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 = EVOLUTION Mosses-> 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