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PowerPoint® Lecture Presentations for
BiologyEighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Chapter 30Chapter 30
Plant Diversity II: The Evolution of Seed Plants
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Overview: Transforming the World
• Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems
• A seed consists of an embryo and nutrients surrounded by a protective coat
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Concept 30.1: Seeds and pollen grains are key adaptations for life on land
• In addition to seeds, the following are common to all seed plants
– Reduced gametophytes
– Heterospory
– Ovules
– Pollen
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Advantages of Reduced Gametophytes
• The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte
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Fig. 30-2
Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition
Reduced, independent (photosynthetic and free-living)
Gametophyte
Sporophyte (2n)
Sporophyte (2n)
Gametophyte (n)
Sporophyte
Example
Gametophyte (n)
Dominant
Dominant DominantReduced, dependent on gametophyte for nutrition
Mosses and other nonvascular plants
Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms)
PLANT GROUP
Gymnosperm AngiospermMicroscopic female gametophytes (n) inside ovulate cone
Microscopic male gametophytes (n) inside pollen cone
Sporophyte (2n) Sporophyte (2n)
Microscopic female gametophytes (n) inside these parts of flowers
Microscopic male gametophytes (n) inside these parts of flowers
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Fig. 30-2a
Gametophyte
Sporophyte (2n)
Gametophyte (n)
Sporophyte
Example
Dominant
Reduced, dependent on gametophyte for nutrition
Mosses and other nonvascular plants
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Fig. 30-2b
Reduced, independent (photosynthetic and free-living)
Sporophyte (2n)
Gametophyte (n)
Dominant
Ferns and other seedless vascular plants
Example
Gametophyte
Sporophyte
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Fig. 30-2c
Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition
Dominant
Seed plants (gymnosperms and angiosperms)
Gymnosperm AngiospermMicroscopic female gametophytes (n) inside ovulate cone
Microscopic male gametophytes (n) inside pollen cone
Sporophyte (2n) Sporophyte (2n)
Microscopic female gametophytes (n) inside these parts of flowers
Microscopic male gametophytes (n) inside these parts of flowers
Example
Gametophyte
Sporophyte
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Heterospory: The Rule Among Seed Plants
• The ancestors of seed plants were likely homosporous, while seed plants are heterosporous
• Megasporangia produce megaspores that give rise to female gametophytes
• Microsporangia produce microspores that give rise to male gametophytes
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Ovules and Production of Eggs
• An ovule consists of a megasporangium, megaspore, and one or more protective integuments
• Gymnosperm megaspores have one integument
• Angiosperm megaspores usually have two integuments
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Fig. 30-3-1
Megasporangium (2n)
Megaspore (n)
(a) Unfertilized ovule
Integument
Spore wall
Immature female cone
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Pollen and Production of Sperm
• Microspores develop into pollen grains, which contain the male gametophytes
• Pollination is the transfer of pollen to the part of a seed plant containing the ovules
• Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals
• If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule
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Fig. 30-3-2
Male gametophyte (within a germinated pollen grain) (n)
Female gametophyte (n)
(b) Fertilized ovule
Micropyle Pollen grain (n)
Spore wall
Discharged sperm nucleus (n)
Egg nucleus (n)
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The Evolutionary Advantage of Seeds
• A seed develops from the whole ovule
• A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat
• Seeds provide some evolutionary advantages over spores:
– They may remain dormant for days to years, until conditions are favorable for germination
– They may be transported long distances by wind or animals
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Fig. 30-3-3
Seed coat (derived from integument)
(c) Gymnosperm seed
Embryo (2n) (new sporophyte)
Food supply (female gametophyte tissue) (n)
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Fig. 30-3-4
Seed coat (derived from integument)
(c) Gymnosperm seed
Embryo (2n) (new sporophyte)
Food supply (female gametophyte tissue) (n)
(b) Fertilized ovule(a) Unfertilized ovule
Integument
Immature female cone
Spore wall
Megasporangium (2n)
Male gametophyte (within a germinated pollen grain) (n)
Megaspore (n) Micropyle Pollen grain (n)
Egg nucleus (n)
Discharged sperm nucleus (n)
Female gametophyte (n)
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Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones
• 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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Fig. 30-UN1
Nonvascular plants (bryophytes)Seedless vascular plantsGymnospermsAngiosperms
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Gymnosperm Evolution
• Fossil evidence reveals that by the late Devonian period some plants, called progymnosperms, had begun to acquire some adaptations that characterize seed plants
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Fig. 30-4
Archaeopteris, a progymnosperm
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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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Phylum Cycadophyta
•
Individuals have large cones and palmlike leaves
•
These thrived during the Mesozoic, but relatively few species exist today
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Fig. 30-5a
Cycas revoluta
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Phylum Ginkgophyta
•
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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Fig. 30-5b
Ginkgo biloba pollen-producing tree
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Fig. 30-5c
Ginkgo biloba leaves and fleshy seeds
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Phylum Gnetophyta
•
This phylum comprises three genera
•
Species vary in appearance, and some are tropical whereas others live in deserts
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Fig. 30-5d
Gnetum
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Fig. 30-5e
Ephedra
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Fig. 30-5f
Welwitschia
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Fig. 30-5g
Welwitschia
Ovulate cones
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Phylum Coniferophyta
•
This phylum is by far the largest of the gymnosperm phyla
•
Most conifers are evergreens and can carry out photosynthesis year round
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Fig. 30-5h
Douglas fir
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Fig. 30-5i
European larch
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Fig. 30-5j
Bristlecone pine
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Fig. 30-5k
Sequoia
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Fig. 30-5l
Wollemi pine
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Fig. 30-5m
Common juniper
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The Life Cycle of a Pine: A Closer Look
• Three key features of the gymnosperm life cycle are:
– Dominance of the sporophyte generation
– Development of seeds from fertilized ovules
– The transfer of sperm to ovules by pollen
• The life cycle of a pine provides an example
Animation: Pine Life CycleAnimation: Pine Life Cycle
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• The pine tree is the sporophyte and produces sporangia in male and female cones
• Small cones produce microspores called pollen grains, each of which contains a male gametophyte
• The familiar larger cones contain ovules, which produce megaspores that develop into female gametophytes
• It takes nearly three years from cone production to mature seed
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Fig. 30-6-1
Microsporangium (2n)
Microsporocytes (2n)
Pollen grains (n)
Pollen cone
Microsporangia
MEIOSIS
Mature sporophyte (2n)
Haploid (n)Diploid (2n)
Key
Ovulate cone
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Fig. 30-6-2
Microsporangium (2n)
Microsporocytes (2n)
Pollen grains (n)
Pollen cone
Microsporangia
MEIOSIS
Mature sporophyte (2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Surviving megaspore (n)
Pollen grain
Megasporangium (2n)
Megasporocyte (2n)
Ovule
IntegumentOvulate cone
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Fig. 30-6-3
Microsporangium (2n)
Microsporocytes (2n)
Pollen grains (n)
Pollen cone
Microsporangia
MEIOSIS
Mature sporophyte (2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Surviving megaspore (n)
Pollen grain
Megasporocyte (2n)
Ovule
IntegumentOvulate cone
FERTILIZATION
Pollen tube
Female gametophyte
Sperm nucleus (n)
Egg nucleus (n)
Archegonium
Megasporangium (2n)
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Fig. 30-6-4
Microsporangium (2n)
Microsporocytes (2n)
Pollen grains (n)
Pollen cone
Microsporangia
MEIOSIS
Mature sporophyte (2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Surviving megaspore (n)
Pollen grain
Megasporocyte (2n)
Ovule
IntegumentOvulate cone
FERTILIZATION
Pollen tube
Female gametophyte
Sperm nucleus (n)
Egg nucleus (n)
Archegonium
Seedling
Seeds
Seed coat (2n)
Food reserves (n)
Embryo (2n)
Megasporangium (2n)
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Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits
• Angiosperms are seed plants with reproductive structures called flowers and fruits
• They are the most widespread and diverse of all plants
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Fig. 30-UN2
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
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Characteristics of Angiosperms
• All angiosperms are classified in a single phylum, Anthophyta
• The name comes from the Greek anthos, flower
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Flowers
• The flower is an angiosperm structure specialized for sexual reproduction
• Many species are pollinated by insects or animals, while some species are wind- pollinated
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• A flower is a specialized shoot with up to four types of modified leaves:
– Sepals, which enclose the flower
– Petals, which are brightly colored and attract pollinators
– Stamens, which produce pollen on their terminal anthers
– Carpels, which produce ovules
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Fig. 30-7
Carpel
Ovule
Sepal
Petal
Stigma
Style
Ovary
Stamen Anther
Filament
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• A carpel consists of an ovary at the base and a style leading up to a stigma, where pollen is received
Video: Flower Blooming (timeVideo: Flower Blooming (time lapse)lapse)
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Fruits
• 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 DevelopmentAnimation: Fruit Development
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Fig. 30-8
Hazelnut
Ruby grapefruitTomato
Nectarine
Milkweed
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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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Fig. 30-9
Barbs
Seeds within berries
Wings
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The Angiosperm Life Cycle
•
The flower of the sporophyte is composed of both male and female structures
•
Male gametophytes are contained within pollen grains produced by the microsporangia of anthers
•
The female gametophyte, or embryo sac, develops within an ovule contained within an ovary 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 pollen tube of the male gametophyte grows down to the ovary
•
The ovule is entered by a pore called the micropyle
•
Double fertilization 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 endosperm
•
The endosperm nourishes the developing embryo
•
Within a seed, the embryo consists of a root and two seed leaves called cotyledons
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Fig. 30-10-1
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollen grains
Microspore (n)
Male gametophyte (in pollen grain) (n)
Mature flower on sporophyte plant (2n)
Haploid (n)Diploid (2n)
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Fig. 30-10-2
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollen grains
Microspore (n)
Male gametophyte (in pollen grain) (n)
Mature flower on sporophyte plant (2n)
Haploid (n)Diploid (2n)
MEIOSIS
Ovule (2n)
Ovary
Megasporangium (2n)
Megaspore (n)
Female gametophyte (embryo sac)
Antipodal cells Central cell Synergids Egg (n)
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Fig. 30-10-3
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollen grains
Microspore (n)
Male gametophyte (in pollen grain) (n)
Mature flower on sporophyte plant (2n)
Haploid (n)Diploid (2n)
MEIOSIS
Ovule (2n)
Ovary
Megasporangium (2n)
Megaspore (n)
Female gametophyte (embryo sac)
Antipodal cells Central cell Synergids Egg (n)
Pollen tube
Pollen tube
Stigma
Sperm (n)
Discharged sperm nuclei (n)
FERTILIZATION
Egg nucleus (n)
Style
Sperm
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Fig. 30-10-4
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollen grains
Microspore (n)
Male gametophyte (in pollen grain) (n)
Mature flower on sporophyte plant (2n)
Haploid (n)Diploid (2n)
MEIOSIS
Ovule (2n)
Ovary
Megasporangium (2n)
Megaspore (n)
Female gametophyte (embryo sac)
Antipodal cells Central cell Synergids Egg (n)
Pollen tube
Pollen tube
Stigma
Sperm (n)
Discharged sperm nuclei (n)
FERTILIZATION
Germinating seed
Embryo (2n) Endosperm (3n) Seed coat (2n) Seed
Nucleus of developing endosperm (3n)
Zygote (2n)Egg nucleus (n)
Style
Sperm
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Video: Flowering Plant Life Cycle (time lapse)Video: Flowering Plant Life Cycle (time lapse)
Animation: Seed DevelopmentAnimation: Seed Development
Animation: Plant FertilizationAnimation: Plant Fertilization
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Angiosperm Evolution
• 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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Fossil Angiosperms
• Primitive fossils of 125-million-year-old angiosperms display derived and primitive traits
• Archaefructus sinensis, for example, has anthers and seeds but lacks petals and sepals
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Fig. 30-11
Carpel
Stamen
Archaefructus sinensis, a 125-million-year-old fossil
(a)
(b) Artist’s reconstruction of Archaefructus sinensis
5 cm
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Angiosperm Phylogeny
• 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
Microsporangia (contain microspores)
Ovules
A possible ancestor of the angiosperms?
(a) (b) Angiosperm phylogeny
Most recent common ancestor of all living angiosperms
Millions of years ago300 250 200 150 100 50 0
Living gymnosperms
Bennettitales
Amborella
Star anise and relatives
Water lilies
Monocots
Magnoliids
Eudicots
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Fig. 30-12a
Microsporangia (contain microspores)
Ovules
A possible ancestor of the angiosperms?
(a)
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Fig. 30-12b
(b) Angiosperm phylogeny
Most recent common ancestor of all living angiosperms
Millions of years ago300 250 200 150 100 50 0
Living gymnosperms
Bennettitales
Amborella
Star anise and relatives
Water lilies
Monocots
Magnoliids
Eudicots
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Developmental Patterns in Angiosperms
• Egg formation in the angiosperm Amborella resembles that of the gymnosperms
• Researchers are currently studying expression of flower development genes in gymnosperm and angiosperm species
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Angiosperm Diversity
• The two main groups of angiosperms are monocots (one cotyledon) and eudicots (“true” dicots)
• The clade eudicot includes some groups formerly assigned to the paraphyletic dicot (two cotyledons) group
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• Basal angiosperms are less derived and include the flowering plants belonging to the oldest lineages
• Magnoliids share some traits with basal angiosperms but are more closely related to monocots and eudicots
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Basal Angiosperms
•
Three small lineages constitute the basal angiosperms
•
These include Amborella trichopoda, water lilies, and star anise
Page 76
Fig. 30-13a
Amborella trichopoda
Page 77
Fig. 30-13b
Water lily
Page 78
Fig. 30-13c
Star anise
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Magnoliids
•
Magnoliids include magnolias, laurels, and black pepper plants
•
Magnoliids are more closely related to monocots and eudicots than basal angiosperms
Page 80
Fig. 30-13d
Southern magnolia
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Monocots
•
More than one-quarter of angiosperm species are monocots
Page 82
Fig. 30-13e
Orchid
Page 83
Fig. 30-13e1
Pygmy date palm (Phoenix roebelenii)
Page 85
Fig. 30-13g
Anther
Barley
StigmaOvary
Filament
Page 86
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Eudicots
•
More than two-thirds of angiosperm species are eudicots
Page 87
Fig. 30-13h
California poppy
Page 88
Fig. 30-13i
Pyrenean oak
Page 89
Fig. 30-13j
Dog rose
Page 90
Fig. 30-13k
Snow pea
Page 91
Fig. 30-13l
Zucchini flowers
Page 92
Fig. 30-13mMonocot
CharacteristicsEudicot
Characteristics
Vascular tissue usually arranged
in ring
Veins usually parallel
Veins usually netlike
Vascular tissue scattered
Leaf venation
One cotyledon
Embryos
Two cotyledons
Stems
Roots
Pollen
Root system usually fibrous (no main root)
Pollen grain with three openings
Taproot (main root) usually present
Pollen grain with one opening
Floral organs usually in
multiples of three
Flowers
Floral organs usually in multiples of
four or five
Page 93
Fig. 30-13n
Monocot Characteristics
Eudicot Characteristics
Vascular tissue usually arranged
in ring
Veins usually parallel
Vascular tissue scattered
Leaf venation
One cotyledon
Embryos
Two cotyledons
Stems
Veins usually netlike
Page 94
Fig. 30-13o
Roots
Pollen
Root system usually fibrous (no main root)
Pollen grain with three openings
Pollen grain with one opening
Floral organs usually in
multiples of three
Flowers
Floral organs usually in multiples of
four or five
Monocot Characteristics
Eudicot Characteristics
Taproot (main root) usually present
Page 95
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Evolutionary Links Between Angiosperms and Animals
• 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: Bat Pollinating Video: Bat Pollinating Agave Agave PlantPlantVideo: Bee PollinatingVideo: Bee Pollinating
Page 96
Fig. 30-14
Common ancestor
Radial symmetry (N = 4)
Bilateral symmetry (N = 15)
Compare numbers of species
Time since divergence from common ancestor
“Radial” clade
“Bilateral” clade
3,000
2,000
1,000
0
EXPERIMENT
RESULTS
Mea
n di
ffere
nce
in n
umbe
r of s
peci
es
Page 97
Fig. 30-14a
Common ancestor
Compare numbers of species
Time since divergence from common ancestor
“Radial” clade
“Bilateral” clade
EXPERIMENT
Page 98
Fig. 30-14b
Radial symmetry (N = 4)
Bilateral symmetry (N = 15)
3,000
2,000
1,000
0
RESULTSM
ean
diffe
renc
ein
num
ber o
f spe
cies
Page 99
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Concept 30.4: Human welfare depends greatly on seed plants
• 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
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Products from Seed Plants
• 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
Page 102
Table 30-1b
Cinchona bark, source of quinine
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Threats to Plant Diversity
• 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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Fig. 30-UN3
Reduced gametophytes
Microscopic male and female gametophytes (n) are nourished andprotected by the sporophyte (2n)
Five Derived Traits of Seed Plants
Male gametophyte
Female gametophyte
Heterospory Microspore (gives rise to a male gametophyte)
Megaspore (gives rise to a female gametophyte)
Ovules
Ovule (gymnosperm)
Pollen Pollen grains make water unnecessary for fertilization
Integument (2n)
Megaspore (2n)
Megasporangium (2n)
Seeds Seeds: survive better than unprotected spores, can be transported long distances
Integument
Food supply
Embryo
Page 105
Fig. 30-UN4
Charophyte green algae
Mosses
Ferns
Gymnosperms
Angiosperms
Page 107
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You should now be able to:
1. Explain why pollen grains were an important adaptation for successful reproduction on land
2. List and distinguish among the four phyla of gymnosperms
3. Describe the life history of a pine; indicate which structures are part of the gametophyte generation and which are part of the sporophyte generation
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You should now be able to:
4. Identify and describe the function of the following floral structures: sepals, petals, stamens, carpels, filament, anther, stigma, style, ovary, and ovule
5. Explain how fruits may be adapted to disperse seeds
6. Diagram the generalized life cycle of an angiosperm; indicate which structures are part of the gametophyte generation and which are part of the sporophyte generation
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7. Explain the significance of Archaefructus and Amborella
8. Describe the current threat to plant diversity caused by human population growth