Transcript Seedless Vascular Plants

Kingdom Plantae
Introduction to Plants
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What is a plant?
Plants:
• are multicellular eukaryotes
• have cell walls made of cellulose
• develop from multicellular embryos
• carry out photosynthesis using green pigments
chlorophyll a and b
Introduction to Plants
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Most plants are autotrophs, although a few are
parasites or saprobes that live on decaying
matter
Some plants can reproduce asexually
Plants have a life cycle with alternation of
generations
They have a haploid gametophyte stage, where the
haploid cells (egg and sperm) fuse together to produce a
diploid cell. They also have a diploid sporophyte stage,
where spores produce a new individual by mitosis.
Sporophyte
Gametophyte
All plants have alternation
of generations. There is an
evolutionary trend from a
dominant autotrophic (selffeeding) gametophyte and a
nutritionally dependent
sporophyte to a dependent
gametophyte and a dominant
autotrophic sporophyte. This
is exemplified by exploring
the life cycles of a moss, a
fern, and an angiosperm.
What do plants need to survive?
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Sunlight ~ photosynthesis, photosynthetic organs on
leaves to absorb energy from the sun
Water and Minerals ~ plants need to obtain and
deliver water and minerals to their cells
Gas Exchange ~ plants require oxygen to support
respiration and carbon dioxide to carry out
photosynthesis
Movement of Water and Nutrients ~ plants have
specialized tissues that distribute he products of
photosynthesis throughout the plant body
Early Plants
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The first plants evolved from an organism much like
the multicellular green algae living today
Early plants were dependent on water to complete
their life cycle
Over time, plants evolved and adapted so that they
were:
-More resistant to the drying rays of the sun
-More capable of conserving water
-More capable of reproducing on dry land
Evolution of plants
The beginning of the
Carboniferous had a
more uniform, tropical,
and humid climate
throughout the year than
exists today. Seasons, if
any, were indistinct. The
number of plants during
the Carboniferous
became more numerous.
Vascular plants began to
dominate the landscape
and gymnosperm-like
plants began to appear.
Angiosperms would
appear much later.
Early Vascular Plants
a. Evolved from Charophytes, a group of green algae
b. Cooksonia oldest vascular plant fossil ; Rhynia
c. Late Silurian (414 - 408 million years BP)
d. No roots or leaves
e. Vascular plants dominated by the Devonian (408 - 362
million BP)
Plant Adaptations
a. Development of a 1) vascular system: xylem and phloem,
2) ground tissues: comprise the main plant body, and 3)
dermal tissue: provide protective covering to plants
b. Developed a waxy cuticle
c. Upright growth habit; lignin (for structure and conduction)
and cellulose
d. Stomata for gas exchange (O2, CO2, H2O)
e. Sex organs are multicellular gametangia
f. Fertilization of egg develops into an embryo
g. Roots evolved from underground stems
A question…
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What was the greatest “challenge” to plants as
they began to live on land?
Answer:
Acquiring, transporting, and conserving water.
Plant Kingdom Overview
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The plant kingdom is divided into 4 groups
based on 3 important features:
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1) water-conducting tissues (vascular)
2) seeds
3) flowers
Four Major Groups of Plants and Their Respective Phyla
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Bryophytes - nonvascular; reproduce via spores, seedless
plants; includes the mosses, liverworts, and hornworts
Phylum Bryophyta (Mosses), Phylum Hepaticophyta (Liverworts), Phylum
Anthocerophyta (Hornworts)
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Seedless Vascular Plants - vascular plants which are
seedless, use spores in reproduction; includes the ferns and
fern allies
Phylum Psilophyta (Whisk ferns), Phylum Lycopodophyta (Club Mosses), Phylum
Sphenophyta (Horsetails), Phylum Pterophyta (Ferns)
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Gymnosperms - vascular, naked seed producing plants;
includes conifers, cypress, cedars, cycads, etc.
Phylum Cycadophyta (Cycads), Phylum Ginkgophyta (Ginkgo), Phylum
Coniferophyta (Conifers), Phylum Gnetophyta (Welwitschia)
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Angiosperms - vascular plants, producing protected seed;
includes all flowering plants
Phylum Anthophyta (Flowering plants)
Class Dicotyledones, Class Monocotyledones, Class Magnoliids
To test your memory…
Question:
What are the 3 most important features of plants
that botanists use to classify them into 4
groups?
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Answer:
Water-conducting tissue, seeds, and flowers.
To test your memory…
Question:
From what kind of organism did all plants
evolve?
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Answer:
Green algae.
NONVASCULAR
AND
SEEDLESS
VASCULAR
PLANTS
Bryophytes- nonvascular; reproduce via spores, seedless plants;
includes the mosses, liverworts, and hornworts
Phylum Anthocerophyta (Hornworts)
Phylum Hepaticophyta (Liverworts)
Phylum Bryophyta (Mosses)
Bryophytes
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Definition:
- nonvascular plants (do not have specialized
tissues that conduct water and nutrients)
- draw up water by osmosis
- have life cycles that depend on water for
reproduction
It is now widely accepted (from morphological and molecular work)
that a group of green algae called the charophytes represent the sister
group to land plants.
Mosses and Liverworts
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Mosses (Bryophytes) form into a green velvety
mass.
Liverworts are flat foliose-like plants and
mosses have thin upright shoot containing
capsules.
Mosses and Liverworts
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The plants are attached to the soil with small root-like
structures called rhizoids, which absorb water and
minerals from the soil. They are not true roots
because they do not contain vascular tissue.
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These plants lack true stems or true leaves. They do
have flat leaf-like structure. In moss, the small leaves
are arranged spirally on thin stem-like structures and
bear a capsule containing spores.
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These plants lack conducting tissue, therefore, they
cannot grow very tall.
Challenge trivia!
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Liverwort, hornwort, milkwort, spiderwort –
these are all names of plants. What does the
ending –wort mean and where did it come
from?
The ending –wort means “plant”, and it can be
traced to Old English, when 800 years ago plants
were referred to as wyrt.
Bryophytes- (9000 Mosses), (6000 Liverworts)
and (100 Hornworts)
a. Have no conductive tissues, thus no way to efficiently assimilate
photosynthates or minerals; since they are reliant on diffusion, they are
typically very small
b. Three distinctive phyla
c. Absorptive structures called rhizoids; “leaflike” blades/leaves
d. Typically separate male and female gametophytic plants; sperm
must swim through a thin film of water to fertilize the egg; a diploid
zygote forms and grows into a mature moss sporophyte; spores will
be released from the sporophyte and will germinate to form a
protonema which further develops into the gametophyte
e. The gametophytic generation is the dominant form of the life
cycle
f. Liverworts may exhibit a leafy morphology or a thalloid (thallus) body
form; some reproduce asexually using gemmae cups containing gemma
(small multicellular spheres that contain many haploid cells)
Homosporousone spore type
produced and
released)
Hetrosporoustwo spore types
produced one
developing into a
male gametophyte,
the other into a
female
gametophyte
Life cycle of a moss
The gametophyte generation
dominates. Differentiation of
the growing tip of the
gametophyte produces
antheridia in males and
archegonia in females. The
sperm and egg are produced
in the antheridia and
archegonia, respectively.
Sperm are carried to the
archegonia in water droplets.
The sperm unites with the
egg to form a diploid zygote.
Life cycle of a moss
The zygote is the sporophyte
generation. A sporophyte
develops an enlarged capsule.
Inside the capsule
(sporangium), meiotic division
takes place and haploid spores
are formed. When the capsule
breaks open these spores are
released and germinate into
new plants when they find a
suitable environment. The
spore develops a branching
filament called a protonema.
After extensive growth, the
protonema develops buds,
which develop into leaf shoots.
More questions to test your memory…
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Is the gametophyte haploid or diploid?
Haploid.
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Where does the sporophyte develop?
It develops within the gametophyte.
More questions to test your memory…
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What does the sporophyte produce?
Spores
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When a spore germinates, what does it
produce?
Protonema
Seedless Vascular Plants
(11,000 Ferns), (Club Mosses 1,000), (Horsetails
15) and (Whisk Ferns 12)
Seedless Vascular Plants- plants which have
distinct tissues for conducting water and nutrients
throughout the plant; use spores for reproduction
instead of seeds; there are four phyla of SVP
1. Phylum Psilophyta (Whisk ferns)
2. Phylum Lycopodophyta (Club Mosses)
3. Phylum Sphenophyta (Horsetails)
4. Phylum Pterophyta (Ferns)
Evolution of Vascular Tissue
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Vascular plants had a new type of cell that was
specialized to conduct water
Tracheids: hollow cells with thick cell walls that resist
pressure, connected end to end
~are key cells in the xylem: a form of vascular tissue
that carries water upward from the roots to the rest of
the plant
Phloem: a second type of vascular tissue that transports
solutions of nutrients and carbohydrates produced by
photosynthesis
Vascular plants also produce lignin, a substance that
makes cell walls rigid and allows plants to grow upright
and tall
Seedless Vascular plants
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Seedless vascular plants include: club mosses,
horsetails, and ferns
Like other vascular plants, they have:
~ roots: underground organs that absorb water and
nutrients
~ leaves: photosynthetic organs that contain
vascular tissue gathered into veins of xylem and
phloem
~ stems: supporting structures that connect roots
and leaves and carry water and nutrients between
them
Another question…
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Why were tracheids one of the great
evolutionary innovations of the plant
kingdom?
Tracheids provided for the movement of water
and plant fluids over great distances, even
against gravity. This allowed plants to grow
large and tall.
Club Mosses
A. Once dominant plants in the landscape, 300my ago
B. Strobilus are present to bear spores
C. Some are homosporous, some are heterosporous; If
heterosporous, male microspores (n) will be produced along
with female megaspores (n); once shed, these spores will
develop into male and female gametophytes which will produce
sperm and egg respectively; when the egg is fertilized a
sporophyte (2n) will form; within the strobilus spores form and
the process repeats
Horsetails
A. Once dominant plants in the landscape,
300my ago
B. True roots, stems and small leaves
(reduced megaphylls); hollow jointed
stems impregnated with silica; green stem
main photosynthesizing part
C. Reproductive branches bear a terminal
cone-like strobilus
D. Life cycle is similar to fern life cycle;
also requires water
Ferns
a. Conductive tissues present; xylem and phloem!! Thus may be larger,
and allowed for true leaf evolution!
b. Two Basic Leaf Types: 1) Microphyll- possess a single vascular
strand and are typically small and 2) Megaphyll- possess more than one
vascular strand and are typically larger than microphylls; webbing effect
seen
c. Sporophyte is the dominant generation! Consists of roots,
rhizomes and fronds; fiddleheads are young fronds; sori appear on the
fronds and house spores
d. Spores (n) germinate into a prothallus (n) which will produce eggs (n)
in the archegonium and sperm (n) in the antheridium; they combine to
form a zygote (2n); the zygote grows into a young sporophyte (2n); the
mauture sporophyte of most ferns produce only one type of spore
(homosporous- one spore type produced and released); some are
hetrosporous, that is they produce two spore types, one developing
into a male gametophyte, the other into a female gametophyte
Water is required for the sperm to use as a medium to swim to the egg
Life cycle of a Fern
The diploid sporophyte
stage is dominant in the
life cycle. Fern
sporophytes produce
haploid spores in
sporangia, which are
grouped into clusters
called sori. Spores are
released from sporangia
and when they
germinate, they
develop into haploid
gametophytes.
Life cycle of a Fern
The gametophyte
develops independently
of the sporophyte. The
underside of the
gametophyte has
antheridia and
archegonia, and
fertilization occurs
when the sperm swims
to the eggs in a thin
film of water. The
diploid zygote grows
into a new sporophyte
plant.
The Sporophyte
continues to
grow while the
Gametophyte
dies.
Final questions…
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Which generation in the life cycle of the fern is
the large, leafy plant we all know?
The sporophyte.
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How is the gametophyte produced?
The sporophyte produces spores. A spore will
grow into a gametophyte.