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Three of these independent gametophyte cells degenerate and the one that remains is the gametophyte mother cell which normally contains one nucleus. [24] In general, it will then divide by mitosis until it consists of 8 nuclei separated into 1 egg cell, 3 antipodal cells , 2 synergid cells , and a central cell that contains two nuclei.
Within each ovule, a megaspore develops by mitosis into a megagametophyte. An archegonium develops within the megagametophyte and produces an egg. The whole of the gametophytic generation remains within the protection of the sporophyte except for pollen grains (which have been reduced to just three cells contained within the microspore wall).
Each male gametophyte typically consists of two to four cells enclosed within the protective wall of a pollen grain. The sporophyte of a flowering plant is often described using sexual terms (e.g. "female" or "male") based on the sexuality of the gametophyte it gives rise to. For example, a sporophyte that produces spores that give rise only to ...
Prothallus of the tree fern Dicksonia antarctica (note new moss plants for scale) Spore-bearing plants , like all plants, go through a life-cycle of alternation of generations . The fully grown sporophyte , what is commonly referred to as the fern , produces genetically unique spores in the sori by meiosis .
These two cells in addition to the spore wall make up an immature pollen grain. As the male gametophyte matures, the generative cell passes into the tube cell, and the generative cell undergoes mitosis, producing two sperm cells. Once the pollen grain has matured, the anthers break open, releasing the pollen.
Heterospory stops self-fertilization from occurring in a gametophyte, but does not stop two gametophytes that originated from the same sporophyte from mating. [8] This specific type of self-fertilization is termed as sporophytic selfing, and in extant plants it occurs most commonly among angiosperms .
The three cells left at the end of the cell near the micropylar become the egg apparatus with an egg cell in the center and two synergids. A cell wall forms around the other set of nuclei and forms the antipodals. The cells in the center develop into the central cell. This entire structure with its eight nuclei is called the embryonic sac.
The gametophyte is the multicellular structure (plant) that is haploid, containing a single set of chromosomes in each cell. The gametophyte produces male or female gametes (or both), by a process of cell division, called mitosis. In vascular plants with separate gametophytes, female gametophytes are known as mega gametophytes (mega=large, they ...