megaspore

Examples of megaspore in the following topics:

• Life Cycle of a Conifer

  • Like all gymnosperms, pines are heterosporous, generating two different types of spores: male microspores and female megaspores.
  • One megaspore mother cell (megasporocyte) undergoes meiosis in each ovule.
  • The gametophytes (1n), microspores and megaspores, are reduced in size.
  • This phase may take more than one year between pollination and fertilization while the pollen tube grows towards the megasporocyte (2n), which undergoes meiosis into megaspores.
  • The megaspores will mature into eggs (1n) .

• Sexual Reproduction in Gymnosperms

  • In the female cone, megaspore mother cells are present in the megasporangium.
  • The megaspore mother cell divides by meiosis to produce four haploid megaspores.
  • One of the megaspores divides to form the multicellular female gametophyte, while the others divide to form the rest of the structure.
  • (f) Within this single ovule are the megaspore mother cell (MMC), micropyle, and a pollen grain.

• The Life Cycle of an Angiosperm

  • Therefore, they generate microspores, which will produce pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes.
  • Within each megasporangium, a megasporocyte undergoes meiosis, generating four megaspores: three small and one large.
  • Only the large megaspore survives; it produces the female gametophyte referred to as the embryo sac.
  • The megaspore divides three times to form an eight-cell stage.

• Sporophytes and Gametophytes in Seedless 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.

• Angiosperm Flowers

  • The megaspores and the female gametophytes are produced and protected by the thick tissues of the carpel.

• Characteristics of Gymnosperms

  • The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes called ovules .

• Sexual Reproduction in Angiosperms

  • First, in the process of megasporogenesis, a single cell in the diploid megasporangium undergoes meiosis to produce four megaspores, only one of which survives.
  • During the second phase, megagametogenesis, the surviving haploid megaspore undergoes mitosis to produce an eight-nucleate, seven-cell female gametophyte, also known as the megagametophyte, or embryo sac.