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The Land Plants
Chapter 23 Part 2
23.5 Ancient Carbon Treasures
 In the Carboniferous, plants with ligninreinforced tissues flourished, died, and became
compacted into coal, a nonrenewable fossil fuel
• Lepidodendron, a Carboniferous lycophyte
Energy from the Carboniferous Forest
stem of a giant lycophyte
(Lepidodendron), which
grew 40 meters (131 feet)
tall
Medullosa , one of
the early seed plants
stem of a giant horsetail
(Calamites), which was
almost 20 meters (66
feet) tall
Fig. 23-16a, p. 378
Fig. 23-16b, p. 378
23.4-23.5 Key Concepts
Seedless Vascular Plants
 Lycophytes, whisk ferns, horsetails, and ferns
have vascular tissues but do not produce seeds
 A large spore-producing body that has internal
vascular tissues dominates the life cycle
 As with bryophytes, sperm swim through water
to reach eggs
23.6 Seed-Bearing Plants
 Seeds and pollen allowed gymnosperms and
angiosperms (flowering plants) to survive and
thrive in drier habitats
Modified Spores
 Microspores become sperm-producing male
gametophytes (pollen grains)
 Megaspores develop into egg-producing female
gametophytes inside ovules
Pollen
 Seed plants release
pollen grains which
allow fertilization to
occur even in the
absence of
environmental water
pine
pollen grains
p. 379
Seeds
 A seed is a mature ovule
• Includes nutritive tissue and a tough seed coat
that protects the embryo sporophyte inside the
seed from harsh conditions
Human Use of Seed Plants
 Humans depend heavily on cultivated seed
plants and have contributed to the widespread
dispersal of seed plants that they favor
•
•
•
•
Food crops
Lumber and wood product
Drugs and medicines
Fabrics and dyes
Edible Flowering Plants
Fig. 23-17a, p. 379
Fig. 23-17b, p. 379
Fig. 23-17c, p. 379
Fig. 23-17d, p. 379
23.7 Gymnosperms—
Plants With Naked Seeds
 Gymnosperms
• Vascular seed plants with “naked” seeds
• One of the two modern lineages of seed plants
 Gymnosperms include conifers (such as pines),
cycads, ginkgos, and gnetophytes
Some Gymnosperms
Fig. 23-18a, p. 380
Fig. 23-18b, p. 380
Fig. 23-18c, p. 380
Fig. 23-18d, p. 380
Fig. 23-18e, p. 380
Fig. 23-18f, p. 380
Fig. 23-18g, p. 380
Fig. 23-18h, p. 380
Gymnosperm Life Cycle
 Gymnosperms release pollen and seeds
 Ovules form in in strobili or, in the case of
conifers, in woody cones
Conifer Life Cycle: Ponderosa Pine
A A female cone has many
scales, each with two
ovules, on its upper section through one
surface.
ovule (the red “cut”
in the diagram
to the left)
I Seed is released,
seed coat
germinates, and the
embryo grows and
embryo
develops into a new
nutritive
sporophyte.
H Ovule develops tissue
into a mature seed.
surface view of
female cone scale ovule
B A male cone has section
many scales, each through
pollenhousing a pollen
producing
sac.
sac ( red
cut)
surface view
of male cone
scale
G One sperm
nucleus fertilizes
the egg, forming a
zygote.
fertilization
spermproducing
cell
pollen tube
F Pollen grain matures into
male gametophyte. Two
nonflagellated sperm nuclei
form as pollen tube grows
through ovule tissue.
(view inside
ovule)
eggs
Diploid Stage
Haploid Stage
meiosis
E Pollination: wind
deposits pollen grain
on seed
cone.
female
gametophyte
C Megaspores
form by
meiosis; one
develops into
the female
gametophyte.
D Microspores form
by meiosis, develop
into pollen grains.
Fig. 23-19, p. 381
Animation: Pine life cycle
23.8 Angiosperms—
The Flowering Plants
 Angiosperms are the most diverse plant lineage
and the only plants that make flowers and fruits
 In the Mesozoic, angiosperms began adaptive
radiation to all land and many aquatic habitats
Adaptive Radiation of Angiosperms
Keys to Angiosperm Success
 Short life cycles and rapid growth
 Specialized reproductive structures (flowers)
 Specialized pollination and dispersal structures
• Wind and animal pollinators
• Fruits that float or stick
• Seeds that survive animal digestive tracts
Specialized Angiosperm Structures
 A flower is a specialized reproductive shoot
 Seeds develop inside the ovaries (chambers
that enclose ovules) of flowers
 After fertilization, an ovary becomes a fruit
Flower Structures
petal
stamen
(microspores
form here)
sepal
carpel
(megaspores
form here)
ovule
in an
ovary
Fig. 23-21, p. 382
Pollination and Coevolution
 Pollinators
• Animals (such as insects that feed on pollen)
move pollen grains from male parts of one flower
to female parts of another
 Coevolution
• Over time, plants and their animal pollinators
jointly evolved; changes in one exerts selection
pressure on the other
Flowering Plant Diversity
Fig. 23-22a, p. 383
Fig. 23-22b, p. 383
Fig. 23-22c, p. 383
Fig. 23-22d, p. 383
Fig. 23-22e, p. 383
Fig. 23-22f, p. 383
Fig. 23-22g, p. 383
Amborella
water
lilies
star
anise
magnoliids
monocots
eudicots
basal groups
Fig. 23-22g, p. 383
23.9 Focus on
a Flowering Plant Life Cycle
 Flowering plants form eggs in ovaries and pollen
in stamens
 Flowering plants make fruits containing seeds
which supply their embryo sporophytes with
endosperm, a nutritive tissue
Life Cycle: Lilium
A
a flowering
stem of the
mature
sporophyte
seedling
(2n)
seed coat
pollen sac, where
embryo (2n)
each one of many
endosperm
cells will give rise
(nutritive tissue)
to microspores
seed
Diploid Stage
meiosis
E double fertilization
Haploid Stage B
D Pollination and
Microspores
pollen tube formation:
form, then
male
develop
gametophyte
into pollen
pollen tube
grains.
sperm (n)
sperm (n)
Pollen is
released.
The pollen tube
enters an ovule.
One sperm will
fertilize the egg,
one will fertilize
the endospermproducing cell.
(line of cut
of diagram
at left)
ovary
ovules
inside
ovary
cell in ovule
that will give
rise to a
megaspore
C meiosis
cell from which
endosperm
will form
egg
Four megaspores
form. Three
disintegrate. One
undergoes three
rounds of mitosis
without any
cytoplasmic
division. Nuclei
migrate and cell
walls form. The
resulting female
gametophyte
includes the egg
and a cell with two
nuclei that will
form endosperm.
female gametophyte
Fig. 23-23, p. 384
seedling
seed coat
embryo (2n)
endosperm
(nutritive tissue)
A
a flowering
stem of the
mature
sporophyte
(2n)
pollen sac, where
each one of many
cells will give rise
to microspores
ovules
inside
ovary
cell in ovule
that will give
rise to a
megaspore
seed
Diploid Stage
meiosis
E double fertilization
Haploid Stage B
Microspores
D Pollination and pollen
form, then
tube formation:
male
develop
gametophyte
into pollen
grains.
pollen tube
sperm (n)
sperm (n)
Pollen is
released.
The pollen tube
enters an ovule.
One sperm will
fertilize the egg,
one will fertilize
the endospermproducing cell.
C meiosis
cell from which
endosperm
will form
egg
(line of cut
of diagram
at left)
ovary
female gametophyte
Four megaspores
form. Three
disintegrate. One
undergoes three
rounds of mitosis
without any
cytoplasmic
division. Nuclei
migrate and cell
walls form. The
resulting female
gametophyte
includes the egg
and a cell with two
nuclei that will
form endosperm.
Stepped Art
Fig. 23-23, p. 384
Animation: Monocot life cycle
23.10 The World’s Most Nutritious Plant
 Botanists use knowledge of plant biology and
genetics to find new ways to feed a hungry world
 Example: Alejandro Bonifacio studies quinoa, a
nutritious native South American grain
Alejandro Bonifacio and
Genetically Modified Quinoa
23.6-23.10 Key Concepts
Seed-Bearing Vascular Plants
 Gymnosperms and, later, angiosperms radiated
into higher and drier environments
 Both produce pollen and seeds
 Nearly all crop plants are seed plants
 In angiosperms, flowers and fruits further
enhanced reproductive success
Summary: Plant Evolutionary Trends
Bryophytes
Seedless vascular plants
• Nonvascular
• Vascular tissue present
• Vascular tissue present
• Vascular tissue present
• Haploid dominance
• Diploid dominance
• Diploid dominance
• Diploid dominance
• Water required for
fertilization
• Seedless
• Water required for
fertilization
• Seedless
whisk
ferns,
club mosses, horsetails,
spike mosses ferns
• Pollen grains; water not
required for fertilization
• “Naked” seeds
• Seeds form inside an
ovary that develops
into a fruit
liverworts
mosses
hornworts
Gymnosperms
gnetophytes, ginkgos,
conifers, cycads
Angiosperms
monocots, dicots,
magnoliids, basal
groups
ancestral alga
Fig. 23-25, p. 386
Animation: Flower parts
Animation: Pinus cones
Video: Beginnings and endings