Permanent Tissues

Epidermal tissues

• Layer the outermost surface of stems, leaves and roots of young plans
• Epidermal cell walls which are exposed to the air have a layer of cuticle

Cuticle layer

• A waxy and waterproof layer that covers the epidermal cells exposed to air
• Functions
  • Reduces water loss through evaporation (transpiration)
  • Protects the leaves from mechanical injuries
  • Protects the leaves from pathogen

• Modified epidermal cells according to their functions:
  • Guard cells: control the opening of stoma
  • Root hair cells: increase the surface area of the root for water and mineral salts absorption

Ground Tissues

(i) Parenchyma tissues

• Made of simplest living cells that have not undergone differentiation
  • They have thinnest cell walls
• Functions of parenchyma tissues:
  • Support: parenchyma tissues in turgid state provide support and maintain the shape of herbaceous plants
  • Involved in photosynthesis
  • Involved in gaseous exchange
  • Help in storange of starch and sugar
  • Involved in repair and regeneration of plant tissues
  • Involved in vascular transport system

(ii) Collenchyma tissues

• Made of living cells that mature into flexible cells
  • Have cell walls made of pectin and hemicellulose
  • Cell walls are thicker than cell walls of parenchyma cells
• Function:
  • Provide mechanical support and elesticity to plants

(iii) Sclerenchyma tissues

• Consist of dead cells when they are matured
  • Have thickest cell walls among the three ground tissues
  • Cell walls have lignin
• Function:
  • Provide support and mechanical strength to the parts of matured plants
  • Help in transport of water and nutrients in plants

Vascular tissues

(i) Xylem

• Consist of dead cells
  • Cells do not contain cytoplasm
  • Cell walls contain lignin
• Consists of xylem vessels that are elongated, hollow and connected to each other from roots to the leaves
• Functions:
  • Transports water and mineral salts from roots to all parts of a plant

(ii) Phloem

• Consists of living cells known as companion cells and sieve tubes
  • Cells contain cytoplasm
  • Sieve tubes
    • Do not have any organelles such as nucleus and ribosome due to degradation / degeneration during the cells development
    • Arranged from end to end of phloem forming elongated and continuous tube structure
• Function
  • Transports organic substances produced from photosynthesis (such as sugar), from leaves to storage organs such as roots, fruits and tubers