1.1 - Organisation of Plant Tissues

Types of Plant Tissues

• A plant consists of meristematic tissues and permanent tissues.
• Meristematic tissues are actively dividing tissues through mitosis.
• Meristematic tissues consist of:
  • Apical meristematic tissues.
  • Lateral meristematic tissues.
• Permanent tissues consist of:
  • Epidermal tissues.
  • Ground tissues: parenchyma, collenchyma and sclerenchyma tissues.
  • Vascular tissues: xylem and phloem tissues.

Permanent Tissues

• Matured tissues which have experienced or are experiencing differentiation.

Epidermal Tissues

• Layer the outermost surface of stems, leaves and roots of young plants.
• Epidermal cell walls exposed to the air have a waxy, waterproof cuticle.
• The cuticle:
  • Reduces water loss through evaporation (transpiration).
  • Protects leaves from mechanical injuries and pathogens.
• Modified epidermal cells:
  • Guard cells control the opening of the stoma.
  • Root hair cells increase the root surface area for water and mineral salt absorption.

Ground Tissues

1. Parenchyma Tissues

• Simplest living cells; do not undergo differentiation.
• Have the thinnest cell walls.
• Remain turgid to support and maintain the shape of herbaceous plants.
• Carry out photosynthesis, store starch and sugar, and take part in gaseous exchange.
• Take part in tissue repair and regeneration and in the vascular system.

2. Collenchyma Tissues

• Living cells that mature into flexible cells.
• Cell walls are made of pectin and hemicellulose and are thicker than those of parenchyma tissues.
• Provide mechanical support and elasticity to plants.

3. Sclerenchyma Tissues

• Dead cells at maturity.
• Have the thickest cell walls among the three ground tissues.
• Provide support and mechanical strength to matured plant parts.
• Help transport water and nutrients in plants.

Vascular Tissues

Xylem

• Made up of dead cells without cytoplasm.
• Cell walls contain lignin.
• Xylem vessels are elongated, hollow and connected from the roots to the leaves.
• Transport water and mineral salts from the roots to all parts of the plant.

Phloem

• Made up of companion cells and sieve tubes.
• Sieve tubes are living cells with cytoplasm.
• Mature sieve tubes lack organelles such as the nucleus and ribosomes because these organelles degenerate at maturity.
• Sieve tubes are arranged end to end to form elongated, continuous tubes.
• Transport sugars produced by photosynthesis from the leaves to storage organs such as roots, fruits and tubers.