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In algae, the egg cell is often called oosphere. [citation needed] Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins, and organelles to the oocytes.
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]
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 ...
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.
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.
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).
In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plants, parthenogenesis is a component process of apomixis. In algae, parthenogenesis can mean the development of an embryo from either an individual sperm or an individual egg.
Embryophyte cells also generally have an enlarged central vacuole enclosed by a vacuolar membrane or tonoplast, which maintains cell turgor and keeps the plant rigid. In common with all groups of multicellular algae they have a life cycle which involves alternation of generations.