Unit 7.1

• Organs of Flowering Plants

  • Root system (roots)
  • Shoot system (stem and leaves)
  • Flowers, seeds and fruits (for reproduction)

  
• Roots

  • Anchor plant in soil
  • Absorb water and minerals from soil
  • Produce hormones
• Root hairs

  Projections from epidermal root-hair cells that greatly increase absorptive capacity of root

  
• Stems


  • Main axis of plant that elongates and produces leaves
  • Nodes where leaves are attached to stem
  • Internodes between nodes
  • Axillary buds can produce new branches or flowers
  • Contain vascular tissue that transports water and minerals

  
• Leaves

  • Major part of plant that carries on photosynthesis
  • Foliage leaves are usually broad and thin
  • Blade - wide portion of foliage leaf
  • Petiole - stalk attaching blade to stem
  • Leaf Axil - upper acute angle between petiole and stem where axillary bud is found
  • Tendrils - leaves that attach to objects
  • Bulbs - leaves that store food

  
• Monocots and eudicots


  Two categories that plants are classified into
• Meristematic tissue


  • Enables flowering plants to grow throughout their lifetime
  • Apical meristems at tips of stems and roots increase length of these tissues
  • Apical meristem produces three types of meristem which produce three specialized tissues: epidermal, ground, and vascular

  
• Epidermal tissue


  • Forms outer protective covering of plant
  • Epidermis contains closely packed epidermal cells
  • Epidermal cells exposed to air are covered with waxy cuticle
  • Root epidermal cells have root hairs
  • Epidermal cells of stems, leaves, and reproductive organs have trichomes
  • Lower leaf surface contains stomata
  • In older woody plants, epidermis of stem is replaced by periderm (major component is cork)

  
• Ground tissue


  • Forms bulk of flowering plant
  • Parenchyma cells - least specialized, found in all organs, can divide and give rise to more specialized cells
  • Collenchyma cells - have thicker primary walls, form bundles underneath epidermis, provide flexible support for immature regions
  • Sclerenchyma cells - have thick secondary walls impregnated with lignin, most are nonliving, primary function is to support mature regions (fibers and sclereids)

  
• Xylem


  • Transports water and minerals from roots to leaves
  • Tracheids - long with tapered ends, water moves across pits in end walls and side walls
  • Vessel elements - larger, with perforated plates in end walls, form continuous vessel for water and mineral transport
• Phloem

  • Transports sucrose and other organic compounds from leaves to roots
  • Sieve-tube members function as conducting cells, contain cytoplasm but lack nuclei
  • Sieve plate - cluster of pores in wall
  • Each sieve-tube member has a companion cell containing a nucleus, connected by plasmodesmata

  
• Root structure

  • Root cap contains root apical meristem
  • Zone of cell division contains primary meristems
  • Zone of elongation contains cells lengthening and becoming specialized
  • Zone of maturation contains fully differentiated cells

  
• Eudicot root tissues

  • Epidermis - outer layer
  • Cortex - composed of parenchyma cells allowing water and mineral movement
  • Endodermis - forms boundary between cortex and vascular cylinder, contains Casparian strip
  • Vascular tissue - contains xylem and phloem, pericycle is mitotically active and can begin development of branch or lateral roots

  
• Monocot root tissues


  • Ground tissue of root's pith is surrounded by vascular ring
  • Have same growth zones as eudicot roots, but do not undergo secondary growth
  • Have pericycle, endodermis, cortex, and epidermis

  
• Root types

  • Primary root (taproot) - fleshy, long single root that grows straight down and stores food
  • Fibrous root system - slender roots and lateral branches that anchor plant to soil
  • Adventitious roots - roots that develop from organs of shoot system instead of root system (e.g. prop roots)
  • Haustoria - rootlike projections found in parasitic plants that make contact with host plant's vascular tissue
  • Mycorrhizae - mutualistic associations between roots and fungi that assist in water and mineral extraction
  • Root nodules - contain nitrogen-fixing bacteria

  
• Shoot apical meristem


  • Produces new cells that elongate and increase stem length
  • Protected by terminal bud enveloped by leaf primordia
  • Specialized primary meristems: protoderm (gives rise to epidermis), ground meristem (gives rise to pith and cortex), procambium (produces primary xylem and phloem)

  
• Herbaceous stems


  • Mature non-woody stems exhibit only primary growth
  • Outermost tissue covered with waxy cuticle
  • Stems have distinctive vascular bundles - eudicots have vascular bundles arranged in distinct ring, monocots have vascular bundles scattered throughout stem

  
• Woody stems


  • Have both primary and secondary tissues
  • Primary tissues formed each year from primary meristems
  • Secondary tissues develop during first and subsequent years from lateral meristems
  • Have both primary and secondary growth - primary growth increases length, secondary growth increases girth
  • Have three distinct regions: bark, wood, pith

  
• Bark

  • Contains cork, cork cambium, and phloem
  • Cork cells are impregnated with suberin, gas exchange is impeded except at lenticels
• Wood


  • Secondary xylem that builds up year after year
  • Vascular cambium is dormant during winter, annual ring is made up of spring wood and summer wood
  • In older trees, inner annual rings called heartwood no longer function in water transport
• Stem types


  • Above ground vertical stems
  • Stolons - above ground horizontal stems that produce new plants when nodes touch ground
  • Rhizomes - underground horizontal stems that contribute to asexual reproduction
  • Variations: tubers (enlarged portions functioning in food storage), corms (underground stems that produce new plants)

  
• Leaf structure

  • Upper and lower epidermis (with waxy cuticle, trichomes, stomata on lower surface)
  • Mesophyll - in eudicots, palisade mesophyll with elongated cells and spongy mesophyll with irregular cells bounded by air spaces, contains many chloroplasts

  
• Leaf diversity


  • Blade can be simple or compound
  • Leaves adapted to environmental conditions (e.g. shade leaves, spines, climbing leaves)