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