Exam 4 Flashcards
Seeds components
Protective seed coat, supply of food for embryo, capability of dormancy.
Seed plant advantages
Water and fertilization: drier environments, distances between plants can be greater
Seed anatomy
Smaller gametophytes, heterospory, ovules, and pollen grain
Phylum Pinophyta
Conifers
Phylum Ginkgophyta
Ginkgo
Phylum Cycadophyta
Cycads
Phylum Gnetophyta
Gnetophytes
Gymnosperm
The seed is exposed. Seeds are produced on surface of sporophylls or similar structures instead of enclosed in a fruit like flowering plants. Seed-bearing and pollen-bearing sporophylls often arranged in cones.
Pollen cones produce
pollen grains
Female gametophyte produced
Inside an ovule that contains a nucellus. Reduced in cell number beyond ferns. Does not grow independently but develops within sporophyte structures
Nucellus
enclosed in integument, which becomes the seed coat after fertilization.
Pinophyta
Pines, firs, spruces, cedars. Most economically important phylum. Contains over 100 species.
Ginkgophyta
Has a single living representative. Tree with fan-shaped leaves. Seeds enclosed in fleshy covering.
Cycadophyta
Leaves superficially palmlike
Gnetophyta
Three genera. Wood with vessels; only hardwood of the gymnosperms
Pines are
dominant trees in coniferous forests of Northern Hemisphere. Include the world’s oldest known living organisms, the bristlecone pines.
Pine structure and form
Leaves needlelike and arranged in clusters of two to five leaves. Modifications allow them to survive harsh conditions; hypodermis located below the epidermis, giving one to two extra layers of thick-walled cells; thick cuticle; recessed or sunken stomata; resin canals; mycorrhizal fungi associated with roots of most conifers
Cluster of pine needles
Fascicles
Fascicles
Short shoots, having restricted growth
Resin
Antiseptic, prevents development of fungi, deters insects
Pine wood
Consists entirely of tracheids. softwood.
Softwood
Conifers. thick-walled cells absent
Hardwood
Broadleaf tree (dicot) wood. Thick-walled vessels and fibers present.
Pine reproduction in pollen cones
Male strobili. Consist of papery or membranous scales. Microsporangia in pairs toward bases of scales. Meiosis produces microspores that then develop into pollen grains, which consist of four cells and a pair of air sacs, which add buoyancy in the wind.
Pine reproduction in seed cones
Megaspores in megasporangia within ovules. pair of ovules at bases of seed cone scales. Seed cones larger than pollen cones. Have woody scales with inconspicuous bracts between. Ovule contains a megasporangium containing a nucellus and a single megasporocyte. Sporangia are surrounded by integument, which has a pore called a micropyle. Sporocyte undergoes meiosis, producing four megaspores. Three degenerate. Remaining megaspore develops into female gametophyte with archegonia at micropyle end.
Pine seed cone development
Seed cones take two years to mature. First year, pollen grains catch on sticky pollen drops oozing out of micropyle; pollen grain produces pollen tube that grows through nucellus; two sperms produced in pollen tube; mature male gametophyte is germinated pollen grain with pollen tube and two sperm; sperm have no flagella and no antheridium is formed; megaspore develops. Second year, female gametophyte and archegonium mature; pollen tube arrives at archegonium; one sperm unites with egg, forming zygote; other sperm degenerates. Embryo is then nourished by female gametophyte; integument becomes seed coat
Yew and California nutmeg
Produce ovules singly at tips of shoots. Each ovule at least partially surrounded by cuplike aril (fleshy nucellus).
Junipers
Seed cones fleshy
Southern hemisphere conifer
Merkus pine. Podocarpus - fleshy-coated seeds with large appendage at base
Phylum Ginkgophyta Characteristics
Only one living species. Only exists in cultivation. Notched, broad, fan-shaped leaves on short, slow-growing spurs. No midrib or prominent veins. Hair-like veins branch dichotomously. Deciduous.
Ginkgophyta life cycle
Similar to pines. Dioecious. Seeds enclosed in fleshy seed coat with unpleasant odor
Dioecious
Male and female structures on separate trees
Phylum Cycadophyta characteristics
Slow growing plants of tropics and subtropics. Tall, unbranched trunks. Crown of large, pinnately divided leaves. Life cycle similar to conifers. Pollinated sometimes by beetles. Dioecious. Has pollen and seed strobili.
Phylum Gnetophyta Characteristics
Unique among the gymnosperms in having vessels in the xylem. 3 Genera
Joint firs (Ephedra)
Gnetophytes. Shrubby plants of drier regions of southwestern North America
Gnetum
Gnetophytes. Vine-like plants with broad leaves found in the tropics
Welwitschia
Gnetophyte. Only one species, confined to the deserts of southwestern Africa. Short stem, long taproot, only two straplike leaves that become tattered and split. Dioecious. Has male and female strobili.
Human relevance of conifers
Edible inner park and needles of white pine and seeds of most pines. Masts in sailing vessels. Crates, boxes, matchsticks, furniture. Telephone poles, railroad ties, mine timbers. Turpentine and rosin (both from resin). Fuel. Pulpwood. Construction lumber. Ornamentals. Pharmaceuticals (taxol from yew trees).