Many of our familiar forest trees are conifers, including pines, spruces, firs, hemlocks, yews, redwoods and cypress trees.
They are an ancient group, dating back mya. They evolved during the Permian, toward the end of the Paleozoic, at a time when the climate was very cool and dry. Their special water conducting cells, called tracheids, allowed them to thrive in these climates and these same adaptations let them continue to dominate in colder and dryer environments today, such as northern latitudes, mountain slopes, and sandy soils.
Because they are superior competitors in such habitats even today, they are the only Division of gymnosperms to successfully compete with the flowering plants. Most conifers are evergreens, with the larch and the bald cypress being notable exceptions. Their needle-shaped leaves are also an adaptation to conserve water. Needles usually occur in small bundles, each bundle emerging from a base that is actually a greatly truncated branch.
Conifers have tremendous economic importance, as a source of timber and for byproducts such as pitch, tar, turpentine, and amber and other resins. Millions are sold each year as Christmas trees. All conifers produce cone shaped strobili, both male cones often called pollen cones and female cones often called seed cones or ovulate cones. Both male and female cones are usually produced on the same tree, but not at the same time, so the trees do not fertilize themselves.
Female cones are large and conspicuous, with thick woody scales. Seed cones can persist on the tree for several years after fertilization. A few species, like junipers and the locally common podocarpus front of Richardson , have seeds that are covered with a fleshy coating, and resemble small berries. The sporangia produced by the sporophytes are located at the bases of the sporophylls, and collected in the strobilus we call a pine cone.
The microspore mother cell in the microsporangia produces the haploid pollen grains. Each scale or sporophyll in the male cone has two microsporangia on its lower surface.
Each pollen grain consists of only four cells. When the immature pollen grain finally reaches the seed cone, the megaspore mother cell in the megasporangium produces four haploid megaspores. Three of these megaspores degenerate, and only the fourth germinates into the female gametophyte. The female gametophyte consists of two or more archegonia, with a single egg in each one. All eggs are usually fertilized.
Each visible scale in the seed cone is really a much reduced lateral branch in itself. So each scale is homologous with the entire male cone. The megasporangium, which is called a nucellus in seed plants, is covered with a layer of protective cells called an integument, which is open at one end.
This tiny opening, the micropyle, marks the point where the male pollen tube will grow into the megasporangium. The megasporangium, together with its integument, makes up the ovule. Seeds develop from ovules. Each scale in the seed cone has two ovules on the upper surface of the scale, and so will ultimately bear two seeds side by side. The pollen grains formed in the microsporangia of pines have tiny wing on either side.
Because they are wind-pollinated? The ovulate cones open to receive pollen, then may close again to protect the developing embryos. When pollen grains land on the ovulate cones, they grow a long pollen tube. By the time this tube reaches the archegonia, about 15 months after pollination, the male gametophyte is fully mature. The pollen tube enters through the micropyle. The sperm nucleus divides in two, and the pollen tube discharges two sperm.
One sperm nucleus degenerates, the other fertilizes the egg. It takes the female gametophyte about 15 months to mature, and about the same time for the pollen tube of the male gametophyte to reach it. The seed develops within the megasporangium.
The seed is the structure containing the embryonic plant and the stored nutrition to support it. A section of the surface of the scale usually detaches along with the seed, giving the seed a little wing to help disperse it farther from the tree. Conifer seeds are very complex little structures, containing cells from three generations of the tree. The nutritive tissues inside the seed are actually the haploid body cells of the female gametophyte.
The seed also contains the developing diploid sporophyte, the little embryonic conifer. The outer wrapping of the seed, the tough and protective seed coat, is formed from the diploid cells of the parent sporophyte. Pine seeds, along with acorns, are the most important source of plant food for North American wildlife.
Examine the cycads and cycad frond on display. How do the leaves of cycads differ from those of angiosperms? Cycad leaves are full of potent neurotoxins, carcinogens, and other toxic chemicals?
Cycads are protected in another way, as you know if you've bumped into one of the many cycads on campus. Why evolve such potent defenses? Examine the ginkgo leaves and seeds. You might detect a faint odor, a reminder of the very nasty smell these seeds make when their fleshy covering starts to rot.
The delicate appearance of the leaves gives the ginkgo its common name, the maidenhair tree. Where can we find these trees on campus? Note the difference between the fleshy-covered seeds of Ginkgo and Podocarpus , and the dry seeds of Pinus. What function would this fleshy covering have served? The answer to this question may also explain why ginkgo seeds really stink.
Compare Ephedra to the other gymnosperms. Until recently, we thought that this curious "stem plant" was closely related to flowering plants. Ephedra undergoes double fertilization , a fundamental trait of flowering plants. Recent evidence, however, suggests that Gnetophytes are more closely related to pines than to angiosperms. Examine the Podocarpus branch. This plant is related to the yew. Depending on the season, the plant may have one or more purplish fleshy-covered seeds, smaller versions of the ginkgo seeds.
The seeds are very tempting to small children, but the seeds, as well as the leaves and other parts of the plant, are toxic. You can find this tree growing all over campus and throughout the city. Note the difference between the broad leaves of the angiosperms on display, and compare them to the needle-shaped leaves of pines.
Needles are an adaptation to conserve water in cold, dry environments. They are also an excellent shape for species like pines that rely on wind pollination why? Examine slides of the megaspore mother cell. Observe the structure of the strobilus female pine cone and note the megasporophylls and megasporangia. You will need to look at several sporangia , and possibly more than one slide, to actually find the megaspore mother cell.
Notice that the sporangia sitting on the sporophylls are directly exposed to the outside air. Gymnosperm means "naked seed". Examine slides of the male strobilus pine cone. Note the microsporangia and the microsporophylls. You can switch to high power and observe the pollen grains in the sporangia or switch to the pollen grain slide.
Notice the two large wings looks like Mickey Mouse. These wings were presumed to aid in wind pollination, but recent evidence suggests they help the pollen grain float up through the micropyle to the egg.
Examine the pine cones on display. The smaller male cones are only on the tree for a short time. Ephedra is the natural source of the drug ephedrin , which is used to treat hay fever, sinus headaches, and asthma eg. Zamia floridana is the only cycad native to the U. Ginkgos are used for bonsai, as a source of herbal medicine, and as popular urban shade trees because of their yellow autumn foliage and their resistance to air pollution.
Conifer seeds are very complex structures, containing cells from three generations of the tree. Can you figure out which tissues come from which generation of the conifer? Just as Gymnosperms forced non-seed plants into the ecological background, the evolution of Angiosperms, sometime during the Cretaceous, forced gymnosperms into restricted habitats.
Wherever the earth was cold or dry, gymnosperms could prevail. But in all other habitats, flowering plants rapidly became the dominant plant life. Flowering plants are able to survive in a greater variety of habitats than gymnosperms. Flowering plants mature more quickly than gymnosperms, and produce greater numbers of seeds. The woody tissues of angiosperms are also more complex and specialized. Their seeds are enclosed in a fruit for easy dispersal by wind, water, or animals.
The leaves of angiosperms are mostly thin, extended blades, with an amazing diversity of shapes, sizes, and types. The surface of the pollen grain has a complex three-dimensional structure. Angiosperms and gymnosperms are two major types of vascular plants plants that have conducting tissue.
Now, angiosperms are more widely distributed and populous, and can be considered the dominant plant life on the planet. Placement of Gymnosperm in Plant Kingdom. Present in flowers; can be unisexual or bisexual.
Angiosperm forms flower that carries reproductive organs and fruits. Gymnosperms are seed-producing plants, but they do not produce fruits like angiosperms. What is the key distinction between an angiosperm and a Gymnosperm quizlet? Found inside — Page I would like to suggest that one characteristic of angiosperms which If you're looking for characteristics then here they are - 1.
Other angiosperms like cotton and flax provide paper and textiles. So roughly they are differentiated by: The leaves are usually thin, like "hairs".
Bare, not enclosed; found on scales, leaves or as cones. They need to get into the ground quickly to take root or they will be damaged by animals, weather conditions or any other factors. To summarize the features that distinguish gymnosperms and angiosperms. Angiosperms are commonly known as flowering plants that can be clearly distinguished from gymnosperms by certain "derived" characteristics.
Gymnosperm is classified into four divisions, namely: According to botanists, Angiosperms form a single coherent group known as Angiophyta. Like angiosperms, gymnosperms also have vessels and companion cells. Read on to explore the difference between angiosperms and gymnosperms. A strength of Concepts of Biology is that instructors can customize the book, adapting it to the approach that works best in their classroom.
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The stamens are made up of anthers, in which pollen grains are produced, and a supportive strand called the filament. The pollen contains two cells— a generative cell and a tube cell—and is covered by two layers called the intine and the exine.
The carpels, which are the female reproductive structures, consist of the stigma, style, and ovary. The female gametophyte is formed from mitotic divisions of the megaspore, forming an eight-nuclei ovule sac. This is covered by a layer known as the integument.
The integument contains an opening called the micropyle, through which the pollen tube enters the embryo sac. The diploid sporophyte of angiosperms and gymnosperms is the conspicuous and long-lived stage of the life cycle. The sporophytes differentiate specialized reproductive structures called sporangia, which are dedicated to the production of spores.
The microsporangium contains microspore mother cells, which divide by meiosis to produce haploid microspores. The microspores develop into male gametophytes that are released as pollen.
The megasporangium contains megaspore mother cells, which divide by meiosis to produce haploid megaspores.
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