| Volvocaceae | |
|---|---|
 | |
| Volvox aureus | |
Scientific classification  | |
| (unranked): | Viridiplantae |
| Division: | Chlorophyta |
| Class: | Chlorophyceae |
| Order: | Chlamydomonadales |
| Family: | Volvocaceae Ehrenberg |
| Genera | |
The Volvocaceae are a family of unicellular or colonial biflagellates, including the typical genus Volvox . The family was named by Ehrenberg in 1834, [1] and is known in older classifications as the Volvocidae. All species are colonial and inhabit freshwater environments.
The simplest of the Volvocaeans are ordered assemblies of cells, each similar to the related unicellular protist Chlamydomonas and embedded in a gelatinous matrix. 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]
Other genera of Volvocaceans represent another principle of biological development as each organism develops differented cell types. In Pleodorina and Volvox , most cells are somatic and only a few are reproductive. In Pleodorina californica a colony normally has either 128 or 64 cells, of which those in the anterior region have only a somatic function, while those in the posterior region can reproduce; the ratio being 3:5. In Volvox only very few cells are able to reproduce new individuals, and in some species of Volvox the reproductive cells are derived from cells looking and behaving like somatic cells. In V. carteri , on the other hand, the division of labor is complete with reproductive cells being set aside during cell division, and they never assume somatic functions or develop functional flagella. [2]
Thus, the simplest Volvocaceans are colonial organisms but others are truly multicellular organisms. Larger volvocaceans have evolved a specialized form of heterogamy called oogamy, the production of small motile sperm by one mating type and relatively larger immotile eggs by another. Among the Volvocaceans are thus the simplest organisms with distinguishable male and female members. In all Volvocaceans, the fertilization reaction results in the production of a dormant diploid zygote (zygospore) capable of surviving in harsh environments. Once conditions have improved the zygospore germinates and undergoes meiosis to produce haploid offspring of both mating types. [2]
Colony inversion during development is a special characteristic of this order that results in new colonies having their flagella facing outwards. During this process reproductive cells first undergo successive cell divisions to form a concave-to-cup-shaped embryo or plakea composed of a single cell layer. Immediately after, the cell layer is inside out compared with the adult configuration—the apical ends of the embryo protoplasts from which flagella are formed, are oriented toward the interior of the plakea. Then the embryo undergoes inversion, during which the cell layer inverts to form a spheroidal daughter colony with the apical ends and flagella of daughter protoplasts positioned outside. This process enables appropriate locomotion of spheroidal colonies of the Volvocaceae. The mechanism of inversion has been investigated extensively at the cellular and molecular levels using a model species, Volvox carteri . [3]
Spheroidal colony inversion evolved twice during evolution of the Chlamydomonadales. In the Volvocaceae inversion first occurred when the Volvocaceae diverged from the closely related Goniaceae (see figure). It also occurred during evolution of Astrephomene. Inversion differs between the two lineages: rotation of daughter protoplasts during successive cell divisions in Astrephomene , and inversion after cell divisions in the Volvocaceae. [3]
The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral- or ribbon-shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.
A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger in 1878.
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. Volvox diverged from unicellular ancestors approximately 200 million years ago.
In biology, a colony is composed of two or more conspecific individuals living in close association with, or connected to, one another. This association is usually for mutual benefit such as stronger defense or the ability to attack bigger prey.
A cell type is a classification used to identify cells that share morphological or phenotypical features. A multicellular organism may contain cells of a number of widely differing and specialized cell types, such as muscle cells and skin cells, that differ both in appearance and function yet have identical genomic sequences. Cells may have the same genotype, but belong to different cell types due to the differential regulation of the genes they contain. Classification of a specific cell type is often done through the use of microscopy. Recent developments in single cell RNA sequencing facilitated classification of cell types based on shared gene expression patterns. This has led to the discovery of many new cell types in e.g. mouse cortex, hippocampus, dorsal root ganglion and spinal cord.
Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae. Chlamydomonadales can form planar or spherical colonies. These vary from Gonium up to Volvox. Each cell has two flagella, and is similar in appearance to Chlamydomonas, with the flagella throughout the colony moving in coordination.
In cellular biology, a somatic cell, or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Somatic cells compose the body of an organism and divide through mitosis.
A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. Most prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but some are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4.8 billion years ago.
A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.
The green algae are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as a sister of the Zygnematophyceae. Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid (spherical), and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae, many of which live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.
Sporogenesis is the production of spores in biology. The term is also used to refer to the process of reproduction via spores. Reproductive spores were found to be formed in eukaryotic organisms, such as plants, algae and fungi, during their normal reproductive life cycle. Dormant spores are formed, for example by certain fungi and algae, primarily in response to unfavorable growing conditions. Most eukaryotic spores are haploid and form through cell division, though some types are diploid sor dikaryons and form through cell fusion.we can also say this type of reproduction as single pollination
Gonium is a genus of colonial algae, a member of the order Chlamydomonadales. Typical colonies have 4 to 16 cells, all the same size, arranged in a flat plate, with no anterior-posterior differentiation. In a colony of 16 cells, four are in the center, and the other 12 are on the four sides, three each. A description by G.M. Smith :
Gonium Mueller 1773: Colonies of 4-8-16 cells arranged in a flat quadrangular plate and embedded in a common gelatinous matrix or connected by broad gelatinous strands. Cells ovoid to pyriform, with a single cup-shaped chloroplast containing one pyrenoid. Each cell with two cilia of equal length, contractile vacuoles at the base of the cilia, and an eyespot. Four- and eight-celled colonies with the cilia on the same side ; sixteen-celled colonies with the four central cells having their cilia on the same side and the twelve marginal cells with radially arranged cilia.
Asexual reproduction by simultaneous division of all cells in the colony to form autocolonies, or by a formation of 2-4 zoospores in each cell.
Sexual reproduction isogamous, by a fusion of biciliatezoogametes.
Astrephomene is a genus of green algae in the family Goniaceae, order Chlamydomonadales. The genus was first described in 1937 by Pocock and named by Pockock in 1953.
Eudorina is a paraphyletic genus in the volvocine green algae clade. Eudorina colonies consist of 16, 32 or 64 individual cells grouped together. Each individual cell contains flagella which allow the colony to move as a whole when the individual cells beat their flagella together. Description by GM Smith :
Volvox globator is a species of green algae of the genus Volvox. It was originally described by Carl Linnaeus in his 1758 work Systema Naturae. In 1856 its sexuality was described by Ferdinand Cohn and is the same as Sphaeropleaannulina. It is colonial flagellate found in freshwaters. The colony consists of thousands of zooids arranged in a single peripheral layer. each zooids shows two flagella, two or more contractile vacuoles, cup like chloroplast, a single nucleus, a red stigma but no gullet. Nutrition is holophytic. Size of colony increases by binary fission. In the colony the zooids called parthenogonidia repeatedly divide to form daughter colonies which are released from parent colony.
Volvox carteri is a species of colonial green algae in the order Volvocales. 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. While vegetative, male and female colonies are indistinguishable; however, in the sexual phase, females produce 35-45 eggs and males produce up to 50 sperm packets with 64 or 128 sperm each.
Allorecognition is the ability of an individual organism to distinguish its own tissues from those of another. It manifests itself in the recognition of antigens expressed on the surface of cells of non-self origin. Allorecognition has been described in nearly all multicellular phyla.
Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly unicellular and microscopic. Many unicellular protists, particularly protozoans, are motile and can generate movement using flagella, cilia or pseudopods. Cells which use flagella for movement are usually referred to as flagellates, cells which use cilia are usually referred to as ciliates, and cells which use pseudopods are usually referred to as amoeba or amoeboids. Other protists are not motile, and consequently have no built-in movement mechanism.
Germ-Soma Differentiation is the process by which organisms develop distinct germline and somatic cells. The development of cell differentiation has been one of the critical aspects of the evolution of multicellularity and sexual reproduction in organisms. Multicellularity has evolved upwards of 25 times, and due to this there is great possibility that multiple factors have shaped the differentiation of cells. There are three general types of cells: germ cells, somatic cells, and stem cells. Germ cells lead to the production of gametes, while somatic cells perform all other functions within the body. Within the broad category of somatic cells, there is further specialization as cells become specified to certain tissues and functions. In addition, stem cell are undifferentiated cells which can develop into a specialized cell and are the earliest type of cell in a cell lineage. Due to the differentiation in function, somatic cells are found only in multicellular organisms, as in unicellular ones the purposes of somatic and germ cells are consolidated in one cell.
| Authority control databases: National |
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