Alternation of Generations
The Alternation of Generations is the plant's' life cycle. It all starts with a multicellular diploid (2n) sporophyte which then, through the process of meiosis, forms haploid (n) spores . These spores then grow, through the process of mitosis, into a haploid gametophyte which then undergo mitosis yet again and develop into male and female gametes. These gametes come together , in the process of fertilization, and form a diploid zygote. This zygote which through mitosis develops into a multicellular diploid sporophyte. The life cycle then repeats time and time again.
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Plant Characteristics
Bryophyta
Bryophytes were the first plants that evolved to be able to be live on land. These are your typical mosses, liverworts and hornworts.
Bryophyta Characteristics: ✏ Non-vascular : No water transport system ✏ No true roots : Have rhizoids ✏ Absorb water/nutrients throughout the entire plant ✏ Produce flagellated swimming sperm ✏ Gametophyte dominant (haploid stage) ✏ Heterosporous and Dioecious ✏ Produce spores for reproduction ✏ Diploid Sporophyte dependant on the Haploid Gametophyte ✏ Do not produce seeds |
Pteridophyta
Pteridophytes are slightly more evolved that Bryophytes. Their main difference being that Pteridophytes have vascular tissue. These include common selaginella, horsetails and ferns.
Pteridophyta Characteristics: ✏ Vascular tissue in their stem: Have xylem and phloem ✏ No true roots: Have hyphae ✏ No true leaves : Have fronds ✏ Sporophyte dominant (diploid stage) ✏ Monoecious: Archegonium and Antheridium develop on the same plant ✏ Homosporous ✏ Produce flagellated swimming sperm ✏ Do not produce seeds ✏ Must live in a moist/humid environment |
Gymnospermae
Gymnosperms are what we know as conifers. They were the first plants to develop complete vascular tissue and true roots. These include the familiar evergreen trees and shrubs.
Gymnospermae Characteristics: ✏ Complete vascular tissue ✏ True Roots ✏ True leaves ✏ Sporophyte Dominant (Diploid stage) ✏ Heterosporous ✏ Dioecious ✏ Produce cones, Needles and Seeds for reproduction ✏ Tend to live in cold and dry climates |
Angiospermae
Angiosperms were the last major advance in land plant evolution. These are your regular flowering plants.
Angiospermae Characteristics: ✏ Specialized reproductive systems : flowers ✏ Vector pollinated ✏ Monoecious ✏ Heterosporous ✏ Complete vascular tissue ✏ True Roots ✏ True leaves ✏ Produce seeds ✏ Have stomata in their leaves : let in CO2 and release 02 ✏ Divided into two sub classes : Monocots and Dicots ✏ |
Plants' Life Cycles
BryophytesBryophytes are gametophyte dominant. The sporophyte grows out of the female gametophyte and has the sporangium on the top. Meiosis occurs in the sporangium to create spores which are then released when the operculum opens. The spores are then released into the air. Since the plant is heterosporous microspores become male gametophytes and megaspores become female gametophytes which then grow through the process of mitosis. When both gametophytes are mature sperm from the antheridium travels through water into the archegonium where fertilization occurs. Thus resulting in a zygote. The zygote then keeps growing ,through mitosis, until it becomes an embryo. The embryo then grows into a sporophyte. Then the life cycle repeats.
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PteridophytesPteridophytes are sporophyte dominant. They are also monoecious which means that they have both male and female reproductive systems in the same plant. Pteridophytes produce flagellated sperm which are carried through water from the antheridium to the archegonium where fertilization occurs, thus creating a zygote. This zygote grows into an embryo which then grows into a sporophyte through mitosis. This grows into a mature sporophyte. On the underside of their fronds, ferns have diploid sori, which contain the sporangia. This is where meiosis occurs to create haploid spores. Spores are then carried by wind until they land. Pteridophytes are the only type of plants that are homosporous, this means that all the spores grow into the same gametophyte. Then the life cycle repeats.
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GymnospermsGymnosperms are sporophyte dominant. The mature sporophyte is both heterosporous and dioecious which means that it produces both male and female gametophytes. The male cone contains microsporocytes that contain microsporangia, which go through the process of meiosis to make pollen (the haploid male gametophyte).The female cone makes megasporocytes which contain a megasporangium. The megasporangium contains a megaspore which undergoes meiosis to form 4 haploid eggs, only one egg survives (this all happens after pollination). Then a haploid megagametophyte grows through mitosis , containing the archegonium. A pollen grain then grows a pollen tube to release its sperm. Fertilization occurs and a zygote is formed which then grows into an embryo. The embryo is kept in the ripe seed until germination. After germination, the new seedling grows into a mature sporophyte by mitosis . Then the life cycle repeats.
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AngiospermsAngiosperms are sporophyte dominant. They begin as a seed which then grows into a sporophyte. In the flower of the mature sporophyte the carpel and stamen reside. In the anther meiosis occurs to produce pollen. This pollen then travels by wind or vectors to the sticky stigma. There it makes its way down the pollen tube and into the ovary where fertilization occurs. The zygote grows into an embryo with the protective coat around it grows into a fruit. The fruit protects the seeds and provides nutrients. When the seed is released it becomes it grows into a sporophyte. Then the life cycle repeats.
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Levels of Organization
Plants have evolved throughout time. With each evolutionary chnage their genetic coding became more complex.
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Amazing Plant Race
We have 8 competitors:
Carrie Cornstalk, Hal Hornwort, Missy Moss, Paul Pinetree, Gus Ginkgo, Hannah Horsetail, Fern and Lily Pad.
Carrie Cornstalk, Hal Hornwort, Missy Moss, Paul Pinetree, Gus Ginkgo, Hannah Horsetail, Fern and Lily Pad.