Activity 5: plant tissues

• Plants are eukaryotic, photoautotrophic organisms
• Common to all plants are cells with rigid cellulosic walls and chloroplasts containing chlorophylls a and b together with accessory pigments
• All plants are multicellular, the cells organized into tissues and organs
• Their bodies consist of two organ systems: the root system and shoot system
• Plant tissues

  • Meristematic tissues
  • Permanent tissues
• Meristematic tissues


  Composed of immature cells undergoing active mitotic division
• Meristematic tissues


  • Largely confined to the root and shoot apices (apical meristems)
  • Responsible for primary growth, the increase in length of the plant body
  • Another group, the lateral meristems, run along the length of the shoot to the root and are responsible for secondary growth or the increase in girth of woody plants
• Permanent tissues


  Composed of matured or differentiated cells
• Permanent tissue systems

  • Dermal tissues
  • Ground tissues
  • Vascular tissues
• Dermal tissues(epidermis and periderm)


  Provide the surface or protective tissues of the plant body
• Ground tissues


  Perform functions like photosynthesis, storage (parenchyma), and mechanical support (collenchyma and sclerenchyma)
• Vascular tissues(xylem and phloem)


  Function in conduction and transport of substances throughout the plant body
• Meristematic tissue in root tip


  1. Root cap

  2. Root apical meristem (gives rise to protoderm, ground meristem, procambium)

  3. Region of elongation

  4. Region of maturation
• Protoderm


  Gives rise to the epidermis
• Ground meristem


  Produces cells of the fundamental tissue
• Procambium


  Gives rise to the primary xylem and phloem
• The uppermost region is the region of maturation where the cells have differentiated into the three tissue systems: dermal, fundamental and vascular
• Epidermal cells of Rhoeo spathacea


  • No intercellular spaces
  • Cells are arranged in a specific shape and pattern
• Parenchyma


  Cells that form the ground tissue, contain numerous chloroplasts and are called chlorenchyma
• Parenchyma cells in the leaf of Ixora sp. are arranged in two distinct layers
• Collenchyma


  • Cells have uneven thickening of the cell walls
  • May or may not have intercellular spaces
• Sclerenchyma


  • Cell walls are thicker compared to collenchyma
• Vascular bundle


  Contains xylem, phloem, parenchyma and sclerenchyma tissues
• Metaxylem


  Primary xylem vessels that are large and thick-walled
• Protoxylem


  Primary xylem vessels that are smaller in diameter and have thin walls
• Phloem


  Contains sieve tube elements and companion cells
• Bundle sheath


  Layer of sclerenchyma fibers enclosing the vascular bundle
• Xylem vessels


  • Differentiated by variations in thickenings of their cell wall
• Vascular tissue arrangements

  • Collateral
  • Bicollateral
  • Concentric (amphivasal, amphicribral)
• Collateral arrangement


  Xylem and phloem tissues located along the same radius of the stem, typical of gymnosperms and angiosperms
• Radial arrangement


  Typical of roots
• Bicollateral arrangement


  Xylem tissue sandwiched between two phloem tissues
• Concentric arrangement


  One tissue completely surrounds the other (amphivasal: xylem surrounds phloem, amphicribral: phloem surrounds xylem)
• The outermost or peripheral layer of plant organs consists of dermal tissue, enclosing the fundamental or ground tissues, with the vascular tissues embedded in the center or scattered in the ground tissue
• Cortex


  Ground tissue layer in the root, between the epidermis and endodermis
• Endodermis


  Single layer of cells enclosing the vascular tissue in the root
• Mesophyll


  Ground tissue layer in the leaf, between the upper and lower epidermis, containing palisade and spongy layers
• Vascular tissue arrangement in dicot stem


  Vascular bundles scattered throughout the stem, with xylem inner to the phloem
• Above root cap


  Region of active cell division
• Dermal tissue I.e.

  Epidermis and periderm