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Biology
A Guide to the Natural World
Chapter 24 • Lecture Outline
Plants: The Diversity of Life 4
Fifth Edition
David Krogh
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24.1 The Roles and Characteristics
of Plants
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Roles of Plants
• The photosynthesis that plants perform
indirectly feeds many life-forms.
• The oxygen plants produce as a by-product of
photosynthesis is vital to many organisms
• Many plant products are important to human
beings.
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Characteristics of Plants
• With a few exceptions, all plants
• Are multicelled
• Fixed in one spot
• Carry out photosynthesis.
• All plant cells have a cell wall and most
contain organelles called chloroplasts,
which are the sites of photosynthesis.
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Characteristics of Plants
cell wall
(made of lignin and cellulose)
cell membrane
nucleus
central vacuole
(contains mostly water)
chloroplast
(site of photosynthesis)
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Figure 24.3
Characteristics of Plants
• Plants reproduce through an alternation of
generations: a life cycle in which successive
plant generations produce either spores
(the sporophyte generation) or gametes
(the gametophyte generation).
• Within a given species, these two
generations can differ greatly in size and
structure.
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(a) Human reproduction
meiosis
egg
multicellular
diploid
adults
sperm
1n
fertilization
2n
mitosis and
development
zygote
(b) Plant alternation of generations
multicellular
gametophyte
spores
meiosis
gametes
1n
fertilization
2n
multicellular
sporophyte
zygote
haploid (1n)
diploid (2n)
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Figure 24.4
24.2 Types of Plants
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Types of Plants
• The four principal categories of plants are:
•
•
•
•
Bryophytes (mosses)
seedless vascular plants (ferns)
Gymnosperms (coniferous trees)
Angiosperms (a wide array of plants)
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Types of Plants
flowering
mosses ferns conifers plants
(a) Moss
(b) Ferns
(c) Conifers
(d) Flowering plants
flowers
seeds
vascular
tissue
multicellularity
green algae
(ancestors)
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Figure 24.6
Bryophytes
• Bryophytes are close living relatives of the
earliest plants that made the transition from
living in water to living on land.
• They lack a fluid transport or vascular system
and thus tend to be low lying.
• Tend to inhabit damp environments and their
sperm get to eggs primarily by swimming
through water
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Bryophytes
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Figure 24.7
Seedless Vascular Plants
• Seedless vascular plants have a vascular
system but do not produce seeds in
reproduction.
• Their sperm must move through water to
fertilize eggs.
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Seedless Vascular Plants
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Figure 24.8
Gymnosperms
• Gymnosperms are seed-bearing plants with
seeds that are not encased in tissue called
fruit.
• There are only about 1000 gymnosperm
species, but their presence is considerable,
particularly in northern latitudes, where
gymnosperm trees, such as pine and spruce,
often dominate landscapes.
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Gymnosperms
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Figure 24.9
Gymnosperm Reproduction
• Gymnosperms produce seeds in carrying
out reproduction.
• Seeds are reproductive structures that
include a plant embryo, its food supply,
and a tough, protective casing.
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Gymnosperms
wing
protective
seed coat
seed
embryo
nutritional
tissue
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Figure 24.10
male cone
1. Wind carries pollen
to female cone.
pollen
female cone
2. Sperm within the
pollen fertilizes one
egg within the cone.
mature
tree
seedling
3. Embryo begins to
develop within seed.
seed
5. New pine tree
begins to grow.
4. Seed germinates.
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Figure 24.11
Angiosperms
• Angiosperms, or flowering plants, produce
seeds that are incased in fruit.
• Angiosperms are easily the most dominant
group of plants on Earth, with some
260,000 species having been identified to
date.
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Angiosperms
• Angiosperm species include not only plants
with flowers, such as roses, but almost all
trees except for the conifers, all important
food crops, cactus, shrubs, and common
grass.
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Angiosperms
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Figure 24.12
24.3 Angiosperm–Animal
Interactions
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Angiosperm–Animal Interactions
• Angiosperm pollen grains generally are
transferred from one plant to another by
animals, such as insects and birds.
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Angiosperm–Animal Interactions
• To induce animals to carry out this
pollination, angiosperm flowers produce
nectar and have developed attractive
colorations and fragrances.
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Angiosperm–Animal Interactions
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Figure 24.13
Endosperm
• Angiosperm seeds contain tissue called
endosperm, which functions as food for the
growing embryo.
• Endosperm supplies much of the food that
human beings eat. Rice and wheat grains
consist largely of endosperm.
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Endosperm
wheat
endosperm
seed coat (bran)
embryo (wheat germ)
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Figure 24.15
Fruit
• Angiosperm seeds are unique in the plant
world due to being wrapped in a layer of
tissue called fruit.
• Fruit that is edible functions in angiosperm
seed dispersal because animals will eat and
digest the fruit but then excrete the tough
seeds inside, often in a different location.
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Seed Carriers
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Figure 24.16
24.4 Responding to External Signals
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Gravitropism
• With gravitropism, plants are able to sense
their orientation with respect to the Earth
and direct the growth of their roots and
shoots accordingly—roots into the Earth,
shoots toward the sky.
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Phototropism
• Plants will bend toward a source of light to
gain additional access through the process
of phototropism, meaning a curvature of
shoots in response to light.
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Thigmotropism
• Thigmotropism is defined as the growth of a
plant in response to touch.
• Some plants can climb upward on other
objects by making contact with them and
then encircling them in growth to gain
additional access to light.
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Differential Growth
• Gravitropism, phototropism, and
thigmotropism are made possible by
differential growth on one side of a root
or stem.
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Responding to Seasons
• In temperate climates, deciduous trees
exhibit a coordinated, seasonal loss of
leaves and enter into a state of dormancy,
existing on stored nutrient reserves in colder
months.
• Dormancy evolved in deciduous trees
because any photosynthesis they could
perform in winter would not offset the water
loss and leaf damage that would result from
leaf retentention
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Responding to Seasons
• Plants can sense the passage of seasons and
time their metabolic and reproductive
activities accordingly.
• One mechanism that assists in this process
is photoperiodism, which is the ability of a
plant to respond to changes it is
experiencing in the daily duration of
darkness relative to light.
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Responding to Seasons
• Some plants that exhibit photoperiodism are
long-night plants, meaning those whose
flowering comes only with an increased
amount of darkness—in late summer or
early fall.
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Responding to Seasons
• Others are short-night plants, meaning those
whose flowering comes only with a
decreased amount of darkness—in early to
midsummer.
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