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PLANTS
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How Are Plants All
Alike?
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Plant Characteristics
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Multicellular
Autotrophic (photosynthesis)
Chlorophylls a and b in thylakoid
membranes
Surrounded by cell walls containing
cellulose (polysaccharide)
Store reserve food as amylose
(starch)
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Plant Structure and Anatomy
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Roots, stems, and leaves
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Roots anchor the plant and draw water and
minerals from the soil
Stems support the body and carry water
and nutrients
Leaves are the main photosynthetic organ
Plant tissue
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Three kinds of tissue in general
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Dermal  Outer covering
Vascular  Fluid-conducting system
Ground  Support and photosynthesis
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Plant Structure and Anatomy
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Plant cells
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Cells within the dermal tissue need to protect
the plant from transpiration yet allowing gas
exchange to occur
Ground tissue contains mainly of parenchyma
cell, which are thin-walled and form the bulk
of tissue in roots, stems, and leaves. These
cells are very active in photosynthesis.
Collenchyma and sclerenchyma cells support
the plant
Vascular tissue has the xylem and phloem,
which carries water and nutrients,
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respectively.
Roots
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A growing seedling first sends a
single primary root into the soil and
as it grows bigger, secondary roots
branch off the primary root
This enlarges the SA dramatically
Epidermis
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Outer covering of the root
Has root hairs that make direct contact
with the soil
The hairs are responsible for the large SA
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Roots
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Cortex
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The layer of spongy cells beneath the
epidermis
Parenchyma cells of the cortex move water
from the epidermis to the vascular tissue
Vascular cylinder
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The central region of xylem and phloem
Carries water and nutrients between roots
and the rest of the plant
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Roots
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How Roots Work
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Osmosis!!
Water moves out of damp soil into root
hairs, which contain high concentrations
of dissolved salts and sugars
The water passes through the root
hairs and eventually into the vascular
cylinder
What would happen if a plant was placed
inside salt water?
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Rapid water loss from roots is known as
“root burn”
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Roots
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Active transport
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Minerals going through cell membrane
This also brings in the water to the core
The Casparian strip
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Endodermis—inner boundary of cortex that
is very tight
Separates cortex from vascular cylinder
Known as the waxy layer that can control
the entry into the core
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Stems
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Connects roots with the leaves: water and
nutrients with photosynthesis
Epidermal tissues on the edge but different
arrangement of ground and vascular tissue 
For later.
Wood
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As stem grows, new cells form between vascular
cells, thus pushing outward and increasing the
diameter
Vascular cambium: layer of dividing cells, usually
the xylem
Phloem cells don’t grow as much and thus can get
‘cracked’  Cork cambium produces cork that
form the bark
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Stems
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Cambium produces much
more xylem in the
summer than in colder
weather
Historical information
can be seen via annual
tree rings
Nutrient transport and
growth occurs within
the thin layers of cells
just under the bark 
very delicate and easily
damaged
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Leaves
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Main site of photosynthesis
Large SA with little mass  efficient in collecting
solar energy
Attached to the stem by a petiole
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Epidermis
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Covered with waxy cuticle
Stomata underneath for gas exchange
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Leaves
Guarded by two guard cells that open and close
Need to balance need for CO2 against need
to conserve water
Mesophyll tissue
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Packed with chloroplasts
Two types
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Tall palisades on top
Spongy ones on bottom—lots of air space
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Leaves
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Leaf veins—
vascular tissue
Xylem and
osmosis
 Xylem and
phloem found as
vascular bundles
called ‘veins’
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Leaves
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Closed
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Photosynthesis halts
Open
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Stomata Activity
Photosynthesis can resume but too much
transpiration could occur
Guard cells
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When water flows in, increase in pressure
causes a structural change that OPENS the
stoma
When water flows out, decrease in pressure
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causes stoma to CLOSE
Stomata Activity
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Several factors cause stomata to close:
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Lack of water reshapes the guard cells
High temperatures stimulates cellular
respiration, which can increase CO2
concentration within the air spaces
Other factors cause stomata to open:
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Depletion of CO2 within the air spaces of the
leaf, which occurs when photosynthesis
begins
An increase in potassium ions (K+) into guard
cells, which causes water to enter
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Xylem
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Water conducting system
Consists of two types of cells
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Tracheids: long, thin cells that overlap and
are tapered at the ends; function to support
the plant as well as to transport the water
Vessel elements: generally wider, shorter,
thinner walled, and less tapered; aligned end
to end and differ from tracheids in that the
ends are perforated to allow free flow
through vessel tubes
Makes up most of wood and dead upon
functional maturity
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Phloem
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Sugar conducting system via active
transport
Consist of chains of sieve tube
members/elements whose end walls
contain sieve plates that facilitate the
flow of fluid from one cell to the next
Alive at maturity, although they lack
nuclei, ribosomes, and vacuoles
Connected to each sieve tube member is
at least one companion cell that contain a
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full complement of cell organelles
Xylem and Phloem
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Fluid Transport
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Xylem transport
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Water gets transported against gravity but doesn’t
require any energy  From root to leaves
Fluid can be pushed up by root pressure via root pressure:
Results from water flowing in to the roots from soil via
osmosis; can push xylem sap upward only a few yards
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The morning dew is due to root pressure  Guttation
Transpirational pull can carry fluid up the world’s tallest
tress. Transpiration causes a negative pressure (tension)
to develop and thus pulls up the sap
Cohesion of water due to strong attraction between
water molecules makes it possible to pull a column of
water from above
Transpirational pull-cohesion tension theory
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Fluid Transport
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Phloem transport
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Phloem sap carries sugar from leaves into root and
often to developing fruits as well
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Translocation: Sugar gets distributed from various sources
to sinks
The source is where sugar is being produced and the sink is
where sugar gets stored or consumed
Movement of sugar into phloem highway creates a
driving force because it establishes a concentration
gradient  Causes water to come in and thus higher
pressure occurs.
This pressure drives the movement of sugars and
water through the phloem
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Plant Growth
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Tropisms: Derived from Greek and means ‘to
turn’; plant responses to cues from their
environment
Geotropism/Gravitropism
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Thigmotropism
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Response to gravity
Helps seedling grow toward sunlight
Different directions for root and stem
Response to touch
Phototropism
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Response to light
First recognized by Darwin and his son (1880s)
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Plant Hormones
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Hormone is a substance produced in one part of an
organism that affects activities in another part
Plant hormones help coordinate growth, development,
and responses to environmental stimuli
Darwin’s experiment with phototropism: Figure 26-11 on
p. 612
Auxin
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Indoleacetic acid (IAA) is a naturally occurring auxin; “To
increase”; first plant hormone discovered
Stimulate cell growth and are produced by cells in the apical
meristem, the rapidly growing region near the tip of a root or
stem; preferential growth upward rather than lateral
Also stimulates stem elongation and growth by softening the
cell wall
Produces phototropism due to unequal distribution
Mainly produced in the shoots and leaves
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Cytokinins
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Plant Hormones
Promotes cell division (cytokinesis, hence the name!) in lateral
branches and leaf enlargement
Slows down the aging of leaves
Ratio between auxin and cytokinin concentration determines
cell growth, rather than the level of either hormone by itself
However, can work antagonistically against auxins in relation to
apical dominance
Produced in roots and travels upward in the plant
Gibberellin
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Promote stem and leaf elongation
Work in concert with auxins to promote cell growth
Induce bolting, the rapid growth of floral stalk
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Ex. Broccoli entering the reproductive stage  Sends up a tall shoot to
ensure pollination and seed dispersal
Induction of growth in dormant seeds, buds, and flowers
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Plant Hormones
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Abscisic acid (ABA)
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Inhibits growth!
Enables plants to withstand drought  Closes stomata during
times of water stress
Promotes seed dormancy: Prevents seeds that have fallen on
the ground in the fall from sprouting until the spring when
conditions are more favorable
Ethylene gas
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Small amount released when fruit tissues respond to auxin;
Large amount released when plant is going through time of
stress
Promotes fruit ripening
Aged flowers and leaves falling off  Facilitates apoptosis
(programmed cell death) and promotes leaf abscission. Prior to
death, cells break down many of their chemical components for
the plant to salvage and reuse
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Works in opposition to auxins
Controlling Plant Life Cycles
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Annuals (marigolds, corn, peas), biennials
(carrots, sugar beets), and perennials (trees
and shrubs)
Whatever category a plant may fall into,
timing is very important to a plant.
Must time their reproductive cycles so their
reproductive cells will be ready at the same
time as those of other members of their
species
The environmental stimulus a plant uses to
detect the time of year is the photoperiod,
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the relative lengths of day and night.
Controlling Plant Life Cycles
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Circadian rhythm: The plant’s biological clock
that is set to a 24-hour day
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Long-day plants = short-night plants
Short-day plants = ?
Phytochrome is a pigment used by plants to
detect day and night via changes in the length
of light and dark periods each day
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There are two forms: Pr (red-light absorbing) and
Pfr (infrared light absorbing)
Pr  Pfr: when there is light present
Pfr  Pr: when it’s dark
This conversion enables the plant to keep track of
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time
Plant Reproduction
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Asexual reproduction
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Plants can clone themselves by vegetative
propagation
A piece of the vegetative part (root, stem,
or leaf) can produce an entirely new plant
genetically identical to the parent plant
Naturally occurring example  Figure 2614
Agricultural use  Grafting to combine
wanted characteristics of two different
plants; done during dormancy
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Plant Reproduction
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The sexual reproduction in flowering plants is
quite unusual
Alternation of generations life cycle
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Diploid (2n) sporophyte stage and haploid (n)
gametophyte stage
Two haploid gametes combine to form diploid zygote
(2n), which then divides mitotically to produce the
diploid multicellular stage called SPOROPHYTE (2n)
The sporophyte undergoes meiosis to produce a
haploid spore.
Mitotic division leads to the production of haploid
multicellular organisms called GAMETOPHYTES (n)
The gametophyte undergoes mitosis to produce
gametes, which combine to form diploid zygotes and34
Alternation of Generations
Gametophyte
2n Sporophyte
2n gametophyte
1n pollen
2n seed with
plant embryo
Sporophyte
Ovary with
1n ovules
(eggs)
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Alternation of Generations
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Alternation of Generations
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For most plants, including ferns, conifers
(cone producing plants), and angiosperms
(flowering plants), the prominent
generation is the sporophyte (2n)
For the moss (bryophyte), the prominent
generation is the gametophyte (n)
The dominant sporophyte generation is
considered more advanced evolutionarily
than a dominant gametophyte generation
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Plant
Divisions
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Plant Classification
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Plants are divided
into two groups
Based on the
presence or
absence of an
internal transport
system for water
and dissolved
materials
Called Vascular
System
Vascular
Bundles
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Plant Classification
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Bryophytes  Non-vascular plants
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Ex) Mosses
Tracheophytes  Vascular plants
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Seedless plants: Ferns (reproduction via
spores)
Seed plants
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Gymnosperms: Cone bearing
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Cedars, sequoias, redwoods, pines, yews, and junipers
Angiosperms: Flowering plants
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Roses, daisies, apples, and lemons
Monocots and dicots
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Vascular System
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Xylem tissue carries water and
minerals upward from the roots
Phloem tissue carries sugars made
by photosynthesis from the leaves
to where they will be stored or
used
Sap is the fluid carried inside the
xylem or phloem
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Multicellular Algae
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Algae are photosynthetic aquatic
organisms that are actually
classified as protists
Although most are unicellular, some
are multicellular (seaweed) and
their reproductive cycles are quite
similar to that of plants
Think of them as ‘honorary’ plants!
All algae contain chlorophyll a
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Multicellular Algae
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Brown algae
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Contain carotenoids and xanthophylls
In the phylum Phaeophyta (dusky plants)
Giant kelps  Can be as long as 100 m
Common form is Fucus, which is found
almost everywhere on the eastern coast of
the US and is sometimes known as
rockweed for the way in which it attaches
itself to rocks
Most are salt-water organisms
Figure 24-2, p. 558
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Multicellular Algae
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Red algae
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Get their color from a pigment called phycobilin
and phycoerythrin
In the phylum Rhodophyta  “red plants”
Most live in the ocean within the deep waters
Can absorb non-visible light via accessory pigments
Green algae
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Most live in fresh water
In the phylum Chlorophyta  “green plants”
Remarkably similar to green plants
Contain cellulose cell walls, chlorophyll a and b, and
store food as starch
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Nonvascular Plants
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Do not have
vascular tissue
for support or
conduction of
materials
Called
Bryophytes
Require a
constantly moist
environment
Sporophyte stage
Gametophyte
Stage
Moss Gametophytes &
Sporophytes
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Nonvascular Plants
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Includes mosses (Bryophyta),
liverworts (Hepatophyta), and
hornworts (Antherophyta)
Liverworts
Hornworts
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Bryophytes
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Plants can’t grow as tall  Lack of ligninfortified tissue
No true roots, stems, or leaves
Cells must be in direct contact with
moisture and thus live close to the ground
Materials move by diffusion cell-to-cell
Sperm must swim to egg through water
droplets  Contains flagella
Exhibit alternation of generations
 Gametophyte generation is dominant
Partial adaptation to life away from water
 Waxy covering
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Sporophytes
Gametophytes
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Bryophytes
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To a limited extent, bryophytes are able to
gather water from moist soil as they are
anchored by rhizoids, which are thin
filaments that absorb water and nutrients
from the soil.
Mosses
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When a moss spore lands on wet soil, it
germinates and grows into a tangle of protonema
As the protonema gets larger, its filaments
become more organized and starts growing
upward
These moss plants are the gametophyte stage of
the moss life cycle
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Moss
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Gamete formation and
fertilization
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Gametes produced from
gametophytes
Must be in water for sperm
to swim
Diploid zygote grows into
sporophyte, which becomes
dependent on the
gametophyte
Spore formation
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From capsule of sporophyte
 Meiosis
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Spore
Capsule
•Sporophyte lacks
chlorophyll & gets food
from the gametophyte.
•Sporophyte has a long,
slender stalk (setae)
topped with a spore
producing capsule
setae
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Hornworts and Liverworts
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Liverworts: Name
comes from the way in
which the lobes of
liverwort
gametophytes
resemble the lobes of
liver
Both are dependent
upon water and like
the mosses, contain a
waxy cuticle, rhizoids,
and have alternation
of generations.
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Main Parts of Vascular
Plants
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Shoots
-Found above ground
-Have leaves attached
-Photosynthetic part of
plant
Roots
-Found below ground
-Absorb water & minerals
-Anchors the plant
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Tracheophytes
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Characteristics include:
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Xylem and phloem for transport
Lignified transport vessels for support
Roots to absorb water while also anchoring
and supporting the plant
Leaves that increase the photosynthetic
surface
Life cycle with a dominant sporophyte
generation
Subdivided into two groups: Seedless
vascular plants and seed-bearing
vascular plants
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Seedless Tracheophytes
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Includes club moss (Lycophyta),
horsetails (Sphenophyta), whisk
ferns (Psilophyta), and ferns
(Pterophyta)
Whisk ferns
Horsetails
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Tracheophytes
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Club mosses and horsetails
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Believed to have formed the Earth’s first great
forests and the largest land plants for more than 100
million years
Have large, independent sporophytes
Ferns
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Excellent vascular system but still need moist habitat
Well-developed underground stems  Rhizomes
Large leaves known as fronds
Sporophyte: Produce haploid spores via meiosis. They
form on the undersides of the fronds in little
chambers called sori, which bursts open when the
spores are mature
Gametophyte: Independent and small. On the
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underside, gametes develop in tiny reproductive organs
Club Moss Spores
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Contain chemicals that
explode & burn quickly
Yellowish powdery
spores used in
fireworks and
explosives
Spore
Burning Lycopodium powder 57
Club Moss Sporophylls
Strobili
Sporophylls
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Fronds
Rhizome
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Seed-Producing Vascular
Plants
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Includes two groups: Gymnosperms
and Angiosperms
Gymnosperms have naked seeds in
cones
Angiosperms have flowers that
produce seeds to attract
pollinators and produce seeds
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Seed-Producing Vascular
Plants
Seeds
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Ability to form seeds is important. Why?
A seed is a reproductive package that
contains a plant embryo and a supply of
stored food inside a protective covering
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Resistant to drying
Tougher and more resistant to hard
compared to spores
Can grow just about anywhere and
reproduce at times of the year that are
much too dry for ferns or mosses to
reproduce
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Seed-Producing Vascular
Plants
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Reproduction
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Cones and flowers
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Gametophyte lives inside the sporophyte,
specifically in the cones or flowers
Spores
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Heterosporous  Produce two different forms of
spores, also known as mega and microspores
Megaspores develop into female gametophytes,
which produce the eggs
Microspores develop into male gametophytes ,
which produce the sperm, usually contained within
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the pollen
Gymnosperms
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Coniferophyta
are known as
conifers
Includes pine,
cedar, spruce,
and fir
Cycadophyta –
cycads
Ginkgophyta Ginkgo
ginkgo
Cycad
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Gymnosperms
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Contains the
oldest living
plant – Bristle
cone pine
Contains the
tallest living
plant – Sequoia
or redwood
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Gymnosperms: The Conifers
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First seed plants to appear
Seeds are ‘naked’ because they are not
enclosed inside a fruit. Instead, they are
exposed on modified leaves that form
cones
Better adapted for dry environments
Needle-shaped leaves that have a thick,
protective cuticle and a small SA
Depend on wind for pollination
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Gymnosperms: The Conifers
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Reproduction cycle  p. 582
Most have two kinds of cones
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Process of fertilization and seed formation may
take as long as a year
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Male cones produce pollen
Female cones produce eggs. Also called the seed
cones because they eventually contain the mature
seeds
After fertilization, can take up to a full year before
actual release of the seeds
Embryo is 3n=Sporophyte (2n) surrounded by
food-storing tissues of the gametophyte (n);
All this is enclosed in a seed coat as well
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Angiosperms
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Flowering plants
Seeds are formed when an
egg or ovule is fertilized
by pollen in the ovary
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Ovary is within a flower
Flower contains the male
(stamen) and/or female
(ovaries) parts of the
plant
Fruits are frequently
produced from these
ripened ovaries and it
protects the dormant
seeds
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From Gymno to Angiosperms
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Unlike naked seeds, angiosperms
produce seeds encased in a
protective tissue of the sporophyte
known as the ovary
The combination of seed and ovary
is known as a fruit
Method of reproduction 
independence from water and fast
reproduction
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The Flower
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A typical flower  Both male and female
gametophytes
Exceptions: Corn (separate flowers on same
plant) and willows (separate flowers on different
plants)
Formed from four types of specialized leaves
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Sepals and petals
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Sepals enclose and protect developing flower; leaf-like
Petals are brightly colored  Attracts insects
Stamens and carpels
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Stamens are the male leaves  Produce pollen; thin filaments
that contain anther sacs
Carpels are the female leaves that includes the ovary with one
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or more ovules
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The Seed
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Protective seed coat
Embryo
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Hypocotyl  Lower
stem
Epicotyl  Upper
stem
Radicle  Embryonic
root; first organ to
emerge
Cotyledon
/Endosperm
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Food for the growing
embryo
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The Fruit
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In most plants, the
nutrients flow into the
wall of an ovary, which
surrounds the seeds, as
well as ‘feeding’ the
developing embryo.
Gradually, the wall
thickens and joins with
other parts of the
flower stem to form a
fruit.
This is how the seed
gets enclosed inside the
walls of the ovary
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Angiosperm Reproduction
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Pollination  One pollen grain containing 3 monoploid
nuclei, 1 tube nuclei, and 2 sperm nuclei, land on the
sticky stigma of the flower
Pollen tube formation as it burrows down the style
into the ovary
DOUBLE FERTILIZATION: 2 sperm nuclei travel
down the tube and once inside the ovary, one sperm
fertilizes the egg and becomes the embryo (2n). The
other sperm fertilizes the two polar bodies and
becomes a 3n endosperm, the food for the growing
embryo
Ovule becomes the seed and the ripened ovary
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becomes the fruit
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Angiosperm
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Angiosperms are further classified into two groups
based on the number of cotyledons, the large seed
leaves that contain food to nourish the plant embryos
of seeds.
Monocot
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One cotyledon
Grass, irises, and cattails
Dicot



Two cotyledons
Roses, clover, tomatoes, oaks, and daisies
Also includes the flowering trees: maple, oak, elm, apple, and
dogwood
78
Monocots




Parallel venation
in leaves
Flower parts in
multiples of 3
Vascular tissue
scattered in
cross section of
stem
Figure 25-9a on
p. 589
79
Dicots




Net venation in
leaves
Flower parts in
multiples of 4
or 5
Vascular tissue
in rings in cross
section of stem
Figure 25-9b on
p. 589
80
Monocots vs. Dicots
Characteristic
Monocots
Dicots
Cotyledons (seed One
leaves)
Vascular
Scattered
bundles in stem
Leaf venation
Parallel
Two
Floral parts
Usually in 4s or
5s
Usually in 3s
In a ring
Netlike
81
Types of Fruits

Simplest fruits have a single seed enclosed by a single ovary wall



Nuts




Peaches and cherries
Ovary walls are soft and fleshy and encloses a single tough, stony seed
Legumes



Acorns and chestnuts
Ovary wall hardens and forms a protective shell around the seed
Drupes (flesh)


Grains: Wheat and corn
Wall of the ovary is so thin that it actually fuses to the seed coat
Peas, beans, and even peanuts!
Seeds are within a pod that splits open
Berries


Grapes and tomato
Soft ovary wall encloses many seeds
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Modes of Dispersal

Dispersal by wind




Dispersal by water



Maple and ash trees have winged fruits that carry their seeds
Dandelions have a parasol of tiny filaments
Dwarf mistletoes, a parasitic plant, produces sticky seeds
enclosed within a fluid-filled chamber. As the fruit matures,
the fluid pressure builds up so it blows away the end of the
fruit, pushing out the seeds
Some fruits contain air pockets to keep the seeds afloat
Coconut palm fruits are packed with corklike tissue and air
spaces
Dispersal by animals


Some fruits have ‘bribes’ that entice the animals  Edible
flesh
The tough seeds can pass through the digestive system, totally
83
unharmed