Download Chapter 21 Most land plants have (but charophyceans do not):

What characteristics or structures
are common to ALL plants?
•
•
•
•
•
Chapter 21
The Evolution of Plants
Eukaryotic
Multicellular
Photosynthetic autotrophs
Chloroplasts
Cell walls made of cellulose
To which domain and kingdom
do algae belong?
But some of these characteristics are also true of other
organisms…especially algae…and especially especially
green algae…and MOST especially charophyceans.
Plant Phylogeny:
here’s the “big picture” of all extant plant life
Why did
land plants
evolve?
Most land plants have
(but charophyceans do not):
Charophyceans
•freshwater green algae, closest
ancestral relative of plants
•four characteristics of plants
shared only with charophytes
(other algae differ):
•Rosette cellulose-synthesizing
complexes (as opposed to
linear)
•Peroxisome enzymes to limit
loss of organic product due to
photorespiration
•Structure of flagellated sperm
•Formation of a phragmoplast
(cell plate)
•
•
•
•
•
Apical meristems
Alternation of generations
Walled spores produced in sporangia
Multicellular gametangia
Multicellular, dependent embryos
Briefly, about each of these:
1
When your light and CO2 are ABOVE GROUND, and your water
and minerals are BELOW GROUND, you need specialized tissues
and organs in both locations.
Life cycles
Apical meristems are areas of concentrated cell division and
differentiation (sometimes described as “perpetually embryonic”).
Alternation of Generations
“sporophytes make spores make gametophytes make gametes”
~unique to plants and
some algae (but not
charophyceans, so a
derived characteristic)
Gametes: haploid
Gametes:
Spores: haploid
Spores: reproductive
reproductive cells that fuse
with another cell
cells that do not fuse with
another cell
Reduction in Size of
Gametophyte
~all sexually
reproducing
organisms have
haploid and diploid
stages– but only in
“alternation of
generations” do both
the haploid and
diploid stages include
multicellular stages
Multicellular sporophytes possess sporangia which contain
diploid sporocytes which produce haploid spores with walls
made of sporopollenin. Plant spores are specialized to deal with
harsh, drying conditions. (Do you think algae spores have
sporopollenin?)
C-fern (Ceratopteris richardii)
sporangium with spores
C-fern spores, showing trilene
marks (where three other spores
were attached as a tetrad after
meiosis)
2
More C-Fern beauty…
Hermaphrodite gametophyte with
4 archegonia and 2 antheridia on
notch margins
Gametophytes have
multicellular
gametangia
(female=archegonia,
male=antheridia)
which produce
haploid gametes
(egg and sperm)
Male gametophyte with
spherical antheridia
Antheridia close-up
And, note
the
meristem
notch
Close-up of sperm release; they begin round and nonmotile. Here, one is swimming away, propelled by a
helical structure.
Sperm release
Plants are classified as
“embryophytes”
because the embryos
are retained in the
female parental tissue.
Protection of Eggs and Embryos
Found in embryo, to
enhance the transfer of
nutrients via
ingrowths in wall and
plasma membrane
3
Remember, what we’re looking at are
characteristics that land plants have and
charophyceans do not– in other words, what are
the derived traits that separate them from their
ancestors
•
•
•
•
•
Apical meristems
Alternation of generations
Walled spores produced in sporangia
Multicellular gametangia
Multicellular, dependent embryos
Leaves of Vascular Plants
Other Terrestrial Adaptations
• Vascular tissue transports water and
nutrients to the body of the plant.
• Cuticle provides an effective barrier to
water loss.
• Stomata bordered by guard cells that
regulate opening, and thus water loss.
Recall the “big picture”… now,
classify land plants as nonvascular
or vascular
BRYOPHYTES (mosses)--nonvascular
•Have flagellated sperm, so need to be near water,
tend to grow in moist, dark areas
•Spores with sporopollenin (resists potential
environmental damages)
•Lack lignin-fortified tissues (lignin “hardens” the
cell walls) to grow taller, so grow in “mats”
Nonvascular Plants
• Lack specialized means of transporting
water and organic nutrients.
•Gametophyte is dominant generation
• Do not have true roots, stems, and leaves.
• Produces eggs in archegonia and
flagellated sperm in antheridia.
4
Nonvascular Plants
• Hornworts have small sporophytes that
carry on photosynthesis.
Figure 29.15x1 Hornwort
Nonvascular Plants
• Liverworts have either flattened thallus or
leafy appearance.
Nonvascular Plants
Moss Life Cycle
• Mosses (phylum Bryophyta) usually have
a leafy shoot, although some are
secondarily flattened.
5
Figure 29.18 A moss sporangium with a “spore-shaker” tip
Sphagnum moss, or “peat moss” is an
ecologically important bryophyte
• Many mosses
produce phenolic
compounds that
absorb radiation
• Sphagnum also
releases compounds
that reduce bacterial
activity, so it slows
decay
• Huge reservoir for
carbon (400 billion
tons worldwide) for
the carbon
cycle…and as a fuel
source
Figure 29.19x A peat moss bog in Norway
Next classification:
vascular without seeds (seedless), and vascular with seeds
SEEDLESS VASCULAR
PLANTS
Vascular Plants
• Xylem conducts water and dissolved
minerals up from roots.
• Phloem conducts sucrose and other
organic compounds throughout the plant.
• Lignin strengthens walls of conducting
cells in xylem.
•Sporophyte is dominant generation
Sporphylls=
leaves that
bear
sporangia
(clusters in
ferns called
sori)
•Pterophytes (ferns) primary
example
•Flagellated sperm (so need at least
a film of water)
•Homosporous= produces one type
of spore which results in a bisexual
gametophyte; other option is to be
heterosporous:
megaspores= female,
microspores= male)
6
Figure 29.20 Cooksonia, a vascular plant of the Siluria
Vascular Plants
Vascular Tissue
Club Mosses
• Most seedless vascular plants are
homosporous.
– Windblown spores are dispersal agents.
• All seed plants are heterosporous and
have male and female gametophytes.
Seedless Vascular Plants
Horsetail
• Ferns and Allies
– Horsetails
– Rhizome produces tall aerial stems.
• Contains whorls of slender, green branches.
• Small, scalelike leaves also form whorls at the
joints.
7
Figure 29.21 Pteridophytes: club "moss" (top left), whisk fern (top right), horsetail
(bottom left), fern (bottom right)
Ferns
• Whisk Ferns
– Branched rhizome has rhizoids.
– Mutualistic mycorrhizal fungus helps gather
nutrients.
• Ferns
– Large conspicuous fronds.
• Divided into leaflets.
• Dominant sporophyte produces windblown spores.
Figure 29.23 The life cycle of a fern
Whisk Ferns and Ferns
Figure 29.0 Ferns
Avoids self-fertilization by
archegonium and
antheridium maturing at
different times
Figure 29.23x1 Life cycle of a fern: mature fern
8
Figure 29.24a Fern sporophyll, a leaf specialized for spore production
Figure 29.24b Fern sporophyll, a leaf specialized for spore production
Figure 29.24c Fern sporophyll, a leaf specialized for spore production
Figure 29.23x3 Life cycle of a fern: sporangium
Figure 29.23x5 Life cycle of a fern: germinating
Figure 29.23x6 Life cycle of a fern: gametophyte
9
Figure 29.23x7 Life cycle of a fern: archegonia
Figure 29.23x8 Life cycle of a fern: sporophytes
Figure 30.1 Three variations on gametophyte/sporophyte relationships
Two classifications of seed plants
All seed plants
have:
*seeds
(obviously)
*reduced
gametophytes
*heterospory
*ovules
*pollen
• Reduction of
the
gametophyte
stage allows for
protection of
gametophytes,
and
gametophytes
can gain
nutrition from
the sporophytes
Development of the seed
–Another reproductive strategy
for protecting the embryo and
dispersing offspring –has the
nutrient source and embryo
packaged in a protective coat
Evolution of pollen
A way to transfer sperm that lack
a flagella without a need for water
(microspores develop into the
male gametophyte pollen grain,
which contains the male gamete
sperm)
10
“sporophytes make spores make gametophytes make gametes”
Seed Plants
• Seed plants are the most plentiful plants in
the biosphere.
– Seed coat and stored food allow an embryo to
survive harsh conditions during long period of
dormancy.
– Heterosporous
• Drought-resistant pollen grains.
• Ovule develops into seed.
• Ovary becomes the fruit.
GYMNOSPERMS
~largest division is the conifers
Male cone
Female cone
~ “naked seeds” because they
lack ovaries (have ovules)
~modified leaves = needles
An ovule contains a megaspore which produces a female
gametophyte (called an embryo sac) that produces female
gametes (eggs)
Conifers
• Conifers, as well as other gymnosperm
phyla, bear cones.
– Tough, needlelike leaves of pines conserve
water with a thick cuticle and recessed
stomata.
• Confiers
• Cycads
• Ginkgoes
• Gnetophytes
Pine Life Cycle
• Considered a “soft” wood because it consists
primarily of xylem tissue.
Pine Life Cycle
11
Figure 30.8bx Sequoias
Conifers
Figure 30.8c Phylum Coniferophyta: Cypress
Figure 30.8x2 Frasier fir
Figure 30.10 A closer look at pine cones (Pinus sp.)
Figure 30.3 Winged seed of a White Pine (Pinus strobus)
12
Figure 30.10x3 Pine embryo
Cycads
• Cycads have large, finely divided leaves that
grow in clusters at the top of the stem.
– Pollen and seed cones on separate plants.
• Pollinated by insects.
Figure 30.5c Phylum Ginkgophyta: Ginkgo biloba
Ginkgoes
• Ginkgoes are dioecious, with some trees
producing seeds and others producing
pollen. Thus only the “female” trees
produce fruit.
– One surviving species. (Gingko biloba)
Angiosperms
• Angiosperms are an exceptionally large
and successful group of plants
– Ovules are always enclosed within diploid
tissues.
Monocots and Eudicots
• Two classes of flowering plants.
– Monocotyledones (Monocots)
• One cotyledon in seed.
• Examples: corn, grasses, lilies
– Eudicotyledones (Dicots)
• Two cotyledons in seed.
• Examples: beans, oak tree, roses
• Cotyledons (seed leaf)- an embryonic organ
that stores and digests reserve materials
13
Figure 35.1 A comparison Mof monocots and dicots
Monocots versus Eudicots
• One cotyledon
• Flower parts in 3s or
multiples of 3
• Usually herbaceous
• Usually parallel veins
• Scattered vascular
bundles in stems
• Fibrous root system
• Two cotyledons
• Flower parts in 4s or
5s or multiples of 4 or
5
• Woody or herbaceous
• Usually net venation
• Vascular bundles in a
ring in stems
• Taproot system
14