Units 22 and 23
•SEED PLANTS
Life Llife Cylce of
Nonseed Plant Life CycleFlagellated sperm must swim
Seed Plant Life CyclePollination
Highlights in the History of Seed Plants
• Late in the Devonian, some plants developed
secondary growth: thickened woody stems
of xylem
How Did Seed Plants Become Today’s Dominant Vegetation?
Surviving seed plants fell
into two groups:
• Gymnosperms: pines and cycads
• Angiosperms: flowering plants
Gymnosperms
• Any vascular plant that reproduces by means of an exposed seed, or ovule
• “Naked Seed”
Gymnosperm
Gymnosperms
Four major phyla of living gymnosperms:
• (a)Cycads: Cycadophyta Sago palm
• Cone-bearing
• palm like
• tropical
• dinosaur food ?
Gymnosperms
• b)Ginkgos: Ginkgophyta
• One living species, Ginkgo biloba
• Seed coat stinks
• Polluted areas
• 1945 atom bomb
The ginkgo is a living fossil, recognizably similar to fossils dating back 270 million years.
Gymnosperms
• (c) Gnetophytes: Gnetophyta
• Shrubs , trees, or vines
• the group is a small one, consisting of three families, each with one genus, totaling 68 species
Ephedra
*ephedrine
Gymnosperms
• (D)Conifers Coniferophyta
• largest group of gymnosperms
• pines, hemlock, spruce, evergreen conifers
• leaves stay all season sap ----antifreeze
• first real development of wood dead transport tissue
Gymnosperms
• Softwood
Angiosperms
•Flowering plants are the dominant
plant today
Angiosperms
• They are the largest group of plants with about 90% of all plant species.
.
A
• Angiosperm Protected Seeds
Angiosperms
• FLOWERS are the exclusive reproductive organ of angiosperms
• “The earth laughs in flowers” Ralph Waldo Emerson
What Features Distinguish the Angiosperms?
Angiosperm: “enclosed seed”
Angiosperms• Male reproductive structures
Stamen Anther Filament bear microsporangia - sperm ( pollen)
Female reproductive structuresCarpelStigma, style, and ovary bear megasporangia -egg
(one or more carpel make up a pistil)
Angiosperm
• Pollen• B - Dandelion (Taraxacum sp.) Transmission electron microscopy
• F - Pine (Pinus sylvestis): Light microscopy
• G - Mixed pollen grains (bright field light microscopy, stained)
Anigosperms
• Flowers may have contributed to the enormous success of angiosperms.
• The flowers attract a pollinators which carry pollen to other individuals of the same species
Angiosperms
Attracted to sweet smellsNeed landing platform
Attracted to strong smellsCan hover; nocturnal
Can hoverPrefer red color
Need bigger landing platformLike bright colors
Angiosperms
• Double fertilization
Sperm A leads to the formation of a Seed
Sperm B leads to the formation of an endosperm
(a nutritive tissue within the seed that feeds the developing plant embryo)
Flowering plants are divided into two groups
• Cotyledon?
• Embryonic seed
• is the first leaf or set of leaves that sprout from a seed
• Store nutrients for the embryo
• A cotyledon – “seed leaf”
• contain nutrients for growth during embryonic development
• upon germination, the cotyledon may become the embryonic first leaves of a seedling.
• Dry fruit vs. Fleshy fruit
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