Stylonematophyceae
Stylonematophyceae is a grouping of red algae. Data related to Stylonematophyceae at Wikispecies Media related to Stylonematophyceae at Wikimedia Commons Stylonematophyceae at AlgaeBase
Red algae
The red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest phyla of algae, containing over 7,000 recognized species with taxonomic revisions ongoing; the majority of species are found in the Florideophyceae, consist of multicellular, marine algae, including many notable seaweeds. 5% of the red algae occur in freshwater environments with greater concentrations found in the warmer area. There are no terrestrial species, assumed to be traced back to an evolutionary bottleneck where the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity; the red algae form a distinct group characterized by having eukaryotic cells without flagella and centrioles, chloroplasts that lack external endoplasmic reticulum and contain unstacked thylakoids, use phycobiliproteins as accessory pigments, which give them their red color. Red algae store sugars as floridean starch, a type of starch that consists of branched amylopectin without amylose, as food reserves outside their plastids.
Most red algae are multicellular, macroscopic and reproduce sexually. The red algal life history is an alternation of generations that may have three generations rather than two. Chloroplasts evolved following an endosymbiotic event between an ancestral, photosynthetic cyanobacterium and an early eukarytoic phagotroph; this event resulted in the origin of the red and green algae, the glaucophytes, which make up the oldest evolutionary lineages of photosynthetic eukaryotes. A secondary endosymbiosis event involving an ancestral red alga and a heterotrophic eukaryote resulted in the evolution and diversification of several other photosynthetic lineages such as Cryptophyta, Stramenopiles, Centrohelids and Telonemi; the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse and laver are a traditional part of European and Asian cuisines and are used to make other products such as agar and other food additives. Unicellular members of the Cyanidiophyceae are thermoacidophiles and are found in sulphuric hot springs and other acidic environments.
The remaining taxa are found in freshwater environments. Most rhodophytes are marine with a worldwide distribution, are found at greater depths compared to other seaweeds because of dominance in certain pigments within their chloroplasts; some marine species are found on sandy shores, while most others can be found attached to rocky substrata. Freshwater species account for 5% of red algal diversity, but they have a worldwide distribution in various habitats. A few freshwater species are found in black waters with sandy bottoms and fewer are found in more lentic waters. Both marine and freshwater taxa are represented by free-living macroalgal forms and smaller endo/epiphytic/zoic forms, meaning they live in or on other algae and animals. In addition, some marine species have adopted a parasitic lifestyle and may be found on or more distantly related red algal hosts. In the system of Adl et al. 2005, the red algae are classified in the Archaeplastida, along with the glaucophytes and green algae plus land plants.
The authors use a hierarchical arrangement. No subdivisions are given. However, other studies have suggested; as of January 2011, the situation appears unresolved. Below are other published taxonomies of the red algae using molecular and traditional alpha taxonomic data. If one defines the kingdom Plantae to mean the Archaeplastida, the red algae will be part of that kingdom If Plantae are defined more narrowly, to be the Viridiplantae the red algae might be considered their own kingdom, or part of the kingdom Protista. A major research initiative to reconstruct the Red Algal Tree of Life using phylogenetic and genomic approaches is funded by the National Science Foundation as part of the Assembling the Tree of Life Program; some sources place all red algae into the class "Rhodophyceae". A subphylum - Proteorhodophytina - has been proposed to encompass the existing classes Compsopogonophyceae, Porphyridiophyceae and Stylonematophyceae; this proposal was made on the basis of the analysis of the plastid genomes.
Over 7,000 species are described for the red algae, but the taxonomy is in constant flux with new species described each year. The vast majority of these are marine with about 200; some examples of species and genera of red algae are: Cyanidioschyzon merolae, a primitive red alga Atractophora hypnoides Gelidiella calcicola Lemanea, a freshwater genus Palmaria palmata, dulse Schmitzia
Starch
Starch or amylum is a polymeric carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants as energy storage, it is the most common carbohydrate in human diets and is contained in large amounts in staple foods like potatoes, maize and cassava. Pure starch is a white and odorless powder, insoluble in cold water or alcohol, it consists of two types of molecules: the branched amylopectin. Depending on the plant, starch contains 20 to 25% amylose and 75 to 80% amylopectin by weight. Glycogen, the glucose store of animals, is a more branched version of amylopectin. In industry, starch is converted into sugars, for example by malting, fermented to produce ethanol in the manufacture of beer and biofuel, it is processed to produce many of the sugars used in processed foods. Mixing most starches in warm water produces a paste, such as wheatpaste, which can be used as a thickening, stiffening or gluing agent; the biggest industrial non-food use of starch is as an adhesive in the papermaking process.
Starch can be applied to parts of some garments before ironing. The word "starch" is from a Germanic root with the meanings "strong, strengthen, stiffen". Modern German Stärke is related; the Greek term for starch, "amylon", is related. It provides the root amyl, used as a prefix for several 5-carbon compounds related to or derived from starch. Starch grains from the rhizomes of Typha as flour have been identified from grinding stones in Europe dating back to 30,000 years ago. Starch grains from sorghum were found on grind stones in caves in Ngalue, Mozambique dating up to 100,000 years ago. Pure extracted wheat starch paste was used in Ancient Egypt to glue papyrus; the extraction of starch is first described in the Natural History of Pliny the Elder around AD 77–79. Romans used it in cosmetic creams, to powder the hair and to thicken sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. Rice starch as surface treatment of paper has been used in paper production in China since 700 CE.
In addition to starchy plants consumed directly, by 2008 66 million tonnes of starch were being produced per year worldwide. In 2011 production was increased to 73 million ton. In the EU the starch industry produced about 8.5 million tonnes in 2008, with around 40% being used for industrial applications and 60% for food uses, most of the latter as glucose syrups. In 2017 EU production was 11 million ton of which 9,4 million ton was consumed in the EU and of which 54% were starch sweeteners. US produced about 27,5 million ton starch in 2017 of which about 8,2 million ton high fructose syrup and 6,2 million ton glucose syrups and 2,5 million ton starch products, the rest of the starch was used for producing ethanol. Most green plants use starch as their energy store; the extra glucose is changed into starch, more complex than glucose. An exception is the family Asteraceae. Inulin-like fructans are present in grasses such as wheat, in onions and garlic and asparagus. In photosynthesis, plants use light energy to produce glucose from carbon dioxide.
The glucose is used to generate the chemical energy required for general metabolism, to make organic compounds such as nucleic acids, lipids and structural polysaccharides such as cellulose, or is stored in the form of starch granules, in amyloplasts. Toward the end of the growing season, starch accumulates in twigs of trees near the buds. Fruit, seeds and tubers store starch to prepare for the next growing season. Glucose is soluble in water, binds with water and takes up much space and is osmotically active. Glucose molecules are bound in starch by the hydrolyzed alpha bonds; the same type of bond is found in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin and peptidoglycan, which are bound by beta bonds and are much more resistant to hydrolysis. Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase; this step requires energy in the form of ATP. The enzyme starch synthase adds the ADP-glucose via a 1,4-alpha glycosidic bond to a growing chain of glucose residues, liberating ADP and creating amylose.
The ADP-glucose is certainly added to the non-reducing end of the amylose polymer, as the UDP-glucose is added to the non-reducing end of glycogen during glycogen synthesis. Starch branching enzyme introduces 1,6-alpha glycosidic bonds between the amylose chains, creating the branched amylopectin; the starch debranching enzyme isoamylase removes some of these branches. Several isoforms of these enzymes exist, leading to a complex synthesis process. Glycogen and amylopectin have similar structure, but the former has about one branch point per ten 1,4-alpha bonds, compared to about one branch point per thirty 1,4-alpha bonds in amylopectin. Amylopectin is synthesized from ADP-glucose while mammals and fungi synthesize glycogen from UDP-glucose. In addition to starch synthesis in plants, starch can be synthesized from non-food starch mediated by an enzyme cocktail. In this cell-free biosystem, beta-1,4-glycosidic bond-linked cellulose is hydrolyzed to cello
Asexual reproduction
Asexual reproduction is a type of reproduction by which offspring arise from a single organism, inherit the genes of that parent only. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many plants and fungi sometimes reproduce asexually; some Asexual cells die when they are young. While all prokaryotes reproduce without the formation and fusion of gametes, mechanisms for lateral gene transfer such as conjugation and transduction can be likened to sexual reproduction in the sense of genetic recombination in meiosis. A complete lack of sexual reproduction is rare among multi-cellular organisms animals, it is not understood why the ability to reproduce sexually is so common among them. Current hypotheses suggest that asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, while sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments.
Developmental constraints may underlie why few animals have relinquished sexual reproduction in their life-cycles. Another constraint on switching from sexual to asexual reproduction would be the concomitant loss of meiosis and the protective recombinational repair of DNA damage afforded as one function of meiosis. An important form of fission is binary fission, where the parent organism is replaced by two daughter organisms, because it divides in two. Only prokaryotes reproduce asexually through binary fission. Eukaryotes may reproduce in a functionally similar manner by mitosis. Many Asexual cells die off. Multiple fission at the cellular level occurs in e.g. sporozoans and algae. The nucleus of the parent cell divides several times by mitosis; the cytoplasm separates, creating multiple daughter cells. In apicomplexans, multiple fission, or schizogony appears either as merogony, sporogony or gametogony. Merogony results in merozoites, which are multiple daughter cells, that originate within the same cell membrane, sporogony results in sporozoites, gametogony results in microgametes.
Some cells split via budding. The offspring organism is smaller than the parent. Budding is known on a multi-cellular level; the buds grow into matured individuals which break away from the parent organism. Internal budding is a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii, it involves an unusual process in which two or more daughter cells are produced inside a mother cell, consumed by the offspring prior to their separation. Budding is present in some worm like Taenia or Echinococci. Vegetative propagation is a type of asexual reproduction found in plants where new individuals are formed without the production of seeds or spores by meiosis or syngamy. Examples of vegetative reproduction include the formation of miniaturized plants called plantlets on specialized leaves and some produce new plants out of rhizomes or stolon. Other plants reproduce by forming tubers; some plants produce adventitious shoots and may form a clonal colony, where all the individuals are clones, the clones may cover a large area.
Many multi-cellular organisms form spores during their biological life cycle in a process called sporogenesis. Exceptions are animals and some protists, who undergo meiosis followed by fertilization. Plants and many algae on the other hand undergo sporic meiosis where meiosis leads to the formation of haploid spores rather than gametes; these spores grow into multi-cellular individuals without a fertilization event. These haploid individuals give rise to gametes through mitosis. Meiosis and gamete formation therefore occur in separate generations or "phases" of the life cycle, referred to as alternation of generations. Since sexual reproduction is more narrowly defined as the fusion of gametes, spore formation in plant sporophytes and algae might be considered a form of asexual reproduction despite being the result of meiosis and undergoing a reduction in ploidy. However, both events are necessary to complete sexual reproduction in the plant life cycle. Fungi and some algae can utilize true asexual spore formation, which involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal.
This method of reproduction is found for example in conidial fungi and the red algae Polysiphonia, involves sporogenesis without meiosis. Thus the chromosome number of the spore cell is the same as that of the parent producing the spores. However, mitotic sporogenesis is an exception and most spores, such as those of plants, most Basidiomycota, many algae, are produced by meiosis. Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the parent; each fragment develops into a mature grown individual. Fragmentation is seen in many organisms. Animals that reproduce asexually include planarians, many annelid worms including polychaetes and
Plant
Plants are multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Plants were treated as one of two kingdoms including all living things that were not animals, all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes. By one definition, plants form the clade Viridiplantae, a group that includes the flowering plants and other gymnosperms and their allies, liverworts and the green algae, but excludes the red and brown algae. Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria, their chloroplasts contain b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is common.
There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants. Green plants provide a substantial proportion of the world's molecular oxygen and are the basis of most of Earth's ecosystems on land. Plants that produce grain and vegetables form humankind's basic foods, have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs; the scientific study of plants is known as a branch of biology. All living things were traditionally placed into one of two groups and animals; this classification may date from Aristotle, who made the distincton between plants, which do not move, animals, which are mobile to catch their food. Much when Linnaeus created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia and Animalia. Since it has become clear that the plant kingdom as defined included several unrelated groups, the fungi and several groups of algae were removed to new kingdoms.
However, these organisms are still considered plants in popular contexts. The term "plant" implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts; when the name Plantae or plant is applied to a specific group of organisms or taxon, it refers to one of four concepts. From least to most inclusive, these four groupings are: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships; these are not yet settled, but one accepted relationship between the three groups described above is shown below. Those which have been called "plants" are in bold; the way in which the groups of green algae are combined and named varies between authors. Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom.
The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, they are no longer classified as plants as defined here; the Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common, they undergo closed mitosis without centrioles, have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria. Two additional groups, the Rhodophyta and Glaucophyta have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour.
These groups differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event; this is the broadest modern definition of the term'plant'. In contrast, most other algae not only have different pigments but have chloroplasts with three or four surrounding membranes, they are not close relatives of the Archaeplastida having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in the broadest modern definition of the plant kingdom, although they were in the past; the green plants or Viridiplantae were traditionally divided into the green algae (including
Flagellum
A flagellum is a lash-like appendage that protrudes from the cell body of certain bacteria and eukaryotic cells termed as flagellates. A flagellate can have several flagella; the primary function of a flagellum is that of locomotion, but it often functions as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. The similar structure in the archaea functions in the same way but is structurally different and has been termed the archaellum. Flagella are organelles defined by function rather than structure. Flagella vary greatly. Both prokaryotic and eukaryotic flagella can be used for swimming but they differ in protein composition and mechanism of propulsion; the word flagellum in Latin means whip. An example of a flagellated bacterium is the ulcer-causing Helicobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic flagellate cell is the mammalian sperm cell, which uses its flagellum to propel itself through the female reproductive tract.
Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are sometimes made according to function or length. Fimbriae and pili are thin appendages, but have different functions and are smaller. Three types of flagella have so far been distinguished: bacterial and eukaryotic; the main differences among these three types are: Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise. They provide two of several kinds of bacterial motility. Archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous. Eukaryotic flagella—those of animal and protist cells—are complex cellular projections that lash back and forth. Eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, are not undulipodia; the bacterial flagellum is made up of the protein flagellin.
Its shape is a 20-nanometer-thick hollow tube. It has a sharp bend just outside the outer membrane. A shaft runs between the hook and the basal body, passing through protein rings in the cell's membrane that act as bearings. Gram-positive organisms have two of these basal body rings, one in the peptidoglycan layer and one in the plasma membrane. Gram-negative organisms have four such rings: the L ring associates with the lipopolysaccharides, the P ring associates with peptidoglycan layer, the M ring is embedded in the plasma membrane, the S ring is directly attached to the plasma membrane; the filament ends with a capping protein. The flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook. In most bacteria that have been studied, including the Gram-negative Escherichia coli, Salmonella typhimurium, Caulobacter crescentus, Vibrio alginolyticus, the filament is made up of 11 protofilaments parallel to the filament axis; each protofilament is a series of tandem protein chains.
However, Campylobacter jejuni has seven protofilaments. The basal body has several traits in common with some types of secretory pores, such as the hollow, rod-like "plug" in their centers extending out through the plasma membrane; the similarities between bacterial flagella and bacterial secretory system structures and proteins provide scientific evidence supporting the theory that bacterial flagella evolved from the type-three secretion system. The bacterial flagellum is driven by a rotary engine made up of protein, located at the flagellum's anchor point on the inner cell membrane; the engine is powered by proton motive force, i.e. by the flow of protons across the bacterial cell membrane due to a concentration gradient set up by the cell's metabolism. The rotor transports protons across the membrane, is turned in the process; the rotor alone can operate at 6,000 to 17,000 rpm, but with the flagellar filament attached only reaches 200 to 1000 rpm. The direction of rotation can be changed by the flagellar motor switch instantaneously, caused by a slight change in the position of a protein, FliG, in the rotor.
The flagellum is energy efficient and uses little energy. The exact mechanism for torque generation is still poorly understood; because the flagellar motor has no on-off switch, the protein epsE is used as a mechanical clutch to disengage the motor from the rotor, thus stopping the flagellum and allowing the bacterium to remain in one place. The cylindrical shape of flagella is suited to locomotion of microscopic organisms; the rotational speed of flagella varies in response to the intensity of the proton motive force, thereby permitting certain forms of speed control, permitting some types of bacteria to attain remarkable speeds in proportion to their size. At such a speed, a bacterium would take about 245 days to cover 1 km. In comparison to macroscopic life forms, it is fast indeed when expressed in terms of number of body lengths p
