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Plant Diversity IIPlant Diversity IILevel 1 Biological DiversityLevel 1 Biological Diversity

Jim ProvanJim Provan

Campbell: Chapter 30Campbell: Chapter 30

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Reproductive adaptations of seed plantsReproductive adaptations of seed plants

Three life cycle modifications led to the success ofThree life cycle modifications led to the success ofterrestrial plants:terrestrial plants:

Reduction of the gametophyte: retained in the moist

Reduction of the gametophyte: retained in the moistreproductive tissue of the sporphytereproductive tissue of the sporphyte

Origin of the seed:Origin of the seed:

Zygotes developed into embryos packaged with a food supplyZygotes developed into embryos packaged with a food supplywithin a protected seed coatwithin a protected seed coat

Seeds replaced spores as the main means of dispersalSeeds replaced spores as the main means of dispersal

Evolution of pollen: plants were no longer tied to water forEvolution of pollen: plants were no longer tied to water forfertilisationfertilisation

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Reduction of gametophytes in seed plantsReduction of gametophytes in seed plantsGametophyte (n)

Sporophyte (2n)

Sporophyte (2n)

Gametophyte(n)

Sporophyte (2n)

Gametophyte (n)

Sporophyte dependent onSporophyte dependent ongametophyte (e.g. bryophytes)gametophyte (e.g. bryophytes)

Large sporophyte and smallLarge sporophyte and smallindependent gametophyteindependent gametophyte

(e.g. ferns)(e.g. ferns)

Reduced gametophyteReduced gametophytedependent on sporophytedependent on sporophyte

(seed plants)(seed plants)

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In seed plants, the seed replaced the sporeIn seed plants, the seed replaced the spore

as the main means of dispersing offspringas the main means of dispersing offspringRelatively harsh terrestrial environment:Relatively harsh terrestrial environment:

Bryophytes and seedless vascular plants release sporesBryophytes and seedless vascular plants release spores

Seeds are more hardy because of their multicellular natureSeeds are more hardy because of their multicellular nature

Seed is a sporophyte embryo and a food supplySeed is a sporophyte embryo and a food supplysurrounded by a protective coatsurrounded by a protective coat

All seed plants are heterosporousAll seed plants are heterosporous

Development of seed associated with megasporangia:Development of seed associated with megasporangia:

Seed plant megasporangia are fleshy structure calledSeed plant megasporangia are fleshy structure called nucellinucelliAdditional tissues (Additional tissues (integumentsinteguments) surround megasporangium) surround megasporangium

Resulting structure is called anResulting structure is called an ovuleovule

Female gametophyte develops in wall of megaspore, isFemale gametophyte develops in wall of megaspore, isfertilised (embryo) and resulting ovule develops into a seedfertilised (embryo) and resulting ovule develops into a seed

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From ovule to seedFrom ovule to seed

Integuments (2n)

Nucellus(megasporangium)

(2n)

Megaspore (n)

Spore case (n)

Pollen tube (n)

Female

gametophyte (n)

Egg

nucleus(n)

Discharged spermnucleus (n)

Seed coat (2n)derived frominteguments

Embryo (2n)new sporophyte

MicropyleMicropyle

Food supplyFood supply(derived from(derived fromfemalefemalegametophytegametophytetissuetissue

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Pollen became the vehicle for spermPollen became the vehicle for sperm

cells in seed plantscells in seed plants

Microspores develop into pollen grains which matureMicrospores develop into pollen grains which matureto form the male gametophytes of seed plants:to form the male gametophytes of seed plants:

Pollen grains coated with a resistant polymer, sporopolleninPollen grains coated with a resistant polymer, sporopolleninCan be carried away by wind or animals (e.g. bees)Can be carried away by wind or animals (e.g. bees)following release from microsporangiafollowing release from microsporangia

A pollen grain near an ovule will extend a tube andA pollen grain near an ovule will extend a tube anddischarge sperm cells into the female gametophytedischarge sperm cells into the female gametophyte

within the ovule:within the ovule:In some gymnosperms, sperm are flagellated (ancestral)In some gymnosperms, sperm are flagellated (ancestral)

Other gymnosperms (including conifers) and angiospermsOther gymnosperms (including conifers) and angiospermsdo not have flagellated sperm cellsdo not have flagellated sperm cells

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GymnospermsGymnospermsDescended from DevonianDescended from Devonianprogymnosperms:progymnosperms:

SeedlessSeedless

Seeds evolved late DevonianSeeds evolved late Devonian

Climatic changes duringClimatic changes duringPermian led to lycopods,Permian led to lycopods,horsetails and ferns beinghorsetails and ferns beingreplaced by conifers andreplaced by conifers andcycadscycads

Lack enclosed chambersLack enclosed chambers(ovaries) in which seeds(ovaries) in which seedsdevelopdevelop

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Four divisions of extant gymnospermsFour divisions of extant gymnosperms

CycadsCycads GingkoGingko

GnetophytesGnetophytes ConifersConifers

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Conifers are the largest division ofConifers are the largest division of

gymnospermsgymnospermsMostly evergreens e.g.Mostly evergreens e.g.pines, firs, spruces, larches,pines, firs, spruces, larches,yews, cypresses etc.yews, cypresses etc.

Include the tallest, largestInclude the tallest, largestand oldest living organismsand oldest living organisms

NeedleNeedle--shaped leavesshaped leavesadapted to dry conditions:adapted to dry conditions:

Thick cuticle covers leafThick cuticle covers leafStomata in pits, reducingStomata in pits, reducingwater losswater loss

Megaphylls cf. other leavesMegaphylls cf. other leaves

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The life cycle of a pineThe life cycle of a pine

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AngiospermsAngiosperms

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Angiosperms (flowering plants)Angiosperms (flowering plants)Flowering plants are theFlowering plants are themost widespread andmost widespread anddiverse (250,000 species)diverse (250,000 species)

Only one divisionOnly one division(Anthophyta), with two(Anthophyta), with twoclasses:classes:

MonocotyledonsMonocotyledons

DicotyledonsDicotyledons

Less dependent on windLess dependent on windpollinationpollination -- use insectsuse insectsand animalsand animals

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Evolution of vascular tissue inEvolution of vascular tissue in

angiospermsangiospermsConifers have waterConifers have water--conducting cells calledconducting cells called

tracheidstracheidsAngiosperms haveAngiosperms have vesselvesselelementselements::

More specialised for transportMore specialised for transport

Less specialised for supportLess specialised for support

Xylem reinforced byXylem reinforced by fibresfibres::Specialised for supportSpecialised for support -- thickthicklignified walllignified wall

Evolved in conifers (conifersEvolved in conifers (coniferslack vessel elements)lack vessel elements)

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The flower is the defining reproductiveThe flower is the defining reproductive

adaptation of angiospermsadaptation of angiospermsSepalsSepals: sterile, enclose: sterile, enclosebudbud

PetalsPetals: sterile, attract: sterile, attract

pollinatorspollinatorsStamenStamen: produces pollen: produces pollen

CarpelCarpel: evolved from seed: evolved from seed--bearing leaf that becamebearing leaf that became

rolled into a tuberolled into a tubeStigmaStigma: sticky structure: sticky structurethat receives pollenthat receives pollen

OvaryOvary: protects ovules,: protects ovules,which develop into seedswhich develop into seeds

after fertilisationafter fertilisation

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Fruits help disperse the seeds ofFruits help disperse the seeds of

angiospermsangiospermsFruits are ripened ovariesFruits are ripened ovariesthat protect dormant seedthat protect dormant seedand aids in its dispersaland aids in its dispersal

Modifications of fruits thatModifications of fruits thataid dispersal include:aid dispersal include:

Seeds within fruits that areSeeds within fruits that areshaped like kites orshaped like kites orpropellors (e.g. maple)propellors (e.g. maple)

BurrBurr--like fruit that cling tolike fruit that cling toanimal furanimal fur

Edible fruitEdible fruit -- tough seedstough seedspass through digestive tractpass through digestive tract

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Life cycle of an angiospermLife cycle of an angiospermAntherAnther

OvuleOvule

OvaryOvary

MITOSISMITOSIS

MITOSISMITOSIS

PollenPollentubetube

StigmaStigmaPollenPollentubetube

PollenPollen

tubetube

StyleStyle

Food supply SeedFood supply Seed

GerminatingGerminatingseedseed

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Angiosperms and animals shapedAngiosperms and animals shaped

one anothers evolutionone anothers evolutionCoevolutionCoevolution: reciprocal: reciprocalevolutionary responsesevolutionary responsesamong two or moreamong two or more

interacting speciesinteracting speciesCoevolution led to diversityCoevolution led to diversityof flowers:of flowers:

FlowerFlower--specific pollinatorsspecific pollinators

Usually adapted for types ofUsually adapted for types ofpollinatorspollinators

Attraction of ripening fruits:Attraction of ripening fruits:Soft, fragrant and sugarySoft, fragrant and sugary

Attractive change of colourAttractive change of colour

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Plants transformed the atmospherePlants transformed the atmosphere

and the climateand the climate

Plants decreasedPlants decreased

atmospheric carbonatmospheric carbondioxide, resulting indioxide, resulting inglobal coolingglobal cooling

2525

2020

1515

1010

55

Colonisation of land by plantsColonisation of land by plants

Diversification of vascular plantsDiversification of vascular plants

Cooler environmentCooler environment

made terrestrial lifemade terrestrial lifemore habitable for othermore habitable for otherorganismsorganisms