Download Categorizing Flowering Plants

BIOLOGY
A GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
The Angiosperms:
Form and Function in Flowering Plants
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25.1 Two Ways of Categorizing
Flowering Plants
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Categorizing Flowering Plants
• Plants can be categorized by how long it takes
them to go through a cycle that runs from
germination to death.
• Those that go through this cycle in a year or
less are annuals; those that go through it in
about 2 years are biennials; those that live for
many years are perennials.
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Categorizing Flowering Plants
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Figure 25.4
Categorizing Flowering Plants
• A cotyledon is an embryonic leaf, present in the
seed.
• Angiosperms are classified according to how
many cotyledons they have:
– one in the case of the narrow-leafed
monocotyledons
– two in the case of the broad-leafed dicotyledons
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Categorizing Flowering Plants
Monocots
Dicots
one
cotyledon
two
cotyledons
embryonic
leaves
mature
leaves
narrow leaves
parallel
veins
broad
leaves
branching
veins
roots
fibrous root
system
taproot
system
vascular
bundles
scattered
throughout
stem
arranged
in ring in
stem
type of
growth
only primary
growth
may have
secondary
woody
growth
flower
parts
multiples of
three
multiples
of four or
five
examples
orchids, wheat, rice, bananas
oak and maple trees, cacti,
sunflowers
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Figure 25.5
Categorizing Flowering Plants
• Monocots and dicots differ in structure in many
ways.
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Categorizing Flowering Plants
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Figure 25.6
25.2 There Are Three Fundamental
Types of Plant Cells
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Types of Plant Cells
• There are three fundamental types of cells in
plants that, alone or in combination, make up
most of the plant’s tissues, meaning groups of
cells that carry out a common function.
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Types of Plant Cells
• These three cell types are:
– parenchyma
– sclerenchyma
– collenchyma
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25.3 The Plant Body and Its Tissue Types
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The Plant Body and Its Tissue Types
• Some plants are capable only of primary
growth, meaning growth at the tips of their
roots and shoots that primarily increases their
length.
• Plants that exhibit only primary growth are
herbaceous plants, composed solely of primary
tissue.
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The Plant Body and Its Tissue Types
• Other plants exhibit both vertical growth and
lateral, or secondary, growth.
• These are the woody plants, composed of
primary and secondary tissue.
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The Plant Body and Its Tissue Types
• There are four tissue types in the primary plant
body:
–
–
–
–
dermal
vascular
meristematic
ground
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Four Types of Tissue
dermal tissue
vascular tissue
ground tissue
meristematic
tissue
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Figure 25.8
Four Types of Tissue
•
•
•
•
Dermal tissue is the plant’s outer covering.
Vascular tissue is its “plumbing.”
Meristematic tissue is its growth tissue.
Ground tissue is almost everything else in the
plant.
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Dermal Tissue
Dermal Tissue
invaders out
sunlight gases
in
exchanged
cuticle
epidermis
guard cells
of stomata
trichome
guard cells: epidermal cells
trichomes: hairlike outgrowths
modified for regulation of gas exchange of epidermal cells
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Figure 25.9
Ground Tissue
Ground Tissue
parenchyma
• thin-walled
• alive at maturity
• many functions
collenchyma
• wall irregularly thick
• structural support
(plastic)
sclerenchyma
• very thick-walled
• dead at maturity
• structural support
(stiff)
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Figure 25.10
Vascular Tissue
Vascular Tissue
vascular
bundle
phloem
xylem
vessel
element
tracheid
sieve
element
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companion
cell
Figure 25.11
Plant Tissue and Growth
PLAY
Animation 25.1: Plant Tissue and Growth
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25.4 How a Plant Grows: Apical Meristems
Give Rise to the Entire Plant
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How a Plant Grows
• The entire plant develops from meristematic
cells in regions called apical meristems.
• Meristematic cells remain perpetually
embryonic, able to continually give rise to cells
that differentiate into all the plant’s tissue types.
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How a Plant Grows
• Shoot apical meristems give rise to the entire
shoot of the plant.
• In addition to providing for vertical growth,
shoot apical meristems produce meristematic
tissue called lateral buds at the base of leaves.
• Lateral buds can give rise to a branch or flower.
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How a Plant Grows
Meristematic Tissue
immature leaf
shoot apical meristem
(terminal bud)
meristematic
tissue
(lateral bud)
root apical meristem
root cap
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Figure 25.13
How a Plant Grows
• Root apical meristems are located just behind a
collection of cells at the very tip of the root,
called the root cap.
• The plant’s tissue types develop in stages from
meristematic cells.
• This development takes place in a series of
regions adjacent to the apical meristem.
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How a Plant Grows
• In a gradual transition, the apical meristem
gives way to a zone of cell division.
• This is followed by a zone of elongation (in
which developing cells lengthen).
• This is followed by a zone of differentiation (in
which cells fully differentiate into different
tissue types).
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Tissue Development from Apical
Meristems
dermal
tissue
zone of
differentiation
ground vascular tissue
tissue
root
hairs
zone of
elongation
zone of
cell division
meristem
root cap
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Figure 25.15
25.5 Secondary Growth Comes from a
Thickening of Two Types of Tissue
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Secondary Growth Tissues
• Secondary growth in plants takes place through
the division of cells in two varieties of
meristematic tissue that develop only in woody
plants:
– Vascular cambium, which continually produces
secondary phloem and secondary xylem tissue
layers to either side of itself.
– Cork cambium, which gives rise to the outer tissues
of woody plants.
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primary growth
Secondary Growth Tissues
secondary
growth
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Figure 25.18
Secondary Growth Tissues
primary
xylem
primary
phloem
vascular
cambium
first-year
growth
secondary
xylem
secondary
phloem
second-year
growth
third-year
growth
lateral growth
vascular secondary secondary
cambium xylem
phloem
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Figure 25.19
Secondary Growth Tissues
• Secondary xylem, also known as wood, is
responsible for most of a tree’s widening.
• Looking at a tree from the secondary phloem
outward to the tree’s periphery, four tissues
constitute the tree’s bark:
–
–
–
–
secondary phloem
phelloderm
cork cambium
cork
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Secondary Growth Tissues
cork
cork
cambium
bark
phelloderm
secondary
phloem
vascular
cambium
secondary
xylem (wood)
xylem ray
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Figure 25.22
Secondary Growth Tissues
• The cork cells are dead in their mature state and
provide layers of protection for the tree.
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25.6 How the Plant’s
Vascular System Functions
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Xylem
• Two types of cells make up the waterconducting portions of xylem tissue: tracheids
and vessel elements, both of which are dead in
their mature, working state.
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Xylem
• Vessel elements, which exist almost solely in
angiosperms, conduct more water than
tracheids.
• Their existence in angiosperms is one of the
reasons for the angiosperms’ dominance in the
plant world.
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Xylem
xylem
tracheid
vessel element
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Figure 25.25
Xylem
• Water movement through xylem is driven by
transpiration, meaning the loss of water from a
plant, mostly through the leaves.
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Xylem
Water Transport by Transpiration
H2O
H2O
Water evaporates
from stomata
on underside of
leaves.
plant’s energy
not required
Water from stem is pulled
up through xylem to replace
water lost from leaves.
Water is pulled out of
soil into roots to replace
water lost from stem.
H2O
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Figure 25.26
Xylem
• As water evaporates into the air, it pulls a
continuous column of water upward through the
plant.
• The energy for this process comes from the sun,
whose rays power the evaporation of water at
the leaf surface.
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Phloem
• The sugar sucrose is the main product that
flows through phloem.
• The fluid-conducting cells in phloem, sieve
elements, lack cell nuclei in maturity.
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Phloem
• Each sieve element has associated with it one
or more companion cells, which retain their
nuclei and seem to take care of the
housekeeping needs of their related sieve
elements.
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Phloem
phloem
sieve element
companion cell
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Figure 25.27
Water Transport in Plants
Suggested Media Enhancement:
Water Transport in Plants
To access this animation go to folder C_Animations_and_Video_Files
and open the BioFlix folder.
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Phloem
• Plants expend their own energy to load the
sucrose they produce into the phloem’s sieve
element cells.
• Once this takes place, there is a greater
concentration of solutes inside the cells than
outside them—a condition that brings about a
flow of water into the cells through osmosis.
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Sugar Transport by Pressure Flow
Sugar Transport by Pressure Flow
source
Photosynthesis in
leaves produces
sugar, which is
loaded into the
phloem.
plant’s energy
required
Sugars are transported
through phloem to fruits,
stems, and roots.
Sugars are stored in
parenchyma.
sink
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Figure 25.28
Sugar Transport by Pressure Flow
• The pressure that results from the increased
water inside the cells is sufficient to move the
solution of water and dissolved sucrose through
the sieve element cells.
• They move from “source” (the cells into which
the sugar was loaded) to “sink” (the cells in
which the sugar is stored or used).
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Phloem Sap Transport and
Phloem-Xylem Linkage
xylem
source
sugar
phloem
Sugar is actively
transported into
phloem (requires
plant’s own energy).
water
leaf cell
Water follows
by osmosis.
Pressure gradient
moves fluid down
phloem.
sink
sugar
Sugar moves by
active or passive
transport into root
cell.
water
root cell
Water follows
by osmosis.
vessel
sieve
element element
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Figure 25.30
Vascular System
PLAY
Animation 25.2: The Vascular System for Plants
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25.7 Sexual Reproduction in Flowering
Plants
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Sexual Reproduction in Flowering
Plants
• All plants, including angiosperms, reproduce
through an alternation of generations.
• A sporophyte generation (the familiar tree or
flower) produces haploid spores that develop
into their own generation of plant, the
gametophyte generation.
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Sexual Reproduction
• In angiosperms, the male gametophyte is the
pollen grain, consisting in maturity of an outer
coat, two sperm cells, and one tube cell.
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Sexual Reproduction
• The female angiosperm gametophyte consists at
maturity of an embryo sac composed of seven
cells, one of which is the egg.
• The female gametophyte is housed inside a
structure of the parent sporophyte plant called
an ovule.
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Sexual Reproduction
anther
ovary
pollen
sac
ovule
microspore
mother cell
(2n)
meiosis
megaspore
mother cell
(2n)
4 microspores
(n)
integument
micropyle
stalk
4 megaspores
(n)
mitosis
3 megaspores
degenerate
mitosis
mitosis
tube cell
generative
cell
mitosis
pollen grain
tube cell
outer coat
sperm cells
pollen
(male gametophyte)
is released from
sporophyte plant
it’s housed in
mitosis
embryo
sac
8 haploid
nuclei
cytokinesis
egg
central cell
mature female
gametophyte
within
sporophyte
The male gametophyte generation takes shape
inside the chambers of the pollen sacs, where the
diploid microspore mother cells will undergo meiosis,
each one of them thereby giving rise to four haploid
microspores. These microspores represent the new,
haploid generation of the plant on the male side.
For the female gametophyte generation, development
begins in a structure inside the parent ovary called an
ovule. A single diploid megaspore mother cell in the
ovule undergoes meiosis, producing four haploid
megaspores. This marks the beginning of the female
gametophyte generation.
The single cell in each microspore goes through cell
division, thereby producing two cells, a tube cell and
a generative cell. Before or during this time, a
protective coat develops around the microspore. The
combination of the cells and protective coat is the
pollen grain. At some point, the generative cell in the
grain divides into two sperm cells. With this cell
division, a mature male gametophyte has developed.
The pollen grain is then released from the anthers to
make its way to a stigma.
Three of the megaspores then die. The remaining
megaspore undergoes mitosis, eventually producing
six cells with a single nucleus each and one central
cell with two nuclei. These seven cells form the
embryo sac, which is the mature female gametophyte.
One of the seven cells in the embryo sac is the egg
that will undergo fertilization by one of the sperm in
the pollen grain.
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Figure 25.34
Sexual Reproduction
• Fertilization of the egg by sperm requires that a
pollen grain land on the stigma of a plant.
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Sexual Reproduction
• The tube cell of the pollen grain then
germinates, sprouting a pollen tube that grows
down through the sporophyte plant’s stigma and
style, eventually reaching the female
reproductive cells inside the ovule.
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Sexual Reproduction
• The sperm cells inside the pollen grain travel
down through the pollen tube, and one of the
sperm cells fertilizes the egg in the ovule,
producing a zygote.
• With this, the new sporophyte generation of
plant has come into being.
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Sexual Reproduction
anther
mature
sporophyte
pollen
microspores
carpel
ovary
gametophyte
generation
(n)
tube cell
sperm cells
pollen
germination
stigma
pollen
tube
seed
germination
and growth
megaspore
sporophyte
generation
(2n)
egg
fertilization
seed
zygote
embryo
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Figure 25.33
Sexual Reproduction
• The second sperm cell in the pollen grain enters
the central cell in the embryo sac, setting in
motion the development of food for the
embryo, endosperm tissue.
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Sexual Reproduction
• This second fertilization completes the process
of double fertilization—a fusion of gametes on
the one hand and of cells producing nutritive
tissue on the other.
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Sexual Reproduction
tube
cell
sperm
cells
pollen grain
stigma
pollen
tube
sperm
cells
style
fusion of one
sperm cell with
nuclei of central
cell to form
endosperm (3n)
micropyle
ovary
ovule
with female
gametophyte
egg (n)
pollination
pollen tube
growth
double
fertilization
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fusion of one
sperm cell with
egg to form
zygote (2n)
Figure 25.35
25.8 Embryo, Seed, and Fruit:
The Developing Plant
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The Developing Plant
• With fertilization, the ovule integuments that
surrounded the embryo sac begin to develop
into the seed coat that will surround the
growing sporophyte embryo.
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The Developing Plant
• The ovary that surrounded the ovule then starts
to develop into a layer of tissue that will
surround the seed: fruit, which is defined as the
mature ovary of a flowering plant.
• Under this definition the pod of a pea plant is
fruit, as is the flesh of an apricot.
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The Developing Plant
Apricot
Pea
Strawberry
carpels
one carpel, one seed
one carpel, many seeds
many carpels, many seeds,
one receptacle
receptacle
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Figure 25.38
The Developing Plant
• The seed with its fruit covering eventually
separates from the sporophyte parent plant and
then germinates in the Earth.
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Plant Reproduction
PLAY
Animation 25.3: Plant Reproduction
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