Transcript Chapter 23

AP Biology
Spring 2011
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Outline evolutionary advances that
converted marine algal ancestors into
plants that could live on land
State the advances that converted
primitive marsh plants into dry-land
flowering plants
Use a diagram to illustrate the evolutionary
trends in plants with specific reference to
sporophyte and gametophyte dominance
Characterize mosses, seedless vascular
plants, gymnosperms, and angiosperms
Discuss why angiosperms are most
successful of all plants
Green algae began invasion of land by
plants 475 million years ago
 Land conditions for plants improving
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› Water based photosynthesis was changing
the atmosphere
› Reduced amount of UV radiation
Charophyte algae
were evolving at the
water’s edge  gave
rise to plants
 Charophytes: share
common ancestor with
all land plants
 Rhyniophytes: first
seedless vascular plants
(Psilophyton)
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After the first invasion, 60 million years
later, plants had radiated throughout the
land
 Seed fossils date back about 385 millions
years
 Angiosperms emerged around 145
million years ago and quickly (within 40
million years) became dominant land
plants
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Life cycle of simple aquatic plants is
dominated by the haploid gametophyte
phase
› Gametes of some green algae are all motile
and of the same size
› Others are differentiated into motile sperm
and immotile eggs
› A watery environment was necessary for
gametes to meet each other
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Life cycle of complex land plants is
dominated by the large, diploid
sporophyte
› Cells within the sporophyte undergo meiosis
to give rise to the haploid spores
› Spores develop into the gametophyte,
which produces the gametes
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Over time, sporophytes, while
developing extensive root and shoot
systems, began holding onto spores and
gametophytes
› Protects and nourishes them
Aboveground parts of plants became
covered by a cuticle
 Stomata became control points for
water balance
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Underground parts of plants developed
into root systems
› Specialized for absorption of water and
minerals through extensive cylindrical tubes
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Vascular tissue became increasingly
extensive
› Xylem: conducting water and minerals
› Phloem: products of photosynthesis
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Extensive growth
of stems and
branches
became possible
due to
strengthening of
cell walls afforded
by deposits of
lignin
Bryophytes and some vascular plants
reproduce by releasing spores
 Seed bearing vascular plants produce
seeds and pollen
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› The male gametophytes- pollen grains- are
released from the parent plant to be carried by
whatever means to the female gametophyte
› Seeds are immature sporphytes with a
waterproof covering
› Many seeds are adapted with a means of
dispersal
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Bryophytes: include mosses, liverworts,
hornworts
› Not a monophyletic group
No lignin in the
stems
 Most less than
20cm tall
 Gametophyte
is the largest
part of the life
cycle
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Cellular protective jacket surrounds
sperm-producing and egg-producing
parts of plant to prevent drying out
 Sperm are flagellated, so water (or
insects) are required for fertilization
 Sporophytes remain attached to the
gametophytes after fertilization
 Bryophyte spores resistant to drought
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Liverworts: root-like rhizoids that attach to
the ground and can reproduce
asexually or sexually
› Ex. Marchantia
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Hornworts: have
pointy sporophyte
that can survive after
the gametophyte dies
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Mosses:
› Egg and sperm develop in the gametangia
at the shoot tips of the moss plants
› After fertilization: zygote develops into a
mature sporophyte, which consists of a
sporangium in which spores develop
› Compressed layers of dead mosses form
peat bogs
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Most seedless vascular plant that
flourished in the past are extinct
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Present day descendents: lycophytes,
horsetails, ferns
› Differ from bryophytes with respect to the
sporophytes
 Develop independently of the gametophyte
 Have well developed vascular tissues
 Are the larger, longer lived phase of the life
cycle
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Although sporophytes of seedless
vascular plants can live on land, their
gametophytes cannot because they
lack vascular tissues
› Male gametes must have water to reach
their eggs
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Lycophytes: once tree sized, now
represented by small club mosses on the
forest floor
› Sporophyte has true roots, stems, and small
leaves containing the vascular tissue
› Strobili bear spores that germinate to form
small, free living gametophytes
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Group is closely tied to aquatic
environment- sperm must swim to eggs
Whisk ferns: not true ferns, shaped like
whisk brooms with tiny reduced leaves
 Sporophytes: have rhizomes that are
short, branched, horizontal underground
stems
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Ancient relatives of horsetails were
treelike; only moderately sized Equisetum
has survived
› Plants are called sphenophytes and include
scouring rushes
› Sporophyte possess underground stems
called rhyizomes
› Scalelike leaves are arranged in whorls
around the hollow, photosynthetic stem
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Spores are produced inside coneshaped clusters of leaves at the shoot
tip, called strobili
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Ferns: largest, most diverse group of
seedless vascular plants
› Mostly native to the tropics and are highly
diverse in size
Bear underground stems (rhizomes) and
aerial leaves (fronds)
 Sori: clusters of sporangia that release
spores that develop into small heartshape gametophytes
 Some species of ferns live as epiphytes,
aerial plants growing attached to tree
branches or trunks
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Sori:
Vast forests of lycophyte trees and
horsetail plants existed in the
Carboniferous
 As sea level rose and fell, forest trees
were submerged in sediments protected
from decomposers
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First peat was formed, but increased
pressure and heat produced coal
It has taken a
remarkably short time
for human
technology to extract
coal, one of
nonrenewable fossil
fuels, from the ground
The most successful of the vascular
plants are the seed-bearing species
 Escaped dependency on water for
fertilization, relying on air currents and
insects
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Seed plants, gymnosperms, and
angiosperms are the 3 main groups and
differ from the seedless vascular plants in
3 ways
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2.
They produce microspores, which
develop into pollen grains that carry the
sperm to the female structures to
accomplish pollination
They also produce megaspores, which
develop into ovules and, at maturity,
produce seeds
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Each seed is a mature ovule consisting of
the embryo sporophyte (egg cell plus
sperm) plus seed coat
3.
Compared to seedless vascular plants,
these plants have thicker cuticles,
stomata recessed below the surface of
the leaf, and other competitive traits
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Humans have domesticated seed plants
to be used as food supplies and for
many other commercially important use