Plant Diversity II: The Evolution of Seed Plants
Transcript of Plant Diversity II: The Evolution of Seed Plants
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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 30
Plant Diversity II: The
Evolution of Seed Plants
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
2
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
3
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
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 plantsSeed plants (gymnosperms and angiosperms)
PLANT GROUP
Gymnosperm Angiosperm
Microscopic femalegametophytes (n) insideovulate 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
Gametophyte/sporophyte relationships in different plant groups
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
6
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
Fig. 30-3-1
Megasporangium
(2n)
Megaspore (n)
(a) Unfertilized ovule
Integument
Spore wall
Immature
female cone
From ovule to seed in a gymnosperm
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
8
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
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)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
10
The Evolutionary Advantage of Seeds
• 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
Fig. 30-3-3
Seed coat(derived fromintegument)
(c) Gymnosperm seed
Embryo (2n)(new sporophyte)
Food supply(femalegametophytetissue) (n)
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
Immature
female cone
Spore wall
Megasporangium
(2n)
Male gametophyte(within a germinatedpollen grain) (n)
Megaspore (n) Micropyle Pollen grain (n)
Egg nucleus (n)
Discharged
sperm nucleus (n)
Female
gametophyte (n)
From ovule to seed in a
gymnosperm
Fig. 30-UN1
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
14
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)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
15
Phylum Cycadophyta
• Individuals have
large cones and
palmlike leaves
• These thrived
during the
Mesozoic, but
relatively few
species exist today
Cycas revoluta
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
16
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
Ginkgo biloba
pollen-producing tree
leaves and fleshy
seeds
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
17
Phylum Gnetophyta
• This phylum
comprises three
genera
• Species vary in
appearance, and
some are tropical
whereas others
live in deserts
Welwitschia
Ovulate cones
Ephedra
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
18
Phylum Coniferophyta
• 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
19
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 Cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
20
• 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
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)
Fig. 30-UN2
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
23
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
• All angiosperms can be classified in a single
phylum, Anthophyta
• The name comes from the Greek anthos,
flower
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
24
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
• 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
Fig. 30-7
Carpel
Ovule
Sepal
Petal
Stigma
Style
Ovary
Stamen Anther
Filament
!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
26
• 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
• 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)
Fig. 30-8
Hazelnut
Ruby grapefruit
Tomato
Nectarine
Milkweed
Some
variations in
fruit structure
Fig. 30-9
Barbs
Seeds within berries
Wings Various fruit
adaptations
help disperse
seeds
Seeds can be
carried by
wind, water,
or animals to
new
locations
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
29
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
30
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
31
• 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
Fig. 30-10-4
MEIOSIS
Key
Microsporangium
Microsporocytes (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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
33
Video: Flowering Plant Life Cycle (time lapse)
Animation: Seed Development
Animation: Plant Fertilization
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
34
Angiosperm Diversity
• The two main groups of angiosperms are
monocots (one cotyledon) and eudicots
(“true” dicots)
• 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
35
Basal Angiosperms
• These include, for
example, water
lilies
Water lily
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
36
Magnoliids
• Magnoliids include
magnolias, laurels,
and black pepper
plants
• Magnoliids are more
closely related to
monocots and
eudicots than basal
angiosperms
Southern magnolia
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
37
Monocots
• More than one-quarter of angiosperm
species are monocots
Fig. 30-13e
Orchid
Fig. 30-13f
Fig. 30-13g
Anther
Barley
Stigma
OvaryFilament
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
41
Eudicots
• More than two-thirds of angiosperm species
are eudicots
Fig. 30-13h
California poppy
Fig. 30-13i
Pyrenean oak
Fig. 30-13j
Dog rose
Fig. 30-13k
Snow pea
Fig. 30-13l
Zucchini flowers
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
48
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
49
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
Table 30-1a
Fig. 30-UN3
Reduced
gametophytes
Microscopic male and
female gametophytes
(n) are nourished and
protected 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
Thank you for
your attention and
participation!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
54
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
55
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