The Plant Kingdom:
Seedless Plants
Chapter 27
Learning Objective 1
•
What are some environmental challenges
of living on land?
•
How do some plant adaptations meet
these challenges?
Colonization of Land by Plants
•
Required anatomical, physiological, and
reproductive adaptations
•
Waxy cuticle
•
•
protects against water loss
Stomata
•
for gas exchange needed for photosynthesis
Alternation of Generations 1
•
2 parts of plant life cycle
•
•
•
haploid gametophyte generation
diploid sporophyte generation
Gametophyte plant
•
•
produces gametes by mitosis
gametes fuse (fertilization) to form zygote
(first stage of sporophyte generation)
Basic Plant Life Cycle
Gametophyte
Spore
Sperm
Egg
HAPLOID (n)
GAMETOPHYTE
GENERATION
Meiosis
Fertilization
DIPLOID (2n)
SPOROPHYTE
GENERATION
Zygote
Embryo
Sporophyte
Fig. 27-2, p. 582
Gametophyte
Spore
Sperm
Egg
HAPLOID (n)
GAMETOPHYTE
GENERATION
Meiosis
Fertilization
DIPLOID (2n)
SPOROPHYTE
GENERATION
Zygote
Embryo
Sporophyte
Stepped Art
Fig. 27-2, p. 582
Alternation of Generations 2
•
Zygote develops into multicellular embryo
•
•
protected and nourished by gametophyte
Mature sporophyte plant
•
•
develops from the embryo
produces sporogenous cells (spore mother
cells)
Alternation of Generations 3
•
Sporogenous cells undergo meiosis to
form spores
•
first stage in gametophyte generation
KEY CONCEPTS
•
Plants undergo an alternation of
generations between multicellular
gametophyte and sporophyte generations
Gametangia 1
•
Most plants have multicellular gametangia
•
with protective jacket of sterile cells
surrounding gametes
Gametangia 2
•
Antheridia
•
•
gametangia that produce sperm cells
Archegonia
•
gametangia that produce eggs
Gametangia
Developing
sperm cells
Sterile cells
Antheridium
Fig. 27-3a, p. 583
Egg
Archegonium
Sterile
cells
Fig. 27-3b, p. 583
Vascular Transport System
•
In ferns and other vascular plants
•
•
xylem conducts water and dissolved minerals
phloem conducts dissolved sugar
KEY CONCEPTS
•
Adaptations to life on land that have
evolved in plants include a waxy cuticle to
prevent water loss; multicellular
gametangia; stomata; and for most plants,
vascular tissues containing lignin
Learning Objective 2
•
From which green algal group are plants
hypothesized to have descended?
•
Describe supporting evidence
Charophytes
•
Plants probably arose from charophytes
•
•
a group of green algae
Based on molecular comparisons of DNA
and RNA sequences
•
close match between charophytes and plants
Plant Evolution
Angiosperms
Gymnosperms
Ferns
Mosses
Liverworts
Hornworts
Club mosses
VASCULAR SEEDLESSVASCULAR SEED
PLANTS
PLANTS
NONVASCULAR
BRYOPHYTES
Evolution
of seeds
Evolution of dominant
sporophyte, vascular
tissue
Green
algal
ancestor
Evolution of cuticle,
multicellular gametangia,
multicellular embryos
Fig. 27-4, p. 584
KEY CONCEPTS
•
Biologists infer that plants evolved from
aquatic green algal ancestors known as a
charophytes
Insert “Evolutionary tree
for plants”
plant_tree_v2.swf
Explore plant evolution by
clicking on the figure in
ThomsonNOW.
Learning Objective 3
•
What features distinguish bryophytes from
other plants?
Bryophytes
•
Nonvascular (lack xylem and phloem)
•
•
Dominant gametophyte generation
•
•
unlike other land plants
unlike other plants
Sporophytes remain permanently attached
•
nutritionally dependent on gametophytes
Learning Objective 4
•
What are the three phyla of bryophytes?
Mosses (Phylum Bryophyta)
•
Gametophytes are green plants that grow
from a filamentous protonema
Liverworts (Phylum Hepatophyta)
•
Many gametophytes are flattened, lobelike
thalli (others are leafy)
Hornworts (Phylum Anthocerophyta)
•
Have thalloid gametophytes
Fig. 27-5, p. 585
Green
algal
ancestor
Fig. 27-5 (1), p. 585
Vascular
seed plants
Vascular
seedless plants
Nonvascular
bryophytes
KEY CONCEPTS
•
Mosses and other bryophytes lack
vascular tissues and do not form true
roots, stems, or leaves
Learning Objective 5
•
Describe the life cycle of mosses
•
Compare their gametophyte and
sporophyte generations
Mosses 1
•
Green moss gametophyte
•
•
bears archegonia / antheridia at top of plant
Fertilization
•
sperm cell fuses with egg cell in archegonium
(zygote)
Mosses 2
•
Zygote
•
•
grows into embryo
develops into moss sporophyte attached to
gametophyte
Mosses 3
•
Meiosis
•
•
•
occurs within capsule of sporophyte
produces spores
When spore germinates
•
•
grows into a protonema
forms buds that develop into gametophytes
Moss Life Cycle
Gametophyte plants
Buds on
protonema
Antheridia at the tip of the
gametophyte shoot
Antheridia
with sperm
cells
1
Spore
germinates
Spores
released
6
Protonema
HAPLOID (n)
GAMETOPHYTE
GENERATION
Sperm cell
2
Archegonium
with egg
Fertilization
Meiosis
DIPLOID (2n)
SPOROPHYTE
GENERATION
5
Calyptra
Sporogenous
cells that
undergo
meiosis
Capsule
Zygote
4
Sporophyte
3
Embryo
Gametophyte
plant
Fig. 27-6, p. 586
Moss
Sporophytes
Capsule
Seta
Foot
Fig. 27-7, p. 587
Liverwort Life Cycle
Antheridiophore
Archegoniophore
Male
thallus
Female
thallus
Germination of spores
and development of
young gametophyte
5
1
Antheridia
with sperm
cells
Gemmae
cup
Spores
released
Sperm
cell
Male and female
gametophyte plants
HAPLOID (n)
GAMETOPHYTE
GENERATION
Meiosis
Archegonia
with eggs
2
Fertilization
DIPLOID (2n)
SPOROPHYTE
GENERATION
4
Foot
Seta
Zygote
Tissue derived
from archegonium
Capsule
Sporogenous
cells that
undergo meiosis
Embryo
3
Sporophyte
Fig. 27-8, p. 588
Insert “Moss life cycle”
moss_life_cycle_v2.swf
Insert “Marchantia, a
liverwort”
liverwort.swf
Watch the life cycles of the
mosses and liverworts by
clicking on the figures in
ThomsonNOW.
Learning Objective 6
•
What features distinguish seedless
vascular plants from algae and
bryophytes?
Seedless Vascular Plants
•
Have adaptations that algae and
bryophytes lack
•
•
•
vascular tissues
dominant sporophyte generation
Reproduction depends on water
•
as transport medium for motile sperm cells
(as in bryophytes)
Learning Objective 7
•
What are the two phyla of seedless
vascular plants?
Club Mosses
(Phylum Lycopodiophyta)
•
Sporophytes consist of roots, rhizomes,
erect branches, and microphylls (leaves)
Stem
Microphyll
Vascular
tissue
Enation
Vein
Smooth
stem
Enation
Vascular
supply to
enation
Microphyll
(one vein)
Fig. 27-10a, p. 590
Club
Mosses
Green
algal
ancestor
Fig. 27-11 (1), p. 591
Vascular
seed plants
Vascular
seedless plants
Nonvascular
bryophytes
Strobilus
Leaves
(microphylls)
Fig. 27-11 (a-b), p. 591
Ferns (Phylum Pteridophyta)
•
Largest and most diverse group of
seedless vascular plants
•
Fern sporophyte consists of a rhizome that
bears fronds and true roots
•
Includes whisk ferns and horsetails
Ferns
Green
algal
ancestor
Fig. 27-12 (1), p. 592
Vascular
seed plants
Vascular
seedless plants
Nonvascular
bryophytes
Fig. 27-12a, p. 592
Fig. 27-12b, p. 592
Fig. 27-12c, p. 592
Fern Life Cycle
Underside of enlarged mature
gametophyte (prothallus)
Germination of spores
and development of
young gametophyte
Egg
5
4
Spores
released
Rhizoids
3
Antheridium
Sporangium
Meiosis
Sorus
2
(cluster of
sporangia)
Archegonium
HAPLOID (n)
GAMETOPHYTE
GENERATION
Sperm cell
Fertilization
Cells within DIPLOID (2n)
SPOROPHYTE
sporangia
GENERATION
undergo
meiosis
Frond 1
Zygote
6
Leaf of young
sporophyte
Leaf cross section
Fiddlehead
Roots
Underside of
a frond
Rhizome
Fern (mature
sporophyte)
Development of
the sporophyte
Haploid
prothallus
Root of young
sporophyte
Fig. 27-13, p. 593
Whisk Ferns
•
Sporophytes have dichotomously
branching rhizomes and erect stems
•
lack true roots and leaves
Green
algal
ancestor
Fig. 27-14a, p. 594
Vascular
seed plants
Vascular
seedless plants
Nonvascular
bryophytes
Sporangia
Aerial stem
with scalelike
outgrowths
(no leaves)
Fig. 27-14b, p. 594
Horsetails
•
Sporophytes have
•
•
hollow, jointed roots, rhizomes, aerial stems
leaves reduced to megaphylls
Thicker
main
Dichotomous
stem
end branches
Equal
branches
Vascular
tissue
Dichotomously
branching
stems
Overtopping
(unequal
branching)
Thinner
side
branch
Planation
(branching in
same plane)
Webbing of
side branch
system
Megaphyll
(many veins)
Fig. 27-10b, p. 590
Horsetails
Green
algal
ancestor
Fig. 27-15a, p. 594
Vascular
seed plants
Vascular
seedless plants
Nonvascular
bryophytes
Strobilus
Vegetative
shoots
Reproductive
shoots
Fig. 27-15b, p. 594
Insert “Seedless vascular
plants”
seedless_vascular.swf
KEY CONCEPTS
•
In club mosses and ferns, lignin-hardened
vascular tissues that transport water and
dissolved substances throughout the plant
body have evolved
Learning Objective 8
•
Describe the life cycle of ferns
•
Compare sporophyte and gametophyte
generations
Fern Sporophytes
•
Roots, rhizomes, leaves are megaphylls
•
Leaves (fronds) bear sporangia in clusters
(sori)
•
Meiosis in sporangia produces haploid
spores
Fern Gametophyte
•
Fern Gametophyte (prothallus)
•
•
develops from haploid spore
bears both archegonia and antheridia
Insert “Fern life cycle”
fern_life_cycle_v2.swf
Watch the life cycle of the ferns
by clicking on the figure in
ThomsonNOW.
Learning Objective 9
•
What is the difference between the
generalized life cycles of homosporous
and heterosporous plants?
Homospory
•
Production of one kind of spore
•
•
in bryophytes, most club mosses, most ferns
including whisk ferns and horsetails
Spores give rise to gametophyte plants
•
produce both egg cells and sperm cells
Heterospory 1
•
Production of two kinds of spores
(microspores and megaspores)
•
•
in some club mosses and ferns
in all seed plants
Heterosporous Life Cycle
Gametophyte
Megaspore
Archegonium
Gametophyte
Microspore
Antheridium
HAPLOID (n)
GAMETOPHYTE
GENERATION
Meiosis
DIPLOID (2n)
SPOROPHYTE
GENERATION
Microsporocyte
Megasporocyte
Sperm
Egg
Fertilization
Zygote
Microsporangium
Embryo
Megasporangium
Sporophyte
Fig. 27-16, p. 595
Heterospory 2
•
Microspores
•
•
give rise to male gametophytes that produce
sperm cells
Megaspores
•
give rise to female gametophytes that
produce eggs
Selaginella Life Cycle
Male gametophyte develops
inside microspore wall
Single antheridium in male
gametophyte produces
many sperm cells
3
Ruptured
megaspore
wall
Microspores
5
Archegonium
containing egg
Female gametophyte
develops and protrudes
from megaspore wall
4
Megaspores
Meiosis
Sperm cell
HAPLOID (n)
GAMETOPHYTE
GENERATION
Microsporangium
DIPLOID (2n)
with microsporocytes SPOROPHYTE
GENERATION
Longitudinal
section through
archegonium Egg
Fertilization
Female
Strobilus gametophyte
First
Leaf
leaves
(microphyll)
Stem
Megasporangium
with megasporocyte
1
Stem
Longitudinal section
through strobilus
Root
Root
Mature
sporophyte
6
Zygote
Young sporophyte
(attached to female
gametophyte)
Fig. 27-17, p. 596
Evolution of Heterospory
•
Essential step in evolution of seeds
•
Rhynia
•
Aglaophyton