Unit XI: Plant Structure and Function

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Unit XI Plant Structure and Function

• Plant biology, perhaps the oldest branch of
  science, is driven by a combination of curiosity
  and need- curiosity about how plants work and a
  need to apply this knowledge judiciously to feed,
  clothe, and house a burgeoning human population.

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Plant Biology- Why?

• Molecular Biology and Plant Biology
• Arabidopsis thaliana
• weed that belongs to the mustard family
• - organism of choice for molecular study
• About Arabidopsis on the Internet

Genomic Sequence of 5 Chromosomes of Arabidopsis
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Evolution of Plants

• All Plants
• multicellular, eukaryotic, autotrophic,
  alternation of generations

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Alternation of Generations

• Sporophyte (diploid)
• produces haploid
• spores via meiosis
• Gametophyte (haploid)
• produce haploid
• gametes via mitosis
• Fertilization
• joins two gametes to
• form a zygote

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Angiosperms

• Monocots vs. Dicots
• named for the number
• of cotyledons present on
• the embryo of the plant
• monocots
• - orchids, palms,
• lilies, grasses
• dicots
• - roses, beans,
• sunflowers, oaks

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Plant Morphology

• Morphology (body form)
• shoot and root systems
• inhabit two environments
• - shoot (aerial)
• stems, leaves, flowers
• - root (subterranean)
• taproot, lateral roots
• vascular tissues
• transport materials between
• roots and shoots
• - xylem/phloem

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Plant Anatomy

• Anatomy (internal structure)
• division of labor
• cells differing in structure and function
• - parenchyma, collenchyma, sclerenchyma (below)
• - water- and food-conducting cells (next slide)

Parenchyma St typical plant cells Fu
perform most metabolic functions Ex fleshy
tissue of most fruit
Collenchyma St unevenly thickened primary
walls Fu provide support but allow growth in
young parts of plants Ex celery
Sclerenchyma St hardened secondary walls Fu
specialized for support dead Ex fibers
(hemp/flax) slereids (nut shells/seed coats)
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Water- and Food-conducting Cells

• Xylem (water)
• dead at functional maturity
• tracheids- tapered with pits
• vessel elements- regular tubes

• Phloem (food)
• alive at functional maturity
• sieve-tube members- arranged
• end to end with sieve plates

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Plant Tissues

• Three Tissue Systems
• dermal tissue
• epidermis (skin)
• - single layer of cells that
• covers entire body
• - waxy cuticle/root hairs
• vascular tissue
• xylem and phloem
• - transport and support
• ground tissue
• mostly parenchyma
• - occupies the space b/n
• dermal/vascular tissue
• - photosynthesis, storage,
• support

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Plant Growth

• Meristems
• perpetually embryonic tissues located at
  regions of growth
• divide to generate additional cells
  (initials and derivatives)
• - apical meristems (primary growth- length)
• located at tips of roots and shoots
• - lateral meristems (secondary growth- girth)

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Primary Growth of Roots

• Primary Growth of Roots
• apical meristem produces
• all 3 tissue systems
• primary meristems
• - protoderm
• - ground meristem
• - procambium
• root cap
• three overlapping zones
• - cell division
• - elongation
• - maturation

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Primary Growth in Shoots

• Primary Growth in Shoots
• apical meristem (1, 7)
• cell division occurs
• produces primary meristems
• - protoderm (4, 8)
• - procambium (3, 10)
• - ground meristem (5, 9)
• axillary bud meristems
• located at base of
• leaf primordia
• leaf primordium (2, 6)
• gives rise to leaves

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Leaf Anatomy

• Epidermal Tissue
• upper/lower epidermis
• guard cells (stomata)
• Ground Tissue
• mesophyll
• palisade/spongy
• parenchyma
• Vascular Tissue
• veins
• xylem and phloem

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Secondary Growth

• Lateral Meristems
• vascular cambium
• produces secondary xylem/phloem (vascular
  tissue)
• cork cambium
• produces tough, thick covering (replaces
  epidermis)
• secondary growth
• occurs in all gymnosperms most dicot
  angiosperms

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Vascular Cambium

• Production of Secondary Vascular Tissue
• Vascular Cambium cells give rise to xylem (X)
  and phloem (P)
• Cambium cell (C) gives rise to initial
  and derivative (D)
• - Derivative differentiates into xylem (X) or
  phloem (P) cell

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Cork Cambium

• Periderm
• protective coat of
• secondary plant body
• cork cambium and
• dead cork cells
• - bark
• cork cambium produces
• cork cells
• cork cells deposit
• suberin and die
• secondary growth
• commences farther down
• the shoot
• transforms older
• regions first

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Plant Nutrition

• What does a plant need to survive?
• 9 macronutrients, 8 micronutrients
• macro- required in large quantities
• - C, H, N, O, P, S, K, Ca, Mg
• micro- required in small quantities
• - Fe, Cl, Cu, Mn, Zn, Mo, B, Ni
• usually serve as cofactors
• of enzymatic reactions

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Mineral Deficiency

• Mineral deficiency
• symptoms related to function of element
• Mg- causes chlorosis
• - ingredient of chlorophyll
• Fe- causes chlorosis
• - required as cofactor in photosynthesis
• symptoms also related to mobility of element
• Mg- chlorosis of older leaves
• - relatively mobile
• Fe- chlorosis of younger leaves
• - relatively immobile
• young, growing tissues have more
• drawing power
• hydroponic culture
• growing plants by bathing roots- no soil!

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Soil

• Texture and Composition
• texture depends on size of particles
• sand-silt-clay
• - loams equal amounts of sand,
• silt, clay
• composition
• horizons
• - living organic matter
• - A horizon topsoil, living
• organisms, humus
• - B horizon less organic, less
• weathering than A horizon
• - C Horizon parent material
• for upper layers
• soil conservation issues
• fertilizers, irrigation, erosion

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Nitrogen

• Soil Bacteria
• decompose humus to release nitrogen in soil
• plants absorb ammonium (NH4), nitrate
  (NO3-)
• - nitrogen-fixing bacteria
• - ammonifying bacteria
• - nitrifying bacteria

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Nutritional Adaptations

• Symbiotic Relationships
• symbiotic nitrogen fixation
• root nodules contain bacteroids
  (Rhizobium bacteria)
• - mutualistic relationship
• mycorrhizae
• symbiotic associations of fungi and roots
• - mutualistic relationship
• ectomycorrhizae
• - mycelium forms mantle over root
• endomycorrhizae
• - does not form mantle hyphae extend inward
• parasitic plants
• plants that supplement their nutrition
  from host
• - mistletoe, dodder plant, Indian pipe
• carnivorous plants
• supplement nutrition by digesting animals

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Transport in Plants

• Transport
• occurs on three levels
• cellular level
• - absorption of water/minerals
• from soil by root cells
• short-distance transport
• - cell to cell at tissue/organ level
• loading of sugar from
• photosynthetic cells to
  phloem
• long-distance transport
• - sap within xylem and phloem
• throughout plant

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Absorption of Water and Minerals by Roots
soil --gt epidermis --gt root cortex --gt xylem
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Uptake of Soil Solution

• Symplastic Route
• continuum of cytosol based
• on plasmodesmata
• Apoplastic Route
• continuum of cell walls and
• extracellular spaces

Lateral transport of soil solution alternates
between apoplastic and symplastic routes until
it reaches the Casparian strip Mycorrhizae
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Casparian Strip
The Casparian strip is a belt of suberin (purple)
that blocks the passage of water and dissolved
minerals. Only minerals that are already in the
symplast or enter that pathway by crossing the
plasma membrane can detour around the Casparian
strip and pass into the stele.
Summary of uptake of soil animation
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Transport of Xylem Sap

• Transpiration
• the loss of water vapor from leaves and other
  aerial parts of the plant
• transpirational pull
• - transpiration-cohesion-tension mechanism

Water vapor diffuses from the moist air spaces of
the leaf to the drier air outside via
stomata. Tension is created by the evaporation
of water and pulls water from locations where
hydrostatic pressure is greater
(xylem). Transpirational pull draws water out of
xylem and through mesophyll tissue to the
surfaces near stomata.
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Cohesion and Adhesion of Water

• Hydrogen Bonding
• cohesion
• water molecules tug on to each other
• adhesion
• water molecules adhering to the
• hydrophillic walls of xylem cells

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Control of Transpiration

• Photosynthesis-Transpiration Compromise
• guard cells help balance plants need to
  conserve water with its
• requirement for photosynthesis
• stomata open (widen) and
• close (narrow)
• - guard cells change their
• shape (turgid/flaccid)
• - reversible uptake/loss of
• potassium (K) ions

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Translocation of Phloem Sap

• Source to Sink
• sugar source
• organ that produces sugar
• sugar sink
• organ that consumes/stores sugar
• phloem loading and unloading
• chemiosmotic mechanism
• actively transports sucrose
• - sucrose is co-transported with
• H back into cell

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Plant Reproduction

• Sporophyte (diploid)
• produces haploid
• spores via meiosis
• Gametophyte (haploid)
• produce haploid
• gametes via mitosis
• Fertilization
• joins two gametes to
• form a zygote

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Angiosperm Life Cycle

• Sporophyte (diploid)
• actual plant with
• flowers
• Gametophyte (haploid)
• male germinated
• pollen grain
• female embryo sac
• Fertilization
• joins two gametes to
• form a zygote

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Moss Life Cycle

• Gametophyte
• dominant generation
• has both sexes and
• produces gametes
• - archegonia (eggs)
• - antheridia (sperm)
• Fertilization
• sperm move along moss to
• find archegonia
• Sporophyte
• grows on top of gametophyte
• sporangia is where spores
• are produced by meiosis

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Fern Life Cycle

• Sporophyte
• produce spores via
• meiosis
• spores develop
• into young
• gametophyte
• Gametophyte
• has both sexes and
• produces gametes
• - archegonia
• (eggs)
• - antheridia
• (sperm)
• Fertilization
• similar to mosses

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Gymnosperm Life Cycle

• Sporophyte
• produce gametophytes inside
• of cones
• Pollen cone (male)
• - produces microspores
• via meiosis
• Ovulate cone (female)
• - produces megaspores
• via meiosis
• Fertilization
• pollen grains discharge sperm
• into egg

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Male and Female Gametophyte of Flowering Plant

• Male Gametophyte
• pollen grain
• microspores produced
• within the anther
• divide once to
• produce two
• sperm cells
• Female Gametophyte
• embryo sac
• megaspore produced
• within the ovule
• divide to produce
• three egg cells
• - 2 polar nuclei

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Double Fertilization

• Double Fertilization
• pollen grain lands on stigma
• pollen tube toward ovule
• both sperm discharged down the tube
• - egg and one of the sperm
• produce zygote
• - 2 polar nuclei and sperm
• cell produce endosperm
• ovule becomes the seed coat
• ovary becomes the fruit

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Seed Structure and Development