chapter 30 presentation
TRANSCRIPT
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PowerPoint® Lecture Presentations for
Biology Eighth 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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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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Fig. 30-1
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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 surroundingsporophyte tissue for nutrition
Reduced, independent(photosynthetic andfree-living)
Gametophyte
Sporophyte(2n)
Sporophyte(2n)
Gametophyte(n)
Sporophyte
Example
Gametophyte(n)
Dominant
Dominant DominantReduced, dependent ongametophyte for nutrition
Mosses and othernonvascular plants
Ferns and other seedlessvascular plants
Seed plants (gymnosperms and angiosperms)
PLANT GROUP
Gymnosperm Angiosperm
Microscopic femalegametophytes (n) insideovulate cone
Microscopic malegametophytes (n) inside pollencone
Sporophyte (2n) Sporophyte (2n)
Microscopic femalegametophytes (n) insidethese partsof flowers
Microscopic malegametophytes (n) insidethese partsof flowers
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Fig. 30-2a
Gametophyte
Sporophyte(2n)
Gametophyte(n)
Sporophyte
Example
Dominant
Reduced, dependent ongametophyte for nutrition
Mosses and othernonvascular plants
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Fig. 30-2b
Reduced, independent(photosynthetic andfree-living)
Sporophyte(2n)
Gametophyte(n)
Dominant
Ferns and other seedlessvascular plants
Example
Gametophyte
Sporophyte
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Fig. 30-2c
Reduced (usually microscopic), dependent on surroundingsporophyte tissue for nutrition
Dominant
Seed plants (gymnosperms and angiosperms)
Gymnosperm AngiospermMicroscopic femalegametophytes (n) inside ovulate cone
Microscopic malegametophytes (n) inside pollencone
Sporophyte (2n) Sporophyte (2n)
Microscopic femalegametophytes (n) insidethese partsof flowers
Microscopic malegametophytes (n) insidethese partsof 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
Immaturefemale 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 germinatedpollen grain) (n)
Femalegametophyte (n)
(b) Fertilized ovule
Micropyle Pollen grain (n)
Spore wall
Dischargedsperm 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 fromintegument)
(c) Gymnosperm seed
Embryo (2n)(new sporophyte)
Food supply(femalegametophytetissue) (n)
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Fig. 30-3-4
Seed coat(derived fromintegument)
(c) Gymnosperm seed
Embryo (2n)(new sporophyte)
Food supply(femalegametophytetissue) (n)
(b) Fertilized ovule(a) Unfertilized ovule
Integument
Immaturefemale cone
Spore wall
Megasporangium(2n)
Male gametophyte(within a germinatedpollen grain) (n)
Megaspore (n) Micropyle Pollen grain (n)
Egg nucleus (n)
Dischargedsperm nucleus (n)
Femalegametophyte (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 plants
Gymnosperms
Angiosperms
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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 bilobapollen-producing tree
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Fig. 30-5c
Ginkgo bilobaleaves 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)
Pollengrains (n)
Pollencone
Microsporangia
MEIOSIS
Maturesporophyte(2n)
Haploid (n)Diploid (2n)
Key
Ovulatecone
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Fig. 30-6-2
Microsporangium (2n)
Microsporocytes(2n)
Pollengrains (n)
Pollencone
Microsporangia
MEIOSIS
Maturesporophyte(2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Survivingmegaspore (n)
Pollengrain
Megasporangium(2n)
Megasporocyte (2n)
Ovule
Integument
Ovulatecone
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Fig. 30-6-3
Microsporangium (2n)
Microsporocytes(2n)
Pollengrains (n)
Pollencone
Microsporangia
MEIOSIS
Maturesporophyte(2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Survivingmegaspore (n)
Pollengrain
Megasporocyte (2n)
Ovule
Integument
Ovulatecone
FERTILIZATION
Pollentube
Femalegametophyte
Spermnucleus (n)
Egg nucleus (n)
Archegonium
Megasporangium(2n)
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Fig. 30-6-4
Microsporangium (2n)
Microsporocytes(2n)
Pollengrains (n)
Pollencone
Microsporangia
MEIOSIS
Maturesporophyte(2n)
Haploid (n)Diploid (2n)
Key
MEIOSIS
Survivingmegaspore (n)
Pollengrain
Megasporocyte (2n)
Ovule
Integument
Ovulatecone
FERTILIZATION
Pollentube
Femalegametophyte
Spermnucleus (n)
Egg nucleus (n)
Archegonium
Seedling
Seeds
Seed coat(2n)
Foodreserves(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 (time lapse)Video: Flower Blooming (time 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 grapefruit
Tomato
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
Pollengrains
Microspore(n)
Male gametophyte(in pollen grain)(n)
Mature flower onsporophyte plant(2n)
Haploid (n)Diploid (2n)
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Fig. 30-10-2
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollengrains
Microspore(n)
Male gametophyte(in pollen grain)(n)
Mature flower onsporophyte 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
Pollengrains
Microspore(n)
Male gametophyte(in pollen grain)(n)
Mature flower onsporophyte 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)
Pollentube
Pollentube
Stigma
Sperm(n)
Discharged sperm nuclei (n)
FERTILIZATION
Eggnucleus (n)
Style
Sperm
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Fig. 30-10-4
MEIOSIS
Key
MicrosporangiumMicrosporocytes (2n)
Generative cell
Anther
Tube cell
Pollengrains
Microspore(n)
Male gametophyte(in pollen grain)(n)
Mature flower onsporophyte 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)
Pollentube
Pollentube
Stigma
Sperm(n)
Discharged sperm nuclei (n)
FERTILIZATION
Germinatingseed
Embryo (2n)Endosperm (3n)Seed coat (2n)
Seed
Nucleus ofdevelopingendosperm(3n)
Zygote (2n)Eggnucleus (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, a125-million-year-old fossil
(a)
(b) Artist’s reconstruction ofArchaefructus 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(containmicrospores)
Ovules
A possible ancestor of theangiosperms?
(a) (b) Angiosperm phylogeny
Most recent common ancestorof all living angiosperms
Millions of years ago
300 250 200 150 100 50 0
Livinggymnosperms
Bennettitales
Amborella
Star anise andrelatives
Water lilies
Monocots
Magnoliids
Eudicots
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Fig. 30-12a
Microsporangia(containmicrospores)
Ovules
A possible ancestor of theangiosperms?
(a)
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Fig. 30-12b
(b) Angiosperm phylogeny
Most recent common ancestorof all living angiosperms
Millions of years ago
300 250 200 150 100 50 0
Livinggymnosperms
Bennettitales
Amborella
Star anise andrelatives
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
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Fig. 30-13a
Amborella trichopoda
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Fig. 30-13b
Water lily
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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
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Fig. 30-13d
Southern magnolia
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Monocots
• More than one-quarter of angiosperm species are monocots
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Fig. 30-13e
Orchid
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Fig. 30-13e1
Pygmy date palm (Phoenix roebelenii)
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Fig. 30-13f
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Fig. 30-13g
Anther
Barley
Stigma
OvaryFilament
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Eudicots
• More than two-thirds of angiosperm species are eudicots
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Fig. 30-13h
California poppy
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Fig. 30-13i
Pyrenean oak
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Fig. 30-13j
Dog rose
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Fig. 30-13k
Snow pea
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Fig. 30-13l
Zucchini flowers
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Fig. 30-13mMonocot
CharacteristicsEudicot
Characteristics
Vascular tissueusually arranged
in ring
Veins usuallyparallel
Veins usuallynetlike
Vascular tissuescattered
Leafvenation
One cotyledon
Embryos
Two cotyledons
Stems
Roots
Pollen
Root systemusually fibrous(no main root)
Pollen grain withthree openings
Taproot (main root)usually present
Pollen grain withone opening
Floral organsusually in
multiples of three
Flowers
Floral organs usuallyin multiples of
four or five
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Fig. 30-13n
MonocotCharacteristics
EudicotCharacteristics
Vascular tissueusually arranged
in ring
Veins usuallyparallel
Vascular tissuescattered
Leafvenation
One cotyledon
Embryos
Two cotyledons
Stems
Veins usuallynetlike
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Fig. 30-13o
Roots
Pollen
Root systemusually fibrous(no main root)
Pollen grain withthree openings
Pollen grain withone opening
Floral organsusually in
multiples of three
Flowers
Floral organs usuallyin multiples of
four or five
MonocotCharacteristics
EudicotCharacteristics
Taproot (main root)usually present
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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 Agave PlantVideo: Bat Pollinating Agave PlantVideo: Bee PollinatingVideo: Bee Pollinating
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Fig. 30-14
Commonancestor
Radialsymmetry (N = 4)
Bilateralsymmetry (N = 15)
Comparenumbersof species
Time since divergencefrom common ancestor
“Radial” clade
“Bilateral” clade
3,000
2,000
1,000
0
EXPERIMENT
RESULTS
Mea
n d
iffe
ren
cein
nu
mb
er o
f sp
ecie
s
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Fig. 30-14a
Commonancestor
Comparenumbersof species
Time since divergencefrom common ancestor
“Radial” clade
“Bilateral” clade
EXPERIMENT
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Fig. 30-14b
Radialsymmetry (N = 4)
Bilateralsymmetry (N = 15)
3,000
2,000
1,000
0
RESULTSM
ean
dif
fere
nce
in n
um
ber
of
spec
ies
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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
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Table 30-1a
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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
Reducedgametophytes
Microscopic male andfemale gametophytes(n) are nourished andprotected by thesporophyte (2n)
Five Derived Traits of Seed Plants
Malegametophyte
Femalegametophyte
Heterospory Microspore (gives rise toa male gametophyte)
Megaspore (gives rise toa female gametophyte)
Ovules
Ovule(gymnosperm)
Pollen Pollen grains make waterunnecessary for fertilization
Integument (2n)
Megaspore (2n)
Megasporangium (2n)
Seeds Seeds: survivebetter thanunprotectedspores, can betransportedlong distances
Integument
Food supply
Embryo
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Fig. 30-UN4
Charophyte green algae
Mosses
Ferns
Gymnosperms
Angiosperms
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Fig. 30-UN5
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Fig. 30-UN6
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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