pollen

Examples of pollen in the following topics:

• Sexual Reproduction in Angiosperms

  • The microsporangia, usually bi-lobed, are pollen sacs in which the microspores develop into pollen grains.
  • Mature pollen grains contain two cells: a generative cell and a pollen tube cell.
  • Upon maturation of the pollen (bottom), the pollen sac walls split open and the pollen grains (male gametophytes) are released.
  • Pollen develops from the microspore mother cells.
  • The mature pollen grain is composed of two cells: the pollen tube cell and the generative cell, which is inside the tube cell.

• The Evolution of Seed Plants and Adaptations for Land

  • Pollen grains are male gametophytes carried by wind, water, or a pollinator .
  • Male gametes reach female gametophyte and the egg cell gamete though a pollen tube: an extension of a cell within the pollen grain.
  • The sperm of modern gymnosperms lack flagella, but in cycads and the Gingko, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.
  • This fossilized pollen is from a Buckbean fen core found in Yellowstone National Park, Wyoming.
  • The pollen is magnified 1,054 times.

• Pollination and Fertilization

  • In gymnosperms, pollination involves pollen transfer from the male cone to the female cone.
  • Upon transfer, the pollen germinates to form the pollen tube and the sperm that fertilize the egg.
  • In some species, the pollen and the ovary mature at different times.
  • By the time pollen matures and has been shed, the stigma of this flower is mature and can only be pollinated by pollen from another flower.
  • This allows insects to easily cross-pollinate while seeking nectar at the pollen tube.

• Life Cycle of a Conifer

  • In the male cones (staminate cones), the microsporocytes give rise to pollen grains by meiosis.
  • In the spring, large amounts of yellow pollen are released and carried by the wind.
  • Pollination is defined as the initiation of pollen tube growth.
  • The pollen tube develops slowly as the generative cell in the pollen grain divides into two haploid sperm cells by mitosis.
  • Pollen from male cones moves up into upper branches where it fertilizes female cones.

• Double Fertilization in Plants

  • After pollen is deposited on the stigma, it must germinate and grow through the style to reach the ovule.
  • The microspores, or the pollen, contain two cells: the pollen tube cell and the generative cell.
  • The pollen tube cell grows into a pollen tube through which the generative cell travels.
  • The germination of the pollen tube requires water, oxygen, and certain chemical signals.
  • As it travels through the style to reach the embryo sac, the pollen tube's growth is supported by the tissues of the style.

• Sexual Reproduction in Gymnosperms

  • Upon landing on the female cone, the tube cell of the pollen forms the pollen tube, through which the generative cell migrates towards the female gametophyte through the micropyle.
  • Pollen from male cones blows up into upper branches, where it fertilizes female cones.
  • (b) Pollen grains are visible in this single microsporophyll.
  • (c) This micrograph shows an individual pollen grain.
  • (f) Within this single ovule are the megaspore mother cell (MMC), micropyle, and a pollen grain.

• Pollination by Bats, Birds, Wind, and Water

  • As the bats seek the nectar, their faces and heads become covered with pollen, which is then transferred to the next flower.
  • The pollen is deposited on the exposed feathery stigma of the flower.
  • The pollen floats on water.
  • In the process, the bee picks up the pollen to be transported to another flower.
  • The male wasp is attracted to the scent, lands on the orchid flower, and, in the process, transfers pollen.

• Pollination by Insects

  • Bees collect energy-rich pollen or nectar for their survival and energy needs.
  • The pollen sticks to the bees' fuzzy hair; when the bee visits another flower, some of the pollen is transferred to the second flower.
  • The nectar provides energy while the pollen provides protein.
  • The pollen is picked up and carried on the butterfly's limbs.
  • The moth deposits pollen on the sticky stigma for fertilization to occur later.

• Mendelian Crosses

  • In the pea, which is a naturally self-pollinating plant, this is done by manually transferring pollen from the anther of a mature pea plant of one variety to the stigma of a separate mature pea plant of the second variety.
  • In plants, pollen carries the male gametes (sperm) to the stigma, a sticky organ that traps pollen and allows the sperm to move down the pistil to the female gametes (ova) below.
  • To prevent the pea plant that was receiving pollen from self-fertilizing and confounding his results, Mendel painstakingly removed all of the anthers from the plant's flowers before they had a chance to mature.

• 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.
  • Inside the anthers' microsporangia, male gametophytes divide by meiosis to generate haploid microspores, which, in turn, undergo mitosis and give rise to pollen grains.
  • Each pollen grain contains two cells: one generative cell that will divide into two sperm and a second cell that will become the pollen tube cell.
  • When a pollen grain reaches the stigma, a pollen tube extends from the grain, grows down the style, and enters through the micropyle, an opening in the integuments of the ovule.
  • Anthers and carpels are structures that shelter the actual gametophytes: the pollen grain and embryo sac.