells
  • Xylem on top, phloem below

Plant Tissues

• Types: Dermal, Vascular, Ground
• Dermal Tissue: Epidermal and endodermal
• Vascular Tissue: Xylem and Phloem
• Ground Tissue: Parenchyma, Collenchyma, Sclerenchyma

Ground Tissue Cells:

• Parenchyma: Thin cell walls, found in mesophyll and cortical cells, functions in photosynthesis, storage, and cell division
• Collenchyma: Thicker cell walls, provides structural support, found in outer cortical cells
• Sclerenchyma: Very thick cell walls, provides support to hardened stems and tree branches

Xylem and Phloem

• Xylem: Transports water and provides structural support
  • Includes vessel elements, tracheids, fibers, and parenchyma cells
• Phloem: Transports assimilates (sucrose, amino acids)
  • Includes sieve tube elements and companion cells

Xylem Structure & Function

• Elongated cells joined end-to-end: Form continuous tubes
• Non-living: Hollow lumen, no cytoplasm or organelles (greater volume, less resistance)
• Thick cell walls: Made of cellulose & lignin (provides structure and waterproofing)
• Pits: Allow lateral movement & bypass of air bubbles

Phloem Structure & Function

• Sieve Tube Elements: Living cells, few organelles, no nucleus, sieve plates present
• Companion Cells: Close association with sieve tubes, many mitochondria and ribosomes

Summary

• Xylem: Transports water from roots to leaves (one-way), made of dead cells
• Phloem: Transports organic molecules (two-way), made of living cells with companion cells

Preview of Next Topic

• Focus on Transport: Water, gases, and products of photosynthesis
• Key Transport Processes: Simple diffusion for gases, specialized transport for water and nutrients