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Plant Diversity II: The Evolution of Seed Plants
Adapted for Union City High School by Greg Campbell From Campbell, N. and Reece, J. (2008). Biology 8th Ed. San Francisco, Ca. Pearson Benjamin
Cummings.
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Seeds changed the course of plant
evolution, enabling their bearers to
become the dominant producers in most
____________ecosystems
A ______consists of an embryo and
nutrients surrounded by a protective coat
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In addition to seeds, the following are
common to all seed plants
1.
2.
3.
4.
____________________
____________________
____________________
____________________
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The ____________of seed plants develop
within the walls of spores that are retained
within tissues of the parent ____________
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Fig. 30-2
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte Dominant
Sporophyte
Ferns and other seedless
vascular plants
Seed plants (gymnosperms and angiosperms)
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on surrounding
sporophyte tissue for nutrition
Reduced, dependent on
Dominant
gametophyte for nutrition
Dominant
Gymnosperm
Sporophyte
(2n)
Microscopic female
gametophytes (n) inside
ovulate cone
Sporophyte
(2n)
Gametophyte
(n)
Angiosperm
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Example
Microscopic male
gametophytes (n)
inside pollen
cone
Sporophyte (2n)
Gametophyte
(n)
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte (2n)
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The ancestors of seed plants were likely
_____________, while seed plants are
heterosporous
_________________produce megaspores that
give rise to _________ gametophytes
_________________produce microspores
that give rise to _______ gametophytes
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An _________ consists of a
megasporangium, megaspore, and one or
more protective _______________
________________ megaspores have one
integument
_______________ megaspores usually have
two integuments
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Fig. 30-3-1
Integument
Spore wall
Immature
female cone
Megasporangium
(2n)
Megaspore (n)
(a) Unfertilized ovule
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Microspores develop into pollen grains,
which contain the _________ gametophytes
_____________ is the transfer of pollen to
the part of a seed plant containing the
ovules
Pollen eliminates the need for ___________
and can be dispersed great distances by
air or ___________
If a pollen grain germinates, it gives rise to
a pollen ______ that discharges two _____
into the female gametophyte within the
ovule
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Fig. 30-3-2
Female
gametophyte (n)
Spore wall
Egg nucleus (n)
Male gametophyte
(within a germinated
pollen grain) (n)
Micropyle
(b) Fertilized ovule
Discharged
sperm nucleus (n)
Pollen grain (n)
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A seed develops from the whole ovule
A seed is a ___________ embryo, along with
its food supply, packaged in a protective
coat
Seeds provide some evolutionary
advantages over spores:
1. ____________________________________
2. ____________________________________
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Fig. 30-3-4
Integument
Female
gametophyte (n)
Seed coat
(derived from
integument)
Spore wall
Egg nucleus (n)
Immature
female cone
Megasporangium
(2n)
Megaspore (n)
(a) Unfertilized ovule
Male gametophyte
(within a germinated
pollen grain) (n)
Micropyle
(b) Fertilized ovule
Food supply
(female
gametophyte
tissue) (n)
Discharged
sperm nucleus (n)
Pollen grain (n)
Embryo (2n)
(new sporophyte)
(c) Gymnosperm seed
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The gymnosperms have “naked” seeds not
enclosed by ovaries and consist of four
phyla:
◦ Cycadophyta (cycads)
◦ Gingkophyta (one living species: Ginkgo biloba)
◦ Gnetophyta (three genera: Gnetum, Ephedra,
Welwitschia)
◦ Coniferophyta (conifers, such as pine, fir, and
redwood)
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Living seed plants can be divided into two
clades: gymnosperms and angiosperms
Gymnosperms appear early in the fossil
record and dominated the Mesozoic
terrestrial ecosystems
Gymnosperms were better suited than
nonvascular plants to drier conditions
Today, cone-bearing gymnosperms called
conifers dominate in the northern latitudes
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Individuals have large cones and palmlike leaves
These thrived during the Mesozoic, but relatively
few species exist today
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This phylum consists of a single living species,
Ginkgo biloba
It has a high tolerance to air pollution and is a
popular ornamental tree
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This phylum comprises three genera
Species vary in appearance, and some are tropical
whereas others live in deserts
This phylum is by far the largest of the
gymnosperm phyla
Most conifers are evergreens and can carry out
photosynthesis year round
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Three key features of the gymnosperm life
cycle are:
◦ Dominance of the ____________ generation
◦ Development of _______ from fertilized ovules
◦ The transfer of sperm to ovules by _________
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The life cycle of a pine provides an
example
Animation: Pine Life Cycle
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The pine tree is the __________ and
produces sporangia in male and female
cones
Small cones produce microspores called
pollen grains, each of which contains a
male _____________
The familiar larger cones contain ______,
which produce megaspores that develop
into female ______________
It takes nearly three years from cone
production to mature seed
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 30-6-4
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Megasporocyte (2n)
Integument
Microsporocytes
(2n)
Megasporangium
Pollen (2n)
Pollen grain
grains (n) MEIOSIS
MEIOSIS
Mature
sporophyte
(2n)
Microsporangia
Microsporangium (2n)
Seedling
Archegonium
Female
gametophyte
Seeds
Food
reserves
(n)
Seed coat
(2n)
Embryo
(2n)
Sperm
nucleus (n)
Pollen
tube
FERTILIZATION
Egg nucleus (n)
Surviving
megaspore (n)
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____________ are seed plants with
reproductive structures called flowers and
fruits
They are the most widespread and diverse
of all plants
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All angiosperms are classified in a single
phylum, ____________.
The name comes from the Greek anthos,
flower
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The _________ is an angiosperm structure
specialized for sexual reproduction
Many species are pollinated by insects or
animals, while some species are windpollinated
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A flower is a specialized shoot with up to
four types of modified leaves:
◦ ______ , which enclose the flower
◦ ______ , which are brightly colored and attract
pollinators
◦ ________ , which produce pollen on their terminal
anthers
◦ ________ , which produce ovules
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 30-7
Stigma
Stamen
Anther
Carpel
Style
Filament
Ovary
Petal
Sepal
Ovule
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A carpel consists of an ______ at the base
and a style leading up to a _______, where
pollen is received
Video: Flower Blooming (time lapse)
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A fruit typically consists of a mature ovary
but can also include other flower parts
Fruits protect seeds and aid in their
dispersal
Mature fruits can be either fleshy or dry
Animation: Fruit Development
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Various fruit adaptations help disperse
seeds
Seeds can be carried by wind, water, or
animals to new locations
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The flower of the sporophyte is composed
of both male and female structures
Male gametophytes are contained within
pollen grains produced by the
_____________ of anthers
The female gametophyte, or embryo sac,
develops within an ovule contained within
an ________ at the base of a stigma
Most flowers have mechanisms to ensure
cross-pollination between flowers from
different plants of the same species
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A pollen grain that has landed on a stigma
germinates and the ______________ of the
male gametophyte grows down to the
ovary
The ovule is entered by a pore called the
___________
______________________ occurs when the
pollen tube discharges two sperm into the
female gametophyte within an ovule
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One sperm fertilizes the egg, while the
other combines with two nuclei in the
central cell of the female gametophyte and
initiates development of food-storing
_____________
The endosperm nourishes the developing
_________
Within a seed, the embryo consists of a
root and two seed leaves called
_______________
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 30-10-4
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Microsporangium
Microsporocytes (2n)
Anther
MEIOSIS
Ovule (2n) Microspore
(n)
Ovary
Germinating
seed
MEIOSIS
Megasporangium
(2n)
Embryo (2n)
Endosperm (3n)
Seed
Seed coat (2n)
Nucleus of
developing
endosperm
(3n)
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
Stigma
Pollen
tube
Megaspore
(n)
Antipodal cells
Female gametophyte Central cell
(embryo sac)
Synergids
Egg (n)
Generative cell
Tube cell
Sperm
Style
Pollen
tube
Sperm
(n)
FERTILIZATION
Zygote (2n)
Egg
nucleus (n)
Discharged sperm nuclei (n)
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Clarifying the origin and diversification of
angiosperms poses fascinating challenges
to evolutionary biologists
Angiosperms originated at least 140
million years ago
During the late Mesozoic, the major
branches of the clade diverged from their
common ancestor
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The ancestors of angiosperms and
gymnosperms diverged about 305 million
years ago
Angiosperms may be closely related to
Bennettitales, extinct seed plants with
flowerlike structures
Amborella and water lilies are likely
descended from two of the most ancient
angiosperm lineages
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Fig. 30-12
Living
gymnosperms
Microsporangia
(contain
microspores)
Bennettitales
Amborella
Water lilies
Most recent common ancestor
of all living angiosperms
Star anise and
relatives
Monocots
Magnoliids
Eudicots
Ovules
(a) A possible ancestor of the
angiosperms?
300
250
200
150
100
Millions of years ago
(b) Angiosperm phylogeny
50
0
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The two main groups of angiosperms are
____________(one cotyledon) and _________
(“true” dicots)
The clade eudicot includes some groups
formerly assigned to the paraphyletic dicot
(two cotyledons) group
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More than one-quarter of angiosperm
species are monocots
More than two-thirds of angiosperm
species are eudicots
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Fig. 30-13o
Monocot
Characteristics
Eudicot
Characteristics
Monocot
Characteristics
Roots
Embryos
Taproot (main root)
usually present
Root system
usually fibrous
(no main root)
Eudicot
Characteristics
Two cotyledons
One cotyledon
Leaf
venation
Pollen
Pollen grain with
one opening
Pollen grain with
three openings
Veins usually
parallel
Flowers
Floral organs
usually in
multiples of three
Veins usually
netlike
Stems
Floral organs usually
in multiples of
four or five
Vascular tissue
scattered
Vascular tissue
usually arranged
in ring
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Pollination of flowers and transport of
seeds by animals are two important
relationships in terrestrial ecosystems
Clades with bilaterally symmetrical flowers
have more species than those with radially
symmetrical flowers
This is likely because bilateral symmetry
affects the movement of pollinators and
reduces gene flow in diverging
populations
Video: Bee Pollinating
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Video: Bat Pollinating Agave Plant
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No group of plants is more important to
human survival than seed plants
Plants are key sources of food, fuel, wood
products, and medicine
Our reliance on seed plants makes
preservation of plant diversity critical
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Most of our food comes from angiosperms
Six crops (wheat, rice, maize, potatoes,
cassava, and sweet potatoes) yield 80% of
the calories consumed by humans
Modern crops are products of relatively
recent genetic change resulting from
artificial selection
Many seed plants provide wood
Secondary compounds of seed plants are
used in medicines
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Table 30-1a
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Destruction of habitat is causing
extinction of many plant species
Loss of plant habitat is often accompanied
by loss of the animal species that plants
support
At the current rate of habitat loss, 50% of
Earth’s species will become extinct within
the next 100–200 years
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