the land plants - del mar college :: homedmc122011.delmar.edu/nsci/biology/faculty/brower/pow… ·...
TRANSCRIPT
The Land Plants
Chapter 23 Part 1
Impacts, Issues
Beginnings and Endings
Land plants provide oxygen, food, and shelter to
humans and animals, but human activities are
pushing some species toward extinction
23.1 Evolution on
a Changing World Stage
Changes in atmospheric conditions and shifts in
positions of continents affected the evolutionary
history of land plants
Evolution of Land Plants
Land plants (embryophytes) evolved from a
lineage of green algae (charophytes) after the
ozone layer made life on land possible
p. 370
red algae chlorophytes charophytes land plants
Evolution of Land Plants
Bryophytes include three early diverging land
plant lineages
Nonvascular seedless plants evolved next
The first seed plants were gymnosperms, from
which angiosperms (flowering plants) evolved
Evolutionary Tree for Land Plants
Fig. 23-2a, p. 370
Fig. 23-2a, p. 370
seedless
vascular
plants
angiosperms
(flowering
plants)bryophytes gymnosperms
Seed
Plants
Vascular
Plants
Land
Plants
ancestral green alga
Fig. 23-2b (1), p. 370bryophyte (moss)
Fig. 23-2b (2), p. 370seedless vascular plant (fern)
Fig. 23-2b (3), p. 370gymnosperm (conifer)
Fig. 23-2b (4), p. 370angiosperm (monocot)
Diversity of Modern Land Plants
Timeline for Plant Evolution
Continental movements that caused global
climate to become drier favored groups that
were better adapted to drought (seed plants)
• Silurian: Small seedless vascular plants
• Carboniferous: Large seedless vascular plants
• Devonian: First seeds (gymnosperms)
• Permian-Jurassic: Drought-tolerant conifers
• Jurassic-Cretaceous: Flowering plants
Timeline for Plant Evolution
Fig. 23-3, p. 371
Gondwana 425 425 mya 342 mya Pangea 255 mya 65 mya
Origin of
first land
plants
(bryophytes)
by 475 mya.
Origin of
seedless
vascular
plants.
Bryophytes
and seedless
vascular
plants
diversify.
Seed plants
arise by 385
mya.
Tree-sized
lycophytes
and horsetails
live in swamp
forests. First
conifers
arise late in
Carboniferous.
Ginkgos,
cycads
appear. Most
horsetails and
lycophytes
disappear by
the end of
the Permian.
Adaptive
radiations of
ferns, cycads,
conifers;
by start of
Cretaceous,
conifers are
dominant trees.
Flowering plants
appear in the early
Cretaceous,
undergo adaptive
radiation and
become dominant.
Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Tertiary
Millions of years ago (mya)
488 443 416 359 299 251 146 66200
Early Seedless Vascular Plants
Cooksonia and Psilophyton
23.2 Evolutionary Trends Among Plants
Over time, the spore-producing bodies of plants
became larger, more complex, and better
adapted to dry habitats
From Haploid to Diploid Dominance
Plants shifted from gametophyte-dominated life
cycle (in bryophytes) to sporophyte-dominated
life cycle (in other plants)
• Gametophyte: Haploid stage that forms gametes
by mitosis
• Sporophyte: Diploid stage that forms spores by
meiosis; a sporangium helps protect and
disperse spores
Life Cycle of Land Plants
Fig. 23-5a, p. 372
Fig. 23-5a, p. 372
mitosismulticelled
sporophyte
(2n)
zygote
(2n)
fertilizationDIPLOID
meiosis
HAPLOID
gametes
(n)
spores
(n)multicelled
gametophyte
(n)mitosis mitosis
Fig. 23-5b, p. 372
Fig. 23-5b, p. 372
zygote is only
diploid phase
green algae ferns gymnosperms angiospermsbryophytes
Animation: Haploid to diploid dominance
Roots, Stems, and Leaves
Life on land favored water conserving features
• Cuticle: Waxy layer that restricts evaporation
• Stomata: Openings across the cuticle
Fig. 23-6a, p. 373
cuticle (waxy layer
at leaf surface)
Fig. 23-6b, p. 373
stoma (opening
across cuticle)
Roots, Stems, and Leaves
In vascular plants, a system of vascular tissue
reinforced by lignin distributes materials through
leaves, stems, and roots of sporophytes
• Xylem: Distributes water and minerals
• Phloem: Distributes products of photosynthesis
Vascular Tissues
Fig. 23-7a, p. 373
xylem
Fig. 23-7b, p. 373
xylem phloem
Pollen and Seeds
Bryophytes and seedless plants release spores
Only seed-bearing vascular plants release
pollen grains and seeds
• Pollen grain: A walled, immature gametophyte
that will give rise to the sperm
• Seed: An embryo sporophyte and some nutritive
tissue enclosed inside a waterproof coat
Two Lineages of
Seed-Bearing Vascular Plants
Gymnosperms
• Cycads, conifers, ginkgos, and gnetophytes
Angiosperms (flowering plants)
• Most modern plants
• Seeds form inside floral tissue that later develops
into a fruit
Dispersal Methods: Spores and Seeds
23.1-23.2 Key Concepts
Milestones in Plant Evolution
The earliest known plants date from 475 million
years ago
Ever since then, environmental changes have
triggered divergences, adaptive radiations, and
extinctions
Structural and functional adaptations of lineages
are responses to some of the changes
23.3 The Bryophytes
Bryophytes include three land plant lineages –
liverworts, hornworts, and mosses – with a
gametophyte-dominated life-cycle
Characteristics of Bryophytes
Nonvascular (no xylem or phloem)
Sperm swim through water to eggs
The sporophyte forms on, and is nourished by,
the dominant gametophyte
Spores are the dispersal form
Liverworts
Gametophyte has a thallus that attaches to soil
or surfaces by rootlike rhizoids
Reproduces sexually, or asexually by producing
gemmae in cups on the gametophyte
Liverwort: Marchantia
Fig. 23-9a, p. 374
thallus (leaflike part) with gemmae cups
Fig. 23-9b, p. 374
asexually-produced gemmae in cup
Fig. 23-9c, p. 374
sperm-producing structure of a male plant
Fig. 23-9d, p. 374
egg-producing structure of a female plant
Hornworts
Have a hornlike sporophyte with its base
embedded in gametophyte tissue; spores form
in an upright capsule (sporangium)
• Sporophyte has chloroplasts
• Gametophyte has nitrogen-fixing bacteria
p. 374
sporophyte
gametophyte
Mosses
Sporophyte consists of a capsule (sporangium)
embedded in gametophyte
Life cycle
• Haploid spores form in the capsule by meiosis,
germinate, and develop into gametophytes
• Eggs and sperm form in gametangia
• After fertilization, zygote develops into sporophyte
Moss Life Cycle: Polytrichum
Fig. 23-10, p. 375
A Mature moss sporophyte
consists of a capsule atop
a stalk. It is still attached
to the gametophyte.
G Zygote grows, develops
into a sporophyte while still
attached to gametophyte.
sporophytezygote
fertilization meiosisDiploid Stage
Haploid Stagegametophyte
B Meiosis of cells inside the capsule forms spores, which are released when the capsule pops open.
F Drops of rain
disperse sperm,
which swim to
eggs and fertilize
them.rhizoids
sperm-producing antheridium
maleD Sperm form at tips of male gametophyte. immature
gametophytes egg-
producing
archegonium
female
E Eggs form at tip of
female gametophyte.
C Spores germinate, grow, and
develop into gametophytes.
Fig. 23-10, p. 375
meiosis
B Meiosis of cells inside the capsule forms spores, which are released when the capsule pops open.
male
sperm-producing antheridium
D Sperm form at tips of male gametophyte.
femaleegg-
producing
archegonium
E Eggs form at tip of female
gametophyte.
zygote
fertilization
F Drops of rain
disperse sperm, which
swim to
eggs and fertilize them.
G Zygote grows, develops
into a sporophyte while still attached
to gametophyte.
Stepped Art
C Spores germinate, grow, and
develop into gametophytes.
immature gametophytes
A Mature moss sporophyte
consists of a capsule atop a
stalk. It is still attached to the
gametophyte.
sporophyte
gametophyte
rhizoids
Diploid Stage
Haploid Stage
Animation: Moss life cycle
Importance of Mosses
Mosses are the most diverse group of
bryophytes; peat mosses (Sphagnum) are
ecologically and commercially important
Fig. 23-11a, p. 375
Fig. 23-11b, p. 375
sporophyte
gametophyte
23.3 Key Concepts
Early-Diverging Plant Lineages
Three plant lineages (mosses, hornworts, and
liverworts) are commonly referred to as
bryophytes, although they are not a natural
group
The gamete-producing stage dominates their life
cycle, and sperm reach the eggs by swimming
through droplets or films of water
23.4 Seedless Vascular Plants
A sporophyte with lignified vascular tissue
(xylem and phloem) dominates the life cycle
Two lineages of seedless vascular plants
• Lycophytes (club mosses, spike mosses)
• Monilophytes (whisk ferns, horsetails, ferns)
Some Lycophytes
Club moss (Lycopodium)
• Spores form inside a soft, cone-shaped strobilus
Spike moss (Selaginella) “resurrection plant”
• The most drought-tolerant vascular plants
Whisk Ferns
Whisk ferns (Psilotum)
• Have rhizomes (underground stems) but no
roots
• Photosynthetic stems appear leafless
• Spores form in fused sporangia at tips of
branches
Horsetails
Horsetails (Equisetum)
• Have rhizomes, hollow stems with silica deposits,
and nonphotosynthetic leaves
• Photosynthesis occurs in stems and leaflike
branches
• Spores in strobili form tiny gametophytes
Seedless Vascular Plants
Club moss (Lycopodium), whisk fern (Psilotum),
and horsetails (Equisetum)
Fig. 23-12a, p. 376
strobilus
Fig. 23-12b, p. 376
sporangia
Fig. 23-12c, p. 376
leaflike branch
Fig. 23-12d, p. 376
strobilus
Ferns – No Seeds, Much Diversity
Ferns
• The most diverse seedless vascular plants
• Most sporophytes have leaves and roots that
grow out from rhizomes
• Spores are dispersed from clusters of sporangia
(sori) on lower surfaces of frond leaves
• Many live as epiphytes attached to another plant
Fern Life Cycle: Woodwardia
fertilization
zygote
Diploid Stagerhizome
Fig. 23-13, p. 377
egg-
producing
archegonium
egg
sperm-
producing
antheridium
A spore
germinates,
grows into a
gametophyte.
sperm
mature
gametophyte
(underside)
C
Haploid Stagemeiosis
Spores are
released.Spores develop.
The sporophyte
(still attached to
the gametophyte)
grows, develops.
Stepped Art
sorus
Fig. 23-13, p. 377
The sporophyte
(still attached to
the gametophyte)
grows, develops.
zygote rhizome sorusDiploid Stage
fertilizationHaploid Stage
meiosis Spores are
released.egg-
producing
archegoniumegg
Spores develop.
mature
gametophyte
(underside)sperm-
producing
antheridium
A spore
germinates,
grows into a
gametophyte.
sperm
Animation: Fern life cycle
Fern Diversity
Fig. 23-14a, p. 377
Fig. 23-14b, p. 377
Fig. 23-14c, p. 377
Animation: Alternations of generations
Animation: Evolutionary tree for plants
Animation: Marchantia, a liverwort
Animation: Milestones in plant evolution
Animation: Seedless vascular plants