Plants and the Plants and the Colonization of LandColonization of Land

AP Biology – Chapter 29AP Biology – Chapter 29

Evolution of PlantsEvolution of Plants

There were NO There were NO PLANTS until about PLANTS until about 500 million years 500 million years ago.ago. Until that time all life Until that time all life

had been essentially had been essentially aquatic…aquatic…

Terrestrial Earth – Terrestrial Earth – barrenbarren

It’s hard to Imagine…

Evolution of PlantsEvolution of Plants

The evolutionary The evolutionary history of plants is a history of plants is a story of story of ADAPTATION TO ADAPTATION TO TERRESTRIAL TERRESTRIAL CONDITIONS from CONDITIONS from water. water.

WATER TO WATER TO LAND!!!!!!!LAND!!!!!!!

Water…

To Land

Since their beginnings, Since their beginnings, Plants have been very Plants have been very successful…successful…

Plants have diversified into about Plants have diversified into about

290,000290,000 living species. living species.

The Ancestors of Land The Ancestors of Land Plants…Plants…

Were most likely some type of Were most likely some type of

Green AlgaeGreen Algae

Relatives to ancient Relatives to ancient plants – Green Alageplants – Green Alage

Spirogyra

Coleochaete

Chara

Volvox

“Kingdom” Protists“Kingdom” Protists

The closest algal The closest algal relatives of land plants relatives of land plants todaytoday……

Charophyceans Charophyceans ((CharophytesCharophytes))

It is likely that It is likely that plantsplants and and charophytescharophytes share a share a common ancestorcommon ancestor.. In other words, In other words,

charophytes did charophytes did notnot give give rise to plants, but rise to plants, but shareshare a a common ancestor with common ancestor with them.them.

This makes charophytes This makes charophytes the nearest living algal the nearest living algal relative to plants.relative to plants.

PlantPlant and and AlgaeAlgae shared shared characteristicscharacteristics

These characteristics are shared with These characteristics are shared with manymany algae. algae. MulticellularMulticellular EukaryoticEukaryotic Photosynthetic autotrophsPhotosynthetic autotrophs Cellulose cell wallsCellulose cell walls Chlorophylls Chlorophylls aa and and b b presentpresent Store surplus carbs in form of STARCHStore surplus carbs in form of STARCH

What then is it that links plants specifically to What then is it that links plants specifically to charophytes?charophytes?

Evidence for the green algae/plant

connection

What links the plants to What links the plants to the charophytes?the charophytes?

4 additional characteristics4 additional characteristics Shape of the complexes that make cellulose Shape of the complexes that make cellulose

(rose – shaped)(rose – shaped) Enzymes contained in the peroxisomesEnzymes contained in the peroxisomes Sperm structure is similarSperm structure is similar Certain details of cell division processesCertain details of cell division processes

Also…the Also…the DNADNA!!

Ancient Algae and the Ancient Algae and the Water to Land TransitionWater to Land Transition

Some ancient algae (like modern charophytes) Some ancient algae (like modern charophytes) inhabited shallow waters at edges of inhabited shallow waters at edges of ponds/lakesponds/lakes Survived occasional dryingSurvived occasional drying Had coatings on spores to protect from dryingHad coatings on spores to protect from drying

Natural selection would favor individual algae Natural selection would favor individual algae that can survive periods OUT of water.that can survive periods OUT of water.

Led to Led to ADAPTIVE RADIATIONADAPTIVE RADIATION of plant of plant ancestors onto LANDancestors onto LAND

WhyWhy move to Land? Land move to Land? Land has some big assets!has some big assets!

BrightBright sunlight sunlight unfiltered by waterunfiltered by water

Abundance of Abundance of CO2CO2 in atmospherein atmosphere

SoilSoil rich in rich in mineral mineral nutrientsnutrients

FewFew herbivores and herbivores and pathogens (at least pathogens (at least at first!)at first!)

Problems in taking Problems in taking advantage of Land’s advantage of Land’s assets…assets…

However…to take However…to take advantage of these assets advantage of these assets plants had to figure out plants had to figure out how to how to do without waterdo without water!! !! This means: This means: Prevent BodiesPrevent Bodies from from

drying out…drying out… Prevent GametesPrevent Gametes from from

drying outdrying out FertilizationFertilization without water without water Prevent EmbryosPrevent Embryos from from

drying outdrying out PLANTSPLANTS have solutions to have solutions to

these problems. these problems. ALGAE ALGAE do NOTdo NOT..

So, to distinguish So, to distinguish plantsplants from from AlgaeAlgae we use… we use…

… …the solutions to the problems of the solutions to the problems of land living that plants developed but land living that plants developed but that water-living algae did NOT that water-living algae did NOT develop.develop.

Adaptations to landAdaptations to land

Problem 1 – accessing Problem 1 – accessing resources on landresources on land

Location of Resources in TWO Very Different Location of Resources in TWO Very Different PlacesPlaces Above ground – light,Above ground – light, Below ground – water and mineralsBelow ground – water and minerals How to access these How to access these two different environmentstwo different environments

simultaneously is a simultaneously is a huge problemhuge problem Remember – algae do Remember – algae do NOTNOT have this problem have this problem

Continually bathed in uniform water environmentContinually bathed in uniform water environment No needNo need to protect tissues from to protect tissues from drying outdrying out All tissues have All tissues have equal accessequal access to to lightlight, , dissolved dissolved

nutrientsnutrients, etc., etc.

Problem 1 – accessing Problem 1 – accessing resources on land: SOLUTIONresources on land: SOLUTION

Apical MeristemsApical Meristems Small regions of Small regions of growthgrowth inin

tipstips of of rootsroots and and shootsshoots increase access to increase access to

resources in resources in different different directionsdirections: : soilsoil//lightlight..

Cells produced in these Cells produced in these meristems meristems differentiatedifferentiate into tissues suited for these into tissues suited for these two different environments.two different environments.

Example:Example: ProtectedProtected epidermis for epidermis for

leavesleaves exposed to exposed to airair Cuticle; stomataCuticle; stomata

Roots unprotectedRoots unprotected and and designed for designed for absorptionabsorption

Apical Meristems

Problem 1 – accessing Problem 1 – accessing resources on land: SOLUTIONresources on land: SOLUTION

Access to light and soil, Access to light and soil, generally require a generally require a plant to gain plant to gain lengthlength in in both directionsboth directions

But how to get But how to get substances transported substances transported across across long distanceslong distances within the plant’s body?within the plant’s body?

VASCULAR TISSUEVASCULAR TISSUE Tissue that can move Tissue that can move

LARGE QUANTITIESLARGE QUANTITIES of of material through a plantmaterial through a plant

Without itWithout it, , osmosisosmosis is is the only alternativethe only alternative SLOWSLOW; ; limits sizelimits size a a

land organism can land organism can attain.attain.

Apical MeristemsApical Meristems

Problem 2: Evaporation of Problem 2: Evaporation of water from tissues on Land water from tissues on Land --

Algae is constantly bathed in waterAlgae is constantly bathed in water Evaporation from tissues is NOT a concernEvaporation from tissues is NOT a concern Also, algae tissue freely accepts nutrients from Also, algae tissue freely accepts nutrients from

waterwater thus no need for access to nutrients in soilthus no need for access to nutrients in soil

No need for support – water supports the algae No need for support – water supports the algae and floats it near the surface to receive lightand floats it near the surface to receive light

Algae on land would rapidly lose water from Algae on land would rapidly lose water from tissues with no way to replenish; also, access tissues with no way to replenish; also, access to light would be limited without support to light would be limited without support structuresstructures

Problem 2: Evaporation of Problem 2: Evaporation of water from tissues on Land water from tissues on Land SolutionSolution

Protective tissuesProtective tissues Epidermis and Epidermis and

secretion of waxy secretion of waxy cuticlecuticle Prevents water lossPrevents water loss

StomataStomata Allows gas exchange Allows gas exchange

even though cuticle is even though cuticle is covering the plantcovering the plant

Cross-section through a leaf

Problem 3 – Drying out of Problem 3 – Drying out of sex cells and embryossex cells and embryos

AquaticAquatic organisms do organisms do NOTNOT have to “worry” have to “worry” aboutabout GametesGametes drying out during development drying out during development GametesGametes drying out when released drying out when released EmbryosEmbryos drying out during development drying out during development EmbryosEmbryos drying out when released drying out when released

LANDLAND organisms DO have to “worry” about organisms DO have to “worry” about these things. these things. WaterWater > > LandLand transition required transition required solvingsolving these these

problemsproblems

Problem 3 – Drying out of Problem 3 – Drying out of sex cells and embryos: sex cells and embryos: SolutionSolution Protection of Gametes Protection of Gametes duringduring ProductionProduction

Gamete production is Gamete production is protected inside structures protected inside structures called gametangiacalled gametangia

Prevents drying out of Prevents drying out of sperm/eggsperm/egg

DispersalDispersal In more advanced plants, In more advanced plants,

gametes are protected during gametes are protected during dispersal in structures dispersal in structures (pollen) that can travel (pollen) that can travel through through airair..

NOT dependent on NOT dependent on swimmingswimming sperm.sperm.

Problem 3 – Drying out of sex Problem 3 – Drying out of sex cells and embryos: Solutioncells and embryos: Solution

Protect delicate Embryos from drying out, Protect delicate Embryos from drying out, too!too! Egg fertilization occurs Egg fertilization occurs insideinside gametangiumgametangium Zygote develops into embryo Zygote develops into embryo insideinside

gametangiumgametangium Embryo is retained and nourished Embryo is retained and nourished insideinside

gametangiumgametangium Embryos Embryos disperseddispersed in structures that also in structures that also

prevent drying out:prevent drying out: Spores Spores SeedsSeeds

However, solutions to all However, solutions to all these problems were NOT these problems were NOT achieved at once…achieved at once…

These solutions were generally achieved These solutions were generally achieved in STEPSin STEPS

We can use these steps in evolution of We can use these steps in evolution of land adaptations as a way to determine a land adaptations as a way to determine a “plant family tree” or “plant family tree” or PHYLOGENYPHYLOGENY

Gre

en A

lgae

Algae/Plant Common Ancestor

Mo

ss

Fer

ns

Co

nif

ers

Flo

wer

ing

Pla

nts

Each of these circled branch points indicates some new adaptation that led to even more success on land…

A new period of adaptive radiation followed

Plant ClassificationPlant Classification

DomainDomain Eukarya Eukarya KingdomKingdom Plantae (currently Plantae (currently excludesexcludes the algae, the algae,

but there is DISAGREEMENT about this!)but there is DISAGREEMENT about this!) Some think green algae should be included within Some think green algae should be included within

the plant kingdom!the plant kingdom! 10 major 10 major phyla (actually called phyla (actually called divisions divisions in in

plants)plants) 3 of these are nonvascular (bryophytes)3 of these are nonvascular (bryophytes) 7 are vascular and include the vast majority of 7 are vascular and include the vast majority of

plants (93%)plants (93%)

Generalizations Generalizations Regarding Plant GroupsRegarding Plant Groups

Plants can be Plants can be loosely and informallyloosely and informally placed placed into into two major groupstwo major groups NonvascularNonvascular (the bryophytes/mosses) (the bryophytes/mosses)

More ancient / primitiveMore ancient / primitive Rely on cell to cell diffusion for transportRely on cell to cell diffusion for transport Small (like Small (like mossesmosses)) No true roots, stems or shootsNo true roots, stems or shoots

Vascular Vascular (everything else)(everything else) More recent / advancedMore recent / advanced Use sophisticated “plumbing” (vascular tissue) to move Use sophisticated “plumbing” (vascular tissue) to move

food/waterfood/water Can become quite large Can become quite large True roots, stems and shoots (by definition, True roots, stems and shoots (by definition,

roots/stems/shoots are all structures that contain vascular roots/stems/shoots are all structures that contain vascular tissue)tissue)

Generalizations Generalizations Regarding Plant GroupsRegarding Plant Groups

Vascular Plants can be informally grouped intoVascular Plants can be informally grouped into Seedless Vascular PlantsSeedless Vascular Plants

First to arise from nonvascular ancestorsFirst to arise from nonvascular ancestors Possess (obviously) Possess (obviously) vascular tissuevascular tissue, but that’s about all , but that’s about all

that sets them apart from nonvascular plantsthat sets them apart from nonvascular plants

GymnospermsGymnosperms Naked seed plants / Conifers Naked seed plants / Conifers – – 11stst seeds, but seeds unprotected seeds, but seeds unprotected

AngiospermsAngiosperms Flowering plants – seed development protected inside Flowering plants – seed development protected inside

ovariesovaries

FIRST Period of Plant FIRST Period of Plant Evolution: Origin of Plants Evolution: Origin of Plants from Aquatic Ancestorsfrom Aquatic Ancestors

Living groups from this Living groups from this first period of plant first period of plant evolution:evolution: Division Bryophyta – the Division Bryophyta – the

mossesmosses 10,000 species10,000 species

Division Hepatophyta – Division Hepatophyta – LiverwortsLiverworts 6,500 species6,500 species

Division Anthocerophyta – Division Anthocerophyta – HornwortsHornworts 100 species100 species

Typical Bryophyte (moss) Typical Bryophyte (moss) life cyclelife cycle

Plant Life Cycles called Plant Life Cycles called ALTERNATION OF ALTERNATION OF GENERATIONSGENERATIONS Life cycle alternates between two different Life cycle alternates between two different

multicellular bodies, with each form producing the multicellular bodies, with each form producing the other. other. One body form is One body form is haploidhaploid The other body form is The other body form is diploiddiploid

Do NOT confuse with haploid/diploid stages of Do NOT confuse with haploid/diploid stages of animals, etc. The haploid form in plants is a animals, etc. The haploid form in plants is a multicellular body, not just a gamete.multicellular body, not just a gamete.

Alternation of Alternation of Generations – Why do we Generations – Why do we care?care?

ALL plants undergo this pattern called ALL plants undergo this pattern called alternation of generationsalternation of generations

Why do we care?Why do we care? Differences in plant life cycles give us Differences in plant life cycles give us

important clues about evolutionary important clues about evolutionary advances of each major plant groupadvances of each major plant group

Male Gametophyte

Haploid generation

Female Gametophyte

Haploid generation

Sperm must SWIM to egg

Egg/ ovum

Fertilization In female gametophyte creates DIPLOID ZYGOTE

MITOSIS

DIPLOID Sporophyte grows out of haploid female gametophyte

MEIOSIS occurs in spore capsule

Spore capsule opens and releases HAPLOID spores

Haploid spores land in suitable environment

Haploid spores germinate and grow into haploid gametophytes

FIRST Period of Plant FIRST Period of Plant Evolution: Origin of Plants Evolution: Origin of Plants from from AquaticAquatic Ancestors Ancestors

Adaptations to Adaptations to Terrestrial LifeTerrestrial Life CuticleCuticle Jacketed gametangia protect gametes and embryosJacketed gametangia protect gametes and embryos

BUT, BUT, still tied to waterstill tied to water because… because… Still have Still have swimming spermswimming sperm

MUSTMUST have have waterwater for for fertilizationfertilization to occur to occur LACKLACK vascular tissue vascular tissue

Means no real means of efficiently conducting food and waterMeans no real means of efficiently conducting food and water Size is limited – very smallSize is limited – very small

NoNo seeds – seeds – sporesspores used for embryo dispersal used for embryo dispersal GametophyteGametophyte is dominant generation is dominant generation

Diploid generation is present Diploid generation is present ONLYONLY as as ZYGOTEZYGOTE!!!!

MossMoss

22ndnd Period of Plant Evolution Period of Plant Evolution – Diversification of Vascular – Diversification of Vascular PlantsPlants

Group known as SEEDLESS VASCULAR Group known as SEEDLESS VASCULAR PLANTS PLANTS

AdaptationsAdaptations From Previous Group: From Previous Group:

Cuticle and gametangia of previous plantsCuticle and gametangia of previous plants New to SEEDLESS VASCULAR PLANTS:New to SEEDLESS VASCULAR PLANTS:

Sporophyte is Sporophyte is dominantdominant Generation Generation VASCULAR TISSUE added!! VASCULAR TISSUE added!!

Can efficiently move food and water throughout bodyCan efficiently move food and water throughout body Can attain larger sizeCan attain larger size

Still share these primitive characteristics:Still share these primitive characteristics: Still depend on swimming spermStill depend on swimming sperm Still no seeds – use spores for embryo dispersalStill no seeds – use spores for embryo dispersal

22ndnd Period of Plant Evolution Period of Plant Evolution – Diversification of Vascular – Diversification of Vascular Plants Plants

Living groups from this Living groups from this period of plant evolutionperiod of plant evolution Division Psilophyta – Division Psilophyta –

whisk fernswhisk ferns 10-13 species10-13 species

Division Lycophyta – club Division Lycophyta – club mossesmosses 1,000 species1,000 species

Division Sphenophyta – Division Sphenophyta – horsetailshorsetails 15 species15 species

Division Pterophyta – Division Pterophyta – fernsferns 12,000 species12,000 species

FernsFerns

FernsFerns

3rd Period of Plant 3rd Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants

Group known as GYMNOSPERMS or “Naked Group known as GYMNOSPERMS or “Naked Seed Plants”Seed Plants”

AdaptationsAdaptations From previous groups: From previous groups:

Cuticle, gametangia, dominant sporophyte and vascular Cuticle, gametangia, dominant sporophyte and vascular tissue tissue

NEW to GYMNOSPERMS:NEW to GYMNOSPERMS: SEEDS – to further protect embryos from dessication (and SEEDS – to further protect embryos from dessication (and

other hazards) and aid in dispersal.other hazards) and aid in dispersal. Pollen – air transported sperm – no longer need water to Pollen – air transported sperm – no longer need water to

transport swimming spermtransport swimming sperm Still primitive in that…Still primitive in that…

NO Flowers NO Flowers NO FruitNO Fruit

3rd Period of Plant 3rd Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants

““naked seeds” refers to seeds naked seeds” refers to seeds NOT being enclosed in any NOT being enclosed in any specialized chambers (fruit) specialized chambers (fruit) Seeds are exposed to Seeds are exposed to environment on highly modified environment on highly modified leaf surfaces (ex. Cones)leaf surfaces (ex. Cones)

A seed consists of A seed consists of EmbryoEmbryo Stored food (starch)Stored food (starch) Protective covering (seed coat)Protective covering (seed coat)

Pollen – airborne sperm (sort Pollen – airborne sperm (sort of)of) Highly reduced male gametophyteHighly reduced male gametophyte No longer dependent on water for No longer dependent on water for

fertilizationfertilization

3rd Period of Plant 3rd Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants

Living groups from this Living groups from this period of plant evolutionperiod of plant evolution Division Coniferophyta Division Coniferophyta

(conifers)(conifers) Largest groupLargest group Needle-like leavesNeedle-like leaves 550 species550 species

Division CycadophytaDivision Cycadophyta 100 species100 species

Division GingkophytaDivision Gingkophyta 1 species1 species

Division GnetophytaDivision Gnetophyta 70 species70 species

4th Period of Plant 4th Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants Emergence of Flowering Plants - Emergence of Flowering Plants -

AngiospermsAngiosperms AdaptationsAdaptations

From previous groups: From previous groups: Cuticle, gametangia, dominant Cuticle, gametangia, dominant

sporophyte, vascular tissue, seeds sporophyte, vascular tissue, seeds and pollen of previous groupsand pollen of previous groups

NEW to ANGIOSPERMSNEW to ANGIOSPERMS:: FLOWERS FLOWERS FRUITSFRUITS Double fertilizationDouble fertilization

Fert of eggFert of egg to make to make embryoembryo Fert of 2 polar nuclei to make Fert of 2 polar nuclei to make

endospermendosperm TRIPLOID tissueTRIPLOID tissue

((endospermendosperm

– stored food– stored food 2 polar nuclei + 1 sperm nuc. 2 polar nuclei + 1 sperm nuc.

= 3n= 3n

4th Period of Plant 4th Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants Advantages of flowers and Advantages of flowers and

fruitsfruits Flowers draw pollinators Flowers draw pollinators

which are very efficient at which are very efficient at transferring pollen from transferring pollen from flower to flowerflower to flower

Fruits aid in seed dispersal Fruits aid in seed dispersal either by water, wind or either by water, wind or animalsanimals

Other plants depend on Other plants depend on water or wind for gamete and water or wind for gamete and seed dispersal which is not seed dispersal which is not near as precise.near as precise. Angiosperms may use wind Angiosperms may use wind

also, but fruits allow for also, but fruits allow for elaborate structures to carry elaborate structures to carry seeds FURTHER by wind.seeds FURTHER by wind.

4th Period of Plant 4th Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants

Advantage of triploid tissue in seedsAdvantage of triploid tissue in seeds Has greater ability to pull food resources Has greater ability to pull food resources

from “mother” than embryo does. Thus from “mother” than embryo does. Thus nutrients can be stored in the seed for later nutrients can be stored in the seed for later use.use.

Also, fact that endosperm must be fertilized Also, fact that endosperm must be fertilized ensures that endosperm will not be made if ensures that endosperm will not be made if fertilization has not occurred. Avoids waste.fertilization has not occurred. Avoids waste.

4th Period of Plant 4th Period of Plant Evolution – Diversification of Evolution – Diversification of Vascular PlantsVascular Plants

Living groups from this period of Living groups from this period of evolutionevolution ONE Divison – AnthophytaONE Divison – Anthophyta

235,000 species235,000 species Two Important ClassesTwo Important Classes

MonocotMonocot DicotDicot

Double Fertilization!!

Alternation of Alternation of GenerationsGenerations

Haploid gametophytes and diploid sporophytes Haploid gametophytes and diploid sporophytes take turns producing one another.take turns producing one another.

Gametophyte Gametophyte Plant that makes GAMETES Plant that makes GAMETES HAPLOID PLANTHAPLOID PLANT MAKES HAPLOID CELLSMAKES HAPLOID CELLS

SporophyteSporophyte Diploid plantDiploid plant Cells inside undergo MEIOSISCells inside undergo MEIOSIS Plant that makes SPORES – HAPLOID CELLSPlant that makes SPORES – HAPLOID CELLS Why make spores?Why make spores?

Efficient at dispersal of “babies”Efficient at dispersal of “babies” Wind dispersedWind dispersed

Evolutionary Trends in Evolutionary Trends in Alternation of Alternation of GenerationsGenerations

InitiallyInitially in the evolution of land plants, in the evolution of land plants, gametophytes were the dominant gametophytes were the dominant generation.generation. Larger than sporophyteLarger than sporophyte Sporophyte dependent on gametophyte for Sporophyte dependent on gametophyte for

everything – sporophyte NOT photosynthetic everything – sporophyte NOT photosynthetic

Evolutionary Trends in Evolutionary Trends in Alternation of Alternation of GenerationsGenerations

Trend in plant evolution was for Trend in plant evolution was for SPOROPHYTE to become dominant and SPOROPHYTE to become dominant and GAMETOPHYTE to become dependentGAMETOPHYTE to become dependent

Why? Why? Diploid tissue is less subject to the negative Diploid tissue is less subject to the negative

effects of mutation than haploid tissueeffects of mutation than haploid tissue In diploid tissue there are two copies of In diploid tissue there are two copies of

genes. If one gets damaged, the other may genes. If one gets damaged, the other may be able to function normally.be able to function normally.

Why Study Plant Life Why Study Plant Life Cycles?Cycles?

Features of the life cycles are key Features of the life cycles are key evolutionary adaptations to terrestrial evolutionary adaptations to terrestrial environmentsenvironments Example: replacement of flagellated sperm Example: replacement of flagellated sperm

by pollenby pollen

Egg/ ovum

________

____________ occurs in spore capsule