Download The Importance of Plants

BIOLOGY
A GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
The Angiosperms:
An Introductions to Flowering Plants
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
24.1 The Importance of Plants
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The Importance of Plants
• Plants are vital to many types of living things
on Earth.
• The photosynthesis they carry out indirectly
feeds many other life-forms.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Importance of Plants
• The oxygen plants produce as a by-product of
photosynthesis is vital to many organisms.
• The lumber and paper that trees provide is
important to human beings.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Importance of Plants
• Plants act as an anchoring environmental force
by preventing soil erosion and absorbing carbon
dioxide and pollutants.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Four Types of Plants
• There are four principal varieties of plants:
– Bryophytes, represented by mosses.
– Seedless vascular plants, represented by ferns.
– Gymnosperms, represented by coniferous
(evergreen) trees.
– Angiosperms, or flowering plants.
• Of the four varieties, angiosperms are by far the
most dominant on Earth.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
24.2 The Structure of Flowering Plants
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Structure of Flowering Plants
• Plants live in two worlds, above the ground and
below it.
• Their anatomy can be conceptualized as
consisting of the aboveground shoots and the
below-ground roots.
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Structure of Flowering Plants
• Roots absorb water and nutrients, anchor the
plant, and often act as nutrient storage sites.
• Shoots include the plant’s leaves, stems, and
flowers.
• Leaves serve as the primary sites of
photosynthesis in most plants.
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Shoots: Leaves, Stems, and Flowers
• Leaves have a profusion of tiny pores, called
stomata, that open and close in response to the
presence or absence of light.
• In this way, the stomata control the flow of
carbon dioxide into the plant and the flow of
oxygen and water vapor out of the plant.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Shoots: Leaves, Stems, and Flowers
• Stems give structure to plants and act as storage
sites for food reserves.
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Shoots: Leaves, Stems, and Flowers
• Flowers are the reproductive structures of
plants, with most flowers containing both male
and female reproductive parts.
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Shoots: Leaves, Stems, and Flowers
• The male reproductive structure, called a
stamen, consists of a slender filament topped
by an anther.
• The anther’s chambers contain the cells that
will develop into sperm-containing pollen
grains.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Shoots: Leaves, Stems, and Flowers
• The female reproductive structure, the carpel,
is composed of:
– A stigma, on which pollen grains are deposited
– A tube called a style, which raises the stigma to
such a height that it can catch pollen
– And a structure called an ovary, where fertilization
of the female egg and early development of the
resulting embryo take place.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
24.3 Basic Functions in Flowering Plants
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Reproduction in Angiosperms
• Pollen grains develop from cells called
microspores located inside the plant’s anthers.
• At maturity, each pollen grain consists of two
sperm cells, one tube cell, and an outer coat.
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Reproduction in Angiosperms
• Plant eggs develop from a cell called a
megaspore within the plant’s ovary.
• When a pollen grain from one plant lands on
the stigma of a second plant, the pollen grain
germinates, developing a pollen tube that grows
down through the second plant’s style.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Reproduction in Angiosperms
• Sperm cells from the pollen grain travel
through the pollen tube.
• One of the sperm cells reaches the egg in the
ovary of the second plant and fertilizes it.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Reproduction in Angiosperms
• Once it is fertilized by the sperm cell, the egg
(or zygote) develops into an embryo that
eventually will be surrounded by a tough outer
covering.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Reproduction in Angiosperms
• The combination of embryo, its food supply,
and the outer covering is called a seed.
• A seed is capable of being planted in the ground
and growing into a new generation of plant.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Reproduction in Angiosperms
• Angiosperms can be defined as plants whose
seeds are surrounded by a layer of tissue called
fruit.
• Fruit is the mature ovary of a flowering plant
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Reproduction in Angiosperms
• Plants can reproduce asexually through such
means as grafting.
• This is known as vegetative reproduction.
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Fluid Transport
• Fluid transport in plants is handled through two
kinds of tissue:
– xylem, through which water and dissolved minerals
flow; and
– phloem, through which the food the plant produces
flows, along with hormones and other compounds.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Fluid Transport
• Xylem is composed of two types of fluidconducting cells—vessel elements and
tracheids.
• Phloem is composed of cells called sieve
elements and their related companion cells.
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Hormones
• Plant hormones regulate plant growth and
development and integrate the functioning of
various plant structures.
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Hormones
• Many fruits ripen under the influence of the
plant hormone ethylene.
• The hormone IAA is important in controlling
plant growth.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Growth
• Plants do not grow vertically throughout their
length.
• Instead, they grow almost entirely at the tips of
both their roots and shoots.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Growth
• Some plants, such as trees, thicken through
lateral or “secondary” growth.
• The growth of most plants is indeterminate,
meaning it can go on indefinitely.
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Defense
• Plants have formidable defenses, both structural
(such as cactus spines) and chemical (such as
antifungal compounds).
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Cooperative Relationships
• Plants enter into cooperative relationships with
other organisms.
• Most plant roots are linked to underground
fungal extensions called hyphae.
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Cooperative Relationships
• The hyphae bring added water and nutrients to
the plant and the photosynthesis the plant
performs brings food to the fungi.
• The combined root–hyphae associations are
known as mycorrhizae.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Cooperative Relationships
• Some plants form cooperative relationships
with nitrogen-fixing bacteria.
• The bacteria take in atmospheric nitrogen and
transform it into a form the plants can use.
• The plants provide the bacteria with nutrients.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Leaves, Reproduction, and Fluid
Transport
PLAY
Animation 24.1: Leaves, Reproduction, and Fluid Transport
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Phototropism
• Plants will bend toward a source of light
through the process of phototropism, meaning a
curvature of shoots in response to light.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Differential Growth
• Differential growth on one side of the root or
stem makes possible phototropism,
gravitropism, and thigmotropism.
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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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Responding to Seasons
• Others are short-night plants, meaning those
whose flowering comes only with a decreased
amount of darkness—in early to midsummer.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Phototropism
PLAY
Animation 24.2: Phototropism
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.