Plant Cell Structures and Functions

Plant Cell Structures and Functions

• Plant cells are fundamental units of plant structure, performing specific functions.
• Plant tissues are groups of similar cells performing similar functions.
• Plant tissues are classified as meristematic and permanent.

Meristematic Tissues

• Composed of actively dividing cells primarily for plant growth.
• Found in the growing parts (roots, stems) of plants.
• Two major types: apical and lateral meristems.
• Apical meristems: are responsible for primary growth (height increase), located at root tips and shoot tips.
  • Lead to production of primary plant body and primary meristems. (protoderm, procambium, and ground meristem)
  • Primary meristems differentiate into primary plant tissue systems (epidermis, stele (xylem/phloem), and ground tissue).
• Lateral meristems: responsible for secondary growth (diameter/girth increase), located along the plant's length.
  • Two key types: vascular cambium and cork cambium.

Permanent Tissues

• Composed of non-dividing cells with specialized functions.
• Classified as simple (one cell type) or complex (two or more cell types).
• Simple permanent tissues: ground tissues (parenchyma, collenchyma, sclerenchyma) and epidermis.
• Complex permanent tissues: xylem and phloem.

Simple Permanent Tissues

• Epidermis: Outer protective layer, develops from protoderm.
  • Covered by waxy cuticle (prevents water loss).
  • Root hairs increase absorption.
  • Trichomes (on leaves/stems) reduce water loss/reflect light.
  • Replaced with periderm as woody plants grow.
• Ground Tissues: Fill the spaces between dermal and vascular tissues.

  • Types: parenchyma, collenchyma, sclerenchyma

  • Parenchyma: Least specialized, photosynthesis and storage (starch, food). Flexible primary walls.

  • Collenchyma: Unevenly thickened primary walls (flexible support). No secondary walls or lignin. Found in young stems and petioles.

  • Sclerenchyma: Thick, lignin-strengthened secondary walls (rigid support).

    • Sclereids: Gritty texture in fruits (seeds).
    • Fibers: Used commercially (ropes, flax).

Complex Permanent Tissues

• Xylem: Water-conducting tissue.

  • Composed of tracheids (elongated, water passing-through cells) and vessel elements (perforated plates for efficient water transport).
  • Thick secondary walls for rigidity and water transport.

• Phloem: Food-conducting tissue.

  • Composed of sieve-tube elements (transporting organic substances like sucrose) and companion cells.
  • Lacking nucleus & ribosomes (efficient transport).
  • Sieve plates with pores for nutrient flow.

• Both xylem and phloem combine to form vascular bundles, their arrangement differs in roots (star-shaped) and stems ( scattered or ring-shaped depending on the plant type).

Did You Know?

• Sclerenchyma cells (sclereids) give the gritty texture to fruits like pears.

Summary

• Plants have two major tissue types: meristematic (for growth) and permanent (for function).
• Meristematic differentiates into specialized permanent tissues
• Primary growth increases plant height, driven by apical meristems (roots, stems).
• Secondary growth increases girth, driven by lateral meristems (vascular and cork cambium).
• Ground tissues provide structural support, storage, and photosyinthesis.
• Complex tissues (xylem, phloem) transport water and food throughout the plant.