The Plant Kingdom:The Plant Kingdom:Seedless PlantsSeedless Plants

Chapter 27Chapter 27

Learning Objective 1Learning Objective 1

• What are some environmental challenges What are some environmental challenges of living on land?of living on land?

• How do some plant adaptations meet How do some plant adaptations meet these challenges?these challenges?

Colonization of Land by PlantsColonization of Land by Plants

• Required anatomical, physiological, and Required anatomical, physiological, and reproductive adaptationsreproductive adaptations

• Waxy Waxy cuticlecuticle • protects against water lossprotects against water loss

• StomataStomata• for gas exchange needed for photosynthesisfor gas exchange needed for photosynthesis

Alternation of GenerationsAlternation of Generations 11

• 2 parts of plant life cycle2 parts of plant life cycle• haploid haploid gametophyte generationgametophyte generation • diploid diploid sporophyte generationsporophyte generation

• Gametophyte plantGametophyte plant• produces gametes by mitosisproduces gametes by mitosis• gametes fuse (fertilization) to form gametes fuse (fertilization) to form zygotezygote

(first stage of sporophyte generation)(first stage of sporophyte generation)

Basic Plant Life CycleBasic Plant Life Cycle

Fig. 27-2, p. 582

Gametophyte

Spore Sperm Egg

HAPLOID (n) GAMETOPHYTE GENERATION

Meiosis Fertilization

DIPLOID (2n) SPOROPHYTE GENERATION

Zygote

Embryo

Sporophyte

Fig. 27-2, p. 582

Stepped Art

Spore

DIPLOID (2n) SPOROPHYTE GENERATION

Sporophyte

Zygote

Embryo

Sperm Egg

FertilizationMeiosis

HAPLOID (n) GAMETOPHYTE GENERATION

Gametophyte

Alternation of GenerationsAlternation of Generations 22

• Zygote develops into multicellular Zygote develops into multicellular embryoembryo• protected and nourished by gametophyteprotected and nourished by gametophyte

• Mature Mature sporophyte plantsporophyte plant• develops from the embryodevelops from the embryo• produces sporogenous cells (spore mother produces sporogenous cells (spore mother

cells)cells)

Alternation of GenerationsAlternation of Generations 33

• Sporogenous cells undergo meiosis to Sporogenous cells undergo meiosis to form form sporesspores • first stage in gametophyte generationfirst stage in gametophyte generation

KEY CONCEPTSKEY CONCEPTS

• Plants undergo an alternation of Plants undergo an alternation of generations between multicellular generations between multicellular gametophyte and sporophyte generationsgametophyte and sporophyte generations

Gametangia 1Gametangia 1

• Most plants have multicellular Most plants have multicellular gametangiagametangia• with protective jacket of sterile cells with protective jacket of sterile cells

surrounding gametessurrounding gametes

Gametangia 2Gametangia 2

• AntheridiaAntheridia• gametangia that produce sperm cellsgametangia that produce sperm cells

• ArchegoniaArchegonia• gametangia that produce eggsgametangia that produce eggs

GametangiaGametangia

Fig. 27-3a, p. 583

Developing sperm cells

Antheridium

Sterile cells

Fig. 27-3b, p. 583

Egg

ArchegoniumSterile cells

Vascular Transport SystemVascular Transport System

• In ferns and other vascular plantsIn ferns and other vascular plants• xylemxylem conducts water and dissolved minerals conducts water and dissolved minerals• phloemphloem conducts dissolved sugar conducts dissolved sugar

KEY CONCEPTSKEY CONCEPTS

• Adaptations to life on land that have Adaptations to life on land that have evolved in plants include a waxy cuticle to evolved in plants include a waxy cuticle to prevent water loss; multicellular prevent water loss; multicellular gametangia; stomata; and for most plants, gametangia; stomata; and for most plants, vascular tissues containing ligninvascular tissues containing lignin

Learning Objective 2Learning Objective 2

• From which green algal group are plants From which green algal group are plants hypothesized to have descended?hypothesized to have descended?

• Describe supporting evidenceDescribe supporting evidence

CharophytesCharophytes

• Plants probably arose from Plants probably arose from charophytescharophytes• a group of green algae a group of green algae

• Based on molecular comparisons of DNA Based on molecular comparisons of DNA and RNA sequencesand RNA sequences• close match between charophytes and plantsclose match between charophytes and plants

Plant EvolutionPlant Evolution

Fig. 27-4, p. 584

VASCULAR SEEDLESS PLANTS

VASCULAR SEED PLANTS

NONVASCULAR BRYOPHYTES

Ho

rnw

ort

s

Liv

erw

ort

s

Mo

sses

Clu

b m

oss

es

Fer

ns

Gym

no

sper

ms

An

gio

sper

ms

Evolution of seeds

Evolution of dominant sporophyte, vascular tissue

Evolution of cuticle, multicellular gametangia, multicellular embryos

Green algal

ancestor

KEY CONCEPTSKEY CONCEPTS

• Biologists infer that plants evolved from Biologists infer that plants evolved from aquatic green algal ancestors known as a aquatic green algal ancestors known as a charophytescharophytes

Insert “Evolutionary tree Insert “Evolutionary tree for plants”for plants”

plant_tree_v2.swfplant_tree_v2.swf

Explore plant evolution by Explore plant evolution by clicking on the figure in clicking on the figure in

ThomsonNOW. ThomsonNOW.

Learning Objective 3Learning Objective 3

• What features distinguish bryophytes from What features distinguish bryophytes from other plants?other plants?

BryophytesBryophytes

• Nonvascular (lack xylem and phloem)Nonvascular (lack xylem and phloem)• unlike other land plantsunlike other land plants

• Dominant gametophyte generationDominant gametophyte generation• unlike other plantsunlike other plants

• Sporophytes remain permanently attachedSporophytes remain permanently attached• nutritionally dependent on gametophytesnutritionally dependent on gametophytes

Learning Objective 4Learning Objective 4

• What are the three phyla of bryophytes?What are the three phyla of bryophytes?

Mosses (Phylum Bryophyta)Mosses (Phylum Bryophyta)

• Gametophytes are green plants that grow Gametophytes are green plants that grow from a filamentous from a filamentous protonema protonema

Liverworts (Phylum Hepatophyta)Liverworts (Phylum Hepatophyta)

• Many gametophytes are flattened, lobelike Many gametophytes are flattened, lobelike thallithalli (others are leafy) (others are leafy)

HornwortsHornworts (Phylum Anthocerophyta)(Phylum Anthocerophyta)

• Have thalloid gametophytesHave thalloid gametophytes

Fig. 27-5, p. 585

Fig. 27-5 (1), p. 585

No

nv

asc

ula

r b

ryo

ph

yte

s

Va

scu

lar

see

dle

ss

pla

nts

Va

scu

lar

see

d p

lan

ts

Green algal

ancestor

KEY CONCEPTSKEY CONCEPTS

• Mosses and other bryophytes lack Mosses and other bryophytes lack vascular tissues and do not form true vascular tissues and do not form true roots, stems, or leavesroots, stems, or leaves

Learning Objective 5Learning Objective 5

• Describe the life cycle of mossesDescribe the life cycle of mosses

• Compare their gametophyte and Compare their gametophyte and sporophyte generationssporophyte generations

Mosses 1Mosses 1

• Green moss gametophyteGreen moss gametophyte• bears archegonia / antheridia at top of plant bears archegonia / antheridia at top of plant

• FertilizationFertilization• sperm cell fuses with egg cell in archegonium sperm cell fuses with egg cell in archegonium

(zygote)(zygote)

Mosses 2Mosses 2

• ZygoteZygote• grows into embryogrows into embryo• develops into moss sporophyte attached to develops into moss sporophyte attached to

gametophytegametophyte

Mosses 3Mosses 3

• MeiosisMeiosis• occurs within capsule of sporophyteoccurs within capsule of sporophyte• produces spores produces spores

• When spore germinatesWhen spore germinates• grows into a grows into a protonemaprotonema• forms buds that develop into gametophytesforms buds that develop into gametophytes

Moss Life CycleMoss Life Cycle

Fig. 27-6, p. 586

Gametophyte plants Antheridia at the tip of the gametophyte shootBuds on

protonema 1 Antheridia with sperm cellsSpore

germinates

Spores released 6

ProtonemaSperm cell

2HAPLOID (n) GAMETOPHYTE GENERATION

Archegonium with egg

Meiosis Fertilization

DIPLOID (2n) SPOROPHYTE GENERATION

5

Calyptra Zygote

Sporogenous cells that undergo meiosis

Capsule

Sporophyte4 3

Embryo

Gametophyte plant

Moss Moss SporophytesSporophytes

Fig. 27-7, p. 587

Capsule

Seta

Foot

Liverwort Life CycleLiverwort Life Cycle

Fig. 27-8, p. 588

AntheridiophoreArchegoniophore

Male thallusGermination of spores

and development of young gametophyte

1

Female thallus 5

Gemmae cup

Antheridia with sperm cells

Spores released Male and female

gametophyte plants

Sperm cell

HAPLOID (n) GAMETOPHYTE GENERATION

Archegonia with eggs 2

MeiosisDIPLOID (2n)

SPOROPHYTE GENERATION

Fertilization

4

Foot

SetaZygote

Tissue derived from archegonium Capsule Embryo

Sporogenous cells that undergo meiosis 3

Sporophyte

Insert “Moss life cycle”Insert “Moss life cycle”

moss_life_cycle_v2.swfmoss_life_cycle_v2.swf

Insert “Marchantia, a Insert “Marchantia, a liverwort”liverwort”

liverwort.swfliverwort.swf

Watch the life cycles of the Watch the life cycles of the mosses and liverworts by mosses and liverworts by clicking on the figures in clicking on the figures in

ThomsonNOW. ThomsonNOW.

Learning Objective 6Learning Objective 6

• What features distinguish seedless What features distinguish seedless vascular plants from algae and vascular plants from algae and bryophytes?bryophytes?

Seedless Vascular PlantsSeedless Vascular Plants

• Have adaptations that algae and Have adaptations that algae and bryophytes lackbryophytes lack• vascular tissuesvascular tissues• dominant sporophyte generation dominant sporophyte generation

• Reproduction depends on waterReproduction depends on water• as transport medium for motile sperm cells as transport medium for motile sperm cells

(as in bryophytes)(as in bryophytes)

Learning Objective 7Learning Objective 7

• What are the two phyla of seedless What are the two phyla of seedless vascular plants?vascular plants?

Club MossesClub Mosses (Phylum Lycopodiophyta) (Phylum Lycopodiophyta)

• Sporophytes consist of roots, rhizomes, Sporophytes consist of roots, rhizomes, erect branches, and erect branches, and microphylls microphylls (leaves(leaves))

Fig. 27-10a, p. 590

Stem

Microphyll

Vascular tissue Enation

Vein

Smooth stem

Enation Vascular supply to enation

Microphyll (one vein)

Club Club MossesMosses

Fig. 27-11 (1), p. 591

No

nva

scu

lar

bry

op

hyt

es

Vas

cula

r se

edle

ss p

lan

ts

Vas

cula

r se

ed p

lan

ts

Green algal

ancestor

Fig. 27-11 (a-b), p. 591

Strobilus

Leaves (microphylls)

Ferns (Phylum Pteridophyta) Ferns (Phylum Pteridophyta)

• Largest and most diverse group of Largest and most diverse group of seedless vascular plants seedless vascular plants

• Fern sporophyte consists of a rhizome that Fern sporophyte consists of a rhizome that bears fronds and true roots bears fronds and true roots

• Includes Includes whisk fernswhisk ferns and and horsetailshorsetails

FernsFerns

Fig. 27-12 (1), p. 592

No

nva

scu

lar

bry

op

hyt

es

Vas

cula

r se

edle

ss p

lan

ts

Vas

cula

r se

ed p

lan

ts

Green algal

ancestor

Fig. 27-12a, p. 592

Fig. 27-12b, p. 592

Fig. 27-12c, p. 592

Fern Life CycleFern Life Cycle

Fig. 27-13, p. 593

Underside of enlarged mature gametophyte (prothallus)

Germination of spores and development of young gametophyte Egg

4 5 ArchegoniumSpores released Rhizoids

3Antheridium

Sporangium HAPLOID (n) GAMETOPHYTE GENERATION

Sperm cell

MeiosisCells within sporangia undergo meiosis

Fertilization

Sorus (cluster of sporangia)

DIPLOID (2n) SPOROPHYTE GENERATION

2 Zygote

6Frond 1

Leaf of young sporophyte

Leaf cross section Development of the sporophyte

Fiddlehead Haploid prothallus

Roots RhizomeRoot of young sporophyte

Underside of a frond

Fern (mature sporophyte)

Whisk FernsWhisk Ferns

• SSporophytes have porophytes have dichotomously dichotomously branchingbranching rhizomes and erect stems rhizomes and erect stems• lack true roots and leaves lack true roots and leaves

Fig. 27-14a, p. 594

No

nva

scu

lar

bry

op

hyt

es

Vas

cula

r se

edle

ss p

lan

ts

Vas

cula

r se

ed p

lan

ts

Green algal

ancestor

Fig. 27-14b, p. 594

Sporangia

Aerial stem with scalelike outgrowths (no leaves)

HorsetailsHorsetails

• Sporophytes haveSporophytes have• hollow, jointed roots, rhizomes, aerial stemshollow, jointed roots, rhizomes, aerial stems• leaves reduced to leaves reduced to megaphyllsmegaphylls

Fig. 27-10b, p. 590

Thicker main stem

Dichotomous end branches

Equal branches

Vascular tissue Thinner

side branch

Dichotomously branching

stems

Overtopping (unequal

branching)

Planation (branching in same plane)

Webbing of side branch

system

Megaphyll (many veins)

HorsetailsHorsetails

Fig. 27-15a, p. 594

No

nva

scu

lar

bry

op

hyt

es

Vas

cula

r se

ed

less

pla

nts

Vas

cula

r se

ed

pla

nts

Green algal

ancestor

Fig. 27-15b, p. 594

Strobilus

Vegetative shoots

Reproductive shoots

Insert “Seedless vascular Insert “Seedless vascular plants”plants”

seedless_vascular.swfseedless_vascular.swf

KEY CONCEPTSKEY CONCEPTS

• In club mosses and ferns, lignin-hardened In club mosses and ferns, lignin-hardened vascular tissues that transport water and vascular tissues that transport water and dissolved substances throughout the plant dissolved substances throughout the plant body have evolvedbody have evolved

Learning Objective 8Learning Objective 8

• Describe the life cycle of fernsDescribe the life cycle of ferns

• Compare sporophyte and gametophyte Compare sporophyte and gametophyte generationsgenerations

Fern SporophytesFern Sporophytes

• Roots, rhizomes, leaves are Roots, rhizomes, leaves are megaphyllsmegaphylls

• Leaves (Leaves (frondsfronds) bear sporangia in clusters ) bear sporangia in clusters ((sorisori))

• Meiosis in sporangia produces haploid Meiosis in sporangia produces haploid spores spores

Fern GametophyteFern Gametophyte

• Fern GametophyteFern Gametophyte (prothallus) (prothallus)• develops from haploid sporedevelops from haploid spore• bears both archegonia and antheridiabears both archegonia and antheridia

Insert “Fern life cycle”Insert “Fern life cycle”

fern_life_cycle_v2.swffern_life_cycle_v2.swf

Watch the life cycle of the ferns Watch the life cycle of the ferns by clicking on the figure in by clicking on the figure in

ThomsonNOW. ThomsonNOW.

Learning Objective 9Learning Objective 9

• What is the difference between the What is the difference between the generalized life cycles of generalized life cycles of homosporoushomosporous and and heterosporousheterosporous plants? plants?

HomosporyHomospory

• Production of one kind of sporeProduction of one kind of spore• in bryophytes, most club mosses, most ferns in bryophytes, most club mosses, most ferns

including whisk ferns and horsetailsincluding whisk ferns and horsetails

• Spores give rise to gametophyte plantsSpores give rise to gametophyte plants• produce both egg cells and sperm cellsproduce both egg cells and sperm cells

HeterosporyHeterospory 11

• Production of two kinds of spores Production of two kinds of spores ((microsporesmicrospores and and megasporesmegaspores))• in some club mosses and fernsin some club mosses and ferns• in all seed plantsin all seed plants

Heterosporous Life CycleHeterosporous Life Cycle

Fig. 27-16, p. 595

Gametophyte

Megaspore Gametophyte Archegonium

Microspore Antheridium

HAPLOID (n) GAMETOPHYTE GENERATION

Sperm Egg

Meiosis FertilizationDIPLOID (2n)

SPOROPHYTE GENERATION

Microsporocyte Zygote

Megasporocyte Microsporangium

EmbryoMegasporangium Sporophyte

HeterosporyHeterospory 22

• MicrosporesMicrospores • give rise to male gametophytes that produce give rise to male gametophytes that produce

sperm cellssperm cells

• MegasporesMegaspores• give rise to female gametophytes that give rise to female gametophytes that

produce eggsproduce eggs

SelaginellaSelaginella Life Cycle Life Cycle

Fig. 27-17, p. 596

Male gametophyte develops inside microspore wall

Single antheridium in male gametophyte produces many sperm cells3

Microspores5 Sperm cell

Ruptured megaspore wall

Archegonium containing egg

4Female gametophyte develops and protrudes from megaspore wall

Longitudinal section through archegonium

MegasporesHAPLOID (n)

GAMETOPHYTE GENERATION

Egg

Meiosis FertilizationMicrosporangium with microsporocytes

DIPLOID (2n) SPOROPHYTE GENERATION

Megasporangium with megasporocyte Strobilus

Female gametophyte

First leaves1 Leaf

(microphyll) Stem

Stem6

ZygoteLongitudinal section through strobilus

Root

Root Young sporophyte (attached to female gametophyte)Mature

sporophyte

Evolution of HeterosporyEvolution of Heterospory

• Essential step in evolution of seedsEssential step in evolution of seeds

• RhyniaRhynia

• AglaophytonAglaophyton