PlantsPlants

Chapter 23Chapter 23

Setting the Stage for Setting the Stage for PlantsPlants

Earth’s atmosphere was originally oxygen Earth’s atmosphere was originally oxygen freefree

Ultraviolet radiation bombarded the Ultraviolet radiation bombarded the surfacesurface

Photosynthetic cells produced oxygen and Photosynthetic cells produced oxygen and allowed formation of a protective ozone allowed formation of a protective ozone layerlayer

Invading the LandInvading the Land

Cyanobacteria were probably the first to Cyanobacteria were probably the first to

spread into and up freshwater streamsspread into and up freshwater streams

Later, green algae and fungi made the Later, green algae and fungi made the

journey togetherjourney together

Every plant is descended from species of Every plant is descended from species of

green algae green algae

The Plant KingdomThe Plant Kingdom

Nearly all are multicelled Nearly all are multicelled

Vast majority are photoautotrophs Vast majority are photoautotrophs

Energy from sunEnergy from sun

Carbon dioxide from airCarbon dioxide from air

Minerals dissolved in waterMinerals dissolved in water

Evolutionary Tree for Evolutionary Tree for PlantsPlants

greenalgae

zygophytes, related groups

charophytes bryophytes lycophytes horsetails cycads conifersflowering

plants

seed plants

euphyllophytes

vascular plants

embryophytes (land plants)

(closely related groups)

ferns ginkgos gnetophytes

Nested monophyletic groups

Figure 23.3Page 387

Nonvascular PlantsNonvascular Plants

BryophytesBryophytes

Fewer than 19,000 speciesFewer than 19,000 species

Three groupsThree groups

LiverwortsLiverworts

Hornworts Hornworts

Mosses Mosses

Vascular PlantsVascular Plants

Majority of plantsMajority of plants

Have internal tissues that carry water and Have internal tissues that carry water and

solutessolutes

Two groupsTwo groups

Seedless vascular plantsSeedless vascular plants

Seed-bearing vascular plantsSeed-bearing vascular plants

Seedless Vascular PlantsSeedless Vascular Plants

Arose during the DevonianArose during the Devonian Produce spores but no seedsProduce spores but no seeds Four main groupsFour main groups

Whisk fernsWhisk ferns

LycophytesLycophytes

HorsetailsHorsetails

FernsFerns

Seed-Bearing Vascular Seed-Bearing Vascular PlantsPlants

Gymnosperms arose firstGymnosperms arose first CycadsCycads GinkgosGinkgos GnetophytesGnetophytes ConifersConifers

Angiosperms arose laterAngiosperms arose later MonocotsMonocots DicotsDicots

Evolutionary TrendEvolutionary Trend

zygote

SPOROPHYTE (2n)

GAMETOPHYTE (n)

GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

Figure 23.2Page 386

Adaptations to LandAdaptations to Land

Root systemsRoot systems

Shoot systemsShoot systems

Vascular tissues Vascular tissues

Waxy cuticle Waxy cuticle

Traits of Traits of Seed-Bearing PlantsSeed-Bearing Plants

Pollen grainsPollen grains Arise from megasporesArise from megaspores Develop into male gametophytesDevelop into male gametophytes Can be transported without waterCan be transported without water

SeedsSeeds Embryo sporophyte inside nutritive tissues Embryo sporophyte inside nutritive tissues

and a protective coatand a protective coat Can withstand hostile conditionsCan withstand hostile conditions

BryophytesBryophytes

Small, nonvascular, nonwooody Small, nonvascular, nonwooody Gametophyte dominates life cycle; Gametophyte dominates life cycle;

has leaflike, stemlike, and rootlike has leaflike, stemlike, and rootlike partsparts

Usually live in wet habitatsUsually live in wet habitats Flagellated sperm require water to Flagellated sperm require water to

reach eggsreach eggs

Types of BryophytesTypes of Bryophytes

Mosses (most common)Mosses (most common)

Liverworts (simplest)Liverworts (simplest)

Hornworts Hornworts

Moss Life CycleMoss Life Cycle

Zygote grows, develops into a sporophyte while still attached to gametophyte.

Fertilization

zygote

sperm-producing structure

egg-producing structure

Diploid Stage

Haploid Stage

mature sporophyte

Meiosis

Spores germinate.

male gametophyte

female gametophyteFigure 23.5

Page 388

Peat MossesPeat Mosses

350 species350 species

SphagnumSphagnum is an example is an example

Grow in acidic bogs; important ecosystems of Grow in acidic bogs; important ecosystems of

cold and temperate regionscold and temperate regions

Peat can be harvested and burned as fuelPeat can be harvested and burned as fuel

Marchantia:Marchantia: A Liverwort A Liverwort

Reproduces Reproduces asexually by asexually by gemmae gemmae

Gametophytes are Gametophytes are

male or femalemale or female

Female gametophyte

Do not post on Internet

Figure 23.7 Page 389

Seedless Vascular Seedless Vascular PlantsPlants

Like bryophytesLike bryophytes

Live in wet, humid placesLive in wet, humid places

Require water for fertilizationRequire water for fertilization

Unlike bryophytesUnlike bryophytes

Sporophyte is free-living and Sporophyte is free-living and

has vascular tissueshas vascular tissues

Seedless Vascular PlantsSeedless Vascular Plants

Lycophytes (Lycophyta)Lycophytes (Lycophyta)

Whisk ferns (Psilophyta)Whisk ferns (Psilophyta)

Horsetails (Sphenophyta)Horsetails (Sphenophyta)

Ferns (Pterophyta)Ferns (Pterophyta)

Ferns (Pterophyta)Ferns (Pterophyta)

12,000 species, mostly tropical12,000 species, mostly tropical Most common sporophyte structureMost common sporophyte structure

Perennial underground stem (rhizome)Perennial underground stem (rhizome) Roots and fronds arise from rhizomeRoots and fronds arise from rhizome Young fronds are coiled “fiddleheads”Young fronds are coiled “fiddleheads” Mature fronds divided into leafletsMature fronds divided into leaflets Spores form on lower surface of some Spores form on lower surface of some

frondsfronds

Fern Life CycleFern Life Cycle

Spores are released

Sporophyte still attached to gametophyte

zygote

fertilizationDiploid StageHaploid Stage

egg

sperm

mature gametophyte

Spores develop

meiosis

Spore germinates

rhizomesorus

Figure 23.9Page 391

Rise of Seed-Bearing Rise of Seed-Bearing PlantsPlants Seeds appeared about 360 million Seeds appeared about 360 million

years ago years ago

Seed ferns and gymnosperms were Seed ferns and gymnosperms were

dominant at firstdominant at first

Angiosperms arose laterAngiosperms arose later

CarboniferousCarboniferous

Giant lycophytes and horsetails Giant lycophytes and horsetails

Sea level rose and fell repeatedly Sea level rose and fell repeatedly

Remains of swamp forests were Remains of swamp forests were repeatedly submerged and repeatedly submerged and compressedcompressed

Formation of coalFormation of coal

Seed-Bearing Plants Seed-Bearing Plants

Microspores that give rise to pollen Microspores that give rise to pollen

grainsgrains

Megaspores inside ovulesMegaspores inside ovules

More water-conserving than More water-conserving than

seedless vascular plantsseedless vascular plants

Pollen Pollen

Pollen grains are sperm-bearing male Pollen grains are sperm-bearing male gametophytes that develop from gametophytes that develop from microsporesmicrospores

Allows transfer of sperm to egg without Allows transfer of sperm to egg without waterwater

Can drift on air currents or be carried by Can drift on air currents or be carried by pollinatorspollinators

OvulesOvules

Female reproductive structures that Female reproductive structures that become seedsbecome seeds

Consist of:Consist of: Female gametophyte with egg cellFemale gametophyte with egg cell

Nutrient-rich tissueNutrient-rich tissue

Jacket of cell layers that will form seed coatJacket of cell layers that will form seed coat

GymnospermsGymnosperms

Plants with “naked seeds”Plants with “naked seeds”

Seeds don’t form inside an ovarySeeds don’t form inside an ovary

Four groupsFour groups

ConifersConifers GinkgosGinkgos

CycadsCycads GnetophytesGnetophytes

Conifer Characteristics Conifer Characteristics

Widest known, largest number of living Widest known, largest number of living speciesspecies

Woody trees or shrubs Woody trees or shrubs

Most are evergreenMost are evergreen

Bear seeds on exposed cone scalesBear seeds on exposed cone scales

Most produce woody conesMost produce woody cones

CycadsCycads

Most diverse during Most diverse during age of dinosaursage of dinosaurs

Only 100 living speciesOnly 100 living species Palmlike appearancePalmlike appearance Pollen-bearing and Pollen-bearing and

seed-bearing cones on seed-bearing cones on different plantsdifferent plants Do not

post on Internet

Figure 23.14ePage 394

Strobilus of a “female” cycad

GinkgosGinkgos

Diverse during age Diverse during age of dinosaursof dinosaurs

One surviving One surviving species, species, Ginkgo Ginkgo biloba biloba

Deciduous trees are Deciduous trees are male or female male or female

Do not post

photos on

Internet

Fig. 23.15 Page 395

3 Genera of Gnetophytes3 Genera of Gnetophytes

GnetumGnetum

WelwitschiaWelwitschia

EphedraEphedra Sporophyte of Ephedra

Do not post on Internet

Figure 23.16aPage 395

Pine ConesPine Cones

Woody scales of a “pine cone” are the Woody scales of a “pine cone” are the

parts where megaspores formed and parts where megaspores formed and

developed into female gametophytesdeveloped into female gametophytes

Male cones, where microspores and Male cones, where microspores and

pollen are produced, are not woodypollen are produced, are not woody

section through one ovule

ovule

surface view of one cone scale (houses two ovules)

section through a pollen-producing sac

surface view of one cone scale (houses a pollen-producing sac)

meiosisfertilization

seed coat

embryo

zygote

mature sporophyte

seeding

pollen tube

sperm-producing cell

eggs

female gametophyte

pollination

microspores form

megaspores form

seedDiploid

Haploid

Pine Life CyclePine Life Cycle

Figure 23.17Page 396

Conifer DistributionConifer Distribution

Reproduce more slowly than Reproduce more slowly than angiosperms; at competitive angiosperms; at competitive disadvantage in many habitatsdisadvantage in many habitats

Still dominate in far north, at higher Still dominate in far north, at higher elevations, and in certain parts of elevations, and in certain parts of southern hemispheresouthern hemisphere

AngiospermsAngiosperms Flowering plantsFlowering plants

Dominant land plants (260,000 species)Dominant land plants (260,000 species)

Ovules and (after fertilization) seeds are Ovules and (after fertilization) seeds are enclosed in an ovaryenclosed in an ovary

Three main groups: magnoliids, Three main groups: magnoliids, monocots, and eudicotsmonocots, and eudicots

Angiosperm Evolutionary Angiosperm Evolutionary TreeTree

basal groups

Amborellawater lilies

star anise magnoliids monocots eudicots

Figure 23.19aPage 398

Double Fertilization Double Fertilization

Distinctive feature of angiospermsDistinctive feature of angiosperms

Male gametocyte delivers two sperm to Male gametocyte delivers two sperm to an ovulean ovule

One fertilizes egg; other fertilizes a cell One fertilizes egg; other fertilizes a cell that gives rise to endosperm that gives rise to endosperm

FloweriFlowering Plant ng Plant Life Life Cycle Cycle

Double fertilization Meiosis Meiosis

microspores

female gametophyte

pollination

mitosis without cytoplasmic division

two sperm enter ovule

Diploid

Haploid

Figure 23.20Page 399

sporophyte

People and PlantsPeople and Plants

Plant domestication began about Plant domestication began about 11,000 years ago11,000 years ago

About 3,000 species have been About 3,000 species have been used as foodused as food

Now about 200 plants are major Now about 200 plants are major cropscrops

Nonfood Uses of Plants Nonfood Uses of Plants

Lumber, paper, and fuel Lumber, paper, and fuel

Furniture Furniture

Rope Rope

Thatched roofing Thatched roofing

Natural insecticidesNatural insecticides

Drugs Drugs

Plants of AbusePlants of Abuse

Tobacco plants are Tobacco plants are NicotianaNicotiana sp.sp. Cannabis sativaCannabis sativa is source of marijuana is source of marijuana Coca leaves are used to produce cocaineCoca leaves are used to produce cocaine Toxic plant alkaloids, such as henbane Toxic plant alkaloids, such as henbane

and belladona, have been used as and belladona, have been used as poisons and as medicinepoisons and as medicine