 |
Flowering Plants: Sporophyte to Gametophyte
Sexual activities begin within the ovules and anthers of a flower. Diploid cells in the pollen sacs undergo meiosis to produce four hapliod cells know as microspores (small spores). Each microspore nucleus and divides by mitosis to form two haploid nuclei, the tube nucleus and the generative nucleus. When the outer wall of the microspore hardens, the structure becomes a pollen grain.
|
 |
A similar type of activity takes place within each ovule. A single diploid cell of the ovule undergoes meiosis to produce four haploid cells of which only one survives. This surviving cell is called a megaspore, which means large spore. In some flowers the megaspoes nucleus divides by mitosis to form two haploid nuclei. Mitosis continues until a total of eight haploid nuclei are produced. These nuclei and the cytoplasm around them represent the entire female gametophyte generation. Of the eight nuclei produced, only three are important in reproduction: two polar nuclei in the center of the ovule and the true egg at one end. The remaining five haploid nuclei die.
แหล่งข้อมูล : Biology living system. Page 420.
|
|