Download Mosses and Ferns

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http://www.youtube.com/watch?v=iWaX97p6
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The first multicellular organisms evolved in
water and their entire lives were designed
around an aquatic environment –
photosynthesis and reproduction took place
in the water.
Recall Protista, Algae, Fungi…
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Over time, some organisms adapted to life in
drier environments. These organisms
evolved structures to acquire, transport, and
conserve water, as well as reproductive cycles
that enabled them to survive on land.
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All life needs a constant supply of water as
well as a method to protect the loss of that
water (desiccation).
Land plants need rigid supports to hold
their leaves up to the sun for
photosynthesis.
Land plants need to transport water up from
the roots and food down from the leaves.
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Land plants must exchange water and
carbon dioxide with the environment
without losing too much water in the
process.
Land plants must be able to reproduce in a
dry environment that lacks water in which
the sperm can swim. Also, young embryos
of land plants are in danger of drying out.
Includes the mosses, liverworts, and hornworts.
Like the algae from which they evolved, the
bryophytes have life cycles that involve an
alteration of generations between a haploid
gametophyte and a diploid sporophyte. Also,
like the algae, the need water for reproduction
to occur.
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They lack vascular tissue; therefore, most
are only a few centimeters tall.
They lack a protective surface covering
(cuticle) to keep water from evaporating
from their cells.
The lack true roots which could absorb and
transport water. Instead, they have rhizoids
which anchor them to the ground.
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They have sperm cells that must swim
through water to fertilize the eggs;
therefore, they must live in areas that are
wet for at least part of the year.
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The haploid gametophye is the dominant,
obvious stage. It’s what we call the moss plant.
Standing water is needed for sperm to swim
from the male gametophyte to the female
gametophyte to fertilize the eggs.
The diploid sporophyte is small and can grow
only with nourishment provided by the
gametophyte (the sporophyte is the dependent
on the gametophyte).
http://www.youtube.com/watch?v=xbSZbd02UEg&
feature=g-wl
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The members of the phylum tracheophyta are
“true” land plants because they have evolved
ways of freeing themselves from dependence
on wet environments.
Tracheophytes possess vascular tissues which
transport water and food throughout the
plant. There are two types of vascular tissue:
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Xylem: movement of water from roots to all
parts of the plant.
◦ Xylem tissue is made up of tracheid cells which
transport water and have thick, strong cell walls
that strengthen stems and help plants stand up (the
phylum tracheophyta gets its name from this cell
type).
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Phloem: transport of food and nutrients to all
parts of the plant
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Tracheophytes have also developed true roots
and true leaves.
True roots absorb and transport water from
the soil, and true leaves are organs of
photosynthesis with a waxy protective
covering called a cuticle that prevents water
loss.
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Ferns are well-developed tracheophytes with
vascular tissues, strong roots, creeping stems
called rhizomes, and large leaves called
fronds.
There are over 11,000 species of ferns alive.
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Diploid sporophyte is the dominant stage in
ferns. Gametophyte is tiny, lacks vascular
tissue, and can grow only in moist areas.
Sexual reproduction still depends upon the
presence of standing water for the sperm to
swim to eggs – ferns are seedless vascular
plants!
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Fern sporophytes produce haploid spores in
sporangia on the underside of their fronds.
Sporangia are grouped into larger clusters
called sori. (fig 21-11 pg 458 in text). Note –
a vascular plant is any plant that has
connective tissue (xylem/phloem)
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http://www.youtube.com/watch?v=c4YtOT0Z
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