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Chapter 16
Plants and the Move
onto Land
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
Terrestrial Adaptations of Plants
Structural Adaptations
• A plant is
– A multicellular eukaryote
– A photoautotroph, making organic molecules by photosynthesis
• Plants are terrestrial organisms that include forms that have
returned to water, such as water lilies.
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• In terrestrial habitats, the resources that a photosynthetic organism
needs are found in two very different places:
– Light and carbon dioxide are mainly available in the air
– Water and mineral nutrients are found mainly in the soil
• The complex bodies of plants are specialized to take advantage of
these two environments by having
– Aerial leaf-bearing organs called shoots
– Subterranean organs called roots
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Reproductive
structures (such as
those in flowers)
contain spores
and gametes
Plant
Leaf performs
photosynthesis
Cuticle reduces water
loss; stomata regulate
gas exchange
Shoot supports plant
(and may perform
photosynthesis)
Alga
Surrounding
water supports
the alga
Whole alga
performs
photosynthesis;
absorbs water,
CO2, and
Roots anchor plant;
minerals from
absorb water and
the water
minerals from the
soil (aided by fungi)
Figure 16.1
• Most plants have mycorrhizae, symbiotic fungi associated with
their roots, in which the fungi
– Absorb water and essential minerals from the soil
– Provide these materials to the plant
– Are nourished by sugars produced by the plant
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Roots
Fungus
Root
surrounded
by fungus
Figure 16.2
• Leaves are the main photosynthetic organs of most plants, with
– Stomata for the exchange of carbon dioxide and oxygen with the
atmosphere
– Vascular tissue for transporting vital materials
– A waxy cuticle surface that helps the plant retain water
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Phloem
Xylem
Vascular
tissue
Oak leaf
Figure 16.3
• Vascular tissue in plants is also found in the
– Roots
– Shoots
• Two types of vascular tissue exist in plants:
– Xylem transports water and minerals from roots to leaves
– Phloem distributes sugars from leaves to the roots and other
nonphotosynthetic parts of the plant
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• (1) About 475 million years ago plants originated from an algal
ancestor giving rise to bryophytes, nonvascular plants, including
mosses, liverworts, and hornworts that are nonvascular plants
without
– Lignified walls
– True roots
– True leaves
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• (2) About 425 million years ago ferns evolved
– With vascular tissue hardened with lignin
– But without seeds
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• (3) About 360 million years ago gymnosperms evolved with
seeds that consisted of an embryo packaged along with a store of
food within a protective covering but not enclosed in any
specialized chambers.
• Today, conifers, consisting mainly of cone-bearing trees such as
pines, are the most diverse and widespread gymnosperms.
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• (4) About 140 million years ago angiosperms evolved with
complex reproductive structures called flowers that bear seeds
within protective chambers called ovaries.
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• The great majority of living plants
– Are angiosperms
– Include fruit and vegetable crops, grains, grasses, and most trees
– Are represented by more than 250,000 species
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PLANT DIVERSITY
Bryophytes
(nonvascular plants)
Ferns
(seedless vascular plants)
Gymnosperms
(naked-seed plants)
Angiosperms
(flowering plants)
Figure 16.7
Bryophytes
• Bryophytes, most commonly mosses
– Sprawl as low mats over acres of land
– Need water to reproduce because their sperm swim to reach eggs within
the female gametangium
– Have two key terrestrial adaptations:
–
A waxy cuticle that helps prevent dehydration
–
The retention of developing embryos within the mother plant’s
gametangium
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Figure 16.8
• Mosses have two distinct forms:
– The gametophyte, which produces gametes
– The sporophyte, which produces spores
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Spores
Spore capsule
Sporophyte
Gametophytes
Figure 16.9
• The life cycle of a moss exhibits an alternation of generations
shifting between the gametophyte and sporophyte forms.
• Mosses and other bryophytes are unique in having the
gametophyte as the larger, more obvious plant.
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Spores
(n)
Gametophyte
(n)
Gametes:
sperm
and eggs
(n)
FERTILIZATION
MEIOSIS
Spore
capsule
Sporophyte
(2n)
Zygote
(2n)
Key
Haploid (n)
Diploid (2n)
Figure 16.10-5
Ferns
• Ferns are
– Seedless vascular plants
– By far the most diverse with more than 12,000 known species
• The sperm of ferns, like those of mosses
– Have flagella
– Must swim through a film of water to fertilize eggs
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Spore capsule
“Fiddlehead”
(young leaves
ready to unfurl)
Figure 16.11
Conifers
• Conifers
– Cover much of northern Eurasia and North America
– Are usually evergreens, which retain their leaves throughout the year
– Include the tallest, largest, and oldest organisms on Earth
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Figure 16.13
Terrestrial Adaptations of Seed Plants
• Conifers and most other gymnosperms have three additional
terrestrial adaptations:
– Further reduction of the gametophyte
– Pollen
– Seeds
• A pine tree or other conifer is actually a sporophyte with tiny
gametophytes living in cones.
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Scale
Ovule-producing
cones; the scales
contain female
gametophytes
Pollen-producing
cones; they
produce male
gametophytes
Ponderosa pine
Figure 16.15
• A second adaptation of seed plants to dry land was the evolution
of pollen.
• A pollen grain
– Is actually the much-reduced male gametophyte
– Houses cells that will develop into sperm
• The third terrestrial adaptation was the development of the seed,
consisting of
– A plant embryo
– A food supply packaged together within a protective coat
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• Seeds
– Develop from structures called ovules, located on the scales of female
cones in conifers
– Can remain dormant for long periods before they germinate, as the
embryo emerges through the seed coat as a seedling
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Female cone,
cross section
Integument
Spore
Spore case
Haploid (n)
Diploid (2n)
Cross section
of scale
Spore case
(a) Ovule
Egg nucleus
Female
gametophyte
(b) Fertilized ovule
Pollen tube
Pollen grain
(male
gametophyte)
Food supply
(derived from
female
gametophyte
tissue)
Discharged
sperm nucleus
Seed coat
(derived from
integument)
(c) Seed
Embryo
(new
sporophyte)
Figure 16.16-3
Angiosperms
• Angiosperms
– Dominate the modern landscape
– Are represented by about 250,000 species
– Supply nearly all of our food and much of our fiber for textiles
• Their success is largely due to
– A more efficient water transport
– The evolution of the flower
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Flowers, Fruits, and the Angiosperm Life Cycle
• Flowers help to attract pollinators who transfer pollen from the
sperm-bearing organs of one flower to the egg-bearing organs of
another.
• A flower is actually a short stem with four whorls of modified
leaves:
– Sepals
– Petals
– Stamens
– Carpels
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Petal
Stamen
Anther
Stigma
Style
Filament
Ovary
Ovule
Sepal
Carpel
Figure 16.17
Pansy
Bleeding heart
California poppy
Water lily
Figure 16.18
Germinated pollen grain
(male gametophyte) on
stigma of carpel
Anther at tip of stamen
Pollen tube growing
down style of carpel
Mature
sporophyte
plant with
flowers
Ovary (base of carpel)
Ovule
FERTILIZATION
Endosperm
Embryo sac
(female
gametophyte)
Egg
Zygote
Two
sperm
nuclei
Sporophyte
seedling
Embryo
(sporophyte)
Seed
Germinating
seed
Key
Seed (develops
from ovule)
Fruit (develops
from ovary)
Haploid (n)
Diploid (2n)
Figure 16.19-6
• Although both have seeds
– Angiosperms enclose the seed within an ovary
– Gymnosperms have naked seeds
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• Fruit
– Is a ripened ovary
– Helps protect the seed
– Increases seed dispersal
– Is a major food source for animals
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Wind
dispersal
Animal
transportation
Animal
ingestion
Figure 16.20
Angiosperms and Agriculture
• Gymnosperms supply most of our lumber and paper.
• Angiosperms
– Provide nearly all our food
– Supply fiber, medications, perfumes, and decoration
• Agriculture is a unique kind of evolutionary relationship between
plants and animals.
• The exploding human population is
– Extinguishing plant species at an unprecedented rate
– Destroying fifty million acres, an area the size of the state of Washington,
every year!
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Figure 16.21
• Humans depend on plants for thousands of products including
– Food
– Building materials
– Medicines
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Table 16.1