gymnosperms reproduction and life cycle the naked … · conifer • conifer leaves are needle or...
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GYMNOSPERMS
REPRODUCTION AND LIFE
CYCLE
THE NAKED SEEDS
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SPERMOPHYTA(Gymno & Angio)
seed plants• Vascular tissue
• Use seeds for reproduction
• Cell walls with cellulose
• Don’t require water for reproduction
• Dominant sporophyte
• Microscopic gametophyte
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BODY PLAN – Gymno only!
• Dominant diploid sporophyte
• Have roots, stems, leaves, vascular tissue
• Leaves = large or needle like
• Have two types of cones
– Produce spores gametophyte
• Gametophyte depends on sporophyte for nutrition
• Gametophyte = naked seed produced on outside of
cone
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ADVANTAGES• Transfer of pollen grains and development of
pollen tube eliminates the need for water for sexual reproduction
• Gametophyte is very reduced and does not develop in the soil as an independent generation, instead the tiny gametophyte is contained and protected within the moist reproductive tissue of the sporophyte
• Evolution of the seed = protection of the dormant embryo from drying out, cold …and is used to disperse the seed to new habitats
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DIVERSITY
CYCADS
• Grow in tropical and subtropical regions
• Look like palms except they have naked seeds produced by big cones
• Abundant 300 million years ago
– were the food of herbivorous dinosaurs and the fate of both of these groups of organisms was probably closely linked.
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DIVERSITY
GINKO
• This is a monotypic division, a single species of a
single genus, Ginkgo biloba the maidenhair tree..
Ginkgo biloba was preserved in the gardens of
Buddhist monasteries in China and Japan where it
was encountered by Westerners in the eighteenth
century. It has turned out to be a valuable street
tree because of its unusual foliage and tolerance of
pollution.
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DIVERSITY CONIFER
• Conifer leaves are needle or scale-like
• often large and can dominate the plant life in some ecosystems
• their stems continue to expand in width as well as length throughout the life of the plant
• The older parts of the stem become woody, which provides a further distinction from the seedless vascular plants of which there are no surviving woody representatives.
• EX. Pine, Spruce, Cedar, Fir, Juniper…
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THE CONIFER LIFE CYCLE
NAKED SEEDS BIG TREES
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The Dominant Sporophyte
• Diploid
• Produces male and female cones
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BEGIN WITH DOMINANT
SPRORPHYTE = MATURE TREE
• The plant produces both male and female
cones
• MALE CONES ARE SMALL AND
PRODUCE POLLEN
GRAINS
FEMALE CONES ARE LARGE
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The Male Cone• Appears in the sring
• Cells in the cone divide by meiosis and
produce small haploid spores pollen
grains
• Pollen Grain = immature male gametophyte
• Pollen grains are released into the air
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Pollen grains
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FEMALE CONES
• More familiar
• Larger spores form by meiosis = haploid
egg
• Female gametophyte stay inside tissue of
parent sporophyte
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POLLINATION
• Pollen grain carried to female cone via wind
• When it arrives inside the female cone, each
pollen grain forms a tiny pollen tube• Pollen Grain + Pollen Tube = Mature male
gametophyte
• Pollen tube grows into female gametophyte
until it reaches an egg
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FERTILIZATION• Occurs deep within the protective tissues of
the parent sporophyte
• A sperm nucleus from the pollen grain
unites with the egg zygote
• In Pine it takes 15 months from pollination
to fertilization
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DEVELOPMENT OF THE
EMBRYO
• Zygote cells undergo mitosis embryo sporophyte plant
• Embryo surrounded by food storage tissue (part of gametophyte)
• Protective coat of sporophyte tissue develops around embryo and food
• By the time the food runs out, embryo has chlorophyll and can make its own
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