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Chapter 28
The Life of a Flowering Plant
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.
Biology and Society:
Plants and Human Civilization
• Human progress has always depended upon expanding our use of
plants for
– Food
– Fuel
– Clothing
– Countless other trappings of modern life
• Wheat accounts for about 20% of all calories consumed
worldwide.
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Figure 28.00
• Throughout much of prehistory, humans were nomadic
hunter/gatherers, moving and foraging with the changing seasons.
• About 10,000 years ago a major shift occurred.
– People in several parts of the world began to domesticate wild plants.
– Surplus food was produced.
– Year-round farming villages were formed.
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• During the latter half of the 20th century, a “green revolution” led
to an international effort to improve wheat and other staple crops.
• Through repeated selective breeding
– Wheat yield more than doubled from 1940 to 1980
– The cost of wheat production was cut in half
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• Plants are vital to the well-being of Earth’s biosphere, providing
– Shelter
– Food
– Breeding areas for
–
Animals
–
Fungi
–
Microorganisms
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• Angiosperms
– Make up over 90% of the plant kingdom
– Are the focus of this unit
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THE STRUCTURE AND FUNCTION OF A
FLOWERING PLANT
• Angiosperms
– Have dominated the land for over 100 million years
– Account for about 250,000 species alive today
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• Most of our foods come from a hundred or so domesticated
species of flowering plants including
– Roots such as beets and carrots
– Fruits of trees and vines such as apples, nuts, berries, and squash
– Fruits and seeds of legumes, such as peas, peanuts, and beans
– Fruits of grasses, which are grains such as wheat, rice, and corn
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Monocots and Dicots
• On the basis of several structural features, angiosperms are
classified into two groups:
– Monocots
– Dicots
• The names of the groups refer to cotyledons, or seed leaves found
in the embryo.
• Most angiosperms are dicots.
• The largest group of dicots are eudicots.
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Table 28.1
Plant Organs: Roots, Stems, and Leaves
• Plants have
– Organs composed of different tissues
– Tissues composed of cells of different types
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• The evolution of plants onto land required
– Structures for absorbing water and minerals from the soil
– A large light-collecting surface
– The ability to take in carbon dioxide from the air for photosynthesis
– Adaptations for surviving dry conditions
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• In a land plant, these vital functions are performed by:
– roots (below ground)
– shoots (above ground), including
– Stems
– Leaves
– Flowers
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Terminal bud
Blade
Leaf
Petiole
Flower
Axillary bud
Shoot
system
Stem
Node
Internode
Taproot
Root
system
Root hair
Root
hairs
Figure 28.1
Roots
• A plant’s roots
– Anchor it in the soil
– Store food
– Absorb and transport minerals and water
• All of a plant’s roots make up its root system.
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• Root hairs
– Are tiny projections near the root tips
– Increase the surface area of the root
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• Large taproots in plants such as carrots, turnips, sugar beets, and
sweet potatoes store food in the form of carbohydrates such as
starch.
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• Other types of modified roots include buttress roots, aerial roots
that
– Look like buttresses
– Support the tall trunks of the trees that produce them
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(a) The root of a sugar beet stores
carbohydrates.
(b) The buttress roots of this Indonesian Paldoa tree help
support the trunk.
Figure 28.2
Stems
• The shoot system of a plant is made up of
– Stems
– Leaves
– Structures for reproduction (flowers)
• Stems generally
– Grow above the ground
– Support the leaves and flowers
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• A stem has
– Nodes, the points at which leaves are attached
– Internodes, the portions of the stem between nodes
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• When a plant stem is growing in length, the terminal bud, at the
apex (tip) of the stem has
– Developing leaves
– A compact series of nodes and internodes
• The axillary buds, embryonic shoots in each of the angles
formed by a leaf and the stem, usually remain dormant.
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• In many plants, the terminal bud produces hormones that inhibit
growth of the axillary buds, a phenomenon called apical
dominance.
• Removing the terminal bud can make a plant bushier.
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Terminal bud
Terminal bud
removed
Figure 28.3
• Stems take many forms.
– Strawberry plants have horizontal stems, or runners, that
– Grow along the ground surface
– Serve as a form of asexual reproduction
– Iris or ginger plants have horizontal underground stems called rhizomes.
– A potato plant has rhizomes ending in tubers.
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Taproot
Runner
Rhizome
Rhizome
Tuber at end
of rhizome
(a) Strawberry plants
Root
(b) Ginger plant
(c) Potato plant
Figure 28.4
Leaves
• Leaves are the primary sites of photosynthesis in most plants and
consist of
– A flattened blade
– A stalk, or petiole, which joins the leaf to the stem
• Leaves are highly varied in their
– Arrangements
– Shapes
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LEAF ARRANGEMENT
Simple
Compound
Doubly Compound
Leaflet
Petiole
Axillary
bud
Petiole
Axillary bud
A single individual blade
One blade consisting of
many leaflets
(which lack axillary buds)
Petiole
Axillary bud
Each leaflet divided into
smaller leaflets
Figure 28.5
• Leaves can be modified as
– A tendril that helps plants climb up their supports
– Spines of a cactus that may protect the plant from predatory animals
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(a) Tendrils of a gourd plant
Tendril
(b) Spines of a cactus
Figure 28.6
Plant Tissues and Tissue Systems
• Tissues
– Are a group of cells with a common structure or function
– Form organs of plants
• A tissue system consists of one or more tissues organized into a
functional unit within a plant.
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• Plants have two types of vascular tissues.
– Phloem transports sugars from leaves or storage tissues to other parts of
the plant.
– Xylem conveys water and dissolved minerals upward from the roots to
the stems and leaves.
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• Plant organs
– Include roots, stems, and leaves
– Are made up of three tissue systems:
– The dermal tissue system
– The vascular tissue system
– The ground tissue system
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• Each tissue system is
– Continuous throughout the entire plant body
– Arranged differently in leaves, stems, and root
Video: Root Growth in a Radish Seed (time lapse)
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Leaf
Eudicot
Stem
Monocot
Root
Key
Dermal tissue system
Vascular tissue system
Ground tissue system
Figure 28.7
• The dermal tissue system
– Covers and protects leaves, stems, and roots
– Helps prevent water loss with a waxy coating called the cuticle produced
by epidermal cells
• The vascular tissue system
– Provides support and long-distance transport
– Includes xylem and phloem
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• The ground tissue system functions in
– Photosynthesis
– Storage
– Support
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• A cross section of a eudicot root illustrates the three tissue
systems.
– In the center of the root, the vascular tissue system forms a cylinder, with
– Xylem cells that radiate from the center
– Phloem cells that fill in the wedges between the spokes
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– The ground tissue system forms the cortex, where cells
– Store food
– Take up water and minerals
– The innermost layer of cortex is the endodermis, a thin cylinder one cell
thick that is a selective barrier that regulates the passage of substances
between the cortex and the vascular tissue.
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Xylem
Phloem
LM
Epidermis
Cortex
Endodermis
Figure 28.8
• All plant stems have vascular tissue systems arranged in
numerous vascular bundles.
– The location and arrangement of these bundles differ between monocots
and eudicots.
– In eudicots the pith
– Fills the center of the stem
– Is often important in food storage
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• The three tissue systems occur in eudicot leaves.
– The epidermis contains stomata, tiny pores between two specialized
guard cells that regulate the size of the stomata.
– The ground tissue system of a leaf contains the mesophyll, the main site
of photosynthesis.
– The leaf’s vascular tissue system is made up of a network of veins.
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Cuticle
Upper epidermis
Mesophyll
Lower epidermis
Guard cells
Vein
Xylem
Phloem
Stoma
Key
Dermal tissue system
Vascular tissue system
Ground tissue system
Figure 28.9
Plant Cells
• Most plant cells have three unique structures:
– Chloroplasts, the sites of photosynthesis
– A large central vacuole containing fluid that helps maintain the cell’s
firmness (turgor)
– A supportive cell wall that
– Surrounds the plasma membrane
– Consists largely of the carbohydrate cellulose
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Chloroplast
Central
vacuole
Nucleus
Cell wall
Primary cell wall
Endoplasmic
reticulum
Secondary
cell wall
Mitochondrion
Golgi
apparatus
Cell walls of
adjoining cells
Ribosomes
Plasma membrane
Microtubules
Plasmodesmata
Plasma
membrane
Figure 28.10
• Parenchyma cells
– Are the most abundant type of cell in most plants
– Perform a variety of functions, such as
–
Food storage
–
Photosynthesis
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LM
Primary
wall
(thin)
Parenchyma cells
LM
Primary
wall
(thick)
Collenchyma cells
LM
Secondary wall
Primary wall
Sclerenchyma cells
Figure 28.11a
• Collenchyma cells
– Resemble parenchyma cells in lacking secondary walls but have unevenly
thickened primary walls
– Provide support in parts of the plant that are actively growing
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LM
Primary
wall
(thick)
Collenchyma cells
Figure 28.11ac
• Sclerenchyma cells
– Have thick secondary cell walls usually strengthened with lignin, the
main chemical in wood
– Provide support to the plant
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LM
Secondary wall
Primary wall
Sclerenchyma cells
Figure 28.11ae
LM
Sclerenchyma cells
Figure 28.11af
• Angiosperms have two types of water-conducting cells:
– Tracheids, long, thin cells with tapered ends
– Vessel elements, wider and shorter cells that are less tapered
• Water-conducting cells are
– Dead, with only their cell walls remaining
– Arranged in chains of hollow tubes with overlapping ends
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Tracheids
Vessel element
Openings
in end wall
Water-conducting cells
Colorized SEM
Secondary
wall with
lignin
Plasmodesmata
LM
Primary
wall
Food-conducting cells
Figure 28.11b
• Food-conducting cells are
– Arranged end to end, forming tubes
– Remain alive at maturity
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PLANT GROWTH
• Most animals have determinate growth, ending growth after
reaching a certain size.
• Most plants have indeterminate growth, the ability to grow
throughout life.
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• The life span of plants varies greatly.
– Annuals live for only a year.
– Biennials
– Live for two years
– Typically reproduce in their second year
– Perennials may live for many years.
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PLANT LIFE SPANS
Annuals
(live for just one growing season)
Rice
Biennials
(live for two growing seasons)
Wild chervil
(also called cow parsley)
Perennials
(live for many growing seasons)
Japanese cherry tree
Figure 28.12
Primary Growth: Lengthening
• Growth in all plants is made possible by tissues called meristems,
undifferentiated (unspecialized) cells that divide frequently,
generating new cells and tissues.
• Apical meristems
– Occur at the tips of roots and shoots
– Enable primary growth, growth in length
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Terminal bud
Axillary buds
Key
Direction
of growth
Root
tips
Figure 28.13
• A growing root
– Is pushed through the soil by primary growth
– Contains a root cap that protects the actively dividing cells
• Primary growth in a root is achieved by
– Cell division
– Cell elongation, mainly by taking up water
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Vascular
system
Cortex
Epidermis
Root hair
Zone of
differentiation
Key
Dermal tissue system
Vascular tissue system
Ground tissue system
Zone of
elongation
Apical
meristem
region
Zone of
cell division
LM
Root cap
Figure 28.14
Secondary Growth: Thickening
• The stems and roots of many plant species also thicken by a
process called secondary growth.
• The vascular cambium is a cylinder of actively dividing cells
between the primary xylem and primary phloem.
• Secondary growth adds cells on either side of the vascular
cambium.
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Figure 28.15
Key
Dermal tissue system
Vascular tissue system
Ground tissue system
Year 1
Early Spring
Year 2
Late Summer
Late Summer
Shed
epidermis
Primary
xylem
Epidermis
Vascular
cambium
Primary
phloem
Cortex
Secondary
xylem (wood)
Cork
Bark
Secondary xylem
(2 years’ growth)
Cork
cambium
Secondary
phloem
Figure 28.16-3
• Annual growth rings result from the layering of secondary xylem.
• The layers are visible as rings because of uneven activity of the
vascular cambium during the year.
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Annual rings
Heartwood
Sapwood
Vascular cambium
Bark
Secondary phloem
Cork cambium
Cork
Figure 28.17
The Process of Science: What Happened to the
Lost Colony of Roanoke?
• In 1587, 121 English settlers landed on Roanoke Island in present
day North Carolina.
• Three years later they were gone and the settlement was deserted.
• Observation: A large number of very old bald cypress trees
around Roanoke Island could provide a reliable record of the
climate over the last 800 years.
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• Question: Could the tree ring data provide insight into the
colony’s mysterious disappearance?
• Hypothesis: The loss of the colony corresponded to a period of
drought.
• Prediction: Tree ring data would show abnormal growth during
the years after settlement.
• Experiment: Dozens of trees that covered the period 1185 to
1984 were analyzed.
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Canada
Cape
May
United States
Mexico
Virginia
Roanoke
Island
North
Carolina
Cape
Fear
ATLANTIC
OCEAN
N
Figure 28.18
• Results:
– The colonists arrived at the start of the worst three-year drought in the
southeastern United States during the past 800 years.
– The drought and its effects on the colonists’ vital crops could have forced
them to abandon the settlement.
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• When secondary growth begins
– The epidermis is sloughed off
– It is replaced with a new outer layer called cork, produced by cork
cambium
• Mature cork cells
– Are dead
– Have thick, waxy walls, which protect the underlying tissues of the stem
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• Bark consists of everything external to the vascular cambium:
– The secondary phloem
– Cork cambium
– Cork
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THE LIFE CYCLE OF A FLOWERING PLANT
• Many flowering plants can reproduce sexually and asexually.
• Asexual reproduction allows a single plant to produce many
offspring quickly and efficiently.
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Garlic
Holly trees
Creosote bushes
Figure 28.19
Garlic
Figure 28.19a
Holly trees
Figure 28.19b
Creosote bushes
Figure 28.19c
• Sexual reproduction in plants involves fertilization, the union of
gametes from two parents to produce genetically distinct
offspring.
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The Flower
• In angiosperms, the structure specific to sexual reproduction is the
flower.
• The main parts of a flower are modified leaves:
– Sepals
– Petals
– Stamens
– Carpels
Blast Animation: Flower Structure
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Petal
Stamen
Anther
Stigma
Carpel
Style
Ovary
Filament
Ovule
Sepal
Figure 28.20
• The flower’s reproductive organs are the stamen and the carpel.
• A stamen consists of a stalk tipped by an anther, where meiosis
occurs and pollen grains develop.
Video: Flower Blooming (time lapse)
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• A carpel has a long slender neck (the style) with a sticky stigma
where pollen grains land.
• The base of the carpel is the ovary.
• Within the ovary are ovules, each containing:
– One developing egg
– The cells that support it
• The term pistil is sometimes used to refer to a single carpel or a
group of fused carpels.
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Overview of the Flowering Plant Life Cycle
• The plant life cycle alternates between
– Haploid generation
– Diploid generation
• The diploid plant body is the sporophyte.
• The haploid plant is the gametophyte.
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• The sexual life cycle of an angiosperm involve
– Fertilization
– The ovule of a flower maturing into a seed containing the embryo
– The ovary developing into a fruit
– The seed germinating in a suitable habitat
– The embryo developing into a seedling
– The seedling growing into a mature plant
Video: Flowering Plant Life Cycle (time lapse)
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Embryo
Seed
Fruit
(mature ovary)
containing seed
Ovary,
containing
ovule
Germinating
seed
Mature plant with
flowers, where
fertilization occurs
Seedling
Figure 28.21-4
Pollination and Fertilization
• Fertilization requires gametes, which are produced by
gametophytes.
– The male gametophyte is the pollen grain, which produces sperm.
– The female gametophyte is a multicellular structure called the embryo
sac, which produces the egg.
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Development of male
gametophyte (pollen grain)
Haploid nuclei
of two cells
Anther
Meiosis
Cell within
anther
Mitosis
Four haploid
spores
Two haploid nuclei
of large, central cell
Ovule
Ovary
Meiosis
Pollen grain
(will be released
from anther)
Mitosis
Embryo
sac
Development of female
gametophyte (embryo sac)
Surviving cell
(haploid spore)
Egg cell
(with haploid nucleus)
Figure 28.22-6
• The first step leading to fertilization is pollination, the delivery of
pollen grains from anther to stigma.
• Many angiosperms are dependent on animals to transfer their
pollen.
Video: Bat Pollinating Agave Plant
Animation: Plant Fertilization
Blast Animation: Pollination and Fertilization
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Pollen
grain
Pollination
Germination
of pollen grain
Delivery of two
haploid sperm (n)
to ovule
Stigma
Pollen
tube
Triploid (3n)
endosperm
nucleus
Ovule
Embryo
sac
Double
fertilization
Haploid egg cell (n)
Diploid (2n)
zygote
Two sperm about to be
discharged into ovule
Figure 28.23
• Double fertilization occurs as
– One sperm fertilizes the egg, forming the diploid zygote
– The other sperm
– Contributes its haploid nucleus to the large diploid central cell of
the embryo sac
– Produces a triploid cell that will give rise to the food-storing tissue
called endosperm.
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Seed Formation
• After fertilization, the ovule, containing the zygote and the
triploid central cell, begins developing into a seed.
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• The zygote
– Divides via mitosis
– Forms a ball of cells that becomes the embryo
• The triploid cell
– Divides via mitosis
– Develops into the endosperm
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• The result of embryonic development in the ovule is a mature
seed, a plant embryo and endosperm packaged within a tough
protective covering called a seed coat.
Animation: Seed Development
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Triploid nucleus
of large, central cell
Ovule
Zygote
Cotyledons
Endosperm
Two cells
Seed coat
Shoot
Embryo
Root
Seed
Figure 28.24
Fruit Formation
• A fruit is a mature ovary that acts as a vessel
– Housing and protecting seeds
– Helping disperse seeds from the parent plant
• Pea pods are a type of fruit.
Animation: Fruit Development
Video: Bee Pollinating
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Figure 28.25
• Mature fruits can be either
– Fleshy or
– Dry
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Fleshy fruits
Figure 28.26a
Dry fruits
Figure 28.26b
Seed Germination
• Germination of a seed usually begins when the seed takes up
water.
• The hydrated seed expands and bursts its seed coat.
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Foliage leaves
Cotyledon
Embryonic
shoot
Embryonic
root
Cotyledon
Cotyledon
Seed coat
Figure 28.27
Foliage leaves
Cotyledon
Embryonic
shoot
Cotyledon
Cotyledon
Embryonic
root
Seed coat
Figure 28.27a
Figure 28.27b
Evolution Connection:
The Problem of the Disappearing Bees
• Flowering plants and land animals have had mutually beneficial
relationships throughout their evolutionary history.
– Angiosperms depend on insects, birds, or mammals for
–
Pollination
–
Seed dispersal
– Most land animals depend on angiosperms for food and shelter.
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• In late 2006, U.S. beekeepers noticed a sudden and drastic die off
in their bee colonies.
• The next year, similar problems were reported in Europe.
• Bees pollinate about $15 billion worth of crops each year, which
is about one-third of our food supply.
• The cause of the disorder is still unclear.
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Figure 28.28
Figure 28.UN01
Terminal bud (grows stem)
Flower (reproductive organ)
Stem (supports leaves
and flowers)
Axillary bud (produces
a branch)
Shoot system
(photosynthetic
center)
Internode
Node
Blade
Petiole
Leaf (main
photosynthetic
organ)
Root
Root system
(anchors, absorbs
nutrients, and
stores food)
Root hairs
(microscopic;
increase surface
area for absorption)
Figure 28.UN02
THE THREE TISSUES OF PLANT ORGANS
Dermal Tissue System
• Functions in protection
• Includes the epidermis, an
outer layer that covers and
protects the plant
• Stomata (each surrounded
by two guard cells) are
pores that regulate gas
exchange between the cells
of the leaf and the
environment
Vascular Tissue System
Ground Tissue System
• Functions in support
and transport
• Xylem: transports water
and dissolved minerals
• Phloem: transports
sugar
• Functions mainly in
storage
• Includes leaf mesophyll,
where most
photosynthesis occurs
Figure 28.UN03
Pollen (n)
Ovary
Embryo
sac (n)
Ovule
FERTILIZATION
within ovule
Fruit (from ovary)
Mature
plant (2n)
Seed (from ovule)
Embryo (2n)
Germinating
seed (2n)
Figure 28.UN04