gametophyte

Examples of gametophyte in the following topics:

• Sporophytes and Gametophytes in Seedless Plants

  • Sporophytes (2n) undergo meiosis to produce spores that develop into gametophytes (1n) which undergo mitosis.
  • The gametophyte phase (1n) is dominant in these plants.
  • The male spores are called microspores, because of their smaller size, and develop into the male gametophyte; the comparatively larger megaspores develop into the female gametophyte.
  • Heterosporous plants produce two morphologically different types of spores: microspores, which develop into the male gametophyte, and megaspores, which develop into the female gametophyte.
  • Describe the role of the sporophyte and gametophyte in plant reproduction

• Sexual Reproduction in Gymnosperms

  • Gymnosperms produce both male and female gametophytes on separate cones and rely on wind for pollination.
  • The female gametophyte is contained within a structure called the archegonium.
  • It takes approximately one year for the pollen tube to grow and migrate towards the female gametophyte.
  • In angiosperms, the female gametophyte in the ovule exists in an enclosed structure, the ovary; in gymnosperms, the female gametophyte is present on exposed bracts of the female cone and is not enclosed in an ovary.
  • These series of micrographs shows male and female gymnosperm gametophytes.

• Liverworts and Hornworts

  • The gemmae then land nearby and develop into gametophytes.
  • The gametophytes grow as flat thalli on the soil with embedded gametangia.
  • The haploid spores germinate and produce the next generation of gametophytes .
  • Spores are released from sporophytes and form the gametophyte.
  • The organism in the photograph is in the dominant gametophyte stage.

• Mosses

  • Mosses form diminutive gametophytes, which are the dominant phase of the life cycle.
  • They originate from the base of the gametophyte, but are not the major route for the absorption of water and minerals.
  • The alternation of generations cycle begins when the gametophyte germinates from a haploid spore and forms a protonema.
  • After fertilization, the zygote divides and grows into a sporophyte, which stays attached to the gametophyte.
  • Spores released from the sporophyte germinate and produce gametophytes; the process begins again.

• Life Cycle of a Conifer

  • Some gametophytes will land on a female cone.
  • Three of the four cells break down leaving only a single surviving cell which will develop into a female multicellular gametophyte.
  • The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte that will provide nutrients, and the embryo itself.
  • The gametophytes (1n), microspores and megaspores, are reduced in size.

• Life Cycles of Sexually Reproducing Organisms

  • The haploid multicellular plants are called gametophytes because they produce gametes from specialized cells.
  • The spores will subsequently develop into the gametophytes .
  • In plants such as moss, the gametophyte organism is the free-living plant, while the sporophyte is physically dependent on the gametophyte.
  • In seed plants, such as magnolia trees and daisies, the gametophyte is composed of only a few cells and, in the case of the female gametophyte, is completely retained within the sporophyte.
  • The spores develop into multicellular, haploid plants called gametophytes because they produce gametes.

• Characteristics of Gymnosperms

  • The female gametophyte develops from the haploid (meaning one set of genetic material) spores that are contained within the sporangia.
  • Like all seed plants, gymnosperms are heterosporous: both sexes of gametophytes develop from different types of spores produced by separate cones.
  • The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes called ovules .
  • Incredibly, this whole sexual process can take three years: from the production of the two sexes of gametophytes, to bringing the gametophytes together in the process of pollination, and finally to forming mature seeds from fertilized ovules.

• The Life Cycle of an Angiosperm

  • Angiosperms are seed-producing plants that generate male and female gametophytes, which allow them to carry out double fertilization.
  • Therefore, they generate microspores, which will produce pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes.
  • Inside the anthers' microsporangia, male gametophytes divide by meiosis to generate haploid microspores, which, in turn, undergo mitosis and give rise to pollen grains.
  • Only the large megaspore survives; it produces the female gametophyte referred to as the embryo sac.
  • Anthers and carpels are structures that shelter the actual gametophytes: the pollen grain and embryo sac.

• Sexual Reproduction in Angiosperms

  • In the angiosperm, the haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms.
  • The male gametophyte develops and reaches maturity in an immature anther.
  • The overall development of the female gametophyte has two distinct phases.
  • The micropyle allows the pollen tube to enter the female gametophyte for fertilization.
  • Upon maturation of the pollen (bottom), the pollen sac walls split open and the pollen grains (male gametophytes) are released.

• Ferns and Other Seedless Vascular Plants

  • The gametophytes do not depend on the sporophyte for nutrients.
  • Some gametophytes develop underground and form mycorrhizal associations with fungi.
  • Modern-day horsetails are homosporous and produce bisexual gametophytes.
  • The inconspicuous gametophyte harbors both sex gametangia.
  • The newly-formed zygote grows into a sporophyte that emerges from the gametophyte, growing by mitosis into the next generation sporophyte.