Plant form and function

• are living cells • are isodiametric (roughly spherical) • are structurally and functionally undifferentiated • have a central nucleus • have a dense cytoplasm • have ability to multiply
• A shoot apical meristem is a dome-shaped mass of dividing cells located at the shoot tip.
• Vascular plants main tissue systems

  • Dermal tissue systems
  • Ground tissue systems
  • Vascular tissue systems
• Dermal tissue system

  Outer protective covering of plants
• Dermal tissue system

  • Epidermis
• Epidermis

  • Protective layer in the stems and roots of the primary plant body and leaves
  • Tightly packed single cell layer
  • Normally covered by a cuticle which is a waxy epidermal coating in aerial parts
  • Specialized cells such as guard cells, trichomes and root hairs are also found in epidermis
• Functions of epidermis

  • Defense against physical damage and pathogens
  • Cuticle helps to prevent water loss
• Root hairs

  • Involved in absorption of water and mineral ions
• Guard cells

  • Help gaseous exchange
• Trichomes


  Epidermal outgrowths such as hairs and glands
• Types of trichomes

  • Hair like trichomes
  • Trichomes that secrete chemicals involved in defense against insects/pathogens/herbivores
• Hair like trichomes reduce water loss
• Shiny hairs reflect excess light
• Epidermis in older regions of stems and roots is replaced by a protective layer called periderm after the secondary growth
• Ground tissue system

  Fills the gap between dermal tissue and vascular tissue, mainly consists of cortex (outer to vascular tissue) and pith (inner to vascular tissue)
• Types of cells in ground tissue

  • Parenchyma cells
  • Collenchyma cells
  • Sclerenchyma cells
• Parenchyma cells


  • Living even at functional maturity
  • Mature cells have primary cell walls which are relatively thin, flexible and most of the cells lack secondary walls
  • They have a large central vacuole
• Collenchyma cells • They are generally elongated • They have thicker primary walls than parenchyma cells • Their walls are unevenly thickened • Young stems and petioles often have strands of collenchyma cells just below the epidermis • Even at functional maturity they are living, fl exible and elongating with stems and leaves they support Functions • Give mechanical support to leaves and stems without restraining growth
• Collenchyma cells • They are generally elongated • They have thicker primary walls than parenchyma cells • Their walls are unevenly thickened • Young stems and petioles often have strands of collenchyma cells just below the epidermis • Even at functional maturity they are living, fl exible and elongating with stems and leaves they support Functions • Give mechanical support to leaves and stems without restraining growth
• Phloem tissue

  • Sieve tube elements
  • Companion cells
  • Parenchyma cells
  • Fibers
• Except fibers, other phloem cells are living cells
• Sieve tube elements

  Chains of sieve tube elements are aligned to form sieve tubes
• Sieve tube elements

  The end walls between sieve tube elements contain porous plate called sieve plate
• Sieve plate

  Allows movement of fluid from one sieve element to the next
• Companion cells

  Non-conducting cells found alongside each sieve tube element and connects with sieve tube element by numerous plasmodesmata
• Companion cells

  Nucleus and ribosomes of these cells also serve to adjacent sieve tube element
• Companion cells

  Some companion cells in leaves help in phloem loading and in other organs unloading
• Plants with phloem tissue

  • Angiosperms
  • Seedless vascular plants
  • Gymnosperms
• Sieve tube elements in angiosperms

  Consist of sieve tube elements, companion cells, parenchyma cells and fibers
• Sieve cells in seedless vascular plants and gymnosperms

  Long narrow cells that replace sieve tube elements in these plants
• Sieve tube elements

  Lack nucleus, ribosomes, a distinct vacuole, and cytoskeletal elements
• Sieve tube elements

  Cytoplasm reduced into a thin peripheral layer
• Absence of organelles in sieve tube elements

  Allows passing of nutrients more freely
• Vessel elements

  Contain in all angiosperms and some gymnosperms<br>Cylindrical and long<br>Wider, shorter and have thinner walls than tracheids<br>Secondary walls are thickened by lignin<br>Provide support to prevent collapse under tension of water transport<br>Perforation plates are present at end walls of vessel elements. Other walls are interrupted by pits<br>Form xylem vessel by aligning end to end with perforation plates<br>Water flows freely through perforation plates
• Tracheids

  Found in all vascular plants<br>Long, thin cells with tapering ends<br>Secondary walls are thickened with lignin and often interrupted by pits<br>Water moves from end to end through pits<br>Thickening by lignin provides support to prevent collapse under water transport
• Xylem tissue • It consists of vessel elements, tracheids, fi bers and parenchyma cells in angiosperms and some of the gymnosperms. • Vessel elements and tracheids mainly conduct water. • They are dead at functional maturity. • Fibers give mechanical strength. • Parenchyma functions in storage and in radial transportation.
• In most vascular plants, leaves are the main photosynthetic organs. The exchange of gases occurs through stomata in the upper and lower epidermis. Epidermis is usually a single cell layer. In between the upper and lower epidermis, there is a ground tissue called the mesophyll. This tissue consists of parenchyma cells, specialized for photosynthesis 
• Dicot leaves


  Stomata are mainly found in the lower epidermis
• Mesophyll in dicot leaves

  • Consists of two distinct layers called palisade and spongy
• Palisade mesophyll in dicot leaves

  • Consists of elongated cells that are arranged in one or more layers
  • Found in the upper part of the leaf, just beneath the upper epidermis