Tracheophytes;

Gymnosperms

Jaime Crosby, CHS

Plants with seeds are designed for life on land• They evolved through time and

natural selection—those best suited for the environment survived and reproduced. Others died

• Change over time = EVOLUTIONMosses-> Ferns -> Spermopsida

(seed plants)

Recall what you know about roots, stems and leaves…

• These are all advanced adaptations of seed plants (i.e. cuticle, vascular cylinder, tracheid cells, stoma, roots, etc)

Reproduction is FINALLY FREE from water!!• Still have alternation of

generations– Reduced gametophyte, dominant

sporophyte generation– Pollination– Evolution of the seed to avoid

dessication of zygote

All adaptations allow freedom from dependence on water!!• Sporophyte generation can become

very large• Cones are the actual FEMALE

gametophyte, which develop on the sporophyte plant

• Pollination– The carrying of the entire male

gametophyte (pollen) to the female gametophyte. This process is completely free from water because of insects, animals and wind

SEEDS: protection for zygotes• Store food to nourish embryo:

called a nucellus• Seed coat prevents embryo and

food supply from drying out, called integument

• Adult sporophyte plant begins to grow, or germinate, when conditions are right

Evolution of seed plants

• Seed ferns—look like ferns, but used seeds, not spores. All are now extinct, and we only know of them because of fossils

Evolution of seed plants

• Gymnosperms– Cycads, ginkgos and conifers– Male and female structures and

scales are grouped into cones• Male cones produce pollen• Female cones produce eggs• Both are gametophyte generation

• Once fertilized, seeds develop on the female cone scales covered by a seed coat, but not by any other protection (thus, gymnosperm means “naked seed”)

Modern seed plants

• Only 1 species of ginkgo: Ginkgo biloba remains, along with 7 species of cycads

• 575 species of conifers exist, these are cone-bearing trees like pines, firs and spruce

• Conifers are successful in sandy soil and in cool, moist areas all over the world

• Can live to be 4000 years old and grow up to 100 meters tall

Adaptations

• Long, thin needles are the leaves. – One vein insulated from freezing– “Evergreen” is misleading—leaves

live 2 to 14 years and do fall off, but the tree is never totally bare. • What is the advantage of this?

Reproduction• Male cones produce male gametophytes in

the form of pollen grains• Female cones produces female

gametophytes in the form of ovules• Some plants are hermaphrodites, others

have separate sexes• Fertilization occurs on female cones, zygote

grows on scale of female cone as a seed• Seed gets carried off and germination occurs

when conditions are right

Life Cycle of a Gymnosperm

• “Micro” means male (microsporangia)

• “Mega” means female (megaspore)

• Wind transfers the pollen• Pollen tube grows into ovule and

sperm swims down the tube for fertilization

Relevance of Gymnosperms

• Turpentine• Amber-based fossils• Menthol for cigarettes• Plywoods for beams and buildings• Red dye from Hemlock• Eastern White Cedar is used for

canoes• Mulch (cedar)• Taxol from Pacific Yew is used to treat

cancer