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The egg cell or ovum (pl.: ova) is the female reproductive cell, or gamete, [1] in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capable of movement (non- motile ).
A gametangium (pl.: gametangia) is a sex organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants. In contrast to gametogenesis in animals, a gametangium is a haploid structure and formation of gametes does not involve meiosis.
In many algae (e.g., Chara), the main plant is haploid; oogonia and antheridia form and produce haploid gametes. The only diploid part of the life cycle is the spore (fertilized egg cell), which undergoes meiosis to form haploid cells that develop into new plants. This is a haplontic life cycle (with zygotic meiosis).
At a minimum, two of these cells are egg cells and the rest are haploid somatic cells, but more egg cells may be present and their ploidy, though typically haploid, may vary. [14] [17] In select Gnetophyta, the female gametophyte stays singled celled. Mitosis does occur, but no cell divisions are ever made. [13]
Anisogamy is the form of sexual reproduction that involves the union or fusion of two gametes which differ in size and/or form. [12] The smaller gamete is considered to be male (a sperm cell), whereas the larger gamete is regarded as female (typically an egg cell, if non-motile).
The fertilization of egg cells varies between species of brown algae, and may be isogamous, oogamous, or anisogamous. Fertilization may take place in the water with eggs and motile sperm, or within the oogonium itself. Certain species of brown algae can also perform asexual reproduction through the production of motile diploid zoospores.
The sporophyte develops from the zygote produced when a haploid egg cell is fertilized by a haploid sperm and each sporophyte cell therefore has a double set of chromosomes, one set from each parent. All land plants , and most multicellular algae, have life cycles in which a multicellular diploid sporophyte phase alternates with a multicellular ...
Production of an egg causes swelling of the cell wall. Antheridia are short and disk-shaped, containing 1 to 2 multi-flagellated sperm cells. Motile male gametes will exit the antheridia and are chemotactically attracted to oogonia. A single sperm cell will pass through a pore opening in the oogonial cell wall, allowing fertilization to occur.