Transcript How Plants Colonized onto Land

How Plants Colonized Onto
Land
First Sign of a Plant
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The first plant was a form of green algae called
Charophyceans.
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Molecular homologies present evidence of ancestry to
land plants.
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Similar chlorophyll pigments
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Homologous cell walls
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Homologouus peroxisomes
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Homologous sperm
CHAROPHYCEANS
Necessary Adaptations to Colonize
Terrestrial Habitats.
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Must be able of protect the gametes.
Dispersal of gametes.
Protection against dehydration.
Vascular system.
Support against gravity.
Development of seeds.
Next step up were the
Bryophytes
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Include mosses, hornworts and liverworts.
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Nonvascular plants.
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Contain elongated conducting cells that lack liginin that
were precursor to a vascular system.
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Must have a moist environment to reproduce.
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Offspring arise from multicellular embryos that are still
attached to the mother plant.
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Most predominant form is the gametophyte generation
which is haploid.
Meet the Bryophytes
Bryophyte Reproduction
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Germinating moss spores develop in a filamentous
structure called the protonema.
The large surface area enhances water absorption
minerals.
From the protonema emerges the gametophore that
produces gametes. This whole structure is known as
the gametophyte.
Male gametophyte called the antheridium.
Female gametophyte called the archegonium.
Fertilization produces the sporophyte generation.
Sporophyte grows within the gametophyte giving rise
to the sporangium.
Sporanguim produces spores through meiosis.
Spores undergo mitosis and produce the protonema.
The Protonema
Archegonium and Anthridium
Sporophyte Generation
Moss Life Cycle
Bryophytes
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Lack true stems and leaves.
Are anchored by long tubular cells called
rhizoids.
Have flagellated gametes.
Pteridophytes
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Seedless vascular plants.
Ferns, Equisetum (horsetails), Lycophytes (club mosses).
Most have true roots and lignified vascular tissue.
Have small leaves because vascular system is not as
developed.
Predominant most visible form is the sporophyte
generation.
Most are homosporous. Only aquatic ferns are
heterosporous.
The heterosporous condition is very in important in the
evolution of seeds.
Gametes are still flagellated so ferns must live in a moist
habitat.
Seedless vascular plants formed the “coal forests” of the
Carboniferous.
Meet Pteridophyte’s
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Homosporous
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Sporophyte produces:
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single type of spore bisexaul gametes. That
either produce eggs or sperm.
Heterosporous
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Sporophyte gives rise to:
Megaspores (female) - egg
 Microspore (male) - sperm
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Ferns produce clusters of
sporangia called sori.
Pteridophyte Reproduction
Carboniferous “coal forests”
THE EVOLUTION OF
SEED PLANTS
Seed Plant Evolution
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Seed plants are vascular plants.
Include gymnosperms (conifers) and
angiosperms (flowering plants)
Three primary adaptations:
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Reduction the gametophyte.
Advent of the seed.
Evolution of the seed.
The Sporophyte is the Most Visible
Form in seed Plants
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The gametophyte is contained within the sporangia.
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The gametophyte becomes the reproductive tissue of
the sporophyte and nourishes the developing embryo.
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Advantages
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Do not have to deal with environmental stresses.
Nutrients derived from parent plant.
The female gametophyte and the embryos they produce are
sheltered from drought and U.V. radiation.
Gametophytes in seed plants are microscopic.
Seeds are an important means of
dispersing offspring.
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Seeds resist harsh conditions.
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Seeds contain the developing embryo and a
food supply along with a protective coat.
All seed plants are heterosporous which
means they produce two types of sporangia
with two types of spores.
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Megaspore - female spore
Microspore - male spore
Gymnosperm Seed
Ovulate Cone
Pollen Cone
Pine Embryo
Life Cycle of a Pine
Structure of the Seed of
Megasporangium
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Integuments encase and protect the
megasporangium with the megaspore inside.
The whole structure is known as the ovule.
The megaspore produces one or more eggs and
if fertilized will produce the embryo
sporophyte.
Once the seed is released from the parent it
remains dormant until there is favorable
conditions for the embryo to grow.
Structure of Pollen or
Microsporangium
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Microspores develop into pollen which mature
into the male gametophyte of seed plants.
Transfer of pollen to ovules is called
pollination.
In most gymnosperms and all angiosperms
sperm lack flagella.
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Transfer can airborne, carried on fur or feathers
or “bee fuzz”.
Wider terrestrial range
Gymnosperms
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Conifers or “naked seed” plants.
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Lack ovaries
Possess pine cones.
Seeds develop on special leaves called sporophylls.
Evolved before angiosperms.
Reproduction involves:
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Pollen cone (male)
Ovulate cone (female)
Gymnosperm Fertilization
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Pollen grain is released from microsporangium and
reaches the megasporagium in the ovulate cone.
Pollen is drawn into ovulate cone through the
micropyle and produces a pollen tube.
The megaspore in the megasporangium undergoes
meiosis. Same thing happens in the pollen.
Fertilization occurs when the sperm nuclei is injected
into the egg through the pollen tube.
More than one egg may be fertilized but only one
develops into the zygote.
Sequoia
ANGIOSPERMS (flowering plants)
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Two main classes and recently a third.
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Vascular system of angiosperms are much more
refined than gymnosperms.
Gymnosperms possess trachieds only.
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Monocots
Dicots
Eudicots
Tapered hollow cells that make up the xylem.
Angiosperms contain tracheids and xylem vessels.
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Xylem vessels are much more efficient is transporting
water in all directions.
The Flower
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Structure specialized for reproduction.
Fruit is the mature ovary.
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Seeds develop from the ovules after fertilization.
Fruits help disperse seeds:
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Dandelions – flying propeller seeds
Burrs that cling to animal fur
Delicious fruits attract hungry predators that pass
the seeds along with a supply of fertilizer.
Vessel Elements Verses Tracheids
The Flower
Reproduction of an Angiosperm
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The immature gametophytes are contained
within pollen grains in the anthers of the
stamen.
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Each pollen grain has two haploid cells.
Ovules develop in the ovary contain the female
gametophyte also known as the embryo sac.
Pollen sticks to the stigma which is the tip of
the of the carpel.
Angiosperm Reproduction
Evolution of Seed Pods
The Pollen Grain
Angiosperm Seed Dispersal
Fruits
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The fruit begins to develop after pollination and
trigger hormonal signals that cause the ovary to grow
and the wall to thicken.
The wall is called the pericarp.
Simple fruit - develops form one ovary (cherry)
Aggregate fruit – single flower with several ovaries
or carpels ( raspberry).
Multiple fruit – develop from several flowers packed
together and the ovary walls fuse( pineapple).
Fruits