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Gymnosperms/The beginning of Seeds (Types of Gymnosperms (4 of 10 plant…
Gymnosperms/The beginning of Seeds
From Seedless to Seeds
Seeds!
Self-reliant to some degree
disperse long distances and survive harsh conditions
embryos now have a food supply and a protective coat
Heterospory
Process of fertilization
Megaspore gets fertilized by some pollon
both male and female parts undergo mitosis (megaspore becomes female gametophyte)
Diploid zygote begins to divide--> becomes diploid embryo
Integument becomes seed coat
embryo surrounded by food from female gametophyte
Megasporangia undergoes meiosis to create megaspore which is protected by the integument
2 important terms
Microsporangia
many microspores (male gametophyte)
Megasporangia (diploid)
megaspore is haploid (female gametophyte)
undergoes meiosis to produce one megaspore
Sporophyte dominant life cycle
gametophyte dependent on sporophyte for nutrition
gametophyte further reduced
Types of Gymnosperms (4 of 10 plant phyla are gymnosperms)
Cycads
Only gymnosperms with compound leaves
300 million years old
Gingkos
males planted orientally
they will eventually die out
reduces chances for sexual reproduction
Only 1 extant species
Conifers
small needle like leaves
some of the oldest and largest organisms on earth
generally evergreen
Gnetophytes
Welwitschia only lives in namib desert, plants can be up to 2000 years old.
closely related to angiosperms
The Rise of Gymnosperms
Why they thrived in drier climates
thick cuticles and relatively small surface area of needle leaves--> less water loss
have key terrestrial adaptation found in all seed plants
Earliest Gymnosperms lived in moist Carboniferous ecosystems
As Permian rose, climate became much drier and other seedless plants largely replaced by Gymnosperms
dominated by seedless plants in general
Gymnosperms dominated much of the terrestrial area during Mesozoic era
Origins and characteristics date back to late Devonian era (380 MYA)