Introduction to Plants Section 22-1
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Introduction to
Plants
Section 22-1
Plants:
dominates the landscape
provide the base for food chains on land
provide shelter, shade and oxygen for
animals
oldest fossiI evidence is about 470
million years old
What is a Plant?
• Members of the kingdom Plantae
• Multicellular eukaryotes with cell walls made of
cellulose
• Carry out photosynthesis using the green
pigments chlorophyll a and b
• Autotrophic, do not gather food, move about or
directly struggle with predators
The Plant Life Cycle
• Alternation of Generations
• Gametophyte (N) or haploid, gamete-
producing plant
• Sporophyte (2N) or diploid, spore-
producing plant
• Gametes = egg & sperm
(haploid cells) when fuse produce
a new diploid individual
• Spores are reproductive cells that
produce a new individual by mitosis
• Plants must be able to reproduce in dry
environments where there is no water
through which gametes move from plants
to plant
What Plants Need To Survive
1. Sunlight
Photosynthesis
Leaves are broad and flat to maximize
light absorption
2. Water and Minerals
All cells require a constant supply of
water
Water is a raw material of
photosynthesis
Plants have developed structures that
limit water loss
Minerals are needed for growth
3. Gas Exchange
Plants take in CO2 to carry out
photosynthesis and give off O2 for
respiration
Gas exchange takes place with the
atmosphere without losing excessive
water
4. Movement of Water and Nutrients
Plants take up water and minerals
through their roots
Food is made in their leaves
Plants have specialized tissues that
carry the water and distribute the food
throughout the plant body
Early Plants
Origins in the Water
• first green plants evolved from multicellular
green algae
• algae have similar reproductive cycles to
plants
• green algae have cell walls and
photosynthetic pigments identical
to those in plants
The First Plants
• The first true plants were still dependent
on water to complete their life cycles
• Early plants were similar to mosses in that
they were simple and grew close to the
ground
• Common in damp swampy regions
• From these first plants others began to
evolve:
– mosses and their relatives
– ferns
– cone-bearing plants
– flowering plants
Overview of the Plant
Kingdom
• Botanists divide the plant kingdom into
four groups based on three important
features:
– water-conducting tissues
– seeds
– flowers
• Today, plant scientists classify
plants by their DNA sequences
Bryophytes Section 22-2
Mosses
Liverworts
Hornworts
• Bryophytes (nonvascular plants) are
mosses and their relatives
• Do not have vascular tissues allowing
plants to conduct water and nutrients.
• Life cycle depends on water for
reproduction.
• Sperm must swim through water to reach
the eggs.
Groups of Bryophytes
• Bryophytes are low-growing plants
found in moist shady areas.
• Found from polar regions to tropical
areas as long as there is water.
• Bryophytes include:
• mosses
• liverworts
• hornworts
Mosses
• Mosses are members of the phylum
Bryophyte
• Grow in areas of moisture (swamps and
bogs, near streams and rain forests)
• Tolerate low temperatures so they can
grow in harsh environments where other
plants cannot.
• It is the most abundant plant in the polar
regions.
• Vary in appearance from miniature
evergreen trees to small, filamentous plants
that resemble a carpet of green
• When mosses
reproduce, they
produce thin stalks,
each containing a
capsule (sporophyte
stage)
• Each moss plant has
a thin upright shoot
that looks like a stem
with tiny leaves
(gametophyte stage)
• These are NOT true stems or leaves
because they DO NOT contain vascular
tissue
• "Leaves" are only one cell thick and lose
water quickly if the air is dry
• DO NOT have "true roots" instead they
have rhizoids which anchor them and
absorb water and nutrients
Liverworts
• Liverworts are members of the phylum
Hepaticophyta
• Some species resemble the shape of a liver
• The gametophyte stage produces gametes
in structures that look like little green
umbrellas
• Reproduce asexually by means of
gemmae which are small circular
spheres that contain many haploid cells
• Gemmae are produced in cuplike
structures called gemma cups
Hornworts
• Hornworts are members of the phylum Anthocerophyta
• Found only in soil that is damp year-round
• Hornworts have sporophytes that looklike tiny green horns
Life Cycle of Bryophytes
• Reproduce with alternation of
generations
• The gametophyte is the dominant,
recognizable stage and the stage that
carries out the most photosynthesis
• The sporophyte is dependent on the
gametophyte for supplying water and
nutrients
Dependence on Water
• For fertilization to occur, the sperm must
swim to an egg
• Sometimes raindrops splash sperm from
one plant to another
• Bryophytes must live in habitats where
water is available
Life Cycle of a Moss
1. A moss spore lands in a moist place, grows into a mass of tangled green filaments called a protonema.
2. The protonema grows and forms rhizoids that grow into the ground and shoots that grow into the air.
3. Shoots grow into the familiar green moss plants which are the gametophyte stage.
4. Gametes are formed in reproductive structures at the tips of the gametophytes.
5. Sperm in the antheridia and eggs cells in archegonia.
Haploid (N)
Diploid (2N) MEIOSIS
FERTILIZATION
Mature sporophyte
(2N)
Gametophyte (N)
Gametophyte (N)
Young sporophyte (2N)
Zygote (2N)
Sperm (N)
Sperm (N)
Egg (N)
Spores (N)
Capsule (sporangium)
Protonema (young gametophyte) (N)
Male gametophyte
Female gametophyte
Antheridia
Archegonia
Life Cycle of a Moss
6. Sperm are released, reach egg cells and
fertilization produces a diploid zygote.
7. The zygote is the beginning of the sporophyte
stage.
8. It grows directly out of the body of the
gametophyte and depends on it for water and
nutrients.
9. The mature sporophyte is a long stalk ending
in a capsule.
10. Inside the capsule, haploid spores are
produced and when the capsule ripens, it opens
releasing the spores to start the cycle again.
Human Use of Mosses
• Sphagnum mosses thrive in acidic water of
bogs. They absorb many times their own weight
and act as a "natural sponge".
• Dead remains of sphagnum accumulate to form
thick deposits of peat and can be cut from the
ground and burned as a fuel.
• Peat moss is also used in gardening.
– Added to soil to improve the soil's ability to retain
water.
– low pH so it increases the soiI's acidity. Plants,
such as azaleas, grow well in acidic soil.
Seedless Vascular Plants
Section 22-3
Evolving about 420 million years ago
were plants that contained vascular
tissue, a type of tissue that is
specialized to conduct water and
nutrients through the body of the plant.
Evolution of Vascular Tissue
• Tracheids are the key cells that
make up the xylem.
–a form of vascular tissue that
carries water up from the roots.
–are hollow cells
with thick cell
walls that resist
pressure.
–connected end
to end like a
series of
drinking straws.
• Phloem is the second type of vascular
tissue.
– it transports nutrients and carbohydrates
produced by photosynthesis
• Vascular plants also produce lignin, a
substance that makes cell walls rigid. It
allows the plant to grow upright and
reach great heights.
Ferns and Their Relatives
• Seedless vascular
plants include:
• Club mosses
• Horsetails
• Ferns (most
numerous)
• Ferns and their
relatives have true
roots, leaves and
stems.
• Roots are underground organs that
absorb water and minerals. Water
conducting tissues are in the center of
the root.
• Leaves are photosynthetic organs and
contain one or more bundles of vascular
tissue.
– This vascular tissue is gathered into veins
made up of xylem and phloem.
• Stems are supporting structures that
connect roots and leaves, carrying water
and nutrients between them.
Club Mosses
• Club mosses belong in the phylum
Lycophyta
• They are small plants that live in
moist woodlands and near
streambeds and marshes.
• Lycopodium,
the common
club moss
looks like a
miniature pine
tree
• Club moss is
also called
"ground pine"
Horsetails
• The only living genus in the phylum
Arthrophyta is Equisetum.
• Its leaves are arranged in whirls at
joints along the stem.
• Equisetum is called
horsetail or
scouring rush
because its stem
look similar to
horses' taiIs and
contain crystals of
silica.
• During Colonial
times, horsetails
were commonly
used to scour pots
and pans.
Ferns
• Ferns are members of the phylum
Pterophyta
• They have true vascular tissue, strong
roots, creeping or underground stems
called rhizomes and large leaves called
fronds.
• Thrive in areas with little light, found in
shadows of forest trees and are
abundant in the Pacific Northwest rain
forests.
Life Cycle of Ferns
• Ferns and other vascular plants have a
life cycle in which the diploid
sporophyte is the dominant stage.
• Fern sporophytes produce haploid
spores on the underside of their fronds
in tiny containers called sporangia.
• Sporangia are grouped into
clusters called sori.
1. When spores germinate, they develop
into haploid gametophytes.
2. The small gametophyte first grows a set
of rootlike rhizoids and then flattens into
a thin, heart shaped, green structure
that is the mature gametophyte.
3. The gametophyte grows independently
of the sporophyte.
4. The antheridia and archegonia are
found on the underside of the
gametophyte.
Haploid gametophyte (N)
Diploid sporophyte (2N)
MEIOSIS
FERTILIZATION
Mature sporophyte (2N)
Gametophyte (N)
Frond
Sperm
Egg
Spores (N)
Antheridium
Archegonium
Developing sporophyte (2N)
Sporophyte embryo (2N)
Mature gametophyte (N)
Young gametophyte (N)
Sporangium (2N)
Life Cycle of a Fern
5. Fertilization requires a thin film of
water for the sperm to swim to the egg.
6. The diploid zygote immediately begins
to grow into a new sporophyte plant.
7. As the sporophyte grows, the
gametophyte withers away.
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