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Exam 2, life cycle evolution, life on land, stomata, Vascularization -…
Exam 2
xylem
no specialized cells; poikilohydric, water content changes w mosisture in surrounding evniro. equilibrate water potemtial through environ source, water storage extend,
hydroids; byrpohytes, water conducting cell no plasmodesmata inperforate , aid in reilling form cavitation, apomorphic trait similar function but different origin to true vascular tissue, no lignin
tracheary elements, die at matuity, thickened lignin walls waterproffing structural support
stepwise progression, partially thickened, lignified trachieds, during devonian increase in xylem content increase in trachied sixze incresed in trahied reinforement,
early tracheids, water transport only, lignified, long and wide, ferms, lycophytesm pit membranes
true trachieds, lignified w ornamented wallsm evol, likely once, function in water transport and support, tapered at ends rather narrow
pine tracheids; function in water movement and support, torus-margo pit membrane move to prevent cavitation.
vassel element, angiosperm, large diameter. dead at maturity, open digested end walls
tracheid vs vessel element,
Pit membranes are absent in perforations of mature vessel elements
Conductive area greater in end wall of vessel elements compared to lateral walls; tracheids are similar
Perforation plate morphology different than lateral-wall pitting in vessel elements; tracheid endwall similar to lateral
Vessel elements have a greater diameter than tracheids
Vessel elements are shorter than tracheids
Gymnosperm vs Angiosperm
Vessels can have greater
maximum diameters
Maximum lengths
Vessel elements may be short but the vessel can be much longer
yields greater conductivity in vessel elements
Lowers the cost (construction & transpiration)
Having vessels permits more fiber (hardwood vs softwood)
Downside is greater cavitation risk
Vessel element differentiation
Apical meristem
Vacuolization
Elongation
Secondary cell wall
annular
Helical
Reticulate
Porous
Dead at maturity
wood
enviro changes, amt water loss/ carbon gained increased after Silurian... carboniferous period greatly drained atmosphere co2,,,, water demand is realtively high ,,, minimal maintenance = cell death,, water filtration close to soil access
selection pressure for wood, increased competition for light selected for taller and more developed plants + tree canopies... higher rates of transpiration more xylem & longer conduits... likely evolved 5 times
loss of secondary growth; monocotyledonae, arborescent no secondary growth
secondary growth; complex plant development growth in girth produce secondary xylem (wood) phloem(inner bark) ground tissue(rays) continuous circular ring growth
vascular cambium; fusiform initials, ray initials, periacinal division, anticlerical division
divisions 3d
wood block, initials -fusiform- longitudinal-- ray- radial
annular rings`
xylem secondary cell wall robust, phloem is crushed, ring width determined by seaason at enviro., alterations of early and late wood
sap vs hearwood
sapwood functions in water, heartwood functions in storage can no longer transport water
soft vs hardwood
soft; tracheids only little room for fibers, gymnosperms,,, hardwood; vessel elements effiency permit space for fibers, angiosperms
eudicot cross section,
ground tissue; rays connect pith and cortex, vascular tissue; xylem, wood and primary & secondary, phloem; inner bar, secondary primary squished lots of fibers
plant armor
periderm; phellem cork, phellogen cork cambium, phelloderm outer bark inner bark phloem & cortex
primary tissue arrangement in shoots
arrangement changes w a plant
root and shoot have diff arrang. key features to monocots,root w pith stem w/out pith an eudicots, roots w/out pith stem w pith
increasing commplexity
stem diameter incresed, plant height inc lead to compartmentalization, selected for woody habit
3 major stele types
protostele; phloem surrounds zylem or intersperded
siphonostele; ring ofphloem xylem surrounding pith
eustele. complex, strand of phloem and xylem separated by parenchema, progymnosperm
archs
lychophyte
protostele, exarch
ferns
siphonostele; xylem surrounded by phloem,,, endarch
monocotyledonae
atactosrele, no pith, vasculer bundles often surrounded by sclerenchyma
eudicotyledonae
eustele; phloem outside xylem bundles separate by parenchyma;;; endarch, vascular bundle supported y sclerenchyma, bundle cap
leaves
phyllad evol
initial constraints
High atmospheric global temperatures
Low stomatal densities
Increase permit greater evaporative cooling
Low capacities for water uptake prior to root evolution
Lacking efficient vascular transport in leaves
Burn up leaf
Vascular embolism
Polyphyletic origin
Earliest evidence of true leaves
Lycophytes
microphylls/ lycophylls
Euphyllophytes
Independent evolution
Optimal light interception
Indeterminate growth proceeded leaf development
Leaves initiated in regular patterns around stem
Optimize light interception for photosynthesis
Varied leaf development
Mitosis of a single cell
Liverwort
Moss
Moss midvein cell layer
Microphyll
Lycophyte
Mitosis of 2 epidermal cells
Frond
Monilophyte
Mitosis of single apical cell
Shoot like development
Euphylls
Seed plants
Pool of recruited cells
From flanks of multicellular shoot apical meristem
Enation theory
Lycophyte leaves
Progressive elaboration of epidermal outgrowths
Vascular strands entered later
Fossils consistent
Asteroxylon
Living evidence
Selaginella draussiana
2 epidermal cells grow to form leaf pair
Zimmerman telome theory
Evolution of euphylls
Overtopping
Unequal branching (primary & side)
Planation
Flattening of axes into 2 dimensional
Webbing
Develop thin tissue between axes of branches
Branches becomes veins
Webbing becomes mesophyll
By Devonian euphylls widespread
Convergent evolution
Leaves had at least 5 independent origins
Liverwort gametophyte
Moss gametophyte
Lycophyte sporophyte
Monilophyte sporophyte
Spermatophyte sporophyte
phyllad tissues
Chlorenchyma
Ground tissue
Specialized parenchyma
Contains chloroplasts
Main function is photosynthesis
Aerenchyma
Ground tissue
Specialized parenchyma
Contains air spaces from cells being digested
Main function permit gas-exchange
Large air pockets for buoyancy in aquatic plants
Collenchyma
Ground tissue
Thickened primary cell walls
Main function in flexible support
Found in bundle sheath of veins in some species
Vascular tissue
Xylem
Tracheids
Water transport
Phloem
Sieve tube element/ sieve cells
Companion cells/ albuminous cells
Photosynthate transport
In veins
Epidermis
Dermal tissue
Epidermal cells
Guard cells
Often cutenized
Main function in protecting the internal tissues
phyllad organization
Lycophylls
Microphyll
Single vascular trace along center of blade
Vascular strand connects directly to stem
Mesophyll
Epidermis
Stomata
Monocot leaf
Epidermis
Adaxial (outer) & abaxial (towards stem)
Covered by cuticle
Contains stomata
bulliform cells
helpful for the rolling and unrolling
Mesophyll
Veins
Surrounded by bundle sheaths
Eudicot leaf
Epidermis
Dermal tissue
Epidermal cells
Guard cells
Cuticle
Upper & lower
Mesophyll
Palisade
Photosynthesis
Spongy
Gas exchange
Veins
Bundle sheath cells
Xylem on top phloem on bottom
major evol. innovations
key innovations:
permanents tetrads and dyads
stomata/phytes
leafless sporophytes
cryptospores
trilete spores
vascular tissue (tracheophytes)
increased branching complexity (anisotomy)
inderterminate growth w lateral insertions of bivalved sprangia
non-vascularized enations
vascilarized lycophylls and positioning of sporangia
simple lateral to first or second orger branches
complex lateral branching systems w dichotomies
planar fronds w laminae and sporangia
increased complexity in lateral branching systems w dichotomies lateral to first or second order branches and terminal sporangia
planar euphylls on lateral branching systems w sporangia positioned on adaxial surfaces
seeds arising on lateral branches
sporophyte generation
alternation of gen., gametophyte dominant in early land plants, sporophyte evolved dominance
vascular tissue
water and food conducting cells
leaves and stomata
all lang plants sporophytes but liverworts, Ordovician many seen by silurian, often aerial surfaces covered w cuticle
roots
downward growing rhizomes, positive gravitropism, negative phototropism, evolved a root cap, evolved new way to branch; early roots branched at tip, some lineages may have evolved from leaves
seed evolution
gametophyte; completely dependent on sporophyte, egg protected by special layers of tissue, seed ferns (all extinct), gymnosperm; naked seed, angiosperm; hidden seed
flower evol.
stem specialization, attraction, dispersal, coevolution
summary
many morphological changes as plants adapted to life on land
further selection from competition
diversification; accommodate life cycle changes and coevolution
evidence for embryophyte emergence
more CO2
O2: 20.9%, 535x more O2 than CO2.
while appearance of land plants 8-15x higher in CO2, 4% O2, kept tissues thin as internal enviro quick anoxic, very weak ozone
terrestrialization
470Ma; major evol. changes in morphology & reproduction, multicellular sporophyte, retain the zygote & embrio in female gametophyte, apical cells w 3 cutting faces allow for 3d parenchymatous tissue
evo from algae
charophycean green algae, streptophyta; embryophyta and charophytes, grows as flat disc very similar to liverwarts
fossil evid
early, spores and tissue fragments, mid-ordocician 470 ma, sporopollenin wall, trilete mark, cryptospores prob. liverwarts
liverwarts macrofossils
390ma, middle devonian, dichotomously branched Y
first microfossils
cooksonia sporophytes, mid-late silurian, 425ma, gametophytees comple; stomata conducting elements similar to extant liverwarts
vascular plants
specialixed conducting cells, evid from spores 443ma, tracheid fossils 415ma, diversity exploded in devonian 415-360ma, sonimant sporophyte no longer restricted to damper areas.
sporophyte dominant, gametophyte reduced
gymnosperm
pine; microgametophyte no longer restricted to water, megagametophyte protected by integuments
sporophyte
large dominant diploid stage, gametophyte reduced to microscopic structures
gametophyte
microgametophyte; pollen
megagametophyte; becomes nutritive tissue, protected by integuments within an ovule
angiosperms
lily; sporophyte dominant, gametophytes microscopic
sporophyte
flowering plants very diverse, annual to perennial, indeterminate growth
microgametophyte
multicellular haploid stage
pollen grain; immature, mature germinating
megagametophyte
multicellular haploid individual, egg on of the cells (nuclei)
mature angiosperm megagametophyte has 8 nuclei
Sporophyte dominant, gametophyte & sporophyte independent
Lycophyte
Selaginella ex.
Heterosporas
Retained w/in spore walls
Sperm must still swim to egg
female spores are contained in a megasporangium
Gametophyte
Both male and female developer/in spare wall
Small
Sporophyte
Heterosporous
Reduction in megasporocytes to 1 per megasporangium
Micro = male
Mega = female
Monilophyta
Polypod fern ex
independent gametophyte
independent sporophyte
gametophyte
microgametophytes
male, antheridium, sperm
megagametophytes
female, archegonium, egg
sporophyte
sori
sporangia, indusia
large persistent diploid
sporophyte evolution
algal ancestor
haplontic (single being)
alterations of generations
current land plants
haplodiplontic (double being)
antithetic theory
interpolation theory
predictions
heteromorphic generations
sporophyte, short lived, simple
gametophyte, relatively complex, persistent
gametophyte dominant
marchantiophyta
marchania liverwort
dominant leafy gametophyte
temporary diploid sporophyte
Gametophyte
Dominant life stage
Antheridiophere male, antheridia contains perm
Archegoniphere female, archegonia contains eggs
Sporophyte
Small, temporary structure
Parasitic on gametophyte
Genesis occurs w/in sporangiumsporecytes 2 n spores I n
Bryophyta
Minimum moss
Gametophyte
Temporary diploid sporophyte
Gametophyte
Dominant life stage
Antheridia Head male ) Antheridia contains sperm
Archegonia headfemale, archegoniaL contains eggs
Sporophyte
Small temporary structure
Parasitic ongametophyte
Meiosis occurs within sporangium
origins & derivations
stomata
small spore bounded by specialized epide4rmal cells & guard cells
permit rapid gas exchange in higher plants; O2 OUT, CO2 IN
control of H2O loss permit giants among plants
aid in desiccating sporophyte
likely the origin of stomata
stomata near sporophyte sporangia
aid in spore dispersal
likely not regulated, may have permitted some CO2 to enter; no intercellular space
lower stomatal frequency
support early role diff from today,
location no non-photosynthetic sporophyte tissue in early lineages,
extant early lineages have stomata that only open
intercellular spaces
pseudostomata continuous w epidermis or hypodermis, no space
space filled w fluid w space mad by cells pulling apart
stomatal canal, small air space
aid in diffusion of minerals and nutrients from gametophyte to sporophyte, cell death
flowering plants
monocot (grasses); dumbbell shape, same direction as epidermal cells
eudicot; kidney-shaped, random orientation
organizational diversity
lycophytes
Selaginella sp example
No root cap
No root hairs
monocots
Diversity
Pith in center
Endodermis
Surrounded by cortex
Monocot details
Epidermis
Cortex
Endodermis
Casparian strip
Pericycle
Xylem
Phloem
Pith
Eudicot
Diversity
No pith
Endodermis
Cortex
Eudicot detail
Epidermis
Cortex
Endodermis
Casparian strip
Pericycle
Xylem
Phloem
In summary
Vascularization changes with organ
Root organization varies across taxa
Next… leaves
phloem
Food conducting cells
Widespread in bryophytes
Specialized plasmodesmata in end walls
Alignment along longitudinal arrays of endoplasmic microtubules*
Plastids
Mitochondria
ER vesicles
Breakdown of tonoplast
Mix vacuolar & cytoplasmic contents
Rarely some species have nuclear breakdown
Features common to sieve cells
Sieve cells & albuminous cells
Sieve area pores narrow
Uniform sieve areas
ac aka Strasburger cells
Gymnosperms only these Earlier lineages with various types including transitional = sieve elements
Transport of
Photosynthate
Hormones
Electric signals
Sieve tube element features
Sieve plate
Area with many sieve pores
Usually on end wall
Many sieve tube elements together = sieve tube
Primary cell wall
Living protoplasts at maturity
Few organelles (ER)
Callose & callose plugs
& companion cell features
Transport of
Photosynthate
Hormones
Electric signals
Sieve tube element
Sieve plate
Sieve pore
Lateral sieve area
P protein
Plastid
Smooth ER
Mitochondria
Companion cell
Branched plasmodesmata
Vacuole
Nucleus
mitochondria
Plasmodesmata connections
Sieve tube & companion cell from same mother cell
Connected by a large quantity of plasmodesmata
One pore in sieve tube area branched into many on companion cell side
Sieve tube contents
P-proteins May help in plug pores in response to leakage
Forisomes; Legumes, Plug pores
Sieve element plastids
Mitochondria Very few
Endoplasmic reticulum; Lost ribosomes, Highly folded
evol. perspecive
tracheophytes; synapo, all have vascular tissue, cell type varies, vascular architecture diverse
earlhy evid, trachieds, annular thickenings, coodonia, tought to be true trachied
lychophytes; ealy vascular group, created towering foresrs during carboniferous.
function considerations
guard cell control
active metrabolic processes; increase turgor pressure move ions. water foolows by osmosis; hypotonic to hypertonic
cytoskeleton microfibrils radially orientated
photosynthetic dependent
provides ATP for potassium pump, protons are pumped out, potassium moved in, ancestorial conditions filled with chloroplasts; independent of blue light closure at night or under water stress
water use efficiency
amount of water loss to carbon gains, close pore during water stress; reduce transpiration, maintain hydration,, derived character, reduced probability of cavitation, aba responsive in seed plants; angiosperms additionally respond to VPD
transportation
watermovement
transpiration
moves water from soil to atmosphere
major input of water cycle
water free energy
potential for water to react or move
due to its polarity
attracted to other substances
lower potential when its surrounded by ions
water potential
based on the free energy of water , water moves from less negative water potentials to areas of more negative water potentials
components
ψ = ψp + ψπ + ψm
ψp = pressure potential:
effect that pressure has on ψ
If water is under pressure, both pressure potential and water potential increase.
ψπ = osmotic potential:
effect that solutes have on ψ
Adding solutes decreases water’s free energy, so ψπ is always negative.
ψm = matric potential:
adhesion to structures such as cell walls, membranes, and soil particles
Adhesion can only decrease water’s free energy, so ψm is always negative.
Pressure potential ψp
Hydrostatic pressure exerted on water in a cell
In turgid plant cells positive value
Xylem cells negative pressure due to tension
Water at atmospheric pressure has a pressure potential of zero
Osmotic potential ψπ
Difference between the solution and pure solvent resulted after adding solutes
Matric potential
Adhesion of water molecules to nondissolved structures
Example, soil particles
Always negative
Significant only outside living systems in very dry soils
cohesion-tension theory
Transpiration stream
Water movement from soil to atmosphere
Follows relatively high to low moisture level
From less negative to more negative water potential
Water evaporates out of open stomata to drier atmosphere, creating water potential differential
Stomata open shortly after daybreak
Close at times of stress
Close at night
Water potential gradient from mesophyll cells all the way back to xylem draws water from vein
Open stomata
Water evaporates from intercellular spaces
Starts the domino effect of water potentials
Water pulled up stem under tension, in an unbroken column
As H2O diffuses out of xylem in the leaves, cohesive forces pull H2O upward through the xylem, all the way from the roots.
H2O in the uppermost tracheary elements must lift the weight of the entire H2O column.
Tension is on these molecules, and consequently, the pressure potential is a negative number.
Water pases through endodermis, filtering solution, preventing embolism and foreign invaders
Casparian strip of root endodermis
Forces symplastic movement
Embolism is an air pocket
Completely makes tracheary element non functional
Water enters through root hair via osmosis due to hypotonic soil solution
Water moves from hypotonic to hypertonic solutions
Root hairs greatly increase surface area
Water remains unbroken due to cohesion of water molecules
Cohesion due to water polarity
Adhesion along cell walls helps to fight gravity
pressure-flow hypothesis
Source to sink
Transport assimilate from areas where it’s made = sources
Materials moved to sinks
Actively growing areas
Storage areas
Assimilate/ photosynthate loaded into sieve tube elements with help of companion cells from source
Sugars transported as sucrose
Actively transported into sieve elements
Decreases water potential of STE
Increases osmotic concentration, decreases water potential in sieve tube
Creates a water potential gradient between sieve tube elements and surrounding cells
Photosynthate moves by bulk flow to nearest/ strongest sink and is unloaded
Sucrose actively transported from sieve tube
By companion cells
Stored as starch
Used in metabolism
Aerobic respiration
Water enters sieve tube from xylem due to water potential differential, creating turgor pressure
Phloem is always close to xylem
Xylem has a much higher water potential than phloem
Water moves from less negative water potential to more negative water potential
In summary
Water moves from root to atmosphere in a single direction
Assimilate moreves from source to closest sink
intermediate growth
trait evolu.`
apomorphy; derived novel trait
synapomorphy; apomorphy shared by 2+ taxa, hypothesized to have evol. in their most recent common ancestor
autapomorphy; character newer than
plesipmorphy; character older than
homoplasy; trait has gained or lost independently in separate lineages guring evolution
convergence; independent evol. of somilar trait in 2+ taxa
Aical meristem
totipotent region, ancestral found in charophytes, growth by mitosis
Mitosis review; mitosis
prophase, metaphase, anaphase, telophase,
cytokinesis.
synapomorphy; charophytes mainly filamentous, bryophytes protonema, filamentous, apical bud
2D to 3D switch; linear growth such as fila,emtous algae, only divide at tip, cytokinesis in a single plane,, leafy shoot growth in 3d, cytokinesis in oblique planes
Bifurcating sporophyte; splitting shoot tip into 2, laid foundation for multiple sporangia ( polysporangiate), large complex plants, specialized organ systems,, bryophytes are not unique mutant, simple early fossils cooksonia eg, current day lycophytes
terminal sporophyte replaced, displace sporangium side acial on leaf, some tips sterile, necessary prior to indeterminacy, polysporantiate
bifurcate branching; evolved prior to vascularization, lycophytes various vranching structues, equal branching isotomous, unequal branching anisotomous
indeterminacy; vascular plant synapomorphy, grow contunuously produce new organs, tissue, from shoot apex, sisplace terminal sporangia onto lateral branches, likely evolfed after vscular based on fossil evidence.
convergent evolution: indeterminat4e meristems evolve independently, bryophyte gametophyte, Fern monophyte gametophyte, vascular plant sporophyte,, vascular plant meristems may have evolved independently, lychophytes multicelllular, monilophytes single cell, spermatophytes multicellular
shoot apical meristem; totipotent region, contunuously divides, mature into transition tissues, ground meristem, procambium, protoderm
roots
origins
rhizoid
uni- milticellular
projections
anchorage
some w mineral uptake
genes; prdate land plants, play a role in rood hair develpment
rhizomorphs
Lepidodendrales extinct
Dichotomous rooting system
Lateral stigmarian rootlets
Root hairs, mixed reports
Highly branched
Similar to roots
No chlorophyll
No stomata
Develop gravitropically
No root cap
Extant species lycophyte
Bifurcating
With root hairs
No quiescent center
Shoot turned root
Rhynie chert, Zosterophyllophyta, Early Devonian
Upright stem, prostrate stems, downward (rootlike) stems
root transition
Early without root hairs
Intact epidermis covered root tip
Anticlinal divisions only
Devonian lycophyte Asteroxylon mackiei
Independent evolution of
Endodermis
Root cap
Root meristem
Diversity of arrangement used to infer phylogeny
Number of initial cells differs
Similar genes across plant taxa
Similar genes in shoot to root
body plan
Root types
Primary root
Derived from radicle
Main root
Mainly dominant in eudicots
Mainly ephemeral in monocots
Lateral roots
Adventitious roots
Derived from stems & leaves
Dominant in monocots
Seminal roots
Derived from mesocotyl
General root plan
Highly differentiated multicellular axis
Found only in sporophytes of vascular plants
Functions
Anchors plant body to substrate
Absorbs water
Absorbs dissolved minerals
Common features
Apical meristem & root cap
Pericycle
Endodermis
Root hairs
Cortex
Apical meristem
Quiescent center
Rarely divides
Backup plan
Maintains initial cells
Behind root cap
root cap
Evolved independently
Lycophyte
Euphyllophyte
Protect underlying tissues
Cells that slough off
Secrete mucilage
pericycle
Pluripotent
Initiation of lateral root development
Just inside the endodermis
root hairs
Single celled
Major absorption of water and minerals
Via osmosis from hypotonic soil solution to hypertonic cells
Delicate
Short-lived
endodermis
Casparian strip
Prevents apoplastic movement of water
Forces water to move through cell membranes to be filtered
cortex
Large storage area
Outermost layers may show
Hypodermis
Exodermis
Casparian strip
Suberized lamella
Bound by endodermis and epidermis
life cycle evolution
life on land
stomata
Vascularization
