Plant form and function

Subdecks (3)

Cards (130)

  • 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