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Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. Volvox species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700.
In the genus Gonium, for example, each individual organism is a flat plate consisting of 4 to 16 separate cells, each with two flagella. Similarly, the genera Eudorina and Pandorina form hollow spheres, the former consisting of 16 cells, the latter of 32 to 64 cells. In these genera each cell can reproduce a new organism by mitosis. [2] Volvox sp.
Volvox carteri [1] is a species of colonial green algae in the order Volvocales. [2] The V. carteri life cycle includes a sexual phase and an asexual phase.V. carteri forms small spherical colonies, or coenobia, of 2000–6000 Chlamydomonas-type somatic cells and 12–16 large, potentially immortal reproductive cells called gonidia. [3]
Green algae are also found symbiotically in the ciliate Paramecium, and in Hydra viridissima and in flatworms. Some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia (class Ulvophyceae), can be found in symbiotic associations with fungi to form lichens. In general the fungal species that ...
In the smaller forms, typically all cells are involved, but larger forms have anterior vegetative and posterior reproductive cells. Sexual reproduction varies from isogamy (both genders produce flagellated gametes of equal size) to oogamy (one gender produces a much larger, nonmotile gamete). The classification of the Chlamydomonadales varies.
Other examples of colonial organisation in protista are Volvocaceae, such as Eudorina and Volvox, the latter of which consists of up to 500–50,000 cells (depending on the species), only a fraction of which reproduce. [38] For example, in one species 25–35 cells reproduce, 8 asexually and around 15–25 sexually.
The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content.
Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane-bound organelle. [10] Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. [11] Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus. Eukaryotic cells are found in ...