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Chlorophyceae

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31-437: See text . 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

62-414: A group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva , follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology). In haplobiontic species only the haploid generation,

93-463: A multicellular gametophyte. All land plants have a diplobiontic common ancestor, and diplobiontic forms have also evolved independently within Ulvophyceae more than once (as has also occurred in the red and brown algae). Diplobiontic green algae include isomorphic and heteromorphic forms. In isomorphic algae, the morphology is identical in the haploid and diploid generations. In heteromorphic algae,

124-594: A starch sheath) that are localised around the chloroplast. Some algae may also store food in the form of oil droplets. The inner cell wall layer is made of cellulose and the outer layer of pectose. Chlorophyceae can reproduce both asexually and sexually. Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated zoospores . And haplospore, perennation (akinate and palmella stage). Asexual reproduction by mitospore absent in spyrogyra. Also by aplanospores, hypnospores, Palmella stage, etc. Sexual reproduction shows considerable variation in

155-468: Is a unicellular, isogamous charophycean alga group that is the closest unicellular relative to land plants. Heterothallic strains of different mating type can conjugate to form zygospores . Sex pheromones termed protoplast-release inducing proteins (glycopolypeptides) produced by mating-type (-) and mating-type (+) cells facilitate this process. The green algae, including the characean algae, have served as model experimental organisms to understand

186-433: The (green) plants (with chloroplasts ) the red algae (with rhodoplasts) and the glaucophytes (with muroplasts). Green algae are often classified with their embryophyte descendants in the green plant clade Viridiplantae (or Chlorobionta ). Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, also known as Archaeplastida or Plantae sensu lato . The ancestral green alga

217-497: The gametophyte is multicellular. The fertilized egg cell, the diploid zygote , undergoes meiosis , giving rise to haploid cells which will become new gametophytes. The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by mitosis and grows into a multicellular diploid sporophyte . The sporophyte produces haploid spores by meiosis that germinate to produce

248-502: The supralittoral zone , is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies. Green algae have chloroplasts that contain chlorophyll a and b , giving them a bright green colour, as well as the accessory pigments beta carotene (red-orange) and xanthophylls (yellow) in stacked thylakoids . The cell walls of green algae usually contain cellulose , and they store carbohydrate in

279-1074: 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. A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in dinoflagellates of

310-708: The Mesostigmatophyceae, Chlorokybophyceae and spirotaenia are only more conventionally basal Streptophytes. The algae of this paraphyletic group "Charophyta" were previously included in Chlorophyta, so green algae and Chlorophyta in this definition were synonyms. As the green algae clades get further resolved, the embryophytes, which are a deep charophyte branch, are included in " algae ", "green algae" and " Charophytes ", or these terms are replaced by cladistic terminology such as Archaeplastida , Plantae / Viridiplantae , and streptophytes , respectively. Green algae are

341-420: 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 . Depending on the species, Chlorophyceae can grow unicellular (e.g. Chlamydomonas ) , colonial (e.g. Volvox ), filamentous (e.g. Ulothrix ), or multicellular. They are usually green due to

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372-413: The class Chlorophyceae undergo closed mitosis in the most common form of cell division among the green algae, which occurs via a phycoplast . By contrast, charophyte green algae and land plants (embryophytes) undergo open mitosis without centrioles . Instead, a 'raft' of microtubules, the phragmoplast , is formed from the mitotic spindle and cell division involves the use of this phragmoplast in

403-610: The concept of the life cycle of Chlorella, which at present is considered to be strictly asexual in character. Asexual reproduction in Chlorella ellipsoides has been studied in detail and the following four phases have been observed during the asexual reproduction. As of May 2023, AlgaeBase accepted the following orders in the class Chlorophyceae: Along with these genera, AlgaeBase recognizes several taxa that are incertae sedis (i.e. unplaced to an order): Other orders that have been recognized include: In older classifications,

434-427: The form of starch . All green algae have mitochondria with flat cristae . When present, paired flagella are used to move the cell. They are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the motile male gametes of charophytes bryophytes, pteridophytes, cycads and Ginkgo , but are absent from the gametes of Pinophyta and flowering plants . Members of

465-435: The fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. Trentepohlia is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae . Also the macroalga Prasiola calophylla (Trebouxiophyceae) is terrestrial, and Prasiola crispa , which live in

496-580: The genus Lepidodinium , euglenids and chlorarachniophytes were acquired from ingested endosymbiont green algae, and in the latter retain a nucleomorph (vestigial nucleus). 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

527-405: The genus Nitellopsis , which has both extant and extinct species, in the family Feistiellaceae . Other sources place Nitellopsis in the family Characeae, with Feistiellaceae containing only fossil species, so that all extant species are in the family Characeae. The Interim Register of Marine and Nonmarine Genera accepts a further three extinct families: Body fossils of representatives of

558-402: The heat of late summer. As their environment dries out, asexual V. carteri quickly die. However, they are able to escape death by switching, shortly before drying is complete, to the sexual phase of their life cycle that leads to production of dormant desiccation-resistant zygotes . Sexual development is initiated by a glycoprotein pheromone (Hallmann et al., 1998). This pheromone is one of

589-511: The light microscope. This process is called conjugation and occurs for example in Spirogyra . Sex pheromone production is likely a common feature of green algae, although only studied in detail in a few model organisms. Volvox is a genus of chlorophytes . Different species form spherical colonies of up to 50,000 cells. One well-studied species, Volvox carteri (2,000 – 6,000 cells) occupies temporary pools of water that tend to dry out in

620-574: The mechanisms of the ionic and water permeability of membranes, osmoregulation , turgor regulation, salt tolerance , cytoplasmic streaming , and the generation of action potentials . Charales See text Charales is an order of freshwater green algae in the division Charophyta , class Charophyceae , commonly known as stoneworts . Depending on the treatment of the genus Nitellopsis , living (extant) species are placed into either one family ( Characeae ) or two (Characeae and Feistiellaceae ). Further families are used for fossil members of

651-587: The morphology and size are different in the gametophyte and sporophyte. Reproduction varies from fusion of identical cells ( isogamy ) to fertilization of a large non-motile cell by a smaller motile one ( oogamy ). However, these traits show some variation, most notably among the basal green algae called prasinophytes . Haploid algal cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under

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682-417: The most potent known biological effector molecules. It can trigger sexual development at concentrations as low as 10 M. Kirk and Kirk showed that sex-inducing pheromone production can be triggered experimentally in somatic cells by heat shock . Thus heat shock may be a condition that ordinarily triggers sex-inducing pheromone in nature. The Closterium peracerosum-strigosum-littorale (C. psl) complex

713-470: The order Charales do exist, but are rare. The fossil record of the Charales consists mostly of gyrogonites , that is, calcified fructifications or, more exactly, calcified spiral cells surrounding the oospores. It may be noted that the gyrogonites are studied by palaeontologists , but not often destroyed (using acids) during neontological research to liberate the oospores. The oldest known representative of

744-497: The order. Linnaeus established the genus Chara in 1753. The higher level classification of green algae was unsettled as of February 2022 . AlgaeBase places Charales within the class Charophyceae and its circumscription of the division Charophyta . The number of families and their division into genera varies. As of February 2022 , AlgaeBase accepts two families containing some extant species and four families containing only fossil species: AlgaeBase places

775-741: The presence of chlorophyll a and chlorophyll b ; they can also contain the pigment beta-carotene . There are two clades of Chlorophyceae as defined by the arrangement of their flagella , called CW and DO. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales . Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales . The chloroplast may be discoid, cup-shaped (e.g. Chlamydomonas ), spiral or ribbon shaped. Most chlorophytes have one or more storage bodies called pyrenoids (central proteinaceous body covered with

806-404: The presence of phytochromes, flavonoids, and the chemical precursors to the cuticle. The sole method of reproduction in Chlorella is asexual and azoosporic. The content of the cell divides into 2,4 (B), 8(C) sometimes daughter protoplasts. Each daughter protoplast rounds off to form a non-motile spore. These autospores (spores having the same distinctive shape as the parent cell) are liberated by

837-413: The production of a cell plate . Photosynthetic eukaryotes originated following a primary endosymbiotic event, where a heterotrophic eukaryotic cell engulfed a photosynthetic cyanobacterium -like prokaryote that became stably integrated and eventually evolved into a membrane-bound organelle : the plastid . This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids:

868-547: The rupture of the parent cell wall (D). On release each autospore grows to become a new individual. The presence of sulphur in the culture medium is considered essential for cell division. It takes place even in the dark with sulphur alone as the source material but under light conditions nitrogen also required in addition. Pearsall and Loose (1937) reported the occurrence of motile cells in Chlorella . Bendix (1964) also observed that Chlorella produces motile cells which might be gametes. These observations have an important bearing on

899-580: The term Chlorophyceae is sometimes used to apply to all the green algae except the Charales , and the internal division is considerably different. Green alga The green algae ( sg. : green alga ) 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

930-409: The type and formation of sex cells and it may be isogamous e.g. Chlamydomonas, Ulothrix , anisogamous e.g. Chlamydomonas, Eudorina or Oogamous e.g. Chlamydomonas, Volvox . Chlamydomonas has all three types of sexual reproduction. They share many similarities with the higher plants, including the presence of asymmetrical flagellated cells, the breakdown of the nuclear envelope at mitosis, and

961-963: Was a unicellular flagellate. The Viridiplantae diverged into two clades. The Chlorophyta include the early diverging prasinophyte lineages and the core Chlorophyta, which contain the majority of described species of green algae. The Streptophyta include charophytes and land plants. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data. Palmophyllophyceae (prasinophyte clade VI) Prasinodermophyceae Ulvophyceae Chlorophyceae Trebouxiophyceae Chlorodendrophyceae Pedinophyceae Prasinophytes Clade VIIA Prasinophytes Clade VIIC Pycnococcaceae Nephroselmidophyceae Mamiellophyceae Pyramimonadales Mesostigmatophyceae Spirotaenia Chlorokybophyceae Streptofilum Klebsormidiophyceae Charophyceae Coleochaetophyceae Zygnematophyceae Mesotaeniaceae s.s. Embryophyta (land plants) The basal character of

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