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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 31
Plant Structure, Reproduction,
and Development
Modules 31.1 – 31.4
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
A Gentle Giant
• This giant sequoia,
the General Sherman,
is the largest plant on
Earth
– It is 84 m (275 ft) tall
– Its trunk is 10m in
diameter
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• The General Sherman
has been growing for
about 2,500 years
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• Growth rings mark each ______ in a tree's life
– Rings vary in thickness depending on weather
conditions during the growing season
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• Humans depend on plant products
– ______
– ______
– ______
– ______
– Industrial chemicals
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• Plants are vital to Earth's well-being
– They provide ______ for land animals
– They offer ______ and breeding areas for
animals, fungi, and microorganisms
– Their roots ______ soil erosion
– Photosynthesis in plant leaves helps ______
carbon dioxide and ______ oxygen to the air
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PLANT STRUCTURE AND FUNCTION
31.2 The two main groups of angiosperms are the
monocots and the dicots
• ___________, or flowering plants, are the
most familiar and diverse plants
• There are two main types of angiosperms
– ______ include orchids, bamboos, palms,
lilies, grains, and other grasses
– ______ include shrubs, ornamental plants,
most trees, and many food crops
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• Monocots and dicots differ in seed leaf number
and in the structure of roots, stems, leaves, and
flowers
SEED LEAVES
LEAF VEINS
STEMS
FLOWERS
ROOTS
MONOCOTS
One
cotyledon
Main veins
usually parallel
Vascular bundles in
complex arrangement
Floral parts usually
in multiples of three
Fibrous
root system
DICOTS
Two
cotyledons
Main veins
usually branched
Vascular bundles
arranged in ring
Floral parts usually in
Taproot
multiples of four or five usually present
Figure 31.2
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31.3 The plant body consists of roots and shoots
• Root system
– Provides ___________
– ______ and ______ minerals and water
– Stores ______
• Root hairs ______ the surface area for
absorption
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• Shoot system
– Consists of ______ , ______ , and ______ in
angiosperms
– Stems are located ______ the ground and
support the leaves and flowers
– ______ are the main sites of photosynthesis in
most plants
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Terminal bud
Blade
Leaf
Flower
Petiole
Axillary bud
Stem
SHOOT
SYSTEM
Node
Internode
Taproot
ROOT
SYSTEM
Root
hairs
Figure 31.3
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• The terminal bud is located at the tip of a
______
– It is the growth point of the stem
• Axillary buds can give rise to ______
• In ______ dominance, the terminal bud
produces hormones that inhibit the growth of
axillary buds
– This results in a taller plant that has greater
exposure to light
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31.4 Many plants have modified roots and shoots
• Roots and stems are adapted for a variety of
functions
– Storing ______
– ______ reproduction
– ______
• Plant breeders have improved
the yields of root crops by
selecting varieties, such as
the sugar beet plant, with
very large taproots
Figure 31.4A
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• Modified stems
include
STRAWBERRY
PLANT
– ______, for
asexual
reproduction
Runner
POTATO
PLANT
– ______, for plant
growth and food
storage
– ______, for food
storage in the
form of starch
Rhizome
IRIS
PLANT
Rhizome
Tuber
Taproot
Root
Figure 31.4B
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• Modified leaves include tendrils and spines
– ______ help plants to climb
– ______ may protect the plant from plant-eating
animals
Figure 31.4C
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31.5 Plant cells and tissues are diverse in structure
and function
Figure 31.5A
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• There are five major types of plant cells
– __________
– _________
– _________
– Water-conducting cells (______ )
– Food-conducting cells (______ )
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• Parenchyma cells function in ______ storage,
photosynthesis, and aerobic respiration. They
have a primary cell wall that is thin and flexible
and ______ a secondary cell wall.
Primary
wall
(thin)
Pit
Figure 31.5B
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• Collenchyma cells provide ______ in parts of
the plant that are still growing. They have an
unevenly thick primary cell wall and ______ a
secondary cell wall. The “strings” of celery are
made of collenchyma cells.
Primary
wall
(thick)
Figure 31.5C
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• Sclerenchyma cells provide a rigid scaffold that
supports the plant. They have very ______
primary and secondary cell walls that are fortified
with ______ . Their function is purely for support.
– Fiber cells
Pits
Secondary
wall
Fiber
cells
Primary
wall
FIBER
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Figure 31.5D
– Sclereids (stone cells)
Secondary
wall
Primary
wall
Sclereid
cells
Pits
SCLEREID
Figure 31.5D continued
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• Water-conducting cells, generally known as
______ , convey water from the roots to the
stems and leaves
Pits
– Chains of
______ or
______
______ form
a system of
tubes for water
transport
Tracheids
Vessel element
Pits
Openings
in end wall
Figure 31.5E
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• Food-conducting cells, generally known as
______ , function in the transport of sugars,
other compounds, and some mineral ions
– _________ members are arranged end-to-end,
forming tubes
– Their end walls are perforated with
plasmodesmata, forming ______ plates
– At least one companion cell flanks each sievetube member
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Sieve plate
Companion
cell
Cytoplasm
Primary
wall
Figure 31.5F
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• Complex ______ are composed of more than
one type of plant cell
• Vascular tissues are complex tissues that
conduct ______ and ______
– ______ contains water-conducting cells that
convey water and dissolved minerals
– ______ contains sieve-tube members that
transport sugars
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31.6 Three tissue systems make up the plant body
• Roots, stems, and
leaves are made
of three tissue
systems
Leaf
Stem
– The ______
– The ______
tissue system
– The ______
tissue system
Root
Epidermis
Ground
tissue system Vascular
tissue system
Figure 31.6A
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• The epidermis covers and protects the plant
– The ______ is a waxy coating secreted by
epidermal cells that helps the plant retain water
• The vascular tissue contains xylem and phloem
– It provides support and transports water and
nutrients
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• The ground tissue system functions mainly in
______ and _____________
– It consists of parenchyma cells and supportive
collenchyma and sclerenchyma cells
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• The ground tissue system of the root forms the
______
– The cortex consists mostly of parenchyma tissue
• The selective barrier forming the innermost
layer of the cortex is the ___________
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VASCULAR
TISSUE
SYSTEM
Xylem
Phloem
Epidermis
GROUND
TISSUE
SYSTEM
Cortex
Endodermis
Figure 31.6B
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• These microscopic cross sections of a dicot and
a monocot indicate several differences in their
tissue systems
Figure 31.6C
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• The three tissue systems in dicot leaves
– The epidermis consist of pores called ______
(singular, stoma) flanked by regulatory ______
______
Figure 31.6D
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– The ground tissue system of a leaf is called
______ and is the site of photosynthesis
Figure 31.6D
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– The vascular tissue consists of a network of
veins composed of xylem and phloem
Figure 31.6D
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PLANT GROWTH
31.7 Primary growth lengthens roots and shoots
• Most plants exhibit indeterminate growth
– They continue to grow as long as they live
• In contrast, animals are characterized by
determinate growth
– They cease growing after reaching a certain size
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Terminal bud
Axillary buds
Arrows =
direction
of growth
Root
tips
Figure 31.7A
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• ______ complete their life cycle in a single
year or growing season
– Examples: wheat, corn, rice, and most
wildflowers
• ______ complete their life cycle in two years,
with flowering occurring in the second year
– Examples: beets and carrots
• ______ live and reproduce for many years
– Examples: trees, shrubs, and some grasses
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• Growth in all plants originates in tissues called
______
– Meristems are areas of unspecialized, dividing
cells
• ______ meristems are located at the tips of
roots and in the terminal buds and axillary
buds of shoots
– They initiate ______ growth, lengthwise
growth by the production of new cells
– Roots and stems lengthen further as cells
elongate and differentiate
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Cortex
Epidermis
DIFFERENTIATION
Vascular
cylinder
CELL
DIVISION
ELONGATION
Root hair
Cellulose
fibers
Apical meristem
region
Root
cap
Figure 31.7B
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31.8 Secondary growth increases the girth of
woody plants
• An increase in a plant's ______ results from
secondary growth
• ___________ growth involves cell division
in two cylindrical meristems
– ______ cambium
– ______ cambium
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Figure 31.8A
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• Vascular cambium thickens a stem by adding
______ of secondary xylem, or wood, next to
its inner surface
– It also produces the secondary phloem, which
is a tissue of the bark
• Cork cambium produces protective ______
cells located in the bark
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• Everything external to the vascular cambium is
considered bark
– Secondary phloem
– Cork cambium
– Protective cork cells
• Heartwood in the center of the trunk consists
of older, clogged layers of secondary xylem
• Sapwood consists of younger, secondary xylem
that still conducts water
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• A woody log is the result of several ______ of
secondary growth
Sapwood
Rings
Wood
rays
Heartwood
Sapwood
Vascular cambium
Bark
Secondary phloem
Cork cambium
Cork
Heartwood
Figure 31.8B
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PLANT REPRODUCTION
31.9 Overview: The sexual life cycle of a flowering
plant
• The angiosperm
flower is a
reproductive shoot
consisting of
Anther
Carpel
Stigma
Ovary
– ______
– ______
Stamen
– ______
Ovule
– ______
Sepal
Petal
Figure 31.9A
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• Sepals are usually ______ and resemble leaves
in appearance
– Sepals enclose and ______ the flower bud
before the flower opens
• Petals are often ______ and ______
– They attract insects (___________ )
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• ______ are the male reproductive organs of
plants
– Pollen grains develop in anthers, at the tips of
stamens
– Each pollen grain contains ______ haploid
cells (a ______ cell and two ______ cells)
• ______ are the female reproductive organs of
plants
– The ovary at the base of the carpel houses the
ovule
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Figure 31.10
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• The life cycle of an angiosperm involves several
stages
Ovary, containing
ovule
Embryo
Fruit,
containing seed
Seed
Mature plant with
flowers, where
fertilization occurs
Seedling
Germinating seed
Figure 31.9B
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31.11 The ovule develops into a seed
• After fertilization, the ovule becomes a seed
– The fertilized egg (first sperm cell) within the
seed divides to become an ______
– The other fertilized cell (second sperm cell)
develops into the endosperm, which stores food
for the ______
• A resistant seed coat ______ the embryo and
endosperm
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Triploid cell
OVULE
Zygote
Two cells
Cotyledons
Endosperm
Seed coat
Shoot
Embryo
Root
SEED
Figure 31.11A
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• Seed ___________ is an important
evolutionary adaptation in which growth and
development are suspended temporarily
– It allows time for a plant to disperse its seeds
– It increases the chance that a new generation of
plants will begin growing only when
environmental conditions favor survival
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• Comparison between dicot and monocot seeds
Seed coat
Embryonic
shoot
Embryonic
leaves
Embryonic
root
Cotyledons
COMMON BEAN (DICOT)
Fruit tissue
Cotyledon
Seed coat
Endosperm
Embryonic
leaf
Sheath
CORN (MONOCOT)
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Embryonic
shoot
Embryonic
root
Figure 31.11B
31.12 The ovary develops into a fruit
• The ovary develops into a ______ which
helps protect and ______ the seeds
Figure 31.12A
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• There is a correspondence between flower and
fruit in a pea plant
– The wall of the ovary becomes the ______
– The ovules develop into the ______
Upper part
of carpel
Ovule
Seed
Ovary
wall
Sepal
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Pod
(opened)
Figure 31.12B
– The small, threadlike structure at the end of the
pod is what remains of the upper part of the
flower's carpel
– The sepals of the flower stay attached to the
base of the green pod
Upper part
of carpel
Ovule
Seed
Ovary
wall
Sepal
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Pod
(opened)
Figure 31.12B
• ______ fruits develop from a flower with a
single carpel and ovary
– Apples, pea pods, cherries
• ______ fruits develop from a flower with
many carpels
– Raspberries
• ______ fruits develop
from a group of flowers
clustered tightly together
– Pineapples
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Figure 31.12C
31.13 Seed germination continues the life cycle
• A seed starts to ______ when it takes up
water, expands, and bursts its seed coat
• Metabolic changes cause the embryo to
resume growth and absorb nutrients from the
endosperm
• An embryonic root emerges, and a shoot
pushes upward and expands its leaves
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• Pea
germination
(a dicot)
Foliage leaves
Embryonic
shoot
Cotyledons
Embryonic
root
• Corn
germination
(a monocot)
Foliage
leaves
Protective sheath
enclosing shoot
Embryonic
root
Cotyledon
Figure 31.13A, B
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31.14 Asexual reproduction produces plant clones
• Many plants can reproduce asexually via
______ , ______ , or ______
• Asexual reproduction often involves
_____________
– Fragmentation is
the separation of
parts from the
parent plant and
regeneration of
those parts into
whole plants
Figure 31.14A
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• Sprouts from the roots of a coast redwood tree
may eventually take the place of its parent in
the forest
Figure 31.14B
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• These creosote bushes came from generations
of vegetative reproduction by roots
Figure 31.14C
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• Most grasses can propagate asexually by
sprouting shoots and roots from runners
Figure 31.14D
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31.15 Connection: Vegetative reproduction is a
mainstay of modern agriculture
• Propagating plants from cuttings or bits of
tissue can increase agricultural productivity
– But it can also reduce genetic diversity
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• Test-tube cloning is the growth of a plantlet
from a few meristem cells cultured on a
chemical medium
– A single plant can be
cloned into thousands of
copies that will continue
to grow when planted in
soil
– Orchids and certain pine
trees used in mass
plantings are propagated
this way
Figure 31.15A
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• "GM" (genetically modified) plants are created
when foreign genes are incorporated into a
single parenchyma cell
– The cell is then cultured until it develops into a
new plantlet
• The commercial adoption of GM crops has
been rapid
– However, many people are concerned about
the potential environmental risks associated
with their use
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• Monocultures are large areas of land planted
with a single crop
• Gene-cloning techniques and monocultures
have led to crop plants with little genetic
diversity
– This increases the likelihood that a small
number of diseases could devastate large crop
areas
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THE UPTAKE AND TRANSPORT OF PLANT
NUTRIENTS
32.1 Plants acquire their nutrients from soil and air
• As a plant grows, its
roots absorb water,
minerals (inorganic
ions), and some
oxygen from the soil
– Its leaves take carbon
dioxide from the air
Figure 32.1A
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• Photosynthesis makes use of the uptake of
water, carbon dioxide, and minerals to produce
______
– These sugars are composed of carbon,
oxygen, and hydrogen
• The nitrogen and magnesium absorbed from
the soil are components of __________
• _________, also absorbed from the soil, is
a major component of nucleic acids,
phospholipids, and ATP
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– The ability to move
water from roots to
leaves and to deliver
sugars to specific
areas of the body are
remarkable feats of
evolutionary
engineering
Figure 32.1B
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32.2 The plasma membranes of root cells control
solute uptake
• Root hairs greatly
___________ a root's
absorptive surface
Figure 32.2A
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• In order for upward transport, water and
solutes must enter the ______ by passing
through the Casparian Strip.
• Water and solutes move through the root's
epidermis and cortex by two main routes
– Through cells (intracellular route)
– Between cells (extracellular route)
• Water and solutes typically follow a
combination of routes and passages through
numerous plasma membranes and cell walls en
route to the xylem
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Epidermis
Root hair
Cortex
Phloem
Xylem
Casparian
strip
Endodermis
EXTRACELLULAR ROUTE,
via cell walls; stopped
by Casparian strip
Casparian strip
Xylem
Root hair
INTRACELLULAR ROUTE,
via cell interiors; through
plasmodesmata
Epidermis
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Cortex
Endodermis
Figure 32.2B
• The Casparian strip stops ______ and
______ from entering the xylem via cell walls
– Thus water and ions that travel the extracellular
route can enter the xylem only by crossing a
plasma membrane into an endodermal cell
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32.3 Transpiration pulls water up xylem vessels
• Xylem ______ is the solution of inorganic
nutrients conveyed in xylem tissue from a
plant's roots to its shoots
• Root ______ can push xylem sap up only a few
meters
– Solute transport raises water pressure in the
xylem
• Plants ______ xylem sap upward from the soil
through the transpiration-cohesion-tension
mechanism
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• Transpiration is the loss of ______ from the
leaves
– It exerts a ______ on the xylem sap
• Cohesion causes water molecules to ______
together
– It relays the ______ of transpiration along a
string of water molecules all the way to the roots
• The adhesion of water molecules to xylem cell
walls helps counter the effect of gravity
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Figure 32.3
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32.4 Guard cells control transpiration
• Guard cells surrounding stomata in the leaves
control transpiration
– The opening and closing of stomata is an
adaptation to help plants regulate their water
content and adjust to changing environmental
conditions
H2O
Guard cells
H2O
H2O
H2O
H2O
H2O
K+
Vacuole
H2O
H2O
H2O
H2O
Stoma opening
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Stoma closing
Figure 32.4
32.5 Phloem transports sugars
• While xylem sap flows ______ from the
roots, phloem sap moves throughout the plant
in ______ directions
• The main function of phloem is to transport
the ______ made by photosynthesis
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• Phloem contains
food-conducting
cells arranged
end-to-end as
tubes
Sievetube
member
Sieve
plate
Figure 32.5A
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• Phloem transports
food molecules
made by
photosynthesis by a
pressure-flow
mechanism
– Sugar is ______
into a phloem tube
at the sugar
source, raising the
solute
concentration
inside the tube
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Figure 32.5B
– Water is drawn
into the tube by
______ , raising
the pressure in
the tube
– Sugar and water
leave the tube at
the sugar sink
Figure 32.5B
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– The increase in
______ at the
sugar source and
decrease at the
sugar sink causes
phloem sap to
flow from source
to sink
Figure 32.5B
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• Plant biologists have used aphids to study
phloem sap
– These studies have supported the pressureflow model
Honeydew
droplet
Stylet
of aphid
Figure 32.5C
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PLANT NUTRIENTS AND THE SOIL
32.6 Plant health depends on a complete diet of
essential inorganic nutrients
• A plant must obtain
______ from its
surroundings
• ______________,
such as carbon, oxygen,
nitrogen, and
phosphorus, are needed
in large amounts
– They are used to build
organic molecules
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Figure 32.6B
• ______________, including iron, copper,
and zinc, act mainly as cofactors or enzymes
• Growing plants in
solutions of known
composition enables
researchers to
determine nutrient
requirements
– Hydroponic culture
Complete solution
containing all
minerals (control)
Solution lacking
potassium
(experimental)
Figure 32.6A
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32.7 Connection: You can diagnose some nutrient
deficiencies in your own plants
• Stunting, wilting, and color changes indicate
nutrient deficiencies
– Compared to the healthy tomato plant on the
left, the plant on the right is not getting enough
nitrogen
Figure 32.7A, B
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– Phosphorus
deficiency is
sometimes indicated
by a purplish leaf
color
– Yellow leaves can
result from
potassium deficiency
Figure 32.7C, D
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32.8 Soil contains rock particles, humus,
organisms, water, and crucial solutes
• Soil characteristics determine whether a plant
will be able to obtain the nutrients it needs to
grow
• ______ soil contains a mixture of small rock
and clay particles
– They hold water and ions and allow oxygen to
diffuse into plant roots
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• ______ is decaying organic material
– It provides nutrients, holds water and air, and
supports the growth of organisms that enhance
soil fertility
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• Soil horizons are distinct ______ of soil
• Horizon A, or ______ , contains rock particles
(sand and clay), humus, and living organisms
• Horizon B contains fine clay particles and
nutrients that
have drained
down from
Horizon A
• Horizon C is
composed mainly
of partially
broken-down rock
Figure 32.8A
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• A plant's root hairs are in direct contact with
the water that surrounds the tiny particles of
topsoil
• The root hairs
take up
dissolved
oxygen, ions,
and water from
the film of soil
water that
surrounds them
Soil particle surrounded
by film of water
Root hair
Water
Air space
Figure 32.8B
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• Anions, such as nitrate (NO3-), are readily
available to plants because they are not bound
to soil particles
– But they tend to drain out of the soil quickly
– This reduces soil fertility
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32.9 Connection: Soil conservation is essential to
human life
• Good soil
management
includes
– water-conserving
______
– ______ control
– the ______ use of
herbicides and
fertilizers
Figure 32.9A, B
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32.10 Connection: Organic farmers avoid the use
of commercial chemicals
• ______ farmers rely on the principles of
ecology rather than the use of synthetic
chemicals or pesticides that can damage the
environment
– Organic farmers
try to restore as
much to the soil
as is drawn from
it
Figure 32.10
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32.11 Fungi help most plants absorb nutrients
from the soil
• Relationships with other organisms help
plants obtain nutrients
• Many plants form mycorrhizae
– A network of fungal
threads increases a
plant's absorption
of nutrients and water
– The fungus receives
some nutrients from
the plant
Figure 32.11
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32.12 The plant kingdom includes parasites and
carnivores
• Some plants have
evolved ______ ways
of obtaining food from
other plants
– Dodder obtains
organic molecules
from other plant
species using
specialized roots that
tap into the host’s
vascular tissue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 32.12A
– Mistletoe supplements its diet by siphoning
______ from the vascular tissue of its host
plants
Figure 32.12B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Carnivorous plants obtain some of their
nutrients from ______ tissues
– The sundew and
Venus flytrap use
insects as a source
of ______
– This nutritional
adaptation enables
them to thrive in
highly acidic soil
Figure 32.12C, D
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
32.13 Most plants depend on bacteria to supply
nitrogen
• Plants cannot use atmospheric nitrogen,
gaseous N2, although it is very plentiful
– Instead, nearly all plants depend to some
extent on nitrogen supplies in the ______
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Bacteria in the soil convert N2 from the air and
nitrogen compounds from decomposing organic
matter into forms that plants can take up and
use
– Nitrate ions (N03-) and ammonium ions (NH4+)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• This process of converting atmospheric
nitrogen to ammonium is called nitrogen
______
ATMOSPHERE
N2
Amino
acids
Nitrogen-fixing
bacteria
N2
NH4+
NH4+
(ammonium)
Soil
Ammonifying
bacteria
Organic
material
Nitrifying
bacteria
NO3–
(nitrate)
Root
Figure 32.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
32.14 Legumes and certain other plants house
nitrogen-fixing bacteria
• ______ and
certain other
plants have
nodules in
their roots that
contain
nitrogen-fixing
bacteria
Shoot
Nodules
Roots
Figure 32.14A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Most of the nitrogen-fixing bacteria in legume
nodules belong to the genus ______
• The relationship between the plant and the
nitrogen-fixing bacteria is ______ beneficial
Bacteria
within
vesicle
Figure 32.14B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PLANT NUTRIENTS AND AGRICULTURE
32.15 Connection: A major goal of agricultural
research is to improve the protein content of
crops
• Plants are the main nutritional source for most
people in the world
– Therefore,
improving the
protein content
of crops is an
important
research goal
Figure 32.15A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• One of the most promising lines of agricultural
research is directed toward improving the
output of the Rhizobium bacteria that inhabit
the root nodules of legumes
Rhizobium
DNA
Genes for
nitrogen fixation
TURN OFF
GENES
Nitrogen compounds
in root nodules
Nitrogen-fixing
enzymes
N2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 32.15B
PLANT HORMONES
33.1 Experiments on how plants turn toward light
led to the discovery of a plant hormone
• Hormones coordinate the
activities of plant cells
and tissues
• The study of plant
hormones began with
observations of plants
bending toward light
– This phenomenon is
called phototropism
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 33.1A
• Experiments carried out by Darwin and others
showed that the tip of a grass seedling detects
light and transmits a signal down to the
growing region of the shoot
Light
Control
Figure 33.1C
Tip
removed
Tip covered
by opaque
cap
Tip
covered
by transparent cap
DARWIN AND DARWIN (1880)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Base
covered
by opaque
shield
Tip
separated
by gelatin
block
Tip
separated
by mica
BOYSEN-JENSEN (1913)
• It was discovered in the 1920s that a hormone
was responsible for the signaling Darwin
observed
– This hormone was dubbed ______
– Auxin plays an important role in
phototropism
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
33.2 Five major types of hormones regulate plant
growth and development
• Hormones regulate plant growth and
development by affecting
– cell ______
– cell ______
– cell ______
• Only small amounts of hormones are
necessary to trigger the signal-transduction
pathways that regulate plant growth and
development
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Table 33.2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Plants produce ______ (IAA) in the apical
meristems at the tips of shoots
– At different concentrations, auxin stimulates or
inhibits the elongation of ______ and
______
STEMS
ROOTS
0.9 g/L
Figure 33.3B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Phototropism results from faster cell growth on
the ______ side of the shoot than on the
illuminated side
Shaded
side of
shoot
Light
Illuminated
side of
shoot
Figure 33.1B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The effect of auxin on pea plants
Figure 33.3A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Auxin stimulates cell division and the
development of vascular tissues in vascular
cambium
– This promotes growth in stem diameter
• Auxins are also used as a rooting powder to
develop roots quickly in plant cuttings.
• Synthetic auxins can be sprayed on tomato
plants to induce fruit production without
pollination producing seedless tomatoes
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
33.4 Cytokinins stimulate cell division
• ___________ are hormones that promote
cell division and delay senescence (aging) by
inhibiting protein breakdown.
– They are produced in actively growing roots,
embryos, and fruits
• The antagonistic interaction of auxin and
cytokinin may be one way a plant coordinates
the growth of its root and shoot systems
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cytokinins from roots may balance the effects
of auxin from apical meristems, causing lower
buds to develop into branches
– The basil plant on the right has had its terminal bud
removed
– The inhibitory effect of
auxin on axillary buds
was thus eliminated
Terminal bud
No terminal bud
– Cytokinins from the
roots activated the
axillary buds, making
the plant grow more
branches
Figure 33.4
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
33.5 Gibberellins affect stem elongation and have
numerous other effects
• ____________ stimulate cell elongation and
cell division in stems and leaves. This causes
rapid growth in some stems known as bolting.
Figure 33.5A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Gibberellins, in combination with auxin, can
influence fruit development
– Gibberellins can make grapes grow ______ and
farther apart in a cluster
– The grapes
at right were
treated with
gibberellin,
while those
at left were
not
Figure 33.5B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Fig. 40.23
• Gibberellin-auxin sprays can make apples,
currants, and eggplants develop without
fertilization
• Gibberellins released from embryos function
in some of the early events of seed
germination
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
33.6 Abscisic acid inhibits many plant processes
• Abscisic acid (ABA) ______ the germination
of seeds
• The ratio of ABA to gibberellins often
determines whether a seed will remain
dormant or will germinate
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Seeds of many plants
remain dormant until
their ABA is inactivated
or washed away
– These flowers grew
from seeds that
germinated after a
rainstorm in the
Mojave Desert
Figure 33.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• ABA also acts as a “stress hormone”
– It causes stomata to close when a plant is
dehydrated
– Thus the rate of transpiration is decreased and
further water loss prevented
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
33.7 Ethylene triggers fruit ripening and other
aging processes
• Ethylene is a gaseous hormone that triggers
fruit ______
• Ethylene is given off as cells age
• These bananas
were exposed
to different
amounts of
ethylene over
the same time
period
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 33.7A
• Fruit growers use ethylene to control ripening
– Apple farmers take measures to retard the
ripening action of natural ethylene
– Tomato farmers pick unripe fruit and then
pipe ethylene into storage bins to promote
ripening
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The shorter days of
autumn trigger a
changing ratio of
auxin to ethylene
Leaf
stalk
Stem
(twig)
– This is the likely
cause of the
changes seen in
deciduous trees —
color changes,
drying, and the
loss of leaves
Protective
layer
Figure 33.7B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Stem
Abscission
layer
Leaf stalk
33.8 Connection: Plant hormones have many
agricultural uses
• Plant hormones have a variety of agricultural
uses
– Farmers use auxin to delay or promote fruit
drop
– Auxin and gibberellins are used to produce
seedless fruits
– A synthetic auxin (2,4-D) is used to kill weeds
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• There are many questions and concerns about
the safety of using such chemicals in food
production
Figure 33.8
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
GROWTH RESPONSES AND BIOLOGICAL
RHYTHMS IN PLANTS
33.9 Tropisms orient plant growth toward or away
from environmental stimuli
• Plants sense and respond to environmental
changes in a variety of ways
• Tropisms are growth responses that change
the shape of a plant or make it grow toward or
away from a stimulus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Phototropism is the bending ______ light
– It may result
from auxin
moving from
the illuminated
side to the
shaded side of
a stem
Figure 33.1A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Gravitropism is a response to ______
– It may be caused
by the settling of
special organelles
on the low sides
of shoots and
roots
– This may trigger a
change in the
distribution of
hormones
Figure 33.9A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Gravitropism is an important adaptation
– It ensures that the shoot will grow upward
toward light and the roots will grow down into
the soil, no matter how the seed lands in the
soil
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Thigmotropism is a response to ______
– It is responsible for the coiling of tendrils and
vines around objects
– It enables plants
to use other
objects for
support while
growing
toward sunlight
Figure 33.9B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Haploid Art)
Fig. 29.03(TE
Gametophyte
(n)
Mitosis
Spore
Sperm
Egg
n n
n n Spores
Meiosis
Gamete fusion
Spore mother
2n cell
2n Zygote
2n Embryo
Sporangia
Sporophyte
(2n)
Diploid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 29.05(TE Art)Sperm
Antheridium
FERTILIZATION
Zygote
Egg
Archegonium
Developing
sporophyte in
archegonium
Mature
sporophyte
n 2n
Male
Female
Gametophytes
Sporangium
MEIOSIS
Bud
Mitosis
Rhizoid
Germinating
Spores
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Inc. publishing as Benjamin Cummings
spores
Parent
gametophyte
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 29.13(TE Art)
Mitosis
Archegonium
Antheridium
Rhizoids
Spore Gametophyte
n Sperm
MEIOSIS
FERTILIZATION
2n
Mature
sporangium Mature
frond
Egg
Embryo
Sorus (cluster
of sporangia)
Leaf of young
sporophyte
Adult
sporophyte
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Rhizome
Gametophyte
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 29.15(TE Art)
Megaspore
Pollen
tube
Mature seed
cone (2nd year)
Mitosis
Pollination
Pollen FERTILIZATION
(15 months after
n pollination)
Mitosis
Mitosis
Embryo
Microspores
Longisection of
seed, showing
Microspore
mother cell 2n embryo Pine
seed
Pollen-bearing
Scale
Mitosis
cone
Megaspore
mother cell
Seedling
Scale
Ovulate (seed-bearing)
cone
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Sporophyte
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings