The micrometre or micrometer commonly known by the previous name micron, is an SI derived unit of length equalling 1×10−6 metre. The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria, for grading wool by the diameter of the fibres; the width of a single human hair ranges from 10 to 200 μm. The longest human chromosome is 10 μm in length. Between 1 μm and 10 μm: 1–10 μm – length of a typical bacterium 10 μm – Size of fungal hyphae 5 μm – length of a typical human spermatozoon's head 3–8 μm – width of strand of spider web silk about 10 μm – size of a fog, mist, or cloud water droplet Between 10 μm and 100 μm about 10–12 μm – thickness of plastic wrap 10 to 55 μm – width of wool fibre 17 to 181 μm – diameter of human hair 70 to 180 μm – thickness of paper The term micron and the symbol μ were accepted for use in isolation to denote the micrometre in 1879, but revoked by the International System of Units in 1967; this became necessary because the older usage was incompatible with the official adoption of the unit prefix micro-, denoted μ, during the creation of the SI in 1960.
In the SI, the systematic name micrometre became the official name of the unit, μm became the official unit symbol. In practice, "micron" remains a used term in preference to "micrometre" in many English-speaking countries, both in academic science and in applied science and industry. Additionally, in American English, the use of "micron" helps differentiate the unit from the micrometer, a measuring device, because the unit's name in mainstream American spelling is a homograph of the device's name. In spoken English, they may be distinguished by pronunciation, as the name of the measuring device is invariably stressed on the second syllable, whereas the systematic pronunciation of the unit name, in accordance with the convention for pronouncing SI units in English, places the stress on the first syllable; the plural of micron is "microns", though "micra" was used before 1950. The official symbol for the SI prefix micro- is a Greek lowercase mu. In Unicode, there is a micro sign with the code point U+00B5, distinct from the code point U+03BC of the Greek letter lowercase mu.
According to the Unicode Consortium, the Greek letter character is preferred, but implementations must recognize the micro sign as well. Most fonts use the same glyph for the two characters. Metric prefix Metric system Orders of magnitude Wool measurement The dictionary definition of micrometre at Wiktionary
Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a paraphyletic group of all the green algae within the green plants and thus includes about 7,000 species of aquatic photosynthetic eukaryotic organisms. In newer classifications, it refers to the sister of the streptophytes/charophytes; the clade Streptophyta consists of the Charophyta. In this sense the Chlorophyta includes only about 4,300 species. Like the land plants, green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids; the Chlorophyta contains both multicellular species. Some members of the group form symbiotic relationships with protozoa and cnidarians. Others form symbiotic relationships with fungi to form lichens, but the majority of species are free-living; some conduct sexual reproduction, oogamous or isogamous.
All members of the clade have motile flagellated swimming cells. While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields. Others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiense, an edible green alga cultivated worldwide and most expensive among green algae, belongs to this group. Species of Chlorophyta are common inhabitants of marine and terrestrial environments. Several species have adapted to specialised and extreme environments, such as deserts, arctic environments, hypersaline habitats, marine deep waters and deep-sea hydrothermal vents; some groups, such as the Trentepohliales are found on land. Several species of Chlorophyta live in symbiosis with a diverse range of eukaryotes, including fungi, forams and molluscs; some species of Chlorophyta are either free-living or parasitic.
Two common species of the heterotrophic green alga Prototheca are pathogenic and can cause the disease protothecosis in humans and animals. Characteristics used for the classification of Chlorophyta are: type of zoid, cytokinesis, organization level, life cycle, type of gametes, cell wall polysaccharides and more genetic data. A newer proposed classification follows Leliaert et al. 2011 and modified with Silar 2016, Leliaert 2016 and Lopes dos Santos et al. 2017 for the green algae clades and Novíkov & Barabaš-Krasni 2015 for the land plants clade. Sánchez-Baracaldo et al. is followed for the basal clades. Simplified phylogeny of the Chlorophyta, according to Leliaert et al. 2012. Note that many algae classified in Chlorophyta are placed here in Streptophyta. Viridiplantae Chlorophyta core chlorophytes Ulvophyceae Cladophorales Dasycladales Bryopsidales Trentepohliales Ulvales-Ulotrichales Oltmannsiellopsidales Chlorophyceae Oedogoniales Chaetophorales Chaetopeltidiales Chlamydomonadales Sphaeropleales Trebouxiophyceae Chlorellales Oocystaceae Microthamniales Trebouxiales Prasiola clade Chlorodendrophyceae prasinophytes Pyramimonadales Mamiellophyceae Pycnococcaceae Nephroselmidophyceae Prasinococcales Palmophyllales Streptophyta charophytes Mesostigmatophyceae Chlorokybophyceae Klebsormidiophyceae Charophyceae Zygnematophyceae Coleochaetophyceae Embryophyta A possible classification when Chlorophyta refers to one of the two clades of the Viridiplantae is shown below.
Class Prasinophyceae T. A. Chr. ex Ø. Moestrup & J. Throndsen Class Chlorophyceae Wille Class Trebouxiophyceae T. Friedl Class Ulvophyceae Division Chlorophyta Subdivision Chlorophytina Class Chlorophyceae Order Chlamydomonadales Order Sphaeropleales Order Oedogoniales Order Chaetopeltidales Order Chaetophorales Incertae Sedis Class Ulvophyceae Order Ulotrichales Order Ulvales Order Siphoncladales/Cladophorales Order Caulerpales Order Dasycladales Class Trebouxiophyceae Order Trebouxiales Order Microthamniales Order Prasiolales Order Chlorellales Class Prasinophyceae Order Pyramimonadales Order Mamiellales Order Pseudoscourfieldiales Order Chlorodendrales Incertae sedis Division Charophyta Class Mesostigmatophyceae Class Chlorokybophyceae Class Klebsormidiophyceae Class Zygnemophyceae Order Zygnematales Order Desmidiales Class Coleochaetophyceae Order Coleochaetales Subdivision Streptophytina Class Charophyceae Order Charales Class Embryophyceae Classification of the Chlorophyta, treated as all green algae, according to Hoek and Jahns 1995.
Class Prasinophyceae Class Chlorophyceae Class Ulvophyceae Class Cladophorophyceae Class Bryopsidophyceae Class Dasycladophyceae Class Trentepohliophyceae
The Embryophyta, or land plants, are the most familiar group of green plants that form vegetation on earth. Embryophyta is a clade within the Phragmoplastophyta, a larger clade that includes several green algae groups, within this large clade the embryophytes are sister to the Zygnematophyceae/Mesotaeniaceae and consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, mosses, lycophytes and flowering plants; the Embryophyta are informally called land plants because they live in terrestrial habitats, while the related green algae are aquatic. All are complex multicellular eukaryotes with specialized reproductive organs; the name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With few exceptions, embryophytes obtain their energy by photosynthesis, by using the energy of sunlight to synthesize their food from carbon dioxide and water.
The evolutionary origins of the embryophytes are discussed further below, but they are believed to have evolved from within a group of complex green algae during the Paleozoic era from terrestrial unicellular charophytes, similar to extant Klebsormidiophyceae. Embryophytes are adapted for life on land, although some are secondarily aquatic. Accordingly, they are called land plants or terrestrial plants. On a microscopic level, the cells of embryophytes are broadly similar to those of green algae, but differ in that in cell division the daughter nuclei are separated by a phragmoplast, they are eukaryotic, with a cell wall composed of cellulose and plastids surrounded by two membranes. The latter include chloroplasts, which conduct photosynthesis and store food in the form of starch, are characteristically pigmented with chlorophylls a and b giving them a bright green color. Embryophyte cells 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'. A multicellular generation with a single set of chromosomes – the haploid gametophyte – produces sperm and eggs which fuse and grow into a multicellular generation with twice the number of chromosomes – the diploid sporophyte; the mature sporophyte produces haploid spores which grow into a gametophyte, thus completing the cycle. Embryophytes have two features related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures, fertilization of the ovum takes place within the archegonium rather than in the external environment. Secondly, most the initial stage of development of the fertilized egg into a diploid multicellular sporophyte, take place within the archegonium where it is both protected and provided with nutrition; this second feature is the origin of the term'embryophyte' – the fertilized egg develops into a protected embryo, rather than dispersing as a single cell.
In the bryophytes the sporophyte remains dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant and capable of independent existence. Embryophytes differ from algae by having metamers. Metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is the same for each cell; the whole organism is thus constructed from repeating parts or metamers. Accordingly, these plants are sometimes termed'metaphytes' and classified as the group Metaphyta. In all land plants a disc-like structure called a phragmoplast forms where the cell will divide, a trait only found in the land plants in the streptophyte lineage, some species within their relatives Coleochaetales and Zygnematales, as well as within subaerial species of the algae order Trentepohliales, appears to be essential in the adaptation towards a terrestrial life style. All green algae and land plants are now known to form a single evolutionary lineage or clade, one name for, Viridiplantae.
According to several molecular clock estimates the Viridiplantae split 1,200 million years ago to 725 million years ago into two clades: chlorophytes and streptophytes. The chlorophytes are more diverse and were marine, although some groups have since spread into fresh water; the streptophyte algae are less diverse and adapted to fresh water early in their evolutionary history. They have not spread into marine environments; some time during the Ordovician period one or more streptophytes invaded the land and began the evolution of the embryophyte land plants. Present day embryophytes form. Becker and Marin speculate that land plants evolved from streptophytes rather than any other group of algae because streptophytes were adapted to living in fresh water; this prepared them to tolerate a range of environmental conditions found on land. Fresh water living made.
Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in plant and algal cells. They use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions, including fatty acid synthesis, much amino acid synthesis, the immune response in plants; the number of chloroplasts per cell varies from one, in unicellular algae, up to 100 in plants like Arabidopsis and wheat. A chloroplast is a type of organelle known as a plastid, characterized by its two membranes and a high concentration of chlorophyll. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll and do not carry out photosynthesis. Chloroplasts are dynamic—they circulate and are moved around within plant cells, pinch in two to reproduce.
Their behavior is influenced by environmental factors like light color and intensity. Chloroplasts, like mitochondria, contain their own DNA, thought to be inherited from their ancestor—a photosynthetic cyanobacterium, engulfed by an early eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each daughter cell during cell division. With one exception, all chloroplasts can be traced back to a single endosymbiotic event, when a cyanobacterium was engulfed by the eukaryote. Despite this, chloroplasts can be found in an wide set of organisms, some not directly related to each other—a consequence of many secondary and tertiary endosymbiotic events; the word chloroplast is derived from the Greek words chloros, which means green, plastes, which means "the one who forms". The first definitive description of a chloroplast was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, A. F. W. Schimper would name these bodies as "chloroplastids".
In 1884, Eduard Strasburger adopted the term "chloroplasts". Chloroplasts are one of many types of organelles in the plant cell, they are considered to have originated from cyanobacteria through endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium that became a permanent resident in the cell. Mitochondria are thought to have come from a similar event, where an aerobic prokaryote was engulfed; this origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Schimper observed in 1883 that chloroplasts resemble cyanobacteria. Chloroplasts are only found in plants and the amoeboid Paulinella chromatophora. Cyanobacteria are considered the ancestors of chloroplasts, they are sometimes called blue-green algae though they are prokaryotes. They are a diverse phylum of bacteria capable of carrying out photosynthesis, are gram-negative, meaning that they have two cell membranes. Cyanobacteria contain a peptidoglycan cell wall, thicker than in other gram-negative bacteria, and, located between their two cell membranes.
Like chloroplasts, they have thylakoids within. On the thylakoid membranes are photosynthetic pigments, including chlorophyll a. Phycobilins are common cyanobacterial pigments organized into hemispherical phycobilisomes attached to the outside of the thylakoid membranes. Somewhere around 1 to 2 billion years ago, a free-living cyanobacterium entered an early eukaryotic cell, either as food or as an internal parasite, but managed to escape the phagocytic vacuole it was contained in; the two innermost lipid-bilayer membranes that surround all chloroplasts correspond to the outer and inner membranes of the ancestral cyanobacterium's gram negative cell wall, not the phagosomal membrane from the host, lost. The new cellular resident became an advantage, providing food for the eukaryotic host, which allowed it to live within it. Over time, the cyanobacterium was assimilated, many of its genes were lost or transferred to the nucleus of the host. From genomes that originally contained over 3000 genes only about 130 genes remain in the chloroplasts of contemporary plants.
Some of its proteins were synthesized in the cytoplasm of the host cell, imported back into the chloroplast. Separately, somewhere around 500 million years ago, it happened again and led to the amoeboid Paulinella chromatophora; this event is called endosymbiosis, or "cell living inside another cell with a mutual benefit for both". The external cell is referred to as the host while the internal cell is called the endosymbiont. Chloroplasts are believed to have arisen after mitochondria, since all eukaryotes contain mitochondria, but not all have chloroplasts; this is called serial endosymbiosis—an early eukaryote engulfing the mitochondrion ancestor, some descendants of it engulfing the chloroplast ancestor, creating a cell with both chloroplasts and mitochondria. Whether or not primary chloroplasts came from a single endosymbiotic event, or many independent engulfments across various eukaryotic lineages, has long been debated, it is now held that organisms with primary chloroplasts share a single ancestor that took in a cyanobacterium 600–2000 million years ago.
It has been proposed. The exception is the amoeboid Paulinella chromatophora, which descends from an ancestor that took in a Prochlorococcus cyanobacterium 90–500 million years ago; these chloroplasts
Prasinovirus is a genus of large double-stranded DNA viruses, in the family Phycodnaviridae that infect phytoplankton in the Prasinophyceae. There are only two species in this genus including the type species Micromonas pusilla virus SP1, that infects the cosmopolitan photosynthetic flagellate Micromonas pusilla. However, there is a large group of genetically diverse but related viruses that show considerable evidence of lateral gene transfer. Group: dsDNA Viruses in Prasinovirus are enveloped, with icosahedral and Round geometries, T=169 symmetry; the diameter is around 104-118 nm. Viral replication is nucleo-cytoplasmic. Replication follows. Dna templated; the virus exits the host cell by lysis via lytic phospholipids. Alga serve as the natural host. Transmission routes are passive diffusion. Viralzone: Prasinovirus ICTV
Deep chlorophyll maximum
The deep chlorophyll maximum called the subsurface chlorophyll maximum, is the region below the surface of water with the maximum concentration of chlorophyll. A DCM is not always present - sometimes there is more chlorophyll at the surface than at any greater depth - but it is a common feature of most aquatic ecosystems in regions of strong thermal stratification; the depth, intensity and persistence of DCMs vary widely. The DCM exists at the same depth as the nutricline, the region of the ocean where the greatest change in the nutrient concentration occurs with depth. A common way of determining the DCM is through the use of a CTD rosette, an underwater instrument that measures various parameters of water at specific depths; the location and formation of the DCM depends on multiple factors, such as the resident organisms' nutritional needs and light availability. Some organisms have adapted to lower levels of light through increasing its cellular chlorophyll amounts, others have adapted by migrating vertically with varying nutrient and light levels.
The DCM species composition vary with water chemistry, location and depth. Not only is there a difference in DCM species composition between oceans and lakes, variation is present within different oceans and lakes; because the DCM holds much of the world's primary productivity, it plays a significant role in nutrient cycling, the flow of energy, biogeochemical cycles. The DCM is located tens of meters below the surface, cannot be observed by using traditional satellite remote sensing methods. Estimates of primary productivity are made via these remote sensing methods coupled with statistical models, though these statistical calculations may not have included production in the DCM; the DCM of a study area can be determined in-situ through the use of an underwater instrument to measure various parameters such as salinity, temperature and chlorophyll fluorescence. Collected water samples can be used to determine phytoplankton cell counts; these measurements can be converted into chlorophyll concentrations, phytoplankton biomass, phytoplankton productivity.
Another way to estimate primary productivity in the DCM is to create a simulation of the DCM formation in a region by making a 3D model of the region. This can be done if sufficient biogeochemical data exists for that ocean region. Since its initial discovery, oceanographers have presented various theories to explain the formation of deep chlorophyll maxima. In-situ studies have determined that the depth of DCM formation is dependent on light attenuation levels, the depth of the nutricline, although thermal stratification plays a role. In lakes, the thickness of the DCM layer is controlled by the sizes and maximum depths of lakes; the DCM forms near the bottom of the photic zone. Phytoplankton growth in the DCM is limited by both nutrient and light availability, therefore either increased nutrient input, or increased light availability to the DCM can in turn increase the phytoplankton growth rate; the location and formation of the DCM depends on season. In the Mediterranean Sea, the DCM is present in the summer due to water stratification, is rare in the winter due to deep mixing.
The DCM can be present at shallower depths in the winter and early spring due to light limitation and higher nutrient availability in shallower regions due to mixing, at lower depths during the summer and early fall as nutrients in the surface water are depleted by primary producers and stronger irradiance allows light to penetrate to greater depths. The formation of a DCM correlates with a number of biological processes, affecting nutrient cycling for local heterotrophic bacteria and composition of specialized phytoplankton. Light attenuation factors have been shown to be quite predictive of the DCM depth, since the phytoplankton present in the region require sufficient sunlight for growth, resulting in a DCM, found in the euphotic zone. However, if the phytoplankton population has adapted to lower light environments, the DCM can be located in the aphotic zone; the high chlorophyll concentration at the DCM is due to the high number of phytoplankton that have adapted to functioning in low light conditions.
To adapt to low light conditions, some phytoplankton populations have been found to have increased amounts of chlorophyll counts per cell, which contributes to the formation of the DCM. Rather than an increase of overall cell numbers, seasonal light limitation or low irradiance levels can raise the individual cellular chlorophyll content; as depth increases within the mixing zone, phytoplankton must rely on having higher pigment counts to capture photic energy. Due to the higher concentration of chlorophyll in the phtoplankton present, the DCM does not predict the depth of the biomass maximum in the same region. In addition, compared to shallower regions of the mixing zone, the DCM has high nutrient concentrations and/or lower respiratory and death rates which further promote phytoplankton cell production. Vertical migration, or movement of phytoplankton within the water column, contributes to the establishment of the DCM due to the diversity of resources required by the phytoplankton. Dependent on factors like nutrients and available light, some phytoplankton species will intentionally move to different depths to fulfill their physiological requirements.
A mechanism employed by certain phytoplankton, such as certain species of diatoms and cyanobacteria, is to regulate their own buoyancy to move through the water column. Other species such as dinoflagellates use their flagella to swim t