Download Plant Diversity II – The Evolution of Seed Plants

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Seeds are embryos packaged with a food
supply in a protective coat
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Reduced Gametophyte:
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Gametes mostly microscopic
Dependent on the sporophyte for food
and protection
Protects anteridia and achegonia,
increasing reproductive success
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Heterospory: Production of two
types of spores
Megaspores produce female gametophytes which
produce the egg.
 Microspores produce male gametophytes which
contain sperm nuclei.
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Ovules and Production of Eggs
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Megasporangium, megaspore, and the protective
tissue around them make up the ovule.
Ovule increases protection of the egg and the
developing zygote.
Increases reproductive fitness.
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Pollen and the Production of Sperm
A Pollen grain is a male gametophyte.
 It contains two sperm nuclei.
 Has a waterproof coating, allowing for transfer by
the wind.
 Water no longer required for sperm transfer.
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Seeds
Have many advantages over spores.
 Multicellular and many layered
 Can provide more protection for
devloping embryo
 Have a supply of stored energy which
allows the seed to wait for good
germination conditions.
 Stored energy is used for early growth
of embryo.
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“Naked Seeds” means seeds are not enclosed
in ovaries.
Seeds are exposed on modified leaves that
form cones
Angiosperms (flowering plants) have seeds
enclosed in fruits.
Gymnosperms do not have fruits.
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Cycadophyta
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Ginkophyta
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Gnetophyta
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Coniferophyta:
Largest group of gymnosperms
 Most are evergreen
 Make up large forests in Northern
hemisphere at high latitudes and
altitude.
 Includes the pines, firs, spruces, and
redwoods.
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Flowering plants are in the phyla
Anthophyta
90% of all plant species are
angiosperms.
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Flower consists of four floral organs:
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Sepals - protect the flower before emergence
Petals - attract pollinators
Stamens - male reproductive structure
produces microspores in the anthers that develop
into pollen grains.
Carpels - the female reproductive structure
produces megaspores and their products: female
gametophytes with eggs.
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Fruits are mature ovaries.
Seeds develop from fertilized ovules.
The wall of the ovary thickens to
become the fruit.
Fruits help disperse the seeds of
angiosperms.
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Monocots have:
One cotyledon in the seed
 Parallel leaf veination
 Flowering parts in multiples of threes
 Vascular bundles are scattered through
out the stem.
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 Dicots
 Two
have:
cotyledons in the seed
 Net leaf veination
 Flowering parts in multiples of
fours or fives.
 Vascular bundles are found
around edge of stem.