The Plant Kingdom:
Seed Plants
Chapter 28
Learning Objective 1
•
Compare the features of gymnosperms
and angiosperms
Two Groups of Seed Plants
•
Gymnosperms
•
•
•
seeds are totally exposed or borne on the
scales of cone
ovary wall does not surround the ovules
Angiosperms
•
•
flowering plants
produce seeds within a fruit (a mature ovary)
Gymnosperm and Angiosperm
Evolution
Angiosperms
Gnetophytes
Conifers
Ginkgoes
Cycads
Gymnosperms
Evolution
of flowering
plants
Evolution
of seeds
Fig. 28-2, p. 602
KEY CONCEPTS
•
Seed plants include gymnosperms and
angiosperms
Learning Objective 2
•
Trace the steps in the life cycle of a pine
•
Compare its sporophyte and gametophyte
generations
Conifers
Angiosperms
Gnetophytes
Conifers
Ginkgoes
Cycads
Gymnosperms
Fig. 28-3 (1), p. 603
Fig. 28-3 (a-c), p. 603
Pine Life Cycle 1
•
Pine tree
•
•
a mature sporophyte
Pine gametophytes
•
•
extremely small
nutritionally dependent on sporophyte
generation
Pine Life Cycle 2
•
Pine is heterosporous
•
•
produces microspores and megaspores in
separate cones
Male cones produce microspores that
develop into pollen grains (immature male
gametophytes)
•
carried by air currents to female cones
Pine Life Cycle 3
•
Female cones produce megaspores
•
One of each four megaspores (meiosis)
develops into a female gametophyte
•
within an ovule (megasporangium)
Pine Life Cycle 4
•
Pollination
•
•
Pollen tube
•
•
transfer of pollen to female cones
grows through megasporangium to egg within
archegonium
After fertilization
•
zygote develops into embryo encased inside
seed adapted for wind dispersal
Pine Life Cycle
Male
cone
Meiosis
Each scale bears two microsporangia
Microsporangium
2
Microspores, each of which
develops into a pollen grain
Scale from a
Pollen grains are
3
male cone
transferred to the
4
female cone by wind 3
Scale from a
Female
female cone
gametophyte
Megasporangium
Each scale bears
two ovules
Megaspore
(megasporangia)
Growing pollen
Ovule
tube
HAPLOID (n) GAMETOPHYTE GENERATION
Immature
female
cone
DIPLOID (2n) SPOROPHYTE GENERATION
Zygote
Second sperm
Papery
nucleus
wings
Pollen tube
Seed
coat
Male cones
(pollen cones)
1
6
Embryo
Pine (mature sporophyte)
Newly
germinated
seedling
Fertilization
5
Sperm
nucleus
united
with egg
nucleus
Mature female
cone (seed cone)
Two seeds on the
Female
upper surface of the
gametophyte
scale
(nutritive tissue)
Fig. 28-4, p. 604
Insert “Pine life cycle”
pine_life_cycle.swf
Learning Objective 3
•
What features distinguish gymnosperms
from bryophytes and ferns?
Gymnosperms
•
Are vascular plants
•
•
Produce seeds
•
•
unlike bryophytes
unlike bryophytes and ferns
Produce wind-borne pollen grains
•
unlike ferns and other seedless vascular
plants
KEY CONCEPTS
•
Gymnosperms produce exposed seeds,
usually in cones borne on the sporophytes
Learning Objective 4
•
What are the four phyla of gymnosperms?
Conifers (Phylum Coniferophyta)
•
Largest phylum of gymnosperms
•
Woody plants that bear needles (leaves
that are usually evergreen)
•
•
produce seeds in cones
Most are monoecious
•
have male and female reproductive parts in
separate cones on same plant
Male and Female Cones
KEY CONCEPTS
•
Conifers are the most diverse and
numerous of the four living gymnosperm
phyla
Cycads (Phylum Cycadophyta)
•
Palmlike or fernlike in appearance
•
Are dioecious
•
•
have male and female reproductive structures
on separate plants
but reproduce with pollen and seeds in
conelike structures
Cycads
Angiosperms
Gnetophytes
Conifers
Ginkgoes
Cycads
Gymnosperms
Fig. 28-6 (1), p. 605
Female strobilus
(seed cone)
Fig. 28-6a, p. 605
Fig. 28-6b, p. 605
Phylum Ginkgophyta
•
Ginkgo biloba
•
•
•
only surviving species in phylum
deciduous, dioecious tree
Female ginkgo produces fleshy seeds
directly on branches
Ginkgo
Angiosperms
Gnetophytes
Conifers
Ginkgoes
Cycads
Gymnosperms
Fig. 28-7 (1), p. 606
Fig. 28-7a, p. 606
Fig. 28-7b, p. 606
Gnetophytes (Phylum Gnetophyta)
•
Share some traits with angiosperms
Angiosperms
Gnetophytes
Conifers
Ginkgoes
Cycads
Gymnosperms
Fig. 28-8 (1), p. 607
Gnetophytes
Learning Objective 5
•
What features distinguish flowering plants
from other plants?
Flowering Plants
•
Angiosperms (phylum Anthophyta)
•
Vascular plants that produce flowers and
seeds enclosed within a fruit
•
Most diverse and successful plant group
Flowering Plants
Flowering Plants
•
Flower
•
•
•
Ovules enclosed within ovary
•
•
sepals, petals, stamens, carpels
functions in sexual reproduction
unlike gymnosperms
After fertilization
•
•
ovules become seeds
ovary develops into fruit
Floral
Structure
Fig. 28-10a, p. 609
Female floral parts
Male floral parts
Pollen grain
(each will
produce two
sperm cells)
PISTIL
(consisting
of one or
more
carpels)
Stigma
Style
Anther
Ovary
Ovules (each
producing one
egg cell)
STAMEN
Filament
Petal
Receptacle
Sepal
Peduncle
Fig. 28-10b, p. 609
Parts of a Flower
Petals
Sepals
Fig. 28-11a, p. 610
Stamen
Pistil
Fig. 28-11b, p. 610
Simple and
Compound
Pistils
Stigma
Ovules
Style
Ovary
Ovary wall
Fig. 28-12a, p. 611
One carpel
Ovules
Stigma
Style
Ovary wall
Ovary
Fig. 28-12b, p. 611
One carpel
Ovules
Stigma
Style
Ovary wall
Ovary
Stepped Art
Fig. 28-12b, p. 611
KEY CONCEPTS
•
Angiosperms produce ovules enclosed
within carpels; following fertilization, seeds
develop from the ovules, and the ovaries
of carpels become fruits
Learning Objective 6
•
Explain the life cycle of a flowering plant
•
Describe double fertilization
Flowering Plant Life Cycle 1
•
Sporophyte generation dominant
•
Gametophytes extremely reduced in size
•
•
nutritionally dependent on sporophyte
generation
Heterosporous
•
produce microspores, megaspores in flower
Flowering Plant Life Cycle 2
•
Microspore develops into a pollen grain
(immature male gametophyte)
•
One of each four megaspores (meiosis)
develops into embryo sac (female
gametophyte)
Flowering Plant Life Cycle 3
•
Embryo sac contains seven cells with
eight nuclei
•
Egg cell and central cell with two polar
nuclei participate in fertilization
Flowering Plant Life Cycle
Developing pollen tube of mature
male gametophyte
6
Pollination
Each microspore
develops into a pollen
grain
5
Microspore
Tetrad of
microspores
Embryo sac (mature
female gametophyte)
Pollen grain
(immature
male
gametophyte)
Pollen
tube
3
Polar
nuclei
Megaspore
Meiosis
4
2
Two sperm
cells
HAPLOID (n)
Egg
GAMETOPHYTE
nucleus
GENERATION
Double fertilization
DIPLOID (2n)
7
Ovary
SPOROPHYTE
Endosperm (3n)
GENERATION
Megasporocyte
Zygote (2n)
Megasporangium
(ovule)
Fruit
8
Embryo
Seed coat
Microsporocytes
within
Anther
microsporangia
Seed
Seedling
1
Flower of mature
sporophyte
Fig. 28-13, p. 612
Double Fertilization
•
Characteristic of flowering plants
•
Results in formation of
•
•
diploid zygote
triploid endosperm
Insert “Monocot life
cycle”
angiosperm_cycle.swf
Explore plant life cycles by
clicking on the figures in
ThomsonNOW.
Learning Objective 7
•
Contrast eudicots and monocots, the two
largest classes of flowering plants
Monocots (Class Monocotyledones)
•
Most have floral parts in threes
•
Seeds each contain 1 cotyledon
•
Endosperm
•
nutritive tissue in mature seeds
Eudicots (Class Eudicotyledones)
•
Usually have floral parts in fours or fives
•
or multiples thereof
•
Seeds each contain 2 cotyledons
•
Cotyledons
•
•
nutritive organs in mature seeds
absorbed nutrients in endosperm
Monocot and Eudicot
Learning Objective 8
•
What are the evolutionary adaptations of
flowering plants?
Reproduction
•
Flowering plants reproduce sexually by
forming flowers
•
After double fertilization, seeds form within
fruits
•
Wind, water, insects, animals transfer
pollen grains
Structures
•
Efficient water-conducting vessel elements
in xylem
•
Efficient carbohydrate-conducting sieve
tube elements in phloem
KEY CONCEPTS
•
Angiosperms, which compose a single
phylum, dominate the land and exhibit
great diversity in both vegetative and
reproductive structures
Insert “Flower parts”
flower_parts.swf
Learn more about flower
structure by clicking on the
figure in ThomsonNOW.
Learning Objective 9
•
Summarize the evolution of gymnosperms
from seedless vascular plants
•
Trace the evolution of flowering plants
from gymnosperms
Evolution 1
•
•
Seed plants arose from seedless vascular
plants
Progymnosperms
•
•
•
seedless vascular plants
had megaphylls and “modern” woody tissue
probably gave rise to conifers and seed ferns
•
Progymnosperm
•
Seed Fern
Evolution 2
•
Seed ferns
•
•
probably gave rise to cycads and ginkgo
Evolution of gnetophytes, particularly their
relationship to flowering plants, is unclear
Evolution 3
•
Flowering plants probably descended from
gymnosperms with specialized features
•
•
•
leaves with broad, expanded blades
closed carpels
Flowering plants likely arose only once
Fossil Angiosperms
Carpel
Ovule
5 mm
Fig. 28-17, p. 615
Pistils
Scars on
reproductive axis
7 mm
Fig. 28-18, p. 615
Evolution of Flowering Plants
Eudicots
Monocots
Magnoliids
Core Angiosperms
Star anise
Water lilies
Amborella
Basal Angiosperms
Evolution of
vessel elements
Evolution of
flowering plants
Fig. 28-19a, p. 616
Fig. 28-19b, p. 616
Fig. 28-19c, p. 616
Fig. 28-19d, p. 616
Fig. 28-19e, p. 616
KEY CONCEPTS
•
Gymnosperms and angiosperms evolved
from ancestral seedless vascular plants