Transcript Units 22 and 23

Units 22 and 23
•SEED PLANTS
Life Llife Cylce of
Nonseed Plant Life Cycle
Seed Plant Life Cycle
Flagellated sperm must swim
Pollination
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



Female reproductive structures
Carpel
Stigma, style, and ovary
bear megasporangia -egg
(one or more carpel make up a pistil)
Anther
Filament
bear microsporangia - sperm ( pollen)
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 smells
Need landing platform
Attracted to strong smells
Can hover; nocturnal
Need bigger landing platform
Like bright colors
Can hover
Prefer red color
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