The term gametophyte may refer to the gametophyte phase of the plant life cycle or to the particular plant body or organ that produces gametes. Tiered like a terrestrial rainforest with a canopy and several layers below, the kelp forests of the eastern Pacific coast are dominated by two canopy-forming, brown macroalgae species, giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis leutkeana). In plants with vascular tissue systems, the sporophyte phase is the primary phase of the life cycle. These spores develop into two distinct types of gametophytes; one type produces sperm and the other produces eggs. Kelp forests grow predominantly on the Pacific Coast, from Alaska and Canada to the waters of Baja California. In animal cells, haploid cells (gametes) are only produced by meiosis and only diploid cells undergo mitosis. The expression of “sporophytic” genes must therefore be repressed in the gametophyte, probably from the time of spore formation (sporogenesis). Correspondingly, events associated with gamete formation (gametogenesis) or fertilization must somehow free the sporophytic genes and thus permit the zygote to enter the sporophytic developmental pattern. It may be noted, however, that, in the course of evolution, the capacity for this type of growth has not been lost, since it may be adopted by cells grown in tissue cultures in the laboratory. Depending on the type of plant, most of its life cycle may be spent in either the gametophyte generation or sporophyte generation. Early development: from zygote to seedling, Later development: the sporophyte plant body, Coordination of shoot and root development, https://www.britannica.com/science/plant-development, Understand how roots and leaves transport oxygen, carbon dioxide, and minerals vital to a plant's development. The key difference between sporophyte and gametophyte is that the sporophyte is a diploid structure that participates in asexual reproduction while the gametophyte is a haploid structure that participates in sexual reproduction of plants.. Plants reproduce via asexual reproduction as well as via sexual reproduction. The male gametophyte generation consists of microspores and pollen. Although the two generations are phases of one life cycle, they have independent developmental histories; each begins as a single cell, passes through a juvenile period, matures, and gives rise to the alternate phase. spore (spôr) n. 1. "Gametophyte Generation of the Plant Life Cycle." The lower portion usually becomes a foot that penetrates the gametophyte and anchors the embryonic sporophyte to the gametophyte. Director, Royal Botanic Gardens, Kew, England, 1971–77. The heart-shaped prothallia produce gametes that unite to form a zygote, which develops into a new sporophyte plant. Although it might be supposed that the “switch” is associated with the difference in chromosome number between the haploid spore (a single set) and the diploid zygote (a double set), this has been shown not to be the determining factor. Gametophytes develop from the spores and, like them, are normally haploid; i.e., each cell has one set of chromosomes. Sporophytes develop from a fertilized egg, or zygote, that results from the fusion of gametes (fertilization) formed by the gametophytes and are accordingly diploid; i.e., each cell has two sets of chromosomes. Final development of the male gametophyte, or microgametophyte, usually occurs on the soil prior to the release of biflagellate sperm. Plant Life Cycle: Alternation of Generations, Characteristics of Mosses and Other Non-Vascular Plants, Biology Prefixes and Suffixes: heter- or hetero-, Sexual Reproduction Advantages and Disadvantages, A.S., Nursing, Chattahoochee Technical College. The male spore will develop into a mature gametophyte that contains structures to make male gametes. Sporophytes produce the haploid spores from which haploid gametophytes develop. Most plants are heteromorphic, meaning that they produce two different types of gametophytes. Please select which sections you would like to print: While every effort has been made to follow citation style rules, there may be some discrepancies. The gametophyte phase is the primary phase in non-vascular plants, such as mosses and liverworts. The gametophyte structure of ferns is a heart-shaped plant called a prothallium. The male and female gametes (eggs and sperm) are produced on the gametophyte (in special structures called antheridia and archegonia, respectively) and a fertilized egg will develop into a sporophyte. In Selaginella, usually only four large megaspores are produced in a megasporangium. It is in the haploid gametophyte structure that gametes are formed. Updates? The plant life cycle has mitosis occurring in spores, produced by meiosis, that germinate into the gametophyte phase. Corrections? Male gametes are sperm. In seedless vascular plants, such as ferns, the gametophyte and sporophyte generations are both capable of photosynthesis and are independent. Lester V. Bergman/Corbis Documentary/Getty Images, Gametophyte Generation in Seed Producing Plants. They are mostly sweet to taste, are filled with nutrients and some of them are like tomatoes are also eaten as vegetables. Royal Society Research Professor, University College of Wales, Aberystwyth, University of Wales, 1977–85. Regina Bailey is a board-certified registered nurse, science writer and educator. In animals, gametes are produced in male and female gonads, the cite of hormone production.Read to learn more about how gametes divide and reproduce. The mature haploid gametophyte then produces gametes by mitosis. (1) Clusters (sori) of sporangia (spore cases) grow on the undersurface of mature fern leaves. (2020, August 27). Ferns are examples of these types of plants. This cycle is named alternation of generations and organisms alternate between a sexual phase, or gametophyte generation and an asexual phase, or sporophyte generation. Unlike in non-vascular plants, the gametophyte and sporophyte phases in non-seed producing vascular plants are independent. The sporophyte generation consists of the plant body and seeds. The male gametophyte will develop via one or two rounds of mitosis inside the anther. Once an egg has been fertilized the development of the sporophyte begins. There's more about this in the REPRODUCTION SECTION. After fertilization, the diploid zygote develops into a mature sporophyte plant that arises from the gametophyte. Gametophyte size ranges from three cells (in pollen) to several million (in a "lower plant" such as moss). Plant sporophytes represent the asexual phase of the cycle and produce spores. Many ferns and other vascular plants are homosporous, meaning that they produce one type of spore. The prothallium is the gametophyte phase in the fern's life cycle. Water is needed for fertilization to take place as sperm swim toward the female reproductive organs (archegonia) and unite with the eggs. Life cycle of a typical angiosperm. Pollen is produced in stamens, and is carried to the pistil, which has the ovary at its base where fertilization can take place. Plant development, a multiphasic process in which two distinct plant forms succeed each other in alternating generations. Male gametophytes produce reproductive structures called antheridia, while female gametophytes produce archegonia. In ferns, the sporophyte phase consists of the leafy fronds, sporangia, roots, and vascular tissue. It is in the haploid gametophyte structure that gametes are formed. "Gametophyte Generation of the Plant Life Cycle." The male gametophyte develops and reaches maturity in an immature anther. Although both plants and animals share the chemical basis of inheritance and of translation of the genetic code into structural units called proteins, plant development differs from that of animals in several important ways. The whole structure is protected from desiccation and can reach the female organs without dependence on water. Notable is the lack of cellular movements and fusions that play an important part in tissue and organ development in higher animals. 2. The term gametophyte may refer to the gametophyte phase of the plant life cycle or to the particular plant body or organ that produces gametes. The moss spore germinates into a filamentous plant, the protonema, which later produces a leafy shoot. Bailey, Regina. They are haploid cells that are produced by meiosis in sporophytes. Please refer to the appropriate style manual or other sources if you have any questions. Gametophytes in angiosperms and gymnosperms are pollen grains and ovules. Mosses and liverworts are also heterosporous, meaning that they produce two different types of spores. Pollen is the male gametophyte in angiosperms and gymnosperms. Male gametes reach female gametophyte and the egg cell gamete though a pollen tube: an extension of a cell within the pollen grain. Gametophytes develop from the germination of spores. Spores are reproductive cells that can give rise to new organisms asexually (without fertilization). The development of the moss gametophyte illustrates the transition from a filamentous to a highly organized three-dimensional growth form. ThoughtCo. Let us know if you have suggestions to improve this article (requires login). ThoughtCo, Aug. 27, 2020, thoughtco.com/gametophyte-sexual-phase-4117501. The alternating generations typically have different forms (i.e., are heteromorphic); this is true for the bryophytes and for all vascular plants, including lower vascular plants (ferns and allies), angiosperms (flowering plants), and gymnosperms (conifers and allies). Bailey, Regina. Plant development, a multiphasic process in which two distinct plant forms succeed each other in alternating generations. The pollen grain germinates forming a pollen tube that extends downward to penetrate the ovary and allow a sperm cell to fertilize the egg. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. The life cycle of all tracheophytes (vascular plants), bryophytes (mosses and liverworts), and many algae and fungi is based on an alternation of generations, or different life phases: the gametophyte, which produces gametes, or sex cells, alternating with the sporophyte, which produces spores. The stalked umbrella-shaped structures bear archegonia. The gametophyte generation in these organisms consists of the green, leafy or moss-like vegetation located at the base of the plant. The diploid sporophyte produces haploid spores (by meiosis) in specialized sacs called sporangia. Non-vascular plants, like mosses and liverworts, spend most of their life cycle in the gametophyte generation. (4) When fertilization occurs, a zygote forms and develops into an embryo within the archegonium. SUSUMU NISHINAGA/Science Photo Library/Getty Images. The gametophyte phase consists of the small, heart-shaped plants or prothallia. Development of Male Gametophyte Pollen grains display germination that is initiated in pollen sac which is referred to as precocious germination wherein a large central vacuole formation causes the nucleus to be pushed to one side post which the nucleus goes through mitosis that gives rise to two daughter nuclei. Pollen tube with haploid male gametophyte nuclei. The microsporangia, usually bi-lobed, are pollen sacs in which the microspores develop into pollen grains. https://www.thoughtco.com/gametophyte-sexual-phase-4117501 (accessed March 14, 2021). This creates a 2 or 3 celled male gametophyte which becomes known as the pollen grain once dehiscing occurs. The zygote represents the sporophyte phase, which consists of the plant generation with diploid cells. The sporophyte structure is dependent upon the gametophyte of nourishment because only the gametophyte is capable of photosynthesis. Pollen grains are male gametophytes carried by wind, water, or a pollinator. The neck of the archegonium is a single cell layer thick and sheathes a single thread of cells that forms the neck canal. In seed producing plants, such as angiosperms and gymnosperms, the microscopic gametophyte generation is totally dependent upon the sporophyte generation. In flowering plants, the sporophyte generation produces both male and female spores. Thus the spores are part of the sexual reproduction cycle. One form, the sporophyte, is created by the union of gametes (sex cells) and is thus diploid (contains two sets of similar chromosomes). General rules for vascular plants are that the sporophyte generation is physically the larger, has a more complex developmental history, produces a greater range of cell types, and expresses a more diverse biochemistry; the gametophyte is often diminutive, reduced in the case of the angiosperms to a mere few cells. Other organisms, such as some algae and fungi, may spend most of their life cycles in the gametophyte phase. The life cycle of the fern. The sporophyte generation is represented by the elongated stalks with spore-containing structures at the tip. As the male gametophyte, pollen is a multicellular, haploid stage that produces the sperm.. Pollen development occurs in a structure called the microsporangium (micro = small), located within the … Furthermore, both growth and organ formation in plants are influenced by their possession of a rigid cell wall and a fluid-filled space called the vacuole, two features unique to the plant cell. Male Gametophyte. One form, the sporophyte, is created by the union of gametes (sex cells) and is thus diploid (contains two sets of similar chromosomes). Omissions? (3) Under moist conditions, mature sperm are released from the antheridia and swim to the egg-producing archegonia that have formed on the gametophyte's lower surface. In seed-bearing plants, pollen is a male sperm-producing gametophyte and female sex cells are contained within plant ovules. Within each pollen grain is a male gametophyte … Kelp Forests - a Description. Male microspores (sperm) form in microsporangia (pollen sacs) in the flower stamen. (5) The embryo eventually grows larger than the gametophyte and becomes a sporophyte. Marchantia, Female Gametophyte Archegonium-bearing structures in a liverwort. At maturity, the sporophyte produces haploid (containing a single set of chromosomes) spores, which grow into the gametophyte generation. (2) Released from its spore case, the haploid spore is carried to the ground, where it germinates into a tiny, usually heart-shaped, gametophyte (gamete-producing structure), anchored to the ground by rhizoids (rootlike projections). In seed-bearing vascular plants, such as angiosperms and gymnosperms, the gametophyte is totally dependent on the sporophyte for development. The alternation of generations illustrates an important principle, namely that cell lineages arising from single parental cells containing the same genetic potentiality may pursue mutually exclusive developmental patterns. One cell is the tube cell, and the remaining cell/cells are the sperm cells. Bailey, Regina. By using ThoughtCo, you accept our, Gametophyte Generation in Non-vascular Plants. Each generation has a different physical form. These male and female sex cells, also known as eggs and sperm, unite during fertilization to form a diploid zygote. The cycle begins anew when the diploid sporophyte cells undergo meiosis to produce haploid spores. Get a Britannica Premium subscription and gain access to exclusive content. Once an egg and sperm meet, either from the same gametophyte or from different gametophytes, a zygote is formed.
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