6.1 The Tissue System

Plants have cells as their basic unit → cells form tissues → tissues form organs. Different plant organs show differences in internal structure. Monocots and dicots are anatomically different! Three main tissue systems exist:

🌿 Epidermal Tissue System

The plant’s protective outer layer:

• Epidermis: Outermost layer of elongated, tightly packed cells
  • Covered by cuticle (waxy layer preventing water loss) – absent in roots
  • Cells have thin cytoplasm and large vacuoles
• Stomata: Tiny openings in leaves for gas exchange & transpiration control
  • Made of guard cells (bean-shaped in most plants, dumbbell-shaped in grasses)
  • Guard cells have chloroplasts and thick inner walls
  • Stomatal apparatus = stomata + guard cells + subsidiary cells
• Appendages:
  • Root hairs: Unicellular extensions for water/mineral absorption
  • Trichomes: Stem hairs (usually multicellular) that reduce water loss

🪴 Ground Tissue System

All tissues except epidermis and vascular bundles:

• Contains simple tissues: Parenchyma, Collenchyma, Sclerenchyma
• Found in:
  • Cortex, pericycle, pith, and medullary rays (in stems/roots)
  • Mesophyll in leaves (thin-walled, chloroplast-rich cells)

🌱 Vascular Tissue System

The plant’s “transport network” made of xylem and phloem:

• Vascular bundles = xylem + phloem together
• Types:
  • Open bundles: Have cambium (can form secondary tissues) → found in dicot stems
  • Closed bundles: No cambium → found in monocots
• Arrangements:
  • Radial: Xylem/phloem alternate in rings → roots
  • Conjoint: Xylem/phloem on same radius → stems/leaves (phloem outside xylem)

6.2 Dicot vs. Monocot Anatomy

🌻 Dicot Root (Sunflower Example)

• Epiblema: Outermost layer with root hairs
• Cortex: Multiple layers of thin-walled parenchyma cells
• Endodermis: Innermost cortex layer with waterproof Casparian strips
• Pericycle: Gives rise to lateral roots
• Vascular bundles: Radial arrangement (xylem/phloem in alternating groups)
• Pith: Small or absent in dicots