Transcript chapter21_Sections 1-4.ppt

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 21
Plant Evolution
(Sections 21.1 - 21.4)
Albia Dugger • Miami Dade College
21.1 Speaking for the Trees
• Forests take up carbon dioxide from the air and release
oxygen, and prevent erosion, flooding, and sedimentation that
can disrupt rivers, lakes, and reservoirs
• Deforestation has far-reaching environmental effects,
including increased erosion and climate change
• Individual efforts to reverse deforestation can collectively have
a large positive impact
Maathai’s Practical Solution
• Biologist and Nobel
Peace Prize winner
Wangari Maathai
founded the Green Belt
Movement to restore
forests in Kenya
21.2 Adaptive Trends Among Plants
• Plants evolved from green algae, and underwent an adaptive
radiation on land
• Plants are embryophytes, which form a multicelled embryo
on the parental body
• embryophyte
• Member of the land plant clade
Structural Adaptations to
Life on Land
• Waterproof cuticle with stomata
• Stomata open and close to balance demands for water
conservation and gas exchange with air outside the plant
• Internal vascular tissue that transports water and nutrients
through a plant body
• xylem and phloem
• Vascular tissues reinforced by lignin
• Help plants stand upright and allow them to branch
Key Terms
• cuticle
• Secreted covering at a body surface
• stoma
• Opening across a plant’s cuticle and epidermis
• Photosynthetic cells on either side control its opening and
closing to regulate water loss and gas exchange
• vascular tissue
• Internal pipelines of xylem and phloem in the body of a
vascular plant
Key Terms
• xylem
• Plant vascular tissue that distributes water and dissolved
mineral ions
• phloem
• Plant vascular tissue that distributes sugars
• lignin
• Material that stiffens cell walls of vascular plants
A Vascular Plant Leaf
A Vascular
Plant Leaf
vascular tissue
(a leaf vein)
layer of waxy
cuticle
xylem
phloem
cuticle
stoma
Fig, 21.2, p. 326
A Vascular
Plant Leaf
vascular tissue
(a leaf vein)
layer of waxy
cuticle
xylem
phloem
cuticle
stoma
Fig, 21.2a, p. 326
A Vascular
Plant Leaf
stoma
Fig, 21.2b, p. 326
The Plant Life Cycle
• Life cycle changes adapted vascular plants to life in drier
habitats
• Plant life cycles include two multicelled bodies: the haploid
gametophyte and the diploid sporophyte
• The gametophyte dominates in early-evolving lineages, but in
most plants, the sporophyte is larger and longer lived
Generalized Plant Life Cycle
Generalized
Plant Life
Cycle
zygote
multicelled
sporophyte
Diploid (2n)
Phase of Cycle
Meiosis
Fertilization
gametes
Haploid (n)
Phase of Cycle
spores
multicelled
gametophyte
Fig, 21.3, p. 326
Generalized
Plant Life
Cycle
zygote
multicelled
sporophyte
Diploid (2n)
Phase of Cycle
Meiosis
Fertilization
gametes
Haploid (n)
Phase of Cycle
spores
multicelled
gametophyte
Stepped Art
Fig, 21.3, p. 326
Pollen and Seeds
• Seeds and male gametophytes that can be dispersed without
water (pollen grains) are important adaptations that
contribute to the success of seed plants
• Pollen and seeds allow seed plants to reproduce in dry places
• Many seed features facilitate dispersal from the parent plant
Key Terms
• pollen grain
• Male gametophyte of a seed plant
• seed
• Of seed plants, embryo sporophyte and nutritive tissue
inside a waterproof coat; a mature ovule
Two Lineages of Seed Plants
• There are two lineages of seed plants:
• Gymnosperms were the first to evolve
• Angiosperms make flowers and release their seeds
inside a fruit
The Four Major Plant Groups
The Four Major Plant Groups
Bryophytes
• No xylem or phloem
• Gametophyte
predominant
• Water required for
fertilization
• Seedless
Seedless vascular plants
• Vascular tissue present
• Sporophyte
predominant
• Water required for
fertilization
• Seedless
whisk
ferns,
club mosses, horsetails,
spike mosses ferns
liverworts hornworts mosses
Gymnosperms
• Vascular tissue present
• Sporophyte
predominant
• Pollen grains; water
not required for
fertilization
• “Naked” seeds
Angiosperms
• Vascular tissue present
• Sporophyte
predominant
• Pollen grains; water
not required for
fertilization
• Seeds form in a floral
ovary that becomes a
fruit
gnetophytes, ginkgos,
monocots, eudicots,
conifers, cycads
and relatives
ancestral alga
Fig, 21.4, p. 327
The Four Major Plant Groups
Fig, 21.4a, p. 327
The Four Major Plant Groups
Fig, 21.4b, p. 327
The Four Major Plant Groups
Fig, 21.4c, p. 327
The Four Major Plant Groups
Fig, 21.4d, p. 327
Key Concepts
• Adaptive Trends Among Plants
• Plants evolved from an aquatic green alga
• Over time, new traits evolved that made them increasingly
adapted to life in dry climates
• The process of adaptation involved changes in plant
structure, life cycle, and reproductive processes
ANIMATION: Alternations of Generations
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ANIMATION: Evolutionary Tree for Plants
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21.3 The Bryophytes
• Bryophyte refers to members of three separate lineages:
mosses, hornworts, and liverworts
• bryophyte
• Member of an early plant lineage with a gametophytedominant life cycle; for example a moss
Bryophyte Characteristics
• Bryophytes are nonvascular (no xylem or phloem)
• Their sperm swim through water droplets to eggs
• The sporophyte remains attached to the gametophyte
• Rhizoids attach a gametophyte to the soil or a surface
Mosses
• Mosses are the most diverse bryophytes
• Including about 15,000 species
• Threadlike rhizoids hold the gametophyte in place
• Unlike roots of vascular plants, rhizoids do not distribute
water or nutrients; these resources must be absorbed
across the gametophyte’s leafy surface
Key Terms
• moss
• Nonvascular plant with a leafy green gametophyte and an
attached, dependent sporophyte consisting of a capsule
on a stalk
• rhizoid
• Threadlike structure that anchors a bryophyte
Moss Life Cycle (Polytrichum)
1. The leafy green part of a moss is the gametophyte
2. It supports a sporophyte (stalk and capsule)
3. Spores form by meiosis in the capsule and are released
4. Spores develop into gametophytes that produce eggs or
sperm in gametangia at their tips
5. Sperm released from sperm-producing gametophytes swim
through water to eggs of egg-producing gametophytes
6. Fertilization produces a zygote.
7. Zygote develops into a sporophyte while attached to its eggproducing parent
Moss Life Cycle (Polytrichum)
Moss Life Cycle (Polytrichum)
Fig, 21.5a, p. 328
Moss Life Cycle (Polytrichum)
Fig, 21.5b, p. 328
Moss Life Cycle (Polytrichum)
Diploid (2n) Phase
7
2
zygote
sporophyte
(2n)
Fertilization
6
Meiosis
3
1
gametophyte
(n)
spore (n)
male
gametophyte
sperm
5
4
female
gametophyte
egg
Haploid (n) Phase
Fig, 21.5b, p. 328
Diploid (2n) Phase
7
2
sporophyte
(2n)
zygote
Moss Life
Cycle
(Polytrichum)
Meiosis
Fertilization
3
6
1
gametophyte
(n)
spore (n)
male
gametophyte
4
sperm
5
female
gametophyte
egg
Haploid (n) Phase
Stepped Art
Fig, 21.5b, p. 328
ANIMATION: Moss life cycle
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Peat Mosses
• Peat mosses (Sphagnum) are the dominant plants in peat
bogs that cover hundreds of millions of acres in high-latitude
regions of Europe, Asia, and North America
• The remains form peat, which is dried and burned as fuel
• peat
• Compressed, carbon-rich remains of peat moss
Peat
• Cutting blocks
of peat for fuel
in Ireland
Liverworts and Hornworts
• Liverworts commonly grow in moist places
• In most of the 6,000 species, the gametophyte is flattened
and attaches to soil by rhizoids
• Hornworts are named for a pointy, hornlike sporophyte
• Sporophytes grow continually from their base, and can
survive even after the death of the gametophyte
A Liverwort (Marchantia)
• Stalked structures
produce eggs for sexual
reproduction
• Asexual reproduction:
Clumps of cells in cups
on gametophyte fall and
develop into new plants
A Hornwort
• Hornwort, with a
photosynthetic
sporophyte that can
survive even after death
of the gametophyte
A Hornwort
sporophyte
gametophyte
Fig, 21.8, p. 329
Key Concepts
• The Bryophytes
• Bryophytes are three lineages of low-growing plants
• They are the only modern plants in which the gameteproducing body dominates the life cycle, and the sporeproducing body is dependent upon it
• Bryophytes require water for fertilization to occur, and
disperse by releasing spores
21.4 Seedless Vascular Plants
• seedless vascular plants
• Plants such as club mosses, horsetails, and ferns that
have vascular tissue
• They have flagellated sperm that swim to eggs, and
disperses by producing spores, not seeds
• Sporophytes are the larger, longer-lived phase of the life cycle
• Typically sporophyte roots and shoots grow from a
horizontal stem, or rhizome
• Tiny free-living gametophytes make flagellated sperm
Club Mosses
• A horizontal stem (rhizome) runs along the ground – roots
and upright stems with tiny leaves grow from the rhizome
• Spores form on a strobilus, a soft cone-shaped structure
composed of modified leaves
• rhizome
• Stem that grows horizontally along or under the ground
Club Moss (Lycopodium)
• Lycopodium sporophyte
• Waxy yellow spores are
produced on the surface
of strobili
Horsetails and Rushes
• Sporophyte has a rhizome that produces underground roots
and upright hollow stems with nonphotosynthetic leaves
• Strobili form at tips of photosynthetic stems or on special
chlorophyll-free stems
• Silica deposits inside cell walls support the plant
Horsetail (Equisetum)
• Photosynthetic stems with leaflike branches, and a sporebearing strobilus
Ferns: The Most Diverse
Seedless Plants
• Ferns, the most diverse group of seedless vascular plants,
produce spores in sori
• Many ferns grow as epiphytes
• sorus
• Cluster of spore-producing capsules on a fern leaf
• epiphyte
• Plant that grows on another plant but does not harm it
5 Steps in Life Cycle of a Fern
1. The leafy form is the diploid sporophyte
2. Meiosis produces haploid spores on frond undersides
3. Spores are released, germinate, and grow into tiny
gametophytes that produce eggs and sperm
4. Sperm swim to eggs and fertilize them, forming a zygote
5. Sporophyte develops attached to the gametophyte, but lives
independently after the gametophyte dies
Life Cycle of a Fern
Life Cycle of a Fern
1 The familiar leafy
form is the diploid
sporophyte.
mature sporophyte
2 Meiosis in cells
on the underside of
fronds produces
haploid spores.
1
5
3 After their
release, the spores
germinate and grow
into tiny
gametophytes that
produce eggs and
sperm.
4 Sperm swim to
eggs and fertilize
them, forming a
zygote.
zygote
Fertilization
2
underside of frond
Meiosis
4
egg
5 The sporophyte
begins its
development
attached to the
gametophyte, but it
continues to grow
and live
independently after
the gametophyte
dies.
rhizome
Diploid (2n) Phase
Haploid (n) Phase
sperm
eggproducin
g
structur
e
spermproducing
structure
mature
gametophyte
(underside)
spore
3
Fig, 21.11, p. 331
Life Cycle of a Fern
mature sporophyte
1
5
zygote
rhizome
Diploid (2n) Phase
Haploid (n) Phase
Fertilization
2
underside of frond
Meiosis
4
egg
sperm
eggproducing
structure
spermproducing
structure
mature
gametophyte
(underside)
spore
3
Stepped Art
Fig, 21.11, p. 331
ANIMATION: Fern life cycle
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Fern Diversity
Key Concepts
• Seedless Vascular Plants
• Vascular plants have internal pipelines that carry materials
through the body and provide structural support
• A body that makes spores dominates their life cycle
• Seedless vascular plants such as ferns require water for
fertilization to occur and they disperse by releasing spores