PLANTS

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PLANTS
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How Did Plants Adaptto Dry Conditions?

• Plants had to adapt to conditions where they were
  only partly immersed in water
• The adaptation to the water problem arose in two
  steps (1) preventing water loss from cells, and
  (2) transporting water from tissues with access
  to water to tissues without water access.

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Preventing Water LossCuticle and Stomata

• Cuticle is a waxy, watertight sealant used to
  survive in dry environments.
• Stomata perform gas exchange, which have a pore
  that opens and closes

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Cuticles and stomata
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Plant Reproduction

• All land plants undergo alternation of
  generations.
• Use a multicellular haploid phase called the
  gametophyte
• Also have a multicellular diploid phase known as
  the sporophyte.

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• Two evolutionary changes in the history of land
  plants
• (1) gametes were produced in complex
  multicellular structures
• (2) the embryo was retained on the parent and
  nourished (biologists call the land plants
  embryophytes)

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NONVASCULAR PLANTS

• The nonvascular plants, or bryophytes, are the
  most primitive and ancient of land plants.
• Shortfew taller than 7cm
• 3 lineages with living representatives
  (liverworts, hornworts, and mosses)

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Bryophyte Reproduction

• Require water (sperm swim through water to arrive
  at the egg) during times of rain or dew.
• Usually no stomata
• Have no vascular tissue to transport water
  throughout plant, so utilize osmosis through
  cells instead

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• Preceding characteristics explain why almost
  always found in moist environments
• Homosporous (only one type of spore in life cycle
  unlike in gymnosperms and angiosperms)

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Liverworts

• Liver-shaped leaves can grow on bare rock or
  tree bark, which helps in soil formation (Figure
  29.30).
• Simple rhizoids (water absorbing cell that
  absorbs water from ground)
• Fixed stomata

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Liverwort
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Hornworts

• The sporophytes extending from the gametophyte
  plant look like horns and have stomata
• One chloroplast per cell

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Mosses

• Leaf-like structures held on a stem-like
  structure
• Use rhizoids to absorb water
• Female gametophytes called Archegonium (egg forms
  within this structure)
• Male gametophytes called Antheridium produce many
  flagellated sperm

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Moss Plants
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Other notes

• Divisions (fragmentation) AND rhizoid runners
  underground are two additional asexual means of
  reproduction

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Vascular plants--Seedless

• All species of seedless vascular plants have
  conducting tissues with cells that are reinforced
  with lignin, forming vascular tissue.
• Three clades exist today lycophytes (club
  mosses), spenophyta (ancient woody trees and
  horsetails) and pterophytes (ferns)

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Vascular tissue

• Vascular tissuespecialized cylindrical cells
  forming internal networks for transporting water
  and other substances
• Xylemcarries water AND Phloem carries organic
  molecules

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Vascular Tissue Development
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Fern Life Cycle
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Lycophyta

• Formerly found as woody trees 300 mya
• Now found as club mosses ( club-shaped
  spore-bearing structures) and epiphytes

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Spenophyta

• Horsetails can flourish in waterlogged soils by
  allowing oxygen to diffuse down their hollow
  stems
• Stems are jointed together by NODES

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Pterophyta

• Ferns have clusters of sporangia (spore-producing
  structures) called SORI that form on the
  underside of the fern fronds

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Review Questions

• Explain why living on land has some difficulties
  that living in water does not have. Describe any
  difficulties of living in water.
• What major adaptations are found that cope with
  these difficulties.

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Vascular Seed Plants

• Seeds are structures that protect a plant embryo.
• Contain embryo, seed coat and some storage
  material (endosperm for nutrients and cotyledon
  which are the first leaves to emerge)

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Seed Dispersal
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Seeds contd

• Seeds develop from an ovule
• In gymnosperms, ovules are on edge of female
  sporophyte structures called ovulate cones
• In angiosperms, ovules are protected in an ovary
  (which becomes the fruit)

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Fertilization in seed plants

• Male gametophytes
  
  microspore mother cells? meiosis ? 4
  haploid cells (microspores)? become pollen
  grains (male gametophytes)? divide into pollen
  tube cells and sperm cells

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• Female Gametophytes
  1. Macrosporangia/Nucellus/Megasporangia?
• 2. make a megaspore mother cell?
• 3. meiosis produces 4 haploid cells (only 1
  survives to become the megaspore) ?
• 4. Forms an egg (2 in gymnosperms)

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Fertilization Contd

• Layer(s) called integuments protect
  megasporangium
• Megasporangium, Integuments and Megaspore form
  the ovule
• Integuments have opening for pollen entrance
  called micropyle

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Fertilization

• Pollen attaches to the megasporangium
• Pollen tube then forms from the pollen grain and
  enters the micropyle
• Sperm cells flow toward egg
• Upon fertilization a zygote divides into an
  embryo
• Sporophyte generation has begun

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Gymnosperms

• Include Conifers, Cycads, Gingkos
• Use cones (or cone-like things)
• Pollen-bearing cones (male) and ovule-bearing
  cones (female)

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Gymnosperms

• Gymno (naked) sperm (seed)
• Have seeds produced on surface of the
  reproductive structures
• Fertlztion seed dvlpmnt occur over 1-3 yrs.

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Angiosperms

• The flowering plantsmost advanced, successful
  group of plants thanks to
• Fruit Flower benefits
• Color and scents (aid in pollination)
• Fruit offer protection and dispersion of seeds

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Flower Parts/Function

• Carpel or Pistil-Female portion
• Ovaryproduces eggs, turns into fruit
• Styletube that connects ovary w/stigma
• StigmaSticky end of carpel (helps pollen to
  stick to flower)

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Flower Parts/Function

• Stamenmale portion of flower
• Antherproduces pollen
• Filamentstalk that holds up anther

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Fertilization in Angsprms

• Megaspore mother cell is in ovule dividing into
  megaspores
• Surviving megaspore divides to form eight haploid
  nuclei
• Nuclei form plasma membranes and result in an
  embryo sac
• 1 haploid nuclei is egg, 2 are synergids, 2 are
  polar nuclei, and 3 are antipodals

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Fertilization in Angsprms

• Pollen lands on stigma
• Pollen tube forms from pollen grain
• Tube (vegetative) nucleus forms along w/ 2 sperm
  cells
• Synergids and antipodals disappear upon sperm
  entry

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Fertlztn contd.

• Egg is fertilizedbecomes diploid zygote
• 2 Polar nuclei become fertilized by 2nd sperm to
  become endosperm (nutrients for growing embryo)
• Entire process called double fertilization
• http//www.emunix.emich.edu/ghannan/systbot/doubl
  efertanimation.html

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Angiosperms

• More complex vascular systems
• Varied environmental adaptations
• Subdivided into monocots and dicots
• (one cotyledon vs. two cotyledons in plantling
  among other distinguishing characteristics)

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Plant Tissues

• 1. Ground Tissuessupports plant body/stores
  water nutrients
• Parenchyma-most common, used in secretions,
  photosynthesis and storage also totipotent
• Sclerenchymatough, thick cell walls, rich in
  lignin. Consist of fibers and sclerids for
  strengthening tissues

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Ground Tissues contd.

• Collenchymaprovide support for stems, flexible,
  form strands along veins in leaves

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Plant Tissues

• 2. Dermal Tissueouter layer of epidermis cells
  (including guard cells), hair cells, stinging
  cells, glandular cells (secreting
  toxins)PROTECTS
• 3. Vascular Tissuexylem and phloem, found in
  vascular bundles, help in plant transport of
  water/nutrients

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Vascular Tissue

• Xylemcells are dead at maturity
• Hollow for efficient transport
• Have secondary cell wall for additional strength
• Two xylem cell types Tracheid Vessels

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Xylem Cells

• Tracheidslong, tapered cells
• - have pits at their tapered, overlapping ends
  to transfer water to next cell
• - pits only moderately efficient
• 2) Vessel membersshorter, wider cells with
  little/no tapering of ends, make up a vessel-
  have perforations instead
• H2O goes through vessels via perforations in
  cell walls, so more efficient than tracheid cells

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Vascular Tissue Xylem

• Transpiration of water from leaves drives
  movement of water upward through vascular tissue
  in stems
• Cohesion/adhesion of water helps water adhere to
  become sticky in vessels
• High concentration of certain substances at base
  of plant, so high concentration also initiates
  flow of water

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Vascular Tissue Phloem

• Phloem contains sieve-tube members (or elements)
  that form sieve tubes
• Ends of sieve tube members contain pores, which
  collectively make a sieve plate
• Companion cells aid in structural support and
  assistance (contains nuclei ribosomes unlike
  the phloem cells)

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Phloem cells
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Plant Growth Germination Development

• Seeds dormant until conditions just right
• Germination begins with water absorption
  (imbibition)
• Water initiates enzyme activity, seed coat cracks
• Region called hypocotyl elongates into a shoot

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Plant Growth Meristematic Tissues

• Tips of roots and shoots contain apical meristem
  cells
• meristematic cells are actively dividing cells
  that thus result in plant elongation (called
  primary growth)
• Occurs in seedlings and herbaceous plants (short,
  flexible, non-woody plants)

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Plant Growth Meristematic Tissues

• Root tip/capprotective layer over the apical
  meristem in roots
• Zone of cell divisionThese dividing cells absorb
  water and grow in size
• Zone of elongationrecently divided cells have
  absorbed enough water to begin elongating.
• Zone of maturation-cells mature and differentiate

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Plant Tissue Growth

• Two Types of plant growth
• Primary growthgrowth at apical meristems (tips)
• Secondary growthoccurs in woody plants to
  increase thickness/width (sides)

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Plant Tissue Growth

• 2ndary occurs at lateral meristems
• There are two types of lateral meristem, cork
  cambium and vascular cambium
• (Again, these cells are meristematic, so they
  constantly divide and produce new cells)

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Plant Tissue/Growth Secondary Xylem/Phloem

• Cells produced by the vascular cambium develop
  into secondary phloem and secondary xylem.
• Secondary phloem contributes to bark, and
  secondary xylem forms wood

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Plant Tissue Growth
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Plant Tissues How is bark produced?

• Cork cambium produces cork cells that are a
  component of bark
• Bark forms a protective layer for the mature root
  or shoot.

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Plant Tissues/Bark/Wood

• During periods of rapid growth, secondary xylem
  cells are large and thin-walled.
• During dormant periods, the secondary xylem cells
  are small and thick-walled.
• Resulting variation in cell size results in
  annual growth rings.

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Plant Tissues/Bark/Wood
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The inner xylem is called heartwood the outer
xylem is sapwood.
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Roots Shoots (and did you know that 42 of all
statistics are made up on the spot?)

• RootsPrimary growth results in epidermis,
  cortex, endodermis and vascular cylinder, or
  stele formation
• a. Epidermissurface layer
• - forms root hairs (greater absorption)

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Roots Shoots (Roots contd)

• (b) Cortexbulk of root, stores starch, many
  spaces provide opportunity for respiration
• (c) Endodermispacked cell layer at inner cortex
• Utilize suberin to create casparian strip (fatty
  layer impermeable to water) to direct water flow
  through the cells of the endodermis towards the
  vascular tissue

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Roots Shoots (contd)

• (d) Vascular cylinder, or steletissues inside
  the endodermis
• Pericycle (outer layer of stele, from which
  lateral root growth occurs)
• Xylem Phloem contained w/in
• Piththe center, or core, of the root
• ONLY in monocots

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Can you identify the layers?
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Roots Dicots vs. Monocots
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Roots Shoots Primary Structure of Stems

• 2. Stems contain epidermis, cortex, and vascular
  cylinder
• (a) Epidermishave cuticle layers formed from
  cutin, guard cells, stinging cells
• (b) Cortexcontain ground tissues and many
  chloroplasts w/in cells.
• (c) Time for another nature walk. Everyone line
  up at the door. RIGHT NOW!

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Roots Shoots Primary Str. Stems contd.

• (c) Vascular cylinderxylem, phloem pith
• Note differences between monocot (left) and dicot
  (right) stems

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Roots Shoots Secondary Structure Stems Roots

• Vascular Cambiumcylinder of tissue that
  elongates the roots/stems
• Meristematic cells on inside become secondary
  xylem and cells on outside become secondary phloem

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Roots Shoots Secondary Structure Stems Roots

• As xylem expands, phloem is pushed outward (outer
  layers, i.e. epidermis, eventually shed as new
  cells form)
• New cells called periderm form
• Older, inner layers of xylem are
  nonfunctionalonly used for support

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Joke Break!!!

• Actual College Biology Test Answers
• What is a flowers pistil for?... Fighting off
  the bees!
• Germinate To become a naturalized German
• Dew is formed on leaves when the sun shines down
  on them and makes them perspire.
• How do you know when a turkey is done?
• Two boys are talking. Jimmy says that he has a
  crush on his teacher and his friend says thats
  disgusting. Jimmy says, But everyone has a crush
  on a teacher at some point. His friend says,
  yeah, maybe, but.

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• you are home-schooled!
• The Queen and the Pope make a wager

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Leaf Structure more notes!
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Leaves Cell Layers

• EpidermisHas cutin-laden cuticle layer to reduce
  transpiration and sometimes have trichomes (cool
  leaf and decrease water loss)

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Leaves Cell layers

• Palisade mesophyllPHOTOSYNTHESIS!
• Many chloroplasts/large surface area Spongy
  mesophyllparenchyma cells spaciously configured
  (for air space for gas movement/exchange
• Vascular bundlesblah blah blah (same as in stems
  and roots)

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More Leaf notes we are almost ready to LEAVE
this section of notes

• Guard cellsStomata allow CO2 to enter
  photosynthetically active tissues. Stomata
  consist of 2 guard cells, which change shape to
  open or close the pore

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Leaf structure contd (stomata functions)

• Unevenly thick cell walls on guard cells (thicker
  on stoma side of cell)
• When water diffuses into cell (because of a
  sudden increase in K concentration), guard cell
  swells and thinner-walled side expands while
  thicker-walled side does not.
• This results in a pore forming between the two
  guard cells

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Mechanisms of H2O/Sugar Transport
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Water goes from root hairs to xylem via 2
pathwaysNote the apoplastic route ceases
temporarily at the endodermisWHY?
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Water Transport

• The apoplast consists of the extracellular space
  made up of cell walls. The symplast consists of
  the continuous connection through cells that
  exists via plasmodesmata (gaps in the cell wall
  where the plasma membranes, cytoplasm, and smooth
  ER of two cells connect).

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Water Transport

• Flow of water results from osmosis, capillary
  action and the cohesion-tension theory
• Osmosis results in concentration gradients which
  then result in root pressure.
• Guttation is evidence of thissmall droplets of
  sap appear on ends of small plants leaves

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Water transport

• Cohesion Tension theoryTranspiration of water
  from leaves causes tension in vascular tissue
• Cohesion of water molecules results in
  congregation of water molecules (into a
  single-ish columnar molecule)
• Bulk flow of water occurs as each water molecule
  evaporates off of a leaf, pulling up the next
  molecule below it into a new position

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Water Potential

• Water potential refers to the tendency for water
  to moverepresents free energy and predicts which
  way water will go

• Water potential is the pressure potential (?p)
  plus the solute potential (?s)
• ? ?p ?s

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Water Potential

• Pressure potentialphysical pressure resulting
  from water entering vacuoles (turgor pressure)
• Solute potentialpressure resulting from water
  outside pushing onto the outside of cell
  wallstops osmosis if it equals pressure
  potential from inside of cell

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Water potential

• Pure water with no pressure has a water potential
  of 0.
• Key is to remember that water flows toward the
  area with lower water potential

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Water Potential

• Lets say a cell is sitting in a glucose
  solution.
• The cell has a Solute potential of -0.2MPa and
  Pressure Potential of 0.5 MPa
• The solution has a ?s of -0.2 MPa
• What is the ? of
• Cell?
• Solution?
• Where will the water flow?

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Water Potential Applications
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Water Potential Applications
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Transport of Sugars--Translocation

• Translocationmovement of carbs from a source to
  a sink
• Pressure-Flow Hypothesis explains translocation
  and consists of
• 1. Sugars move into sieve-tube members
  (increasing conc. of solute)
• 2. Water enters sieve-tube cells to even out
  conc. of water

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Sugar Transport

• 3. Increasing pressure in sieve-tube members
  result in water sugar moving to sieve tube
  members at the sink
• 4. Pressure is lower at the sink because sugars
  are being taken up by cells for respiration,
  etc.lower pressure allows the bulk flow of
  H20/sugar to continue towards the sink

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Joke Break!

• Joe Is animal testing a good idea?
• Frank No, because those little creatures always
  get nervous and give the wrong answers.
• What did the polite sheep say as he waited in
  line for the barn?
• A scrubby lookin guy walks into a restaurant and
  orders a steak. The waiter says, No, because I
  dont think you can afford it. The man agrees,
  but has an idea. If I show you something youve
  never seen before, will you give the steak for
  free? The waiter says OK, and the man pulls out
  a hamster, which proceeds to run to the piano and
  begins to play some Chopin.

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Plant Hormones Responses

• Responses to stimulitropisms
• Phototropismgrowth in response to light
  controlled by hormone auxin
• Auxin produced in apical meristem and moves to
  zone of elongation
• If equal amts. of light hit plant, then plant
  grows straight
• If unequal amts, then auxin increases in shady
  area, causing differential growth, and stem bends
  toward light

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Plant Hormones Responses

• Gravitropism (geotropism)growth in response to
  gravity controlled by auxins and gibberellin
  hormones
• If stem horizontal, auxin moves down stem and
  concentrates on lower side, causing stem to bend
  upward
• If root horizontal, similar events occur, but
  process is not as well understood. Roots usually
  grow down in response to gravity.

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Plant Hormones Responses

• Thigmotropismresponse to touch and not well
  understood.
• Explains vine growth
• Common in rainforest plantswhy?

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Plant Hormones Responses

• Hormonessmall molecules that act as messengers,
  affecting physiological activities of cells in
  various locations
• Auxins, Gibberellins, Cytokinins, Ethylene, and
  Abscisic acid are the 5 main types of hormones

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• Auxins (IAAindoleacetic acid)
• Promote plant growth by stimulating cell
  elongation
• Increase H concentration in cell walls
• H conc. loosens fibers incr. plasticity
• Greater plasticity means increased turgor
  pressure results in cell wall expanding and thus
  allowing cell to grow

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Hormones contd.

• 2. Gibberellins aid in cell growth, named GA1,
  GA2, etc.
• Often made in young leaves, seeds, and roots but
  are then transported to other parts of plant
• High conc. In stems cause bolting (rapid stem
  elongation)
• NATURE WALKline up at the door in a single
  follow lineHOLLA BACK!

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Hormones contd.

• 3. Cytokininsstimulate cell division
• Usually produced in roots
• Aid in organ development, root or shoot
  formation, and bud formation
• Also aid in delaying leaf aging (plant aging
  senescence)

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Plant Hormones contd.

• 4. Ethylenepromotes fruit ripening
• Stimulates starch?sugar converssion
• Stimulates abscission, or the aging/losing leaves
• Inhibits elongation of roots and shoots

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Hormones contd.

• 5. Abscisic acid (ABA)growth inhibitor
• Delays bud growth
• Forms scales for winter protection of buds
• Maintains dormancy
• Possibly responsible for leaf abscission

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Plant Defense

• Toxins, tanks, machine guns, and their pistils.
  No, not really.
• Epidermis1st line of defense
• Toxinsusually either contained within a membrane
  so it does not harm the rest of the plant or only
  become harmful once metabolized by animal/fungus
  that eats plant
• Allelopathy is when chemicals are released by
  roots to prevent germination/growth of nearby
  seeds/plants

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Plant Defense

• 3. Animals in mutualistic relationships
• Ex Ants and Acacia tree
• 4. Wound Responsessome plants can release
  chemicals for defense once an injury occurs
  (wounded leaves produce a protein systemin that
  sends a signal)
• 5. SAR (Systemic Acquired Resistance) is a memory
  of past invaders so plant can defend itself
  quicker than last attack

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PhotoperiodismLast of the Plant Notes ?

• Photoperiodlength of day and night
• Circadian Rhythm is the rhythm that plants get
  into that acts as a clock to measure day/night
  length
• Entire circadian rhythm mechanism is
  endogenoustime is kept fairly accurate over time

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Photoperiodism

• Regulated by phytochrome protein
• Pr or P660 absorbs red light w/ wavelength of
  660nm
• Pfr or P730 absorbs far-red light (wavelength of
  730 nm
• They are photoreversible moleculescan be
  converted into one another when it absorbs its
  preferred light wavelength which creates a NATURE
  WALK!!!!!

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Photoperiodism

• Pfr resets the internal-clock based on need (i.e.
  when dusk dawn change through the seasons)
• Pr is made in plant leaves
• Red light and some far-red light is present in
  sunlight, and so Pr Pfr are maintained in
  equilibrium during day (Pr converts to Pfr and
  vice versa)
• Time for a NATURE WALKline up at the doorHOLLA
  BACK!

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Photoperiodism

• Pr levels increase at night because
• No sunlight to convert it to Pfr
• Pfr breaks down faster
• Phytochrome is also responsible for initiating
  seed germinating by producing germinating
  hormones

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Photoperiodism

• Length of Night is responsible for resetting
  circadian-rhythm clock
• If day has a brief dark period, no effect on
  clock
• If night has brief red-light flash, then clock is
  altered (Pr ? Pfr occurs, and Pfr resets clock)

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Photoperiodism
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Photoperiodism Flowering

• Long-day plants flower in spring (daylight
  increases)
• Short-day plants flower in late summer and early
  fall (daylight decreases)
• Day-neutral plants flower based on temp., water,
  or other
• Florigen hormone produced to initiate flowering

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