Transcript 6S_28
Gymnosperms THE TERM OF GYMNOSPERM The gymnosperms are a group of seed-bearing plants. Gymnosperms are usually distributed among four groups, these groups are: Pinophyta- Conifers (pines, cypresses) Ginkgophyta- Ginkgo (a single living species) Cycadophyta- Cycads Gnetophyta –Gnetales From: http://en.wikipedia.org/ GENERAL FEATURES OF GYMNOSPERMS They are large plants with well-developed roots , stems, leaves, and vascular tissue. its leaves are needle-shape and evergreen . Most distinguish feature is that their seeds are develop either on the surface of scaleor leaf- like cones, or at the end of short stalks. Therefore they are naming of "naked seeds“ ,the unenclosed condition of their seeds http://www.backyardnature.net/gymnos.htm THE LEAVES OF GYMNOSPERM The shape of leaves of gymnosperms are different from the leaves of most angiosperms, but they contain more or less the same tissue types. For example: Pines which often live in harsh conditions: hot, dry summers and freezing winters. Therefore, they are good at withstanding environmental stress. Their leaves, with a low surface area which help to reduce damage due to drying out or heavy snows. http://www.deanza.edu/faculty/mccauley/6a-labs-plants-04.htm THE LEAF OF GYMNOSPERM The outer layer : epidermis (one cell thick) protects the leaf from damage Cuticle (a waxy layer ) block the diffusion of carbon dioxide and oxygen as well as water. Stomata (opened or closed by guard cells) open to allow diffusion of gaseous and water. THE LEAF OF GYMNOSPERM Single vascular bundle (contains phloem and xylem) Phloem (phloem cells are small, thin-walled) transports the sugars that are produced in photosynthesis from the leaves to the rest of the plant. Xylem (xylem cells are thick-walled, reinforced with lignin) transports water and inorganic nutrients from the roots up to the rest of the plant. Transfusion tissue (surrounds the vascular bundle) helps transport materials into and out of the vascular tissue. Resin ducts (a hydrocarbon-containing substance) carry resin that may help protect the leaves. Mesophyll cells (undifferentiated and consists of specialized parenchyma cell filled with chloroplasts) (surrounded by intercellular air spaces, which enables them to perform gas exchange) (the cell walls have numerous infolding which compensates for the reduction in leaf surface by increasing surface area of the cells for gas exchange. ) PINOPHYTA - CONIFERS They are cone-bearing seed plants with vascular tissue. All extant conifers are woody plants, the great majority being trees with just a few being shrubs. Typical examples of conifers include cedars, cypresses, firs, pines, redwoods and yews. The division contains approximately eight families, 68 genera, and 630 living species GINKGOPHYTA- GINKGO Ginkgo known as the Maidenhair Tree with no Ginkgo- Biloba leaves close living relatives. Ginkgoes are very large trees, normally reaching a height of 20–35 m ,with some specimens in China being over 50 m . The tree has an angular crown, branches, and usually deep rooted to resistant to wind and snow damage. Ginkgos also have a combination of resistance to disease, insect-resistant wood and the ability to form aerial roots and sprouts makes .Therefore they are long-lived, with some specimens claimed to be more than 2,500 years old. CYCADOPHYTA- CYCADS Cycads are seed plants with a large crown of compound leaves and a stout trunk. They are evergreen. They can grow in sand or even on rock and able to grow in full sun or shade. They are found in South ,Central America (where the greatest diversity occurs), Japan and China, where at least 65 species occur. They have very specialized pollinators .Since they have been reported to fix nitrogen in association with a cyanobacterium (blue-green algae) living in the roots,producing a neurotoxin that is found in the seeds of cycads, therefore the trees can be toxic. From: http://en.wikipedia.org GNETOPHYTA –GNETALES (GNETUM WELWITSCHIA AND EPHEDRA) The plant division Gnetophyta consists of three genera of woody plants ,they are Gnetum,Welwitschia and Ephedra. all three genera are placed in a single order (Gnetales) Gnetum is grow in the tropics, 30 species, grows usually as trees or as vines with large leathery leaves The gnetophytes differ from other gymnosperms (conifers, cycads, and ginkgos) since it having vessel elements as in the flowering From: plants. http://en.wikipedia.org THE REPRODUCTIVE STRUCTURE OF GYMNOSPERMS male cone female cone In most gymnosperms , female reproductive part : cone . male reproductive part: pollen In pine trees and other gymnosperms they produce two types of cones. male cone : pollen cone. female cone: the larger seed cone THE REPRODUCTIVE STRUCTURE OF ANGIOSPERMS In angiosperms, the female and male reproductive structure are found in flowers . Male part : consists of stamen (anther with pollen grain and thread-like filaments) Female part : consists of the stigma, style and ovary with ovule METHOD OF REPRODUCTION OF GYMNOSPERMS http://www.youtube.com/watch?v=D9byVQxvMXs ANGIOSPERMS THE COMPARISON BETWEEN GYMNOSPERMS AND ANGIOSPERMS gymnosperms angiosperms condition of their seeds on the surface of scale- or leaf-like cones, or at the end of short stalks enclosed by mature ovaries, or fruits. Method of Pollination accomplished by wind or downsizing of pollen grains accomplished by wind, insects, and other animals. Produce flower Do not produce flower Produce flower produce real fruits do not produce real fruits produce real fruits