Download Aarssen Lectures 1-12 + Grogan Fungus Lectures Lecture 1

Biology 201 Final Review: Aarssen Lectures 1-12 + Grogan Fungus Lectures
Lecture 1
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Origin, Evolution and Classification of Land Plants.
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The link between life and non-life, photosynthesis: the conversion of light energy and
fixation of carbon, chemical energy, carbon skeletons, oxygen
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Invasion of the land: the “Blob”
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Simple design of photosynthesis machines, mitosis to grow laterally across soil:
minimized wind exposure, maximized water absorption and light uptake.
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Spongiophyton: no vascular tissue, all surface cells are photosynthetic , pores to
uptake CO2
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Why is there no Blob
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i) mechanical constrains: requires continuous uptake of water and minerals from
soil. ii) Inherent limits to tolerance of environmental variation: cannot have one plant
that is adapted to live in all conditions. iii) inherent limits to longevity: immortality if
possible for very few multicellular organisms.
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Why is there diversity
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Mutation: genes are subject to random change; beneficial mutations will remain in a
population and begin speciation. These include: Changes in physiological
tolerance( exploitation of different environments), Roots( more reliable and deeper
extraction of water and minerals), Small propagules(small structure that detachs from
the main plant to give rise to new plants)( allows dispersal over land and have a
protective covering), Increased height( increases light uptake against competition,
and dispersal of propagules).
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Meristems: where mutations accumulate because it is the site of genetic processes:
consists of undifferentiated cells, the way plants have evolved certain phenotypes is
dependent on meristem function.
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Evolution by natural selection: i) there is a variation in traits between individual
organisms due to differences in genetic material that originate initially as mutation. ii)
these genetic differences are inherited. iii) some heritable differences are responsible
for differential survival and reproduction( goal: to make symgamy and meiosis
happen, without species has high risk of extinction)
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Mutation  variation  natural selection  evolution organic diversity.
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Acquiring genetic variability: the role of sex
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Since the environment is not homogeneous, it only makes sense that there is a
mixture of genetic types.
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Two ways to have genetically variable offspring: i) acquire different mutations in
different mitosis centers(meristems) all the cells produced there will have said
mutation ( this is very slow). ii) make new combinations of genes by sexual
reproduction, independent assortment of chromosomes and crossing over are
present in meiosis ( instead of mitosis).
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Advantage of sex required getting ‘small’ during some point( for genetic
recombination and dispersal of propagules) since combining genes happens during
the fusion of two gametes ( haploid) to form the zygote(diploid) . They also need to
get tall for success in competition for light and greater dispersal of seeds.
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Sexual cycles and alternation of generations in land plants
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Three types of cycles: Zygotic, Gametic, and Sporic
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The Origin of Alternation of Generations or Sporic meiosis.
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Two similar eukaryotic(haploid) cells mate and for a 2n zygote, initiation diploidy and
providing two advantages: i) allows sex ( more variability) and ii) protection against
deleterious mutations ( dominance and sexual selection acts as a sieve)
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Some evolutionary lines elaborate the haploid generation, and others the zygote.
The mani evolutionary line was toward alternation , from the sygotic pattern by delay
in meiosis until the multicellular diploid generation had developed so that both
generations are multi-cellular.
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Origin of Land Plants
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Algal ancestors: chlorophyta ( green algae) has the same pigments, stacked
thylakoids and starch storage products as higher plants. The class charophyceae
have the same :phragmoplast at cytokinesis, sterile sheath of cells surround the
gametes, oogamous ( large female games, small male gametes), zygote is formed
and retained in the plant.
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Stages in the evolution series from algae to early land plants: fertilization within
oogonium from zoospores  Mc diploid and emergent sporangium  cuticle forms
around portion out of water and spores are released  the byrophytes ( early land
plants ) begin to develop  early vascular plants form roots, and conduction tissues to
obtain and distribute water.
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Classification of the land Plants:
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Thallophytes : lower plants ; Fertilization outside the plant and no embryo ( algae
fungi and slime molds)
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Embryophytes: higher plants/land plants, fertilization occurs within the plant, embryo
developes and is retained within the plant. They include bryophytes and
tracheophytes
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Bryophytes: not very tough , very weather sensitive. phylums: Anthocertophyta
(Hornworts), Marchantiophyta( liverworts) bryophyte (mosses).
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Tracheophytes: produce tracheal tissue ( vascular plants) include the pteridophytes
(non-seed plants ) Lycopodiaphyta (club mosses)& monilophyta (whisk ferns, ferns
and horsetails.) and the spermatophytes (seed plants ) gymnosperms( non-flowering,
Cycads, Ginkgo, Conifers, gnetophytes) and the angiosperms( flowering plants)
anthophyta.
Lecture 2: The Byrophytes
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General Characteristics
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non-vascular, gametic metois, anchored to substrate with rhizoids: these do not
partake in water of nutrient conduction. They absorb water and inorganic ions directly
through the gametophyte surface. Dries up and becomes dormant in absence of
water, and resumes growth when water becomes available again. Very resistant to
dessication, can survive for long periods without water. They possess a sterile jacket
of cells surrounding gametes( to protect them from desiccation). Gametes
( antheridium = male gametangia, archegonium = female gametangia) produced in
haploid phase, sperm needs water to be able to reach the egg. Vegetative
reproduction by the gemmae, asexual reproduction by fragmentation or by using the
gemmae to self fertilize and produce new gametophytes.
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Liver worts
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Thallose liverworts: most common, undifferentiated , grows on moist soil and rocks,
dichotomous: 2 branches ( Marchantia), unisexual gametophytes( each gametophyte
only produces one of either sperm or eggs). The sporangium’s entire purpose is to
make a sac for meiosis to occur.
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Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium  meiosis.
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Leafy Liverworts: photosynthetic tissue( no vascular tissue so not true leaves), grow
on the leaves and bark of trees in humid or moist environments, most common in the
tropics.
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Spore discharge in the liverworts: involves elators( hygroscopic: change in response
to humidity/ moisture) sporangium splits open when dry/mature, and releases
hundreads of spores. Contains nostoc ( a cyanobacterium) embedded in mucilage,
cells in the thallus including the epidermis screte mucilage which is essential for
water retention. Most gametophytes are unisexuals, some are bisexual.
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Hornworts
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Anthoceros: the genus name for most if not all hornworts. Resemble thalloid
liverworts, bisexual gametophytes, archegonia and atherida embedded within the
thallus, undifferentiated flat thallus ( blob), long sporangium: upright elongated
structures with a cylindrical capsule at the tip and a foot at the base. columella:
central column of sterile cells( maybe an ancestor of higher plants as this is similar to
a stem). Foot penetrates the gametophyte tissue and forms a placenta across which
the sporophyte obtains nourishment from the gameophyte, during development a
basal meristem( active in favorable condtions) between foot and meristem, helps
elongate sporangium. All stages of spore development from meiosis near the base to
mature spores above can be seen in a single sporangium.
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Mosses
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Classes: Bryidae( true mosses) , Sphagnidae (peat mosses), andeaeidae( granite
mosses).
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Bryidae: stem structure, not quite as good at transport as vascular tissue, seta =
stalk, hydroids(kinda like xylem, doesn’t look like it but still conducts water) lack
lignin( permeable and thin) , polytrichum: gametophyte “stem” cross section with
central conductuing tissues. Leptoids are kinda like phloem( transports
photosynthates, more so than the rest of the stem structure). Variety in peristomes:
ring of teeth, movements of teeth in response to splitting cell layer near capsule in
dry environents releases spores to be dispersed by wind.
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Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium  meiosis.
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Sphagnidae: sexual reproduction involves formation of antheridia and archegonia at
the ends of special branches at the tips of the gametophytes. Sporophytes: capsules
with short stalk are attached to the pseudopodium ( remainder of the stalkgametophyte). Unsual protonema: first stage of development of the gametophyte –
does not consit of multicellular branced filaments like most mosses- just a plate of
cells that grows by a marginal meristem, in which most of the cells can divide in one
of only 2 directions.
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Spore Discharge in mosses: as capsule dries it contracts changing from a spherical
to a cylindrical shape and compresses trapped gas within the capsule. This gas
reaches high pressure and blows off the operculum( lid on the top of the sporophyte
capsule) with the explosive release of spores.
Lecture 3: Vascular plants
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No plants made seeds 300million years ago or flowers.
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World became crowed with land plants so it was harder to compete for light, had to
get tall. Most common reason for extinction is because they failed at this life cycle,
did not have successful gamete production and syngamy.
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Evolved roughly 400mya. In the beginning of the land plant the picture would be
made up of bryophytes and vascular plants.
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The dominate generation in vascular plants is the sporophyte ( sporangium produced
on sporophyte which houses spores to keep cycle going).
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First land plants ~400mya , no photosynthesis, nothing in the terrestrial environment
would evolve with them, they produced oxygen, set the stage for fossil fuels, oxygen
atmosphere and the evolution of animals.
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Origin
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Theory one: algae split into Bryophytes( still around , small and successful) and
Tracheophytes( they really provide most f the carbon build up that allows for fossil
fuels and oxygen). Xylem= transports water and nutrients upwards and provides
physical support. Phloem: transports sugars and proteins.
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Theory 2: usually use fossil record if we have it, we can use inference, piecing
together a hypothesis based on debate. Anthoceros-like ancestor  Vascular plants.
Similarities : i) sporophyte has a central columella which may have easily evoloved
into a internal conductive system of xylem and phloem ( sterile) ii) sporophyte has
cutile and stomata with guard cells. ( stomata controls entry of CO2 and release of
water)) iii) sporophyte has an intercalary meristem which provides indeterminate
growth ( important in higher plants, here the sporophyte continues to grow , pushing
up the sporophyte )
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The First Vascular plants and early evolution.
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The oldest fossil plant is the cooksonia.
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Three extint phyla : common features include no roots, no leaves, cuticle ,
dichotomously branching stem , sascular tissue was a protostele, and they were
homosporous.
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Rhyniophyta: Cooksonia(Most of the tips of the dichotomies produce sporangium) ,
Rhynia(produce vegetative and sporangium on tips, more specialized), &
Homeophyton( sporangium are in cluseters on tips).
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Zosterophyilophyta: Sporangium, where meiosis takes place. Evolution is bringing
them to a localized place to keep them together and protected, didn’t have leaves
but had to increase surface area to capture light, didn’t have leaves but had to
increase surface area to capture light , photothesis takes place in stem. Some had
spine like outgrowths roviding increase surface area for light harvesting.
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Trimerophyta: larger with a main axis ( 1-3m tall), increased diameter of stele,
increased xylem lignification( gives added structural support), lateral brances
specialized in photosynthesis, clusters(grouping of sporangia).
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Major Evolutionary trends in Vegetative traits
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Roots: Reliable water source is in the ground, vascular plants at first did not have
roots, worked out OK but not great. Early vascular plants had rhizomes with only
rhizoids functioning only for attachment to the substrate specialized rooting organs
with vascular tissue.
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Evolution of the Axis: A) increase in height: dichotomously branching  sympodial
axis( zig zag)  monopodial axis( straight center). B) Increase in girth: evolution of
thicker, heftier branches, thinckened girth stem with vascular tissue, the tissue that
gives it the strength is around the outside, greater strength per mass ( prevents
falling over and being top heavy).
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Evolution of Vascular Tissue: A) evolution of the siphonostele, protostele
siphonostele  eustele. B) Evolution of xylem tracheid cells and xylem vessel:
increasing amount of secondary wall thickening ( lignin) C) Secondary Growth:
secondary growth from vascular cambien, a secondary lateral meristem allowing
greater increase in stem girth. M cambium ( intiated by the primary cortex)  cork
(phellum, toward the outside and dies to form protective layer) and secondary
cortex(phelloderm, towards the inside). Replacement tissues to replace damaged
tissues as growth pushes outwards. Allows fore more vertical growth.
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Evolution of the leaf: A) origin of the microphyll, increased SA for gas exchange,
outgrowths of cortex and epidermis, later extension of vascular tissue, reduction of
dichotomous branches( these shoots become a microphyll that serves the function of
not producing sporangium but adding more SA B) origin of the megaphyll: 3-D
arrangement of dichotomous branches flattened arrangement in a single plane 
filling in of space between branches with parenchyme  reduction at dichotomies
produces a pinnately veined megaphyll.
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Summary of evolutionof vegetative traits: Obtaining water roots  immobility
crowdedness  tall height from apical dominance and lignin in support tissues 
conducting water up and photosynthesis down & stems buckling  support from the
vascular cambium ( xylem and phloem) and stem strength from siphonosteles
rupturing of external cortex , loss of water, pathogen entry and fire damage 
expanded outer cortex from cork cambium and bark from cork cambium  loss of
photosynthetic function in stem  formation of leaves to increase SA in higher areas.
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Major Evolution trends in reproductive traits
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Reduction in size and life span of gametophyte generation and increasing
dependence on sporophyte , not much going on in gametophyte therefore reduction
of size, loss of sperm cell motility. Loss of archegonia and antherida, Homospory 
heterospory: two kinds of spores produced in two kinds of sporangia and which
develop into separate male and female gametophytes respectively.
Lecture 4: Seedless Vascular Plants
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The ancestors of all these plants were the only plants on eather 300mya ago( have a
long history in fossil records), most of the phyla have gone extinct, the evolution of
seed plants were responsible for many of these phyla extinction.
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Whisk Ferns – order Psilotales (peridophyta)
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Characteristics: underground rhizoids, dichotomous branching, protostele, leaves :
psilotum(none, only scale like outgrowths lacking veins & Tmesipteris( spirally
arranged microphyll-like (with one vein), homosporous. Small gametophyte blob
(green largely undifferernted but has an important role of producing gametes.
Antheridia break open and release sperm, spore must swim to find archegonia, if
they find archegonia on the same plant = selfing, need moisture.
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Origin: Theory one: from Phynia-like ancestors ( No fossil record of psilophyta since
the Devonian period (400mya), where rhynia was found. Theory two: result of
reduction from other pteridophyte groups( as they are less structurally complex then
other pteretophyte groups).
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Interpretation of Psilotum sporangium: inference (don’t really have snapshots of
these throughout evolution. By localizing sporangia, it may have helped during water
shortages and protection against herbivory. Sympodial branching system with
overtopping fertile and sterile branches shortened by reduction  contined
shortening and fusion of 3 sporangia 3 lobed sporpangium in axil of reduced sterile
branch. Advantages of lobed sporangium: protection from desiccation and less
conspicuous to consumers
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Similarities between gametophytes and sporophyte : i) both have rhizoids( help plant
attach to substrate) ii) both are radially symmetrical ( dicated by meristemic
growth( archeridia and archeonia ) iii) both have dichotomous branching. iv) some
gametophytes have vascular tissues ( like sporophyte). Biggest gametophyte in
seedless plants, starts as a spore  grows into blob structure.
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Implications : suggest that gametophyte of early vascular plants were similar in some
ways to the structure of sporophytes. However later selection: increased sporophyte
size and reduced gametophyte size. ( selection presusres that might limit the
success of sporophytes differed from those that might limit gametophytes.)
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Meiosis spores haploid gametophytegametesSyngamyzygotediploid
sporophyte sporangium  meiosis. Gametophytes are very vulnerable to lack of
moisture so they get smaller to conserve moisture. ( seed plants evolved to solve
this) Sporophyte avoided death without sex by getting bigger
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Horsetails – Order Equisetales ( Pteridophyta)
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Characteristic: Extend back to the Devonian period maximum abundance and
diversity in carboniferous period ( 300mya), only one living genus, rhizomes that
have emerged true roots( true roots have xylem and phloem), stems joined with or
without branches at nodes, leaves are microphyll, alternate with brances at nodes,
eventually dry out and photosynthesis occurs mainly in surface layers of the stem,
believe to originated from a reduced of dichotomous branches.
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Stem anatomy: as tissue grows the pith breaks down and becomes just open
air(hollow tubes are stronger per weight than solid) , helps to keep the plant upright,
more photosynthesis occurs in stem( chloroplast packed around epidermis), vascular
tissues is arranged in a ring ( eustele) Has a lot of lignin, nick named scouring rush,
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Reproductive structures: sporangia arranged in a spiral, dangle from plate with
sporangiophore in the middle, Strobilus ( a sporal arrangement of sporagiophores),
have elaters, attached to spore, when they are wet the elator arm like structures
spread out and allows wind to disperse the spore , hydroscopic
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Formation of Sporangiophores: sympodial branching system reduction of branches,
recuraction of sporangial stalks,  reduction and fusion of sporangial axes, packs
together sporangiophores. Makes them less conspicuous to consumers in
sporangium, more resistant to dessication.
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Life Cycle: early life sporophyte is dependent on gametophyte but eventually it will
have its own roots, all started in archegonia where successful fertilization allowed for
the production of sporophytes, gametophyte gives rise to young sporangium
,homosporous : 1 kind of sporangium  1 kind of spore  one gendered gametophyte.
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Extinct forms: Calamites( up to 20m tall, flourish during the carboniferous period,
only herbaceous species are leaft in the extant flora, massive trees.
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Ferns ( several orders, Pteridophyta )
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Characteristics: largest groups of seedless vascular plants, date back to middevonian , sizes range from 2cm long to 24m tall, stm reduced or exsists as a
creaping rhizome, leaves are megaphylls and called fronds, young leaces are coiled
in the bud and uncoiling is refered to as circinate vernation. Successful clonal
propagation seen in growth of horizontal roots, don’t need sex to make babies,
naked sperm have to find moisture to swim around to find egg.
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Origin: monilophyta have prostele, siphonostel and eustele, 2 rings of phloem =
characteristic feauture of vegetative ferns , suggest it’s the prodiuct of natural
selection , why / how did they evolve? Follows the evolution of the dichotomous
branched , early vascular plants, a lot of ferns were trees mya (having a hefty stem
with vascular tissue would have been important). Ferns bulked up but having tissue
grow over bundles of dichotomous branches. Amphiphloic siphonostele= concentric
phloem flanking xylem, Dictoyostele selected for lignin protecting pith.
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Sporangia: sorus= cluster of sporangia, diversity of sorus, used for identifiying
features of different groups of ferns, sori are on adult sporophytes, they are
sporangiophores that contain a cluster of sporangia.
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Origin of fern megaphyll and sporangia position: dichotomously branching
system(sporangia at the tips of branches)  straightening of main axis and planation
of reduced lateral fertile branch system ( planation: branch system is now in a plane
as opposed to 3D)  webbing gives a leaf-like blade with marginal sporangia.
Megaphyll efficient gas exchange and photosynthesis ( high SA) , key reason ferns
are still around.
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Annulus: pod of spores, cell cack in annulus is moist, evaporates as it gets older
causing it to break open, outer walls are thin, once annulus breaks open there is
further evaporation to catapult the spores out.
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Tree Ferns: Growth is entirely by apical meristem( no vascular cambium, stems
cannot get any thicker ) , Arboresecent forms have gone extinct within all the
seedless vascular plant groups with the exception of ferns, ferns are the only group
that hasn’t lost their trees.
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Fern Allies( club mosses, etc) Largest group , they have their own
phylum( lycopodiophyta)
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Lycopodium (club moss)
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Characteristics: rhizomes with true roots, dichotomous branches with microphylls ,
variation of the protosteles, most photosynthesis occurs in microphylls but can occur
in stem, homosporous bisexual gametophyte, sporangia on upper surface of leaf-like
sporophyll arranged loosely in a spiral arrangement on a stroblilus at the end of the
branch, sporophyll=microphyll with sporangium
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Interpretation of Sporangium : stalked sporangium above leaf-like outgrowth 
sporangium moved to auxiliary position, vascular extension into microphyll
sporangium moved onto adaxial surface of microphyll. Advantages include reduced
desiccation of sporangium, improved more by close packing of sporophylls on a
strobilus and less conspicuous to consumers.
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Arborescent Lycopodiophyta ( tree like): Lepidodendron ( dominant tree), up too 20m
tall, flourished during carboniferous period, only herbaceous speices are still present.
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Selaginella: Heterosporous : different spores produce separate male and female
gametophytes , prevents inbreeding as different sexes are on different
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Gametophytes: Very reduced with no morphological similarity to the sporophyte as in
psilotum, develop endosporally i.e within the confines of the spore wall,
megagametophyte also develops while the megaspore is still within the
megasporangium, gametophyte spends it entire life in the ( mega an micro) spore
wall. Flagellated sperm still have to swim to find archegonia
Lecture 5: Evolution of the Seed Plants ( Spermatophytes)
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Progymnosperms
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Appeared in Devonian, exisited throughout the carboniferous (400-300mya),
intermediated between early vascular plants and later gymnosperms, large
gymnosperm like axix with secondary thickening from a vascular cambium, Hence
they were first true “trees” but they produced spores not seeds, they could increase
the girth of the bottom of the tree to support its upward growth.
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Sperm is in a vulnerable stage , but seed plants take care of this, seeded plants
caused the extinction of other less evolved plants by being more successful and
obtaining all the nutrients, gametes produced from gametophytes on different male
and female sporophytes, this allowed for more diversity as it promoted sexual
reproduction.
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In seed plants the entire male gametophyte reaches the ovule, no long need
flagellated sperm to travel through water. Megagametophyte produces eggs and
nourishes the new embryo when it develops.
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Evolution solved the problem of gametes in the seed plants through sporangium
(houses for vulnerable gametes), diploid sporophyte plant produce sporangium
( where fertilization occurs).
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The Seed Habit
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Comparison with Petidophytes: Seedless Vascular: 1 kind of sporophyte (one kinda
of spore), they produce tons of spores (cheap), most of them die out but they only
need one spore to fertilize and spread genetics, exosporal= develops outside the
spore wall. Selaginella: only produces 4 spores, retained within the megaspore wall
(beginnigns of seeded plants), dehiscent= splits open, sporophyte is dominant.
Spermatophytes: rest of the megaspores abort, one remaining megaspore develops
into female gametophyte housed within the megasporangium, sporangium does not
split open, gametophyte spends entire life immersed in the tissue of the sporophyte.
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Two major developments: i) Heterosporyand retention of reduced endosporal female
gametophyte and subsequent embryo within an indehiscent sporangium. ii)
integumentation of megasporagium: the tissue that wraps the gametophyte, provides
protection and nutrition to the developing cell. The seed is the fertilized
ovule( containing the zygote or developing embryo) and the integument becomes the
seed coat.
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Interpretation of the integument: The extinct plants look just like ferns, there could be
some relationship, could be the first seed plant to produce integemented
sporangium, dichotomous branching system with fertile and sterile branches
reduction to a single functional megasporangium surroned by sterile branches 
fusion of sterile branches gives the integumenentary envelope, still doesn’t have a
seed but mana had all the other components, integement is firther protection for the
house.
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The seed developed by a series of progressive closures of the integumentary lobes
to create a enclosed megasporangium.
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Evolution of the Pollen Grain.
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Since they are heterosporous, they male gametophyte was evolving alongside the
female to ensure that they remain compatible. The have a reduced male
gametophyte so that the entire male gametophyte can be delivered to the ovule ( ie
the pollen grain). Gametophyte stays in spore and gets delivered to ovule, doesn’t
get very big because delivery has to take place by wind. The exine (resistant outer
coat) provides: improved protection from desiccation and improved wind transport
from elaborations of the exine. Sperm cells don’t germinate into hundreds of spores
only a few.
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The pollen tube was developed to penetrate the nucellus and delivers the the sperm
to the egg in the archegonia. Pollen tube delivers sperm to egg by growing through
the tissue to reach the egg. Seeds have adaptations to promote growth: female
gametophyte , multicellular and most of the volume is taken up by the female
gametophyte , which provides nutrition for the young embryo ( most of seed is food)
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Major Advantages of the Seed Habit.
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Growth: nutrition for the female gametophyte , embryo and young seedling, seed
may be a mechanism for providing maternal car for embryo. Survival: combined with
the pollen grain, provides freedom from the need of surface water for
fertilixation( uses wind instead), protection for female gametophyte and embryo
provided by the seed coat, & survival through harsh periods and promotion of
germination in favorable periods( by dormancy mechanisms). The embryo will only
emerge from the seed when the conditions are preferable. Reproduction: seeds are
the products of sex, allows dispersal of the sporophyte generation, been successful
in the number of species and extent of control in their environment, seeds are like
the baby that will germinate into a new individual.
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Gymnosperms
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Defintion: naked seed, it is borne exposed on the surface of the sporophylls or
analogous structures, Gymnosperm : refers to mode of seed production. Conifers:
refers to cone-bearing seed plants. Evergreen: duration of leaves. Not all
gymnosperms are conifers but all conifers are gymnosperms
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Female gametophytes: multicellular with several archegonia near the microplar end
of the ovule. virtually all the gymnosperms have several archegonia (each with an
egg) just like the pteridophytes, the fact that there are still several eggs show the
evolution from pteridophytes. More than one egg may be fertilized and therefore,
several embryos may begin to develop- polyembryony( usually only one embryo
survies).
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Cycadophyta ( Cycads)
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Habit: lots of species, do not live in very cold climates, not palm trees
( gymnosperms), have fern like leaves, can grow up to be tall.
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Androstobilus: all cycads have male and female sporangia ( dioecious) , pollen and
ovules being produced on separate plants, heterosporous ( dioecious= unisexual
sporophyte = produces pollen OR seeds, not both. Cycads evolved from seedless
vascular plants , analgous to strobili in seedless vascular plants, clusters of
sporangia on sporophylls, pollen is produced in androsporophylls, each microspores
develops into pollen grain. Strobilus = loose arrangement of sporophylls, cone=
Compact arrangement of sporophylls.
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Male Gametophyte Development: mitotic cell divisions ( 5 cells in total) all sterile
except for 1, sterile cells represent legacy of genetic ancestry, gymnosperms evolved
from species with many gametophytes. Minimizes the development of the male
gametophyte
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Gynostrobilus : seed cone, spiral arrangement of gynosporophylls with ovules borne
on adaxial(upper) surface. All have cones , inside an ovule there are gynospore
mother cells that create the linare tetrad of megaspores.
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Ovule and the Sperm: the pollen tube grows into tissue to get nutrition, some time it
breaks open to let sperm out flagellated sperm swim in cavity of the haustorial pollen
tube, several eggs with several sperm to compete for.
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Similarities between cydads and ferns : 1) pinnate leaves 2) leaves have circinate
vernation 3) microsporangia in clusetes on abaxial surface of leaves (ferns) or
microsporophylls (cycads) 4) flagellated sperm 5) young sporophyte retains some
dependency on gametophyte in cycads, cotyledons of young seedlings remain for
several weeks in contact with the gynogametophyte, to receive important nutrition
from gametophyte.
Lecture 6 Gymnosperms
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Ginkgophyta
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Dioecious = unisexual sporophytes, ovules and pollen are produced on separate
trees. The ovules are where fertilization takes place and the embryo develops, they
posses microstrobili.
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Sperm are now swimming within the ovule , not the forest floor, no need of as uch
water now.
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Coniferophyta
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Two orders: 1) Cordaitales and Coniferales ( one extinct family ( lebachiaceae) and
7 extant families ( largest group and do well in cold).
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Shoots and leaves: leaves are designed well to coduct photosynthesis in harsh
climates, have xylem ( upper surface ) and phloem ( lower surface). Low SA to V
ratio, minimizes opportunity for water loss, adapted to dry condtions as they give up
photosynthetic production for water retention. Epidermis with thick cuticle, thick
walled celled of hypodermis( heavily lignified), Sunken stomata, resin ducts.
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Microstrobilus: each small cone is a separate microstrobili. Most conifers are
monoecious= produce both pollen and seeds on the same tree. The microstrobilus
are clustered on small branches spiral or cyclical arrangement ,
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Microgametophyte: the generative cells need to develop more when it arrives at egg
before it is ready to fertilize.
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Megastrobilus: ovuliferous scale and bract is for protection, spiral or cyclic
arrangement of bract with ovuliferous scales.
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Life Cycle: Angiosperms get sex done quicker which is probably why they displaced
gymnosperms. Year 1 autumn: cones initiated in buds. Year 2 Spring: female
gametophyte isn’t ready yet so male gametophyte has to wait, Male gametophyte
development pollination  pollen tube growth. Year 3 Spring: fertilization  embryo
development Autumn  seed dispersal.
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Gnetophyta
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3 genera : Ephedra, Welwitshcia, Gnetum.
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Angiosperm like features: 1) vessels in the xylem 2) strobili resemble angiosperm
inflorescences 3) reduced male gametophyte ( pollen grain with only 3 cells) 4) lack
of archegonia in Welwitschia and Gnetum 5) reduced female gametophyte in
Gnetum - remains free-nucleate – one of the free-nuclei acts directly as the egg.
However they are gymnosperms because they do not have carpel or double
fertilization.
Lecture 7: Origin and Evolution of Angiosperms
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Evolution trend in the separation of the sexes: Gametophytes have developed to
reduce inbreeding by evolving toward heterospory and consequently unisexual
gametophytes, all seed plants are heterosporous but most have pollen and egg
produced on the same plant= monoecy or hermaphrodite.
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Anthophyta
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The Carpel: Spermatophytes (seed plants) 2 integuments. Carpel = basically a leaf
that folds in lengthwise to enclose ovules.
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Origin: poor fossil record, describe by Darwin as an abominable mystery, believe to
have seed ferns as ancestors during the late Jurassic / early cretaceous no fossil
record of flowering plants, but there is of flowering pollen.
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Stages in the evolution of the carpel: enrolling of cupule to protect ovules, reduction
of ovules from a whole bunch to 1, 2 integuments. The leaves wrap around the
sporangiophore and continue to close until the carpel ( a fully enclosed covering) is
formed.
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Interpretation of Flower Parts
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Flower= a determinate shoot bearing various leaf-like appendages, A reduced stigma
with elongated style sets up a kind of competition between pollen grain , where the
best quality pollen grains are more likely to arrive first to fertilize ovules, effectively
allowing mate choice by the maternal plant. There is no shortage of pollen so we
don’t really need a large female base to maximize fertilization.
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Carpel: some ovules are made up of carpel other are made up of 3 fused carpels or
even several with several cavities. The ovary of a flower may consist of only one
carpel or several which may or may not be completely fused.
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Stamens : look leaf like, flattened have sporangium ( houses for meiosis to take
place) to produce microspores, not photosynthetic. Reduction of lead blade to a
slender stalk with sporangia (anther) near it apex.
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Perianth: sepals= derived from leaves, petals = modified from sepals or from
stamens that loast their sporangia and became specially modified for the role of
attracting pollinators. Evolution of the megaphyll not only provided a specialized
organs representing by the flower. Facilitation of pollen mechanisms wouldn’t have
been possible with the megaphyll modification 1) further protection of ovules and
seeds 2) insect pollination 3) pollen competition and mate choice 4) seed dispersal
using fruit ( carpel becomes the furit).
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Evolutionary trends in Flowers : 1) Primitive traits = many parts, indefinite in number,
parts separate. Advanced traits= few parts , definitie number , parts fused. 2)
PT=complete flowers. AT= incomplete flowers: lacking sepal and /or petals, stamens
or ovaries ( unisexual). 3) PT= superior ovary ( attachment of ovary is above ( or
equal to the rest of the parts) AT= Inferior ovary( tucked into receptacle for
protection). 4) PT= radial symmetry AT= Bilateral symmetry. 5) PT= single flowers
AT= flowers aggregated into inflorescences.
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Proposed Evolution of insect pollination:1) Ovules exude sticky sap and the first
angiosperms ( maybe even seed sperms in general) could have had this , this
attracts insects. 2) attracted beetles which fed on the sap and pollen grains get
attached to them. 3) beetles by travelling between plants transfer the pollen for the
plants ( more efficient than wind) 4) later mutations helps adapt the flowers to attract
certain types of insects.
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These mutations included the evolution of i) nectaries = drinking places in flowers for
easy access, ii) accessory structures ( petals)= attract a particular kind of faithful
pollinator to avoid pollination from another species of plant, iii) closed carpel to
protect ovules from predatory insects, iv) bisexual flowers= made each visit by the
pollinator more efficient as they wer giving away their pollen and receiving pollen at
the same time.
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Evidence that beetles were probably the first insect pollinators for the angiosperms:
beetles have an old fossil history and were already diverse in the early cretaceous
period, when angiosperms originated. Beetles are important pollinators in primitive
angiosperm families.
Lecture 8: Angiosperm Reproduction
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Pollen development
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angiosperms dominante with few exceptions, but we still have all 4 major groups of
plants. Angiosperms are heterosporous with male & female gametophytes . Male
gametophytes reside in the pollen grain. In the evoliton of plants , angiosperms got
smaller and more efficient with a more rapid life cycle. In the evolution of plants
angiosperms got smaller and more efficient with a more rapid life cycle.
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Different taxa can be ID’d by their pollen based on : size, number of pores and
pattern of sculpturing in exine.
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Microsporogenesis: 4 sporangia associated with almost all anthers , microsporcytes
are 2n ( microspore mother cells) and they produce the microspores by meiosis.
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Microgametogensis: whole generation packed inside microspore becoming a pollen
grain, only 2 cells in the pollen grain when it leaves the anther and gets dispersed
( undergoes another cell divison after dispersal) , don’t need flagella because sperm
is delivered by pollen tube, it germinates on the carpel and then is delivered to the
ovule.
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Embryosac Development
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Megasporognesis = to produce spores by meiosis.
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Megagametogenesis : Megasporocytes produces 4 megaspores but only 1 is
functional , in the embryo sac : the fusion of 2 polar nuclei restores diploidy to form a
seconday nucleus, 6 other distinct cells in the embryo sack for a total of 7-8 cells ,
synergids are sterile cells
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Pollination
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In angiosperms the pollen germinates on the carpel , hence the pollination is 2 stage:
1) transport of pollen to carpel( pollen dispersal) 2) growth of the pollen tube through
the carpel tissue. The stigma exudes chemicals to create a chemical gradient so
the pollen knows where to go , events that set up fertilization. Angiosperm pollen
has a tougher journey than gymnosperms pollen , angiosperms have perfected
insect transport.
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Fertilization
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Pollen tube penetrates a synergid one sperm enters egg and one sperm enters
central cell  double fertilization  one sperm forms the zygote(2n) and one forms the
primary endosperm nucleus (3n)
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Seed Development
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Integument seed coat( allows them to lay dormant), zygote  embryo , primary
endosperm nucleus  endosperm ( develops into a multicellular tissue (occupies
most of the seed) and feeds the embryo)
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Interpretation of endosperm: 1) a malformerd second embryo, prevent from normal
development because two female gametophyte nuclei fuse with a sperm nuceleus
forming a a 3n nucleus (accessory zygote) 2) Equivalent to a female gametophyte
that has been delayed in it development. The endosperms role is equivalent to the
female gametophyte in gymnosperms.
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In angiosperms: double fertilization  endosperm . In gymnosperms: polyembriny -/->
female gametophyte. The process of the multiple function is similar in both types but
does not lead to the nutritional product in gymnosperms.
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In gymnosperms: fertilization by two sperm , but only one survives. In Angiosperms
both products of fertilization develop
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The Fruit
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Ovary ( carpels)  wall of the fruit. There is a wide variety of fruit types due to a large
variety of mechanisms for seed dispersal.
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Characteristics of Angiosperms
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Vessels in xylem: endplates are flattened , stacked on top of each other up the stem
of the plant ( dead so water can move through)
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Seive elements with companion cells in phloem( Delivers sugars, products of
photosynthesis to support metabolism of plants.
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Accessory reproductive structures : sepals and petals , assist in sygamy by bringing
gametes together
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Simple stamens with 4 microsporangia
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Ovules with 2 integuments ( bitegmic)
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Reduced gametophytes : males = 2celled pollen grain, females= 7 or 8 celled, no
archegonia
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Carpels enclose ovules – Hence pollen germinates on carpel tissue, never
germinates directly on ovule as in gymnopserms .
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Double fertilization: two nuclei from the female gametophyte are fertilized by the two
sperm from a single pollen grain and both products of fertilization develop into an
egg and endosperm.
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Advantges of Angiosperms over Gymnosperms
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More rapid life cycle: no waiting for female gametophyte, increased generation time,
increase recombination and diversity.
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More efficient resource use for reproduction , double fertilization makes sure that
expensive nutrient rich tissue is only produced when needed.
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Carpel : protects seeds, variety of dispersal mechanism, opportunites for self
incompatility mechanism which prevents inbreedings, opportunites for pollen tube
competition( allows for mate choice)
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Pollination by animals: less wasteful, more direct pollination, more out-crossing in
general
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Vessels in xylem: more efficient water transport.
Lecture 9
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Distribution skewed towards smaller species ( some very large species some very
small) but most are on the smaller side of the middle.
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Most speices are small. Why? There are many hypothesis : 1) evolutionary time 2)
left-wall 3) extinction rate 4) habitat availability 5) selection for reproductive economy
6) physical space niche size distribution.
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Evolutionary Time: The first species were small so smaller species have had more
time to speciate from other small species.
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Left wall : each new species within a linages is equally likely yo be larger or smaller
than their ancestor. Sicne you cannot have organisms smaller than the smallest size
they tend to pile up at that point. You do get big and bigger organisms but they
increase slowly.
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Extinction Rate: Larger species have smaller population sizes, and therefore are
more likely to become extinct. More of the smaller species will physically fit into the
environment preventing them from undergoing mass extinction as easily.
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“More descendant are at the smaller end of the scale simply because their ancestors
were”
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Habitat availability:Large species size is adaptive in habitat types that have been
realatively uncommon across evolutionary time ( high fertility , low disturbance) and
hence so too has been the opportunity for the origination of larger species. more
species origination because habitats with that level of disturbance has been most
common both spatially across the glove over time. More smaller organisms because
the environments that promote smaller organisms have been more common.
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Increasing soil fertility is on average winning out so globally bigger plants and more
species can be sustained,
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changing frequency distribution of habitat types over time. Increase in disturbance
more rapidly than increase in fertility so we have a right wall. Frequency and intensity
of disturbances increases over time.
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Even in a single habitat its ususally skewed to the right, high concentration of
species of an intermediate –small size.
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The problem of the small, has unique consequences for plants because of plasticity :
most individuals are suppressed with a high probability of early mortality , many of
which , manage at least some offspring production.
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Croweded Vegetation at Carrying capacity( skewed right) :Smallest group= high
probability of mortality because they have no sex, cant disperse pollen, cant attract
pollinators, potential for severe natural selection. The larger plants will be very
successful as they do not face these problems.
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Clonal Propagation: produce offspring with no fertilization of ovules, extension of
longevity , long enough to ensure that even small suppressed weakling manage
eventually to out-cross. Strong selection for: smaller size at sexually maturity ( to
increase chance of sex), smaller seed size(produce offspring without large amounts
of resources), increased selfing rate( produce offspring without investing in
outcrossing sexual reproduction), increased clonality ( produce clones without
investing in any form of sexual reproduction). Since the small organisms cant
outcros as often, they self, producing more smaller organisms.
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Selection for Reproductive Economy : when angiosperms appeared in the crowed
plant world, they were dominated by big gymnopserms , most of their evolution and
diverisification subsequent speciation involved selection in favor of strategies that
served to propel their genes into future generations without needing to be big
themselves
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In angiosperms the life cycle is much more efficient
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Physical Space Niche Size Distribution Hypothesis: there ae more smalle species
because there are more niches for small species, most of which are generated by
the presene of larger species. The larger the species , the less efficient it is at
harvesting all of the available resocures units contained its physical-space-niche. A
lot of small species can tuck themselves into all the small ( leftovers) niches in an
environment. Available resources may not be enough to support one large organism
niche , but 3 or 4 small organism niches could still fit.
Lecture 10 Introduction to the Fungi
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Fungal bodies can grow out and infect/share nutrients between speices that wouldn’t
happen without the fungal links
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Features: Mainly terrestrial some aquatic, cell wall of chitin, Heterotrophs only,
mostly aerobic but yeasts can ferment and rumens contain anaerobic fungi, many
catabolic enzymes( can break down almost anything), produce spores with
complex , non-flagellated structures.
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Yeast Form: a morphological group, not taxonomical group, unicellular,
reproduction : asexuall- mitotic budding (haploid) or sexual – substrate deleption or
adverse chage in environment -> syngamy then zygote is formed and often enters a
dormancy stage
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Fungi that cause disease are often dimorphic: animals = yeast form and plants =
hyphal form.
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Some fungi are facultative anaerobes
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Hyphae can extend across several spatial scales, they can continue to branch out
almost indefinitely
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Hyphae range from septate to coenocytic : very rapid growth rates, as it pushes
through soil it realses enzymes to degrade soil and wood, others allow active
transport of the nutrients into the hyphae. Little gaps form in the walls to allow the
cytosol to be continuous throughout the organism.
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Implication of being small and filamentous: rapid growth, large SA to V ratio, able to
interconnect the mosaic of tiny islands of resources that composed the world.
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Nutrient acquisition: Rigid cell wall precluded phagocytosis, uptake across the cell
membrane is limited to small organics and inorganics. Must break down all nutrients
until they are able to pass through the cell membrane by use of enzymes or
hydrolysis.
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Many have storage capacities for carbons, lipids, phosphates sulfur and nirtrogen.
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Reproduction: Asexual ( haploid spores) and sexual( stimulated by harsh conditons,
fusion of cells with compatible nuclei in two steps 1) cytoplasmic fusion 2) nuclear
fusion : produces the zygote(diploid) which will under go meiosis). They also possess
special thick walled spores that are able to rest dormant during periods of harsh
condtions.
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Human uses of fungi: food, medicine, bioremediation, biological research, biofuels.
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Zygomycota: mostly saprotrophs in surface soil, coenocytic, asexual reproduction
from spores on structures that branch off hyphae, and sexual reproduction results in
thick walled zygospore.
-
The life cycle is mostly in the haploid stage, therefore it is a zygotic meiosis type.
-
Scarce nutrients lead to diverse feeding habits in fungi. Can prey on living organism
by using a variety of mechanisms
Lecture 11 Fungi : Ascomycota and Basidiomycota
-
Most of the life cycle is haploid for Ascomycota and dikaryotic for basidiomycota
-
Extended dikaryotic stage is favored becaused : great potential for expressing
phenotypic change through mutations.
-
Ascomycota
-
Major features= 65000 species, unicellular and/or filamentous, hyphae generally
have perforated septa
-
Reproduction: asexual( conidia, multinucleate haploid spores) or sexual ( homothallic
or heterothallic hyphae, sac( ascus ) surrounding ascospores ( haploid).
-
Crozier structure leads to nuclear fusion within dikaryotic cell followed by meiosis
and mitosis to produce the ascus with 8 ascospores.
-
Diseases caused by Ascomycota: food moulds, dutch elm disease, powdery mildews
on leaves of cereals, ornamental shrubs , garden annuals and perennials and
athlete’s foot.
-
Basidiomycota
-
Major Feautres: 30000 species, unicellar and/or filamentous, hyphae always have
perforated speta, most of the life cycle is in dikaryotic phase for many species
requiring specialized cell divison.
-
Clamp connection : dikaryotic cell division
-
Reproduction : asexual ( oidia ( haploid spores) from monokaryotic hyphae) or
sexual : homo or heterothallic hyphae, dikaryon is the dominant growth phase of life
cycle, basidium (only diploid stage) produces basidiospores (haploid)
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Spores= high productions and distance dispersal.
Lecture 12 Fungal Symbioses Lichen Mycorrhizae
-
Lichens = fungus + alga or cyanobacteria: frequence many terrestrial and shoreline
regions( including the harshest ), 13000 species, most of thallus is of fungal origin
-
Structure: stratified thallus common ( fungal cortex protects), asexual reproduction
via fragments and soredia containing both partners.
-
The fungal partner can also often reproduce asexually-> conidia and sexually ->
ascopsores
-
Fungus gains carbon, provides structure , stablises water supply and protects from
intense light. level of mutualism depends on scale.
-
Primary soil formers, nitrogen input into terrestrial ecosystems, winter and summer
subsistence for caribou, air pollution monitoring , and dyes
-
Mycorrhiza= Fungus root symbioses.
-
Hyphal network extend outwards so the fungi can obtain the required amount of
nutrients(P and N mostly) for its self and its partner. The fungus receives carbon
from the plant. Fungus also protects plant from pathogens.
-
Endomycorhizae: fungus penetration of root cell by glomeromycot, 80% of all
vascular plant species .
-
Ectomycorrhizae: fungus grows around the outside of the root cell-sheath,
predominant in temperate and boreal trees and shrubs, many prodce decomposition
enzymes.
-
Hyphae can interconnect plants within forest communities
-
Lichen and mycorrhizae were probably essential for plants to colonise land.