29 plants i7th

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 29
Plant Diversity I
How Plants
Colonized Land

• Overview: The Greening of Earth
• Looking at a lush landscape
– It is difficult to imagine the land without any
plants or other organisms
Figure 29.1

• For more than the first 3 billion years of Earth’s
history
– The terrestrial surface was lifeless
• Since colonizing land
– Plants have diversified into roughly 290,000
living species

• Concept 29.1: Land plants evolved from green
algae
• Researchers have identified green algae called
charophyceans as the closest relatives of land
plants

Morphological and Biochemical Evidence
• Many characteristics of land plants
– Also appear in a variety of algal clades

• There are four key traits that land plants share
only with charophyceans
– Rose-shaped complexes for cellulose
synthesis
30 nmFigure 29.2

– Peroxisome enzymes
– Structure of flagellated sperm
– Formation of a phragmoplast

Genetic Evidence
• Comparisons of both nuclear and chloroplast
genes
– Point to charophyceans as the closest living
relatives of land plants
Chara,
a pond
organism
(a)
10 mm
Coleochaete orbicularis, a disk-
shaped charophycean (LM)
(b)
40 µm
Figure 29.3a, b

Adaptations Enabling the Move to Land
• In charophyceans
– A layer of a durable polymer called
sporopollenin prevents exposed zygotes from
drying out
• The accumulation of traits that facilitated
survival on land
– May have opened the way to its colonization
by plants

• Concept 29.2: Land plants possess a set of
derived terrestrial adaptations
• Many adaptations
– Emerged after land plants diverged from their
charophycean relatives

Defining the Plant Kingdom
• Systematists
– Are currently debating the boundaries of the
plant kingdom
Plantae
Streptophyta
Viridiplantae
Red algae Chlorophytes Charophyceans Embryophytes
Ancestral algaFigure 29.4

• Some biologists think that the plant kingdom
– Should be expanded to include some or all
green algae
• Until this debate is resolved
– This textbook retains the embryophyte
definition of kingdom Plantae

Derived Traits of Plants
• Five key traits appear in nearly all land plants
but are absent in the charophyceans
– Apical meristems
– Alternation of generations
– Walled spores produced in sporangia
– Multicellular gametangia
– Multicellular dependent embryos

APICAL MERISTEMS
Apical
meristem
of shoot
Developing
leaves
100 µm
Apical meristems of plant shoots
and roots. The light micrographs
are longitudinal sections at the tips
of a shoot and root.
Apical meristem
of root
Root 100 µm
Shoot
Figure 29.5
• Apical meristems and alternation of
generations
Haploid multicellular
organism (gametophyte)
Mitosis Mitosis
Gametes
Zygote
Diploid multicellular
organism (sporophyte)
Alternation of generations: a generalized scheme
MEIOSIS FERTILIZATION
2n
2n
n
n
nn
nSpores
Mitosis
ALTERNATION OF GENERATIONS

• Walled spores; multicellular gametangia; and
multicellular, dependent embryos
WALLED SPORES PRODUCED IN SPORANGIA
MULTICELLULAR GAMETANGIA
MULTICELLULAR, DEPENDENT EMBRYOS
Spores
Sporangium
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte
Gametophyte
Sporophyte and sporangium
of Sphagnum (a moss)
Female gametophyte
Archegonium
with egg
Antheridium
with sperm
Male
gametophyte
Archegonia and antheridia
of Marchantia (a liverwort)
Embryo
Maternal tissue
2 µm
Wall ingrowths
Placental transfer cell
10 µm
Embryo and placental
transfer cell of Marchantia
Figure 29.5

• Additional derived units
– Such as a cuticle and secondary compounds,
evolved in many plant species

The Origin and Diversification of Plants
• Fossil evidence
– Indicates that plants were on land at least 475
million years ago

• Fossilized spores and tissues
– Have been extracted from 475-million-year-old
rocks
Fossilized spores.
Unlike the spores of
most living plants,
which are single
grains, these spores
found in Oman are
in groups of four
(left; one hidden)
and two (right).
(a)
Fossilized
sporophyte tissue.
The spores were
embedded in tissue
that appears to be
from plants.
(b)
Figure 29.6 a, b

• Whatever the age of the first land plants
– Those ancestral species gave rise to a vast
diversity of modern plants
Table 29.1

• Land plants can be informally grouped
– Based on the presence or absence of vascular
tissue

• An overview of land plant evolution
Bryophytes
(nonvascular plants) Seedless vascular plants Seed plants
Vascular plants
Land plants
Origin of seed plants
(about 360 mya)
Origin of vascular
plants (about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Charophyceans
Liverworts
Hornworts
Mosses
Lycophytes
(clubmosses,spikemosses,quillworts)
Pterophyte
(ferns,horsetails,whiskfern)
Gymnosperms
Angiosperms
Figure 29.7

• Concept 29.3: The life cycles of mosses and
other bryophytes are dominated by the
gametophyte stage
• Bryophytes are represented today by three
phyla of small herbaceous (nonwoody) plants
– Liverworts, phylum Hepatophyta
– Hornworts, phylum Anthocerophyta
– Mosses, phylum Bryophyta

• Debate continues over the sequence of
bryophyte evolution
• Mosses are most closely related to vascular
plants

Bryophyte Gametophytes
• In all three bryophyte phyla
– Gametophytes are larger and longer-living
than sporophytes

• The life cycle of a moss
Mature
sporophytes
Young
sporophyte
Male
gametophyte
Raindrop
Sperm
Key
Haploid (n)
Diploid (2n)
Antheridia
Female
gametophyte
Egg
Archegonia
FERTILIZATION
(within archegonium)
Zygote
Archegonium
Embryo
Female
gametophytes
Gametophore
Foot
Capsule
(sporangium)
Seta
Peristome
Spores
Protonemata
“Bud”
“Bud”
MEIOSIS
Sporangium
Calyptra
Capsule with
peristome (LM)
Rhizoid
Mature
sporophytes
Spores develop into
threadlike protonemata.
1
The haploid
protonemata
produce “buds”
that grow into
gametophytes.
2
Most mosses have separate
male and female gametophytes,
with antheridia and archegonia,
respectively.
3
A sperm swims
through a film of
moisture to an
archegonium and
fertilizes the egg.
4
Meiosis occurs and haploid
spores develop in the sporangium
of the sporophyte. When the
sporangium lid pops off, the
peristome “teeth” regulate
gradual release of the spores.
8
The sporophyte grows a
long stalk, or seta, that emerges
from the archegonium.
6
The diploid zygote
develops into a
sporophyte embryo within
the archegonium.
5
Attached by its foot, the
sporophyte remains nutritionally
dependent on the gametophyte.
7
Figure 29.8

• Bryophyte gametophytes
– Produce flagellated sperm in antheridia
– Produce ova in archegonia
– Generally form ground-hugging carpets and
are at most only a few cells thick
• Some mosses
– Have conducting tissues in the center of their
“stems” and may grow vertically

Bryophyte Sporophytes
• Bryophyte sporophytes
– Grow out of archegonia
– Are the smallest and simplest of all extant
plant groups
– Consist of a foot, a seta, and a sporangium
• Hornwort and moss sporophytes
– Have stomata

• Bryophyte diversity
LIVERWORTS (PHYLUM HEPATOPHYTA)
HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA)
Gametophore of
female gametophyte
Marchantia polymorpha,
a “thalloid” liverwort
Foot
Sporangium
Seta
500µm
Marchantia sporophyte (LM)
Plagiochila
deltoidea,
a “leafy”
liverwort
An Anthoceros
hornwort species
Sporophyte
Gametophyte
Polytrichum commune,
hairy-cap moss
Sporophyte
Gametophyte
Figure 29.9

“Tolland Man,” a bog mummy dating from 405–100 B.C.
The acidic, oxygen-poor conditions produced by
Sphagnum canpreserve human or other animal bodies
for thousands of years.
Ecological and Economic Importance of Mosses
• Sphagnum, or “peat moss”
– Forms extensive deposits of partially decayed
organic material known as peat
– Plays an important role in the Earth’s carbon cycle
Gametophyte
Sporangium at
tip of sporophyte
Living
photo-
synthetic
cells
Dead water-
storing cells
100 µm
Closeup of Sphagnum. Note the “leafy” gametophytes
and their offspring, the sporophytes.
(b)
Sphagnum “leaf” (LM). The combination of living photosynthetic
cells and dead water-storing cells gives the moss its spongy quality.
(c)
Peat being harvested from a peat bog(a)
Figure 29.10 a–d
(d)

• Concept 29.4: Ferns and other seedless
vascular plants formed the first forests
• Bryophytes and bryophyte-like plants
– Were the prevalent vegetation during the first
100 million years of plant evolution
• Vascular plants
– Began to evolve during the Carboniferous
period

Origins and Traits of Vascular Plants
• Fossils of the forerunners of vascular plants
– Date back about 420 million years

• These early tiny plants
– Had independent, branching sporophytes
– Lacked other derived traits of vascular plants
Figure 29.11

Life Cycles with Dominant Sporophytes
• In contrast with bryophytes
– Sporophytes of seedless vascular plants are
the larger generation, as in the familiar leafy
fern
– The gametophytes are tiny plants that grow on
or below the soil surface

• The life cycle of a fern
Fern sperm use flagella
to swim from the antheridia
to eggs in the archegonia.
4
Sporangia release spores.
Most fern species produce a single
type of spore that gives rise to a
bisexual gametophyte.
1 The fern spore
develops into a small,
photosynthetic gametophyte.
2 Although this illustration
shows an egg and sperm
from the same gametophyte,
a variety of mechanisms
promote cross-fertilization
between gametophytes.
3
On the underside
of the sporophyte‘s
reproductive leaves
are spots called sori.
Each sorus is a
cluster of sporangia.
6
A zygote develops into a new
sporophyte, and the young plant
grows out from an archegonium
of its parent, the gametophyte.
5
MEIOSIS
Sporangium
Sporangium
Mature
sporophyte
New
sporophyte
Zygote
FERTILIZATION
Archegonium
Egg
Haploid (n)
Diploid (2n)
Spore Young
gametophyte
Fiddlehead
Antheridium
Sperm
Gametophyte
Key
Sorus
Figure 29.12

Transport in Xylem and Phloem
• Vascular plants have two types of vascular
tissue
– Xylem and phloem

• Xylem
– Conducts most of the water and minerals
– Includes dead cells called tracheids
• Phloem
– Distributes sugars, amino acids, and other
organic products
– Consists of living cells

Evolution of Roots
• Roots
– Are organs that anchor vascular plants
– Enable vascular plants to absorb water and
nutrients from the soil
– May have evolved from subterranean stems

Evolution of Leaves
• Leaves
– Are organs that increase the surface area of
vascular plants, thereby capturing more solar
energy for photosynthesis

• Leaves are categorized by two types
– Microphylls, leaves with a single vein
– Megaphylls, leaves with a highly branched
vascular system

• According to one model of evolution
– Microphylls evolved first, as outgrowths of
stems
Vascular tissue
Microphylls, such as those of lycophytes, may have
originated as small stem outgrowths supported by
single, unbranched strands of vascular tissue.
(a) Megaphylls, which have branched vascular
systems, may have evolved by the fusion of
branched stems.
(b)
Figure 29.13a, b

Sporophylls and Spore Variations
• Sporophylls
– Are modified leaves with sporangia
• Most seedless vascular plants
– Are homosporous, producing one type of spore
that develops into a bisexual gametophyte

• All seed plants and some seedless vascular
plants
– Are heterosporous, having two types of spores
that give rise to male and female
gametophytes

Classification of Seedless Vascular Plants
• Seedless vascular plants form two phyla
– Lycophyta, including club mosses, spike
mosses, and quillworts
– Pterophyta, including ferns, horsetails, and
whisk ferns and their relatives

• The general groups of seedless vascular plants
LYCOPHYTES (PHYLUM LYCOPHYTA)
PTEROPHYTES (PHYLUM PTEROPHYTA)
WHISK FERNS AND RELATIVES HORSETAILS FERNS
Isoetes
gunnii,
a quillwort
Selaginella apoda,
a spike moss
Diphasiastrum tristachyum, a club moss
Strobili
(clusters of
sporophylls)
Psilotum
nudum,
a whisk
fern
Equisetum
arvense,
field
horsetail
Vegetative stem
Strobilus on
fertile stem
Athyrium
filix-femina,
lady fern
Figure 29.14

Phylum Lycophyta: Club Mosses, Spike Mosses, and
Quillworts
• Modern species of lycophytes
– Are relics from a far more eminent past
– Are small herbaceous plants

Phylum Pterophyta: Ferns, Horsetails, and Whisk
Ferns and Relatives
• Ferns
– Are the most diverse seedless vascular plants

The Significance of Seedless Vascular Plants
• The ancestors of modern lycophytes,
horsetails, and ferns
– Grew to great heights during the
Carboniferous, forming the first forests
Figure 29.15

• The growth of these early forests
– May have helped produce the major global
cooling that characterized the end of the
Carboniferous period
– Decayed and eventually became coal

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