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Evolution of Plants

19-1

19.1 Plants have a green algal ancestor

 Multicellular, photosynthetic eukaryotes

 Evolved from freshwater green algae ~500 MYA

 Green algae and plants

1. Contain chlorophylls a and b plus accessory

pigments

2. Store excess carbohydrates as starch

3. Have cellulose in their cell wall

19-2

19-3 Figure 19.1A

common ancestor

megaphylls

microphylls

seeds

flowers, double fertilization, endosperm, fruit

Flowering plants

Gymnosperms

Ferns and allies

Mosses

Lycophytes

Hornworts

V a s c u

la r

N o

n v

a s c u

la r

S e e d

le s s

B ry

o p

h y te

S e e d

Liverworts

Charophytes

550 400 450 500 350 300 250 PRESENT

common

green

algal

ancestor

embryo

protection

apical

growth

vascular

tissue

Million Years Ago (MYA)

19.1 Plants have a green algal ancestor

 Charophytes

 Algae most closely related to green plants

 The living charophytes most like land plants include:

 Charales

 Stoneworts – encrusted with calcium carbonate

 Coleochaete

 Resembles a flat pancake

 These charophytes have features that would have

promoted the evolution of land plants.

19-4

Figure 19.1B 19-5

(Chara): © Heather Angel/Natural Visions; (Coleochaete): © T. Mellichamp/Visuals Unlimited

Chara

node

Coleochaete

19.2 Plants have an alternation-of-

generations life cycle

 Two multicellular individuals alternate, each

producing the other.

 The sporophyte is the diploid (2n) generation.

 It produces spores by meiosis.

 A spore is a haploid (n) reproductive cell that develops into a

new organism without needing to fuse with another

reproductive cell.

 A spore undergoes mitosis to become a gametophyte.

 The gametophyte is the haploid (n) generation.

 It produces gametes.

 In plants, eggs and sperm are produced by mitosis.

 A sperm and egg fuse, forming a diploid (2n) zygote that

undergoes mitosis and becomes the sporophyte. 19-6

19-7 Figure 19.2A

zygote (2n)

Sporophyte (2n)

spore (n)

Gametophyte (n)

(n) (n)

gametes

sporangium (2n)

diploid (2n)

haploid (n) MEIOSIS FERTILIZATION

19.2 Plants have an alternation-of-

generations life cycle

 Plants differ as to which generation is dominant

(more conspicuous).

 Sporophyte dominance was adaptive to a dry

land environment.

 Only the sporophyte ever has vascular tissue.

 Only plants with a dominant sporophyte attain

significant height.

19-8

The size of the gametophyte is progressively reduced as

the sporophyte becomes more dominant.

19-9

Moss Fern Gymnosperm Angiosperm

roots

rhizoids

(n)

(2n)

seed seed spores spores

rhizoids

Figure 19.2B

 Sporophyte dominance is associated with an

increasing adaptation for reproduction in a dry,

terrestrial environment.

 Ferns are seedless vascular plants with a dominant

sporophyte.

 The water-dependent gametophyte makes it more difficult for

ferns to inhabit dry environments.

 Flowering plants are seed plants with a dominant

sporophyte.

 All reproductive structures are protected from drying out.

19-10

19.2 Plants have an alternation-of-

generations life cycle

Figure 19.2Ca 19-11

surface of

gametophyte

egg becomes

sporophyte embryo

a. Archegonium in seedless plants

flagellated sperm

19-12 Figure 19.2Cb

b. Ovule in seed plants

tissue of

sporophyte

ovule becomes

seed

egg becomes

sporophyte

embryo

 Spophytes have a cuticle.

 This relatively impermeable layer provides an

effective barrier to water loss, but also limits gas

exchange.

 Leaves have openings called stomata (sing., stoma)

that let carbon dioxide enter while allowing oxygen

and water to exit.

19-13

19.2 Plants have an alternation-of-

generations life cycle

19-14 Figure 19.2D

Falsely colored scanning

Electron micrograph

Of leaf surface

Stained photomicrograph

Of a leaf cross section

stomata

Vascular plant leaves

Have a cuticle and stomata.

cuticle

(left): © Kingsley Stern; (right): © Andrew Syred/SPL/Photo Researchers, Inc.

400X

Diversity of Plants

19-15

19.3 Bryophytes protect the embryo and

have apical growth

 Bryophytes are hornworts, liverworts, and

mosses.

 First plants to colonize land

 Protect the embryo and produce wind-blown spores

 No true roots, stems, or leaves – no vascular tissue

 Non-vascular plants

19-16

Figure 19.3A 19-17

Hornwort Liverwort female gametophyte Moss gametophyte

sporophyte

gametophyte

archegonium

gemma cup

(hornwort): © Steven P. Lynch; (liverwort): © Harold Taylor/Getty Images; (moss): © Nigel Cattlin/Photo Researchers, Inc.

19.3 Bryophytes protect the embryo and

have apical growth

 In bryophyte reproduction:

 The gametophyte is the dominant generation.

 The female gametophyte produces eggs in

archegonia.

 The male gametophyte produces flagellated sperm in

antheridia.

 Following fertilization, the zygote becomes a

sporophyte.

 The sporophyte is attached to, and derives its

nourishment from, the photosynthetic gametophyte.

19-18

Moss life cycle

19-19

(top): © Peter Lilja/Getty Images; (bottom): © Steven P. Lynch

zygote

sperm

egg

Archegonia

Antheridia

Spores

Sporangium

Gametophytes

buds

Mitosis

haploid (n)

diploid (2n)

Developing sporophyte:

The sporophyte embryo

is retained within the

archegonium, where

it develops, becoming a

mature sporophyte.

developing

sporophyte

Fertilization:

Flagellated sperm

produced in

antheridia swim in

external water to

archegonia, each

bearing a single egg.

The mature

gametophytes:

In mosses, the

dominant

gametophyte shoots

bear either antheridia

or archegonia, where

gametes are

produced by mitosis.

Spore dispersal:

Spores are released

when they are most

likely to be

dispersed

by air currents.

The immature

gametophyte:

A spore germinates

into the first

stage of the male

and the female

gametophytes.

archegonium

antheridium

The sporophyte:

The dependent sporophyte has a foot buried in female

gametophyte tissue, a stalk, and an upper capsule (the

sporangium), where meiosis occurs and windblown spores

are produced.

MEIOSIS FERTILIZATION

Sporophyte

stalk

foot (n)

Figure 19.3B

19.4 Lycophytes have vascular tissue for

transport

 Vascular plants have vascular tissue.

 Xylem transports water.

 Contains lignin to strengthen cell walls.

 Phloem transports nutrients.

 The first vascular plants were like Cooksonia, a

rhyniophyte of the Silurian period.

 It had no roots or leaves and is an early example of a

seedless vascular plant.

19-20

19-21

sporangia

(Right): Courtesy Hans Steur, the Netherlands Figure 19.4A

Cooksonia

19.4 Lycophytes have vascular tissue for

transport

 Lycophytes or club mosses have true stems,

leaves, and roots.

 Leaves are microphylls

 Only one strand of vascular tissue

 Club-shaped strobili

 Sporophyte is dominant, as in all vascular plants

 Today there are three groups:

1. Ground pines (Lycopodium)

2. Spike mosses (Selaginella)

3. Quillworts (Isoetes)

19-22

Sporophyte of Lycopodium

19-23

sporophyll

sporangia strobili

branches

aerial stem

rhizome

root

Leaf

Strobilus leaves

(microphylls)

Root

stoma

vascular tissue

phloem xylem

Figure 19.4B

19.5 Ferns have large leaves called

megaphylls

 Ferns, horsetails, and whisk ferns are seedless

vascular plants.

 They have megaphylls - broad leaves with

several strands of vascular tissue.

19-24

Figure 19.5A 19-25

a. Microphyll Megaphyll

b. Megaphyll evolution process

branched

vascular tissue single strand of

vascular tissue

branched

stem system

megaphyll

leaf

Tissue filled in the spaces

between the side branches.

The side branches flattened

into a single plane.

One branch began to

dominate the stem system.

19.5 Ferns have large leaves called

megaphylls

 Horsetails

 Belong to one

genus, Equisetum,

with approximately

25 species.

 About 300 MYA,

horsetails were the

dominant plants

and grew as large

as modern trees.

19-26

Figure 19.5B

strobilus

branches

leaves

19.5 Ferns have large leaves called

megaphylls

 Whisk ferns

 Consist of two

genera:

Psilotum and

Tmesipteris

 Are epiphytes -

plants that live

on/in trees

 Lack leaves

19-27

Figure 19.5C

display.

rhizome

sporangium

aerial stem

scale

root

(Left): © CABISCO/Phototake

19.5 Ferns have large leaves called

megaphylls

 Ferns

 11,00 species

 Megaphylls are

called fronds

 Leaves first appear

as fiddleheads

 Two generations

separate and

independent

19-28 Figure 19.5D

Fern life cycle

19-29

Sporophyte

fiddlehead roots

frond

Sporangium

sperm

Antheridium

egg

Archegonium

Gametophyte

Spores

zygote

leaflet

Sorus

sporangium

MEIOSIS

Dryopterus

Mitosis

haploid (n)

diploid (2n)

1 The sporophyte:

The sporophyte is

dominant in ferns.

Young sporophyte:

The sporophyte

embryo develops

inside an

archegonium.

As the distinctive

first leaf appears

above the

gametophyte, and

as the roots

develop below it,

the young sporophyte

becomes visible.

young sporophyte

on gametophyte

FERTILIZATION

The sporangia:

In this fern, the

sporangia are

located within sori

(sing., sorus) on

the underside of

the leaflets.

The spores:

Within a

sporangium,

meiosis occurs

and spores are

produced. When a

sporangium opens,

the spores are

released. germinating

spore

The gametophyte:

A spore germinates into a

heart-shaped gametophyte,

which typically bears archegonia

at the notch and antheridia at the

tip between the rhizoids.

Fertilization:

Fertilization takes

place when

moisture is

present, because

the flagellated

sperm must swim

in a film of water

from the antheridia

to eggs within

archegonia.

(Top right): © Matt Meadows/Peter Arnold/Photolibrary

Sori

Figure 19.5E

19.6 Most gymnosperms bear cones on

which the seeds are “naked”

 Evolution of the seed was the next significant

innovation in the evolution of plants.

 Gymnosperms and angiosperms are seed

plants.

 A seed contains a sporophyte generation, along

with stored food, within a protective seed coat.

 The ability of seeds to survive harsh conditions

largely accounts for the dominance of seed

plants today.

19-30

19.6 Most gymnosperms bear cones on

which the seeds are “naked”

 Diversity of gymnosperms:

 There are four groups of living gymnosperms:

cycads, ginkgoes, gnetophytes, and conifers.

 All have ovules and develop seeds that are exposed

on the surface of cone scales or analogous

structures.

 Conifers

 Consist of about 575 tree species

 Many are evergreens such as pines, spruces, firs, cedars,

and hemlocks.

 Wood of conifers is used extensively in construction.

19-31

19-32

Figure 19.6A

19-33

Pollen sac

Seed

stored food

seed coat

zygote

seed wing

Sporophyte

pollen cone scale

Seed cones

seed cone scale

Pollen cones

sperm

pollen tube

egg

Mature female gametophyte

Pollen grain

Pollination

Megaspores

Microspores

pollen grain

Megaspores:

Megaspore mother cell

in ovule undergoes

meiosis to produce

megaspores.One

megaspore will

become the

egg-producing

The pollen grain:

The pollen grain has two wings and is carried by the

wind to the seed cone during pollination

Mature male gametophyte

200 µm

MEIOSIS MEIOSIS

Ovule

Mitosis

haploid (n)

diploid (2n)

FERTILIZATION

The sporophyte

embryo:After

fertilization, the

ovule matures and

becomes the seed

composed of the

embryo, reserve

food, and a seed

coat. Finally, in the

fall of the second

season, the seed

cone, by

now woody and

hard, opens to

release winged

seeds. When

a seed germinates,

the sporophyte

sporophyte

embryo

Fertilization:

Once a pollen grain

reaches a seed cone,

it becomes a mature

male gametophyte.

A pollen tube digests

its way slowly

toward a female

gametophyte and

discharges

nonflagellated sperm.

The fertilized

egg is

a zygote.

ovule

wall

megaspore

mother cell

microspore

mother cell

The pollen cones:

Typically, the pollen

cones are quite small

and develop near the

tips of lower

branches.

The seed cones:

The seed cones are

larger than the pollen

cones and are located

near the tips of higher

branches.

Microspores:

Microspore mother

cells undergo meiosis

to produce

microspores. Each

microspore becomes a

pollen grain.

(Bottom right): © Phototake Figure 19.6B

HOW LIFE CHANGES

19A Carboniferous Forests Became the

Coal We Use Today

 Our industrial society runs on fossil fuels such

as coal.

 During the Carboniferous period (>300 MYA), a

great swamp forest encompassed what is now

northern Europe, the Ukraine, and the

Appalachian Mountains in the United States.

 Enormous amount of biomass

 Remains became covered by sediment that changed

to sedimentary rock

 With pressure, the organic material became coal.

19-34

Figure 19A 19-35

early gymnosperm

club mosses

horsetail

seed fern

fern

Fossil seed fern

(fossil fern): © Sinclair Stammers/SPL/Photo Researchers, Inc

19.7 Angiosperms have flowers in which

the seeds are “covered”

 Angiosperms are flowering plants.

 Evolved some 200 MYA

 Innovations are flower and fruit

 240,000 known species

 Ovules always enclosed within sporophyte tissue

 Cotyledons are seed leaves with nutrients that

nourish the embryo.

 Monocotyledones (or monocots) – one cotyledon

 Eudicotyledones (or eudicots) – two cotyledons

19-36

Figure 19.7A 19-37

petals (corolla) sepals (calyx)

stamens

anther

filament

receptacle

stigma

ovary

ovule

style

pollen

tube

carpel

Flowering plant life cycle

19-38

ovary

stigma

style

Megaspores

sperm

pollen tube

Microspores

(mature male gametophyte)

Pollen grain

Embryo sac

(mature female gametophyte)

Pollination

polar nuclei

ovule wall

egg

Seed

endosperm (3n)

sporophyte embryo

seed coat

Sporophyte Anther

egg

polar nuclei

Stamen Carpel

stigma style ovary ovule

filament

anther

MEIOSIS MEIOSIS

sperm

ovule

The mature male gametophyte:

A p[ollen grain that lands on the carpel of the same type

of plant germinates and produces a pollen tube,

which delivers two nonflagellated sperm to the female

gametophyte. A fully germinated pollen grain is the

mature male gametophyte.

Mitosis

Ovule

diploid (2n)

haploid (n)

Carpel

Double Fertilization

receptacle

The stamen:

An anther at the top of each

stamen has four pollen sacs.

The carpel:

The ovary at the base of a

carpel contains one or more

ovules. The contents of an

ovule change during the

flowering plant life cycle.

pollen

sac

microspore

mother cell megaspore

mother cell

degenerating

megaspores

Microspores:

Microspore mother cells undergo meiosis to produce

microspores. Each microspore becomes a pollen grain.

Megaspores:

Megaspore mother cell inside ovule undergoes meiosis to

produce megaspores. One megaspore will become the

egg-producing female gametophyte.

pollen

tube

FERTILIZATION

The mature female gametophyte:

The ovule now contains the mature female

gametophyte (embryo sac), which typically consists of

eight haploid nuclei embedded in a mass of cytoplasm.

The cytoplasm differentiates into cells, one of which is

an egg and another of which contains two polar nuclei.

Double fertilization:

On reaching the ovule, the

pollen tube discharges the

sperm. One of the two sperm

migrates to and fertilizes the

egg, forming a zygote; the

other unites with the two

polar nuclei, producing a 3n

(triploid) endosperm nucleus.

The endosperm nucleus

divides to form endosperm,

food for the developing plant.

The seed:

The ovule now develops into

the seed, which contains an

embryo and food enclosed

by a protective seed coat.

The wall of the ovary and

sometimes adjacent parts

develop into a fruit that

surrounds the seed(s).

The sporophyte embryo:

The embryo within a seed

is the immature sporophyte.

When a seed germinates,

growth and differentiation

produce the mature

sporophyte of a flowering

plant.

fruit

(mature ovary) seed

(mature ovule)

Figure 19.7B

HOW BIOLOGY IMPACTS OUR LIVES

19B Flowering Plants Provide

Many Services

 Humans derive most of their sustenance from three

flowering plants:

1. Wheat

 First cultivated in the Middle East about 8000 B.C.

 Thought to be one of the earliest cultivated plants

2. Corn

 Maize first cultivated in Central America about 7,000

years ago

3. Rice

 Originated several thousand years ago in southeastern Asia,

where it grew in swamps

 About 50% of all pharmaceuticals come from plants. 19-39

Figure 19B.1 19-40

Corn plants, Zea Rice plants, Oryza

ear grain head

Wheat plants,Triticum

grain head

(wheat): © Creatas Images RF; (corn plants, rice plant): © Corbis RF; (ear of corn): © Dorling Kindersley/Getty RF; (rice grains): © Dex Image/Getty RF; ©

Corbis RF

Figure 19B.2 19-41

Evolution and Diversity of Fungi

19-42

19.8 Fungi differ from plants and animals

 Fungi are a structurally diverse group of

eukaryotes.

 Fungi are strict heterotrophs that release

digestive enzymes into the external environment

and digest their food outside the body.

 Most are saprotrophs – decomposers.

 A typical fungal body is a mass of filaments

(hypha) called a mycelium.

 The cell walls contain chitin.

 Energy reserves are stored as glycogen. 19-43

Figure 19.8A 19-44

a. Fungal mycelia on a corn tortilla b. Cell structure of hyphae

nuclei

septum

cell wall

nonseptate

hypha

septate

hypha

Evolution of fungi

19-45 Figure 19.8B

19.8 Fungi differ from plants and animals

 Fungi have mutualistic relationships with plants

and algae.

 In a mutualistic relationship, two different species live

closely and benefit one another.

 Mycorrhizal fungi form mutualistic relationships

(mycorrhizae) with the roots of most plants.

 Helps plants grow more successfully in dry or poor soils

 Lichen – a mutualistic association between a

particular fungus and a cyanobacterium or green alga

 Fungal partner acquires nutrients and moisture

 Organic acids produced by fungal partner can be used by

photosynthetic partner

19-46

Figure 19.8D 19-47

sac fungi

reproductive

cups

19.9 Land fungi

occur in

three main

groups

 Zygospore fungi

 Mainly

saprotrophs, but

some are

parasites

 Example: Black

bread mold,

Rhizopus

stolonifer

19-48

1 1

Figure 19.9A

19.9 Land fungi occur in three main

groups

 Sac fungi

 Nearly 75% of all

described fungal

species

 Name from sexual

reproductive

structure, called an

ascus

 Yeast – unicellular

forms

19-49 Figure 19.9B

display.

meiosis

Ascocarp of the cup fungus Sarcoscypha

Cup fungi

Morel

ascocarp

ascospores

male organ

female organ

nuclear

fusion zygote

(2n) mature

ascus

dikaryotic

hyphae

+ mating type (n)

spore

– mating type (n)

spore

Figure 19.9C 19-50

conidia

a. b.

budding

yeast cell

19.9 Land fungi

occur in

three main groups

 Club fungi

 Named for the

reproductive structure,

the basidium

 The basidia are

located within a

basidiocarp

 Mushrooms are

basidiocarps

19-51

Figure 19.9D

basidiocarp

fusion meiosis

Sexual reproduction

spores

nuclei in

basidium

gill of

mushroom

+ -

Figure 19.9D (Cont.) 19-52

Shelf fungi Mushroom

Giant puffball

Researchers, Inc

HOW BIOLOGY IMPACTS OUR LIVES

19C Land Fungi Have Economic

and Medical Importance

 Economic importance

 Fungi help produce medicines and many foods

 Penicillium was the original source of penicillin.

 Mushrooms are a nutritious, low-calorie meat

substitute.

 Fungal pathogens are a major concern for farmers.

 Medical importance

 Certain mushrooms are poisonous.

 Mycoses are diseases caused by fungi.

19-53

Plant fungal disease

19-54 Figure 19C.1

Human fungal diseases

19-55

a. Ringworm c. Thrush

tongue

back of throat

b.Athlete’s foot

Figure 19C.2

Connecting the Concepts:

Chapter 19

 Land plants and fungi most likely evolved from

an aquatic ancestor and went on to adapt to the

land environment.

 Plants

 Plants demonstrate a trend towards gametophyte

dependence on a sporophyte with large leaves and

vascular tissue.

 Angiosperms are the most widely dispersed of the

land plants.

 Fungi

 Fungi produce windblown spores within both asexual

and sexual life cycles.

19-56