Plant Life Cycles and Reproductive Structures PDF

III. Plant Life Cycle and Reproductive Structures Life Cycles and Reproductive Structures Asexual Reproduction Asexual reproduction is natural “cloning.” Parts of the plant, such as leaves or stems, produce roots and become an independent plant. Sexual Reproduct...

III. Plant Life Cycle and Reproductive Structures Life Cycles and Reproductive Structures Asexual Reproduction Asexual reproduction is natural “cloning.” Parts of the plant, such as leaves or stems, produce roots and become an independent plant. Sexual Reproduction Sexual reproduction requires fusion of male cells in the pollen grain with female cells in the ovule. Terms to know: Haploid (n) - having a single set of chromosomes in each cell. Diploid (2n) - having two sets of chromosomes in each cell. Mitosis - cell division, which produces two genetically identical cells. Meiosis - reduction division, which produces four haploid reproductive cells.  PLANT LIFE CYCLE Pollen grains produce sperm cells Pollen grain Haploid (n) S IS GENE GA METO FER Diploid (2n) TIL I ZA TIO Sperm cells N move down GAMETOGENESIS pollen tube, toward egg Many ovules— each contains an egg cell Fertilized egg (zygote) inside ovule Cotyledons Embryo I S ES EN Y OG REP BR R Hypocotyl EM DEV ODUCT ELO I P M E VE NT A TION VEGETATIVE GERMIN DEVELOPMENT Root Seed (mature ovule) Seedling Animals vs. Plants Plant Reproduction Animal Reproduction Alternation of No alternation of Life cycle generations generations Gametes Haploid gametes Haploid gametes Spores Haploid spores No spores Haploid gametophyte, Diploid organism, by Gametes made by by mitosis meiosis Diploid sporophyte, by Spores made by No spores meiosis Alternation of Generations Plants have a double life cycle with two distinct forms: Sporophyte: diploid (2n) , produce haploid spores by meiosis. Gametophyte: haploid (n) , produce gametes by mitosis. Non-flowering plants Mosses, ferns, and related plants have motile, swimming sperm. What kind of environmental conditions would be required for reproduction in these plants? What kinds of limits does external reproduction impose on these plants? Moss Life Cycle Moss Life Cycle: Sporophyte Generation Mitosis of the zygote produces an embryo that grows into the mature sporophyte generation. It consists of: A foot, which absorbs water, minerals, and food from the parent gametophyte. A stalk, at the tip of which is formed a sporangium (the brownish objects in the photo). The sporangium is filled with spore mother cells, sealed by an operculum and covered with a calyptra. The calyptra develops from the wall of the old archegonium and so is actually a part of the gametophyte generation. It is responsible for the common name ("haircap moss") of this species. Fern Life Cycle Conifers The conifers, phylum Coniferophyta, is the largest gymnosperm phylum. The term conifer comes from the reproductive structure, the cone, which is a cluster of scale-like sporophylls. Male gametophyte is contained in a dry pollen grain. Female gametophyte is a few cells inside of the Pine tree stands in Sagada, Mt. Province structures that become the seed. Podocarpus sp. Araucaria sp. Conifer life cycle Reproduction in pines begins with the appearance of cones on a pine tree. 1. Most species produce both pollen cones and ovulate cones. 2. A pollen cone contains hundreds of microsporangia held on small sporophylls. Cell in the microsporangia undergo meiosis to form haploid microspores that develop into pollen grains. 3. An ovulate cone consists of many scales, each with two ovules. Each ovule includes a megasporangium. Reproduction in pines begins with the appearance of cones on a pine tree. 4. During pollination, windblown pollen falls on the ovulate cone and is drawn into the ovule through the micropyle. The pollen grain germinates in the ovule, forming a pollen tube that digests its way through the megasporangium. 5. The megaspore mother cell undergoes meiosis to produce four haploid cells, one of which will develop into a megaspore. The megaspore grows and divides mitotically to form the immature female gametophyte. 6. Two or three archegonia, each with an egg, then develop within the gametophyte Micropyle Reproduction in pines begins with the appearance of cones on a pine tree. 7. At the same time that the eggs are ready, two sperm cells have developed in the pollen tube which has reached the female gametophyte. Fertilization occurs when one of the sperm nuclei fuses with the egg nucleus 8. The pine embryo, the new sporophyte, has a rudimentary root and several embryonic leaves. The female gametophyte surrounds and nourishes the embryo. The ovule develops into a pine seed, which consists of an embryo (new sporophyte), its food supply (derived from gametophyte tissue), and a seed coat derived from the integuments of the parent tree (parent sporophyte). Conifer pollination Conifers are wind-pollinated plants. Chance allows some pollen to land on the scales of female cones. Pollen germinates, grows a pollen tube into the egg to allow sperm to fertilize the egg.  Pollen go-betweens Showy flowers are the result of selection for more efficient pollination strategies. Flower parts are modified leaves. Those that were brightly colored attracted insects in search of pollen. FLOWERS Flower Parts Incomplete flowers Flowers are complete if they have all parts, and perfect if they have both male and female parts. Grass flowers: incomplete, usually imperfect (separate male and female flowers) A tulip is complete (though the sepals are the same color as the petals) and perfect. Imperfect flowers Angiosperm Life Cycle Angiosperm Reproduction All angiosperms are heterosporous, produce microspores that form male gametophytes megaspores that form female gametophytes. The immature male gametophytes are contained within pollen grains and develop within the anthers of stamens. Each pollen grain has two haploid cells. Ovules, which develop in the ovary, contain the female gametophyte, the embryo sac. It consists of only a few cells, one of which is the egg The life cycle of an angiosperm begins with the formation of a mature flower on a sporophyte plant and culminates in a germinating seed. Angiosperm Reproduction ØThe anthers of the flower produce : microspores that form male gametophytes (pollen). ØOvules produce megaspores that form female gametophytes (embryo sacs). Angiosperm Reproduction ØAfter its release from the anther, pollen is carried to the sticky stigma of a carpal. Although some flowers self-pollinate, most have mechanisms that ensure cross-pollination, transferring pollen from flowers of one plant to flowers of another plant of the same species. The pollen grain germinates (begins growing) from the stigma toward the ovary. Angiosperm Reproduction ØWhen the pollen tube reaches the micropyle, a pore in the integuments of the ovule, it discharges two sperm cells into the female gametophyte. Ø In a process known as double fertilization, one sperm unites with the egg to form a diploid zygote and the other fuses with two nuclei in the large center cell of the female gametophyte. Angiosperm Reproduction ØThe zygote develops into a sporophyte embryo packaged with food and surrounded by a seed coat. The embryo has a rudimentary root and one or two seed leaves, the cotyledons. Monocots have one seed leaf and dicots have two ØMonocots store most of the food for the developing embryo in endosperm which develops as a triploid tissue in the center of the embryo sac Beans and many dicots transfer most of the nutrients from the endosperm to the developing cotyledons. Gametogenesis: Male Stamen (Male) The male reproductive organs, are the sporophylls that produce microspores that will give rise to gametophytes. Consists of a stalk (the filament) and a terminal sac (the anther) where pollen is produced, AND which contains microsporangia A typical anther contains four microsporangia. Stamen (Male) Microsporangia form sacs or pockets (locules) in the anther. The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells.  Stamen (Male) These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte called a pollen grain. Gametogenesis: Female  Carpels (Female) Female sporophylls that produce megaspores and their products, female gametophytes. At the tip of the carpal is a sticky stigma that receives pollen. A style leads to the ovary at the base of the carpal. Ovules and, later, seeds are protected within the ovary. Carpels (Female) Carpels are the building blocks of the gynoecium. If a gynoecium has a single carpel, it is called monocarpous. If a gynoecium has multiple, distinct (free, unfused) carpels, it is apocarpous. The Carpel Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Double Fertilization Flower to Fruit Ovule to Seed Seed Anatomy  Seed Germination Germination begins when a seed absorbs water Mature seeds are often extremely dry need enough water to moisten the seeds but not enough to soak them. The uptake of water by seeds is called imbibition, which leads to the swelling and the breaking of the seed coat Often requires an additional environmental signal such as specific wavelength of light Others need to be passed through an animal's digestive tract to weaken the seed coat enough to allow the seedling to emerge Releasing Sugars From Cotyledon...So the Embryo Can Grow Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Releasing Sugars From Cotyledon...So the Embryo Can Grow Embryo produces gibberellic acid -This hormone signals the aleurone (outer endosperm layer) to produce a- amylase -Breaks down the endosperm’s starch into sugars that are passed to embryo  Seed Germination New growth comes from delicate meristems As the sporophyte pushes through the seed coat, it orients with the environment such that the root grows down & shoot grows up -Usually, the root emerges before the shoot -The shoot becomes photosynthetic, and the postembryonic phase is under way Cotyledons may be held above or below the ground -May become photosynthetic or shrivel From the wikimedia free licensed media file repository  Seed Germination Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings ANGIOSPERMS (closed seeds) Ecological & economic significance of flowering plants. source of food. lumber for houses & buildings. gives us fibers & medicines. Products (rubber, tobacco, coffee.etc). Economic Botany - is the subdiscipline of botany that deals with plants of economic importance; most of these are fl owering plants.