Chapter 30
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Transcript of Chapter 30
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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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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 (Micro/Megaspores)
– Ovules (Female)
– Pollen (Male)
• 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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Heterospory: The Rule Among Seed Plants
• The ancestors of seed plants were likely homosporous (all spores are alike), while seed plants are heterosporous (spores are different)
– Megasporangia (2n) produce megaspores (n) that give rise to female gametophytes (n)
– Microsporangia (2n) produce microspores (n) that give rise to male gametophytes (n)
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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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Pollen and Production of Sperm
• Microspores (n) 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, water 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. 30-3-4
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)
From ovule to seed in a gymnosperm
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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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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. 30-6-4
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
– Flowers are specialized for sexual reproduction
– Pollinated by wind, water & biotic vectors
• All angiosperms are classified in a single phylum, Anthophyta
• The name comes from the Greek anthos, flower
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Fig. 30-UN2
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
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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
• 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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Fig. 30-7
Carpel
Ovule
Sepal
Petal
Stigma
Style
Ovary
Stamen Anther
Filament
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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
• Various fruit adaptations help disperse seeds
• Seeds can be carried by wind, water, or animals to new locations
Animation: Fruit DevelopmentAnimation: Fruit Development
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Fig. 30-8
Hazelnut
Ruby grapefruit
Tomato
Nectarine
Milkweed
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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. 30-10-4
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 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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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. 30-13n
MonocotCharacteristics
EudicotCharacteristics
Vascular tissueusually arranged
in ring
Veins usuallyparallel
Vascular tissuescattered
Leafvenation
One cotyledon
Embryos
Two cotyledons
Stems
Veins usuallynetlike
Angi
ospe
rm d
iver
sity
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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
Angio
sper
m d
ivers
ity
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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
Video: Bat Pollinating Agave PlantVideo: Bat Pollinating Agave PlantVideo: Bee PollinatingVideo: Bee Pollinating
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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
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Table 30-1aS
econ
dary
com
poun
ds o
f see
d
plan
ts a
re u
sed
in m
edic
ines
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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