Flowering Plant Life Cycle

During the plant’s life, it alternates between a multicellular diploid sporophyte generation and a multicellular haploid gametophyte generation.  In Angiosperms, the sporophyte generation is dominant and more independent of the gametophyte.  For the same reason, the gametophyte is more minor and dependent on the sporophyte.   Here are a few other unique aspects seen exclusively in Angiosperms: 

Double fertilization:  one fertilization juncture produces a zygote and triploid cell. 

Fruits: A developed ovary that encloses the seeds

Flowers: The reproductive structures in angiosperms

Ovules: protected in the ovaries instead of exposed on the surface

Now, look at the steps involved in an angiosperm’s life cycle.

• • 1) In the flower’s male parts, the anthers and diploid microsporangium undergo meiosis, giving rise to microspores.  These haploid microspores will eventually give rise to haploid pollen grains

  • 2) In the flower’s ovules, the megasporocyst undergoes meiosis, creating four megaspores.  Only one of these four megaspores survives and undergoes three mitotic divisions to produce an eight-nucleate embryo sac or mature megagametophyte

  • 3) Next, pollination occurs.  The pollen grain travels to the stigma via wind, insects, or other transportation devices.  Once on the stigma, it generates a pollen tube down the style.

  • 4) Two sperm travel down each pollen tube into the ovary.  One sperm fertilizes the egg to produce a zygote, and the other fertilizes the central cells to form the endosperm.

  • 5) The zygote will give rise to an embryo and be enclosed with the endospore in a seed.  The endosperm gives the embryo energy to germinate.

  • 6) Once the seed germinates, the diploid zygote will eventually become another sporophyte. 

  • 7) The cycle starts over.