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Adaptations Enabling the Move to Land
• The movement onto land by ancestors
provided unfiltered sun, more plentiful CO2,
nutrient-rich soil, and few herbivores or
pathogens
• Land presented challenges: a scarcity of water
and lack of structural support
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Terrestrial plants are characterized by
• Chlorophylls a and b and carotenoids in their
chloroplast
• Food stored as starch
• Cell walls of cellulose
• Sporic sexual reproduction involving an alternation
of sporophyte and gametophyte generations
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SPORIC SEXUAL REPRODUCTION
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The Origin and Diversification of Plants
• Fossil evidence indicates that plants were on
land at least 475 million years ago
• Fossilized spores and tissues have been
extracted from 475-million-year-old rocks
• First land animal=428 million years ago
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• Those ancestral species gave rise to a vast
diversity of modern plants
• Land plants can be informally grouped based
on the presence or absence of vascular tissue
• Most plants have vascular tissue; these
constitute the vascular plants
• Nonvascular plants are commonly called
bryophytes
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• Seedless vascular plants
Pterophytes (ferns and their relatives)
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• A seed is an embryo and nutrients surrounded
by a protective coat
• Seed plants form a clade and can be divided
into further clades:
– Gymnosperms, the “naked seed” plants,
including the conifers
– Angiosperms, the flowering plants
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Concept 29.2: Mosses and other nonvascular plants
have life cycles dominated by gametophytes
• Bryophytes are represented today by three phyla
of small herbaceous (nonwoody) plants:
– Liverworts, phylum Hepatophyta
– Mosses, phylum Bryophyta
• Mosses are most closely related to vascular
plants
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Key Bryophyte traits
• Lack vascular tissue
• Lack true leaves, roots, and leaves
• Gametophyte dominant life cycle
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Bryophyte Gametophytes
• In all bryophyte phyla, gametophytes are larger
and longer-living than sporophytes
• Sporophytes are typically present only part of
the time
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Multicellular Gametangia
• Gametes are produced within organs called
gametangia
• Female gametangia, called archegonia, produce
eggs and are the site of fertilization
• Male gametangia, called antheridia, are the site
of sperm production and release
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Bryophyta Life Cycle
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• A spore germinates into a gametophyte
composed of a protonema and gameteproducing gametophore
• Rhizoids anchor gametophytes to substrate
• The height of gametophytes is constrained by
lack of vascular tissues
• Mature gametophytes produce flagellated sperm
in antheridia and an egg in each archegonium
• Sperm swim through a film of water to reach and
fertilize the egg
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Bryophyte Sporophytes
• Bryophyte sporophytes grow out of archegonia,
and are the smallest and simplest sporophytes
of all extant plant groups
• A sporophyte consists of a foot, a seta (stalk),
and a sporangium, also called a capsule,
which discharges spores through a peristome
• Hornwort and moss sporophytes have stomata
for gas exchange
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Fig. 29-9d
Polytrichum commune,
hairy-cap moss
Capsule
Seta
Sporophyte
(a sturdy
plant that
takes months
to grow)
Gametophyte
Traits of Vascular Plants
• Living vascular plants are characterized by:
• Life cycles with dominant sporophytes
• Vascular tissues called xylem and phloem
• Well-developed roots and leaves
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Concept 29.3: Ferns and other seedless vascular
plants were the first plants to grow tall
• Vascular tissue allowed these plants to grow
tall WHAT IS AN ADVANTAGE OF HEIGHT?
• Seedless vascular plants have flagellated
sperm and are usually restricted to moist
environments
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Pterophyta (Seedless Vascular plant) Key Traits
• Vascular tissue
• Sporophyte dominant
• Surface water required for sperm mobility
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Pterophyta Life Cycle
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Life Cycles with Dominant Sporophytes
• In contrast with bryophytes, sporophytes of
seedless vascular plants are the larger
generation, as in the familiar leafy fern
• The gametophytes are tiny plants that grow on
or below the soil surface
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Transport in Xylem and Phloem
• Vascular plants have two types of vascular
tissue: xylem and phloem
• Xylem conducts most of the water and minerals
and includes dead cells called tracheids
• Phloem consists of living cells and distributes
sugars, amino acids, and other organic products
• Water-conducting cells are strengthened by
lignin and provide structural support
• Increased height was an evolutionary advantage
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Evolution of Roots
• Roots are organs that anchor vascular plants
• They enable vascular plants to absorb water
and nutrients from the soil
• Roots may have evolved from subterranean
stems
• What would water transport allow?
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Plant can now get water easier and have support but
how do they get away from needing a moist env.?
Seeds
• Gymnosperm-exposed seeds
– Phylum Coniferophyta
• Angiosperms-enclosed seeds
– Phylum Anthophyta
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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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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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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
– Ovules
– Pollen
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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 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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Concept 30.2: Gymnosperms bear “naked” seeds,
typically on cones
• The gymnosperms have “naked” seeds not
enclosed by ovaries and consist of four phyla:
– Coniferophyta (conifers, such as pine, fir, and
redwood)
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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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• 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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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
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Coniferophyta Life Cycle
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Characteristics of Angiosperms
• All angiosperms are classified in a single
phylum, Anthophyta
• The name comes from the Greek anthos,
flower
• 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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Flowers
• The flower is an angiosperm structure
specialized for sexual reproduction
• Many species are pollinated by insects or
animals, while some species are windpollinated
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Fig. 30-7
Stigma
Stamen
Anther
Pistil
Style
Filament
Ovary
Petal
Sepal
Ovule
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• A pistil consists of an ovary at the base and a
style leading up to a stigma, where pollen is
received
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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
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Fig. 30-8
Tomato
Ruby grapefruit
Nectarine
Hazelnut
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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• 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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Anthophyta Life Cycle
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Assignments
1. All-Only Draw Antheridium and Archegonium
2. All-Antheridium and Archegonium can be drawn
as on Prothallium for g
3. All-Only draw Mature pollen grains, Ovulate
cone, Staminate cone
4. Only a,c,d,e,f
5. Omit
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