chapter 35 plant structure and growth. morphology – studies of external structure of plants 1)...
TRANSCRIPT
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Chapter 35
Plant Structure and Growth
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Morphology – studies of external structure of plants
1) Root system –
-anchors plant in soil (land adaptation)
-underground
-absorbs minerals, water
-conducts water & nutrients
-stores food
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taproot – (as seen in dicots)
– 1 lg., vertical root
fibrous root system – (as seen in monocots)
- mat of threadlike roots
- allows for greater exposure to water
root hairs – increase surface area
*mycorrhizae also help with water/minerals
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2) Shoot system - vegetative shoots above ground
stems
axillary buds – embryonic side shoots in the
angle between leaf/stem
terminal buds – at apex
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modified stems:
stolons – grow on surface of ground
rhizome – horizontal underground stem
tubers – swollen ends of rhizomes
bulbs – vertical underground shoots
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leaves – photosynthetic organs
-consist of blade and petiole
modified leaves:
tendrils – modified leaflets that cling to supports
spines – modified leaves on cacti
modified water-storing leaves in succulents
brightly colored leaves – as in poinsettias
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Plant anatomy – concerned with internal structure (tissues)
3 major tissue types:
1) parenchyma – least specialized
- most lack secondary walls
- fleshy tissue of most fruit
- perform most metabolic functions
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2) collenchyma – support young parts of plants
without restricting growth
- alive at functional maturity
3) sclerenchyma – more rigid (have lignin)
- may be dead at functional maturity
a) fibers – long, slender, tapered in bundles
b) sclerids – irregular, shorter, found in
nutshells, seed coats
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Water conducting cells of xylem
1) tracheids – water moves from cell – cell
through pits; also aid in support
(dead at functional maturity)
2) vessel elements – aligned end – end with
perforations at their tips allowing water to flow
freely through them (dead at functional
maturity)
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Food conducting cells of phloem
Sieve tube members (alive at maturity)
-transport sucrose, organic compounds,
mineral ions
-formed by chains of cells
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Plant tissue systems
1) epidermal – single layer of cells covering
the entire body of a young plant
- protects
2) vascular – functions in transport & support
3) ground – mostly parenchyma
-storage, support
-between dermal & vascular tissue
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Chapter 36
Transport in Plants
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Transport in plants
Occurs on 3 levels:
1) uptake of water/solute by individual cells
2) short distance transport to/from neighboring
cells
3) transport of sap over long distances
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Absorption by roots- through root hairs and epidermal cells provided by hydrophilic cell walls (touching root cortex)
- water/minerals enter xylem by:1) symplastic pathway – absorbed into
parenchymal cells & to stele by plasmodesmata
2) extracellular apoplastic pathway – along cellwalls until they reach impervious Casparianstrip at endodermal boundary to stele bycrossing endodermis
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Ascent of sap by xylem-supplies minerals to shoots
-replaces lost water by transpiration
-water potential determines net movement
-increase in solute concentration lowers water
potential; increase in pressure increases water
potential
-water in stele causes upward push of root
pressure that forces water up the xylem
(causes guttation – exudation of water droplets)
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Transpiration-cohesion-adhesion theory
-evaporative water loss during transpiration
lowers water potential of leaf cells compared to
root, cohesion of water due to H bonds,
transpiration pulls water upward & creates
tension (negative pressure)
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Control of transpiration-transpiration to photosynthesis ratio is a
convenient way to determine how efficiently
plants use water
-plants with lower ratios do well in arid climates
since water loss/CO2 exchange are trade off
-important for evaporative cooling & delivering
minerals to leaf
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Control of transpiration
-turgor pressure & stomatal opening are
regulated by -/+ changes in membrane
potentials by proton pumps in guard cell
membranes
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Guard cells-usu. open during the day (at dawn) & closed at
night due to:
1) light stimulates K+ accumulation & makes
cells turgid
2) depletion of CO2
3) inherent circadian rhythms – cycles with
24 hr. intervals
-hormones & water loss in the day can trigger closing
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Xerophytes
-plants adapted to arid environments have
modified leaves:
-thick, small (reduces surface area to volume)
-thick cuticle, water storage in fleshy parts
-CAM metabolic pathways (circadian rhythms
are different)
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Phloem transport
translocation – process of transporting
photosynthetically produced food throughout
plant’s body
-phloem sap carries:
sucrose, minerals, AA’s, & hormones
-transported from sugar sources to sugar sinks
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Chapter 37
Plant Nutrition
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Nutrients
-water (for photosynthesis as a solvent used in
elongation/growth)
-CO2 (from atm. used in carbohydrates)
-hydroponic culture is used to determine which
minerals are necessary for plant growth
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Nutrients
Macronutrients:
C, O, H, N, S, P, Ca, K, Mg
(necessary for organic compounds)
Micronutrients:
Cl, Fe, B, Mn, Zn, Cu, Mb
(cofactors in enzymatic reactions)
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Soil
-a very important factor
-texture (particle size affects drainage)
*loam is usu. most fertile
-amt. of humus (decomposing organic material)
-clay particles (charged negatively; attract H2O)
*soil management is essential in agriculture:
promotes erosion, depletes minerals, taps
water reserves
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Soil
-irrigation drains water reserves, causes NaCl
accumulation but increases crop yield
-bacteria fix N2 in soil (into NH3, NH2)
-legumes, alders, some tropical grasses have
evolved mutualistically
-protein-rich plant breeds genetically engineered
to stop hunger
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Nutritional adaptations
A. Parasitic plants – supplement photosynthesis
ex: mistletoe, dodder
or tap vascular tissues of host plants
(epiphytes – free living)
B. Carnivorous plants – obtain N2 by killing &
digesting insects
ex: sundew, pitcher plant, Venus’ fly trap
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Indian pipe
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Venus’ fly trap & pitcher plant
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Sundew
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Chapter 38
Plant Reproduction
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Angiosperms
Flower (modified leaves) for reproduction
sterile: petals, sepals
fertile: stamens (M), carpels (F)
classified:
monoecious – M & F structures
dioecious – M or F structures
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Monoecious
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Flower
complete – sepals, petals, stamens, carpels
incomplete – missing 1 or more of these
perfect – stamens & carpels
imperfect – staminate or carpellate (pistillate)
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Floral variations have evolved during the 130 million years of angiosperm history.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 38.3
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Flower
• Diploid sporophyte dominates
pollination – pollen placed on stigma
by wind or animal
fertilization – pollen grain germinates, growing
pollen tube extending down style, seed develops
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Fruit
classification:
simple – ex: cherry
aggregate – ex: strawberry
multiple – ex: pineapple
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Seed
germination – seeds imbibe water, frees seed from seed coat & begins metabolic changes triggering growth
radicle – embryonic root
-1st structure to emerge from seed; shoot breaks through soil surface
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Asexual reproduction (vegetative)
• fragmentation of parent plant
• cloning
• apomixis
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Chapter 39
Control Systems in Plants
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Response to the environment occurs on 2 time scales:
1) Individual plants & other orgs. respond adaptively to what goes on around them
2) These control systems themselves are adaptations that evolved over generations of interactions of plant/environment
* plants respond to env. cues by adjusting their pattern of growth & dev. through internal signals & interactions with the env.
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Hormones
• traveling chemical signals that coordinate the functions (growth, development, response) between different parts of an organism
• 1st plant hormone identified: auxin
• found when studying experiments on phototropism
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5 classes of hormones control plant growth & development
1) auxin – stimulates cell elongation in target tissues
-affects secondary growth & differentiation
-promotes fruit growth
-initiates adventitious root formation
-ex: IAA (indolacetic acid)
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2) cytokinins – stimulate cell division (in roots, embryos, fruits) * prolong fruit shelf life-ex: zeatin
3) gibberelins – stimulate leaf/stem growth; -increase elongation in stems (w/ auxin)
-fruit development -support germination (stimulates enzymes for mobilization of seed storage material)
-ex: GA3
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4) abscisic acid – slows plant growth & favors
dormant state by inducing bud scale
development
-inhibits cell division in vascular cambium
-suspends growth in buds & seeds
-stress hormone – helps cope w/ adversity
-ex: ABA
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5) ethylene – (gaseous) – diffuses through
air spaces
-inhibits root growth & development of
axillary buds in an increase of auxin conc.
-stimulates fruit ripening & induces several
aspects of senescence in plant cells & organs
-ethylene increase & auxin decrease results
in leaf abscission
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Tropisms• orient growth of plant organs to/from stimuli
• result in curvature of organs
1) phototropism – enhances phsyn. bending
shoots toward light
2) gravitropism – mediated by statoliths
(specialized plastids w/ dense starch grains)
-negative: shoots grow upward
-positive: roots grow downward
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Tropisms
3) thigmotropism – adaptive coiling of tendrils on
touching a support
ex: thickening of stems in response to chronic
strong winds
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Turgor movements
• rapid, reversible responses
• stimuli cause changes in turgor pressure
ex: sleep movements in legumes
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Circadian rhythms
• physiological cycles w/ 24 hr. frequencies
• absence of env. cues leads to free-running
periods where they may deviate, but still have
their own cycles
• internal biological clocks control this
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Photoperiodism
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Other responses
• to heat stress
• to salt stress
• to drought
• to flooding
• to cold stress
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Defense against pathogens & herbivores
• thorns
• chemical defenses
• airborne attractants