A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids form stacks of disks referred to as grana. Grana are connected by intergranal or stroma thylakoids, which join granum stacks together as a single functional compartment; the word Thylakoid comes from the Greek word thylakos meaning "sac" or "pouch". Thus, thylakoid means "sac-like" or "pouch-like". Thylakoids are membrane-bound structures embedded in the chloroplast stroma. A stack of thylakoids resembles a stack of coins; the thylakoid membrane is the site of the light-dependent reactions of photosynthesis with the photosynthetic pigments embedded directly in the membrane. It is an alternating pattern of light bands measuring each 1 nanometre; the thylakoid lipid bilayer shares characteristic features with prokaryotic membranes and the inner chloroplast membrane.
For example, acidic lipids can be found in thylakoid membranes and other photosynthetic bacteria and are involved in the functional integrity of the photosystems. The thylakoid membranes of higher plants are composed of phospholipids and galactolipids that are asymmetrically arranged along and across the membranes. Thylakoid membranes are richer in galactolipids rather than phospholipids. Despite this unique composition, plant thylakoid membranes have been shown to assume lipid-bilayer dynamic organization. Lipids forming the thylakoid membranes, richest in high-fluidity linolenic acid are synthesized in a complex pathway involving exchange of lipid precursors between the endoplasmic reticulum and inner membrane of the plastid envelope and transported from the inner membrane to the thylakoids via vesicles; the thylakoid lumen is a continuous aqueous phase enclosed by the thylakoid membrane. It plays an important role for photophosphorylation during photosynthesis. During the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH 4.
In higher plants thylakoids are organized into a granum-stroma membrane assembly. A granum is a stack of thylakoid discs. Chloroplasts can have from 10 to 100 grana. Grana are connected by stroma thylakoids called intergranal thylakoids or lamellae. Grana thylakoids and stroma thylakoids can be distinguished by their different protein composition. Grana contribute to chloroplasts' large surface area to volume ratio. Different interpretations of electron tomography imaging of thylakoid membranes has resulted in two models for grana structure. Both posit that lamellae intersect grana stacks in parallel sheets, though whether these sheets intersect in planes perpendicular to the grana stack axis, or are arranged in a right-handed helix is debated. Chloroplasts develop from proplastids. Thylakoid formation requires light. In the plant embryo and in the absence of light, proplastids develop into etioplasts that contain semicrystalline membrane structures called prolamellar bodies; when exposed to light, these prolamellar bodies develop into thylakoids.
This does not happen in seedlings grown in the dark. An underexposure to light can cause the thylakoids to fail; this causes the chloroplasts to fail resulting in the death of the plant. Thylakoid formation requires the action of vesicle-inducing protein in plastids 1. Plants cannot survive without this protein, reduced VIPP1 levels lead to slower growth and paler plants with reduced ability to photosynthesize. VIPP1 appears to be required for basic thylakoid membrane formation, but not for the assembly of protein complexes of the thylakoid membrane, it is conserved in all organisms containing thylakoids, including cyanobacteria, green algae, such as Chlamydomonas, higher plants, such as Arabidopsis thaliana. Thylakoids can be purified from plant cells using a combination of differential and gradient centrifugation. Disruption of isolated thylakoids, for example by mechanical shearing, releases the lumenal fraction. Peripheral and integral membrane fractions can be extracted from the remaining membrane fraction.
Treatment with sodium carbonate detaches peripheral membrane proteins, whereas treatment with detergents and organic solvents solubilizes integral membrane proteins. Thylakoids contain many peripheral membrane proteins, as well as lumenal proteins. Recent proteomics studies of thylakoid fractions have provided further details on the protein composition of the thylakoids; these data have been summarized in several plastid protein databases. According to these studies, the thylakoid proteome consists of at least 335 different proteins. Out of these, 89 are in the lumen, 116 are integral membrane proteins, 62 are peripheral proteins on the stroma side, 68 peripheral proteins on the lumenal side. Additional low-abundance lumenal proteins can be predicted through computational methods. Of the thylakoid proteins with known functions, 42% are involved in photosynthesis; the next largest functional groups include proteins involved in protein targeting and folding with 11%, oxidative stress response and translation.
Thylakoid membranes contain integral membrane proteins which play an important role in light harvesting and the light-dependent reactions of photosynthesis. There are four major protein complexes in the thylakoid membrane: Photosystems I and II Cytochrome b6f complex ATP synthasePhotosystem II is located in the grana thylakoids, whereas photosystem I and ATP synthase are m
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
The cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, occur in marine and brackish habitats; each cell flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are two unequal flagella; some may exhibit mixotrophy. Cryptomonads are distinguished by the presence of characteristic extrusomes called ejectosomes or ejectisomes, which consist of two connected spiral ribbons held under tension. If the cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectosomes, visible under the light microscope, are associated with the pocket. Cryptomonads have one or two chloroplasts, except for Chilomonas, which has leucoplasts and Goniomonas which lacks plastids entirely; these contain chlorophylls a and c, together with phycobiliproteins and other pigments, vary in color. Each is surrounded by four membranes, there is a reduced cell nucleus called a nucleomorph between the middle two.
This indicates that the plastid was derived from a eukaryotic symbiont, shown by genetic studies to have been a red alga. However, the plastids are different from red algal plastids: phycobiliproteins are present but only in the thylakoid lumen and are present only as phycoerythrin or phycocyanin. In the case of "Rhodomonas" the crystal structure has been determined to 1.63Å. A few cryptomonads, such as Cryptomonas, can form palmelloid stages, but escape the surrounding mucus to become free-living flagellates again; some Cryptomonas species may form immotile microbial cysts–resting stages with rigid cell walls to survive unfavorable conditions. Cryptomonad flagella are inserted parallel to one another, are covered by bipartite hairs called mastigonemes, formed within the endoplasmic reticulum and transported to the cell surface. Small scales may be present on the flagella and cell body; the mitochondria have flat cristae, mitosis is open. The first mention of cryptomonads appears to have been made by Christian Gottfried Ehrenberg in 1831, while studying Infusoria.
Botanists treated them as a separate algae group, class Cryptophyceae or division Cryptophyta, while zoologists treated them as the flagellate protozoa order Cryptomonadina. In some classifications, the cryptomonads were considered close relatives of the dinoflagellates because of their similar pigmentation, being grouped as the Pyrrhophyta. There is considerable evidence that cryptomonad chloroplasts are related to those of the heterokonts and haptophytes, the three groups are sometimes united as the Chromista. However, the case that the organisms themselves are related is not strong, they may have acquired plastids independently, they are discussed to be members of the clade Diaphoretickes and to form together with the Haptophyta the group Hacrobia. Parfrey et al. and Burki et al. placed Cryptophyceae as a sister clade to the Green Algae. One suggested grouping is as follows: Cryptomonas, Chroomonas/Komma and Hemiselmis, Rhodomonas/Rhinomonas/Storeatula, Guillardia/Hanusia, Geminigera/Plagioselmis/Teleaulax, Proteomonas sulcata, Falcomonas daucoides.
Superclass Cryptomonada Cavalier-Smith 2004 sta. n. Class Goniomonadea Cavalier-Smith 1993 Order Goniomonadida Novarino & Lucas 1993 Family Goniomonadidae Hill 1991 Genus Goniomonas von Stein 1878 Order Hemiarmida Cavalier-Smith 2017 Family Hemiarmidae Cavalier-Smith 2017 Genus Hemiarma Shiratori & Ishida 2016 Class CryptophyceaeFritsch 1937 Order Tetragonidiales Kristiansen 1992 Family? Tetragonidiaceae Bourelly ex Silva1980 Genus Bjornbergiella Bicudo 1966 Genus Tetragonidium Pascher 1914 Order Pyrenomonadales Novarino & Lucas 1993 Family Pyrenomonadaceae Novarino & Lucas 1993 Genus Rhinomonas Hill & Wetherbee 1988 Genus Rhodomonas Karsten 1898 Genus Storeatula Hill 1991 Order Cryptomonadales Pascher 1913 Family? Butschliellaceae Skvortzov 1968 Genus Butschliella Skvortzov 1968 Genus Skvortzoviella Bourelly 1970 Family? Cryptochrysidaceae Pascher 1931 Genus Cryptochrysis Pascher 1911 Family? Hilleaceae Pascher 1967 Genus Calkinsiella Skvortzov 1969 Genus Hillea Schiller 1925 Family? Pleuromastigaceae Bourrelly ex Silva 1980 Genus Pleuromastix Scherffel 1912 non Namyslowski 1913] Genus Xanthodiscus Schewiakoff 1892 Clade Genus Proteomonas Hill & Wetherbee 1986 Family Chroomonadaceae Clay, Cugrens & Lee 1999 Genus?
Smithimastix Skvortzov 1969 Genus Falcomonas Hill 1991 Genus Chroomonas Hansgirg 1885 Genus Komma Hill 1991 Genus Planonephros Christensen 1978 Genus Nodeana Skvortzov 1968 Genus Protochrysis Pascher 1911 Genus Hemiselmis Parke 1949 Family Baffinellaceae Daugbjerg & Norlin 2018Genus Baffinella Norlin & Daugbjerg 2018 Family Geminigeraceae Clay, Cugrens & Lee 1999 Genus Geminigera Hill 1991 Genus Plagioselmis Butcher 1967 ex Novarino, Lucas & Morrall 1994 Genus Teleaulax Hill 1991 Genus Urgorri Laza-Martinez 2012 clade Guillardia group Genus Guillardia Hill & Wetherbee 1990 Genus Phia phi Özdikmen 2009 Family Cryptomonadaceae Ehrenberg 1831 Genus Cryptomonas Ehrenberg 1832 [
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
Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae, in a single group of land plants, the hornworts. Pyrenoids are associated with the operation of a carbon-concentrating mechanism, their main function is to act as centres of carbon dioxide fixation, by generating and maintaining a CO2 rich environment around the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. Pyrenoids therefore seem to have a role analogous to that of carboxysomes in cyanobacteria. Algae are restricted to aqueous environments in aquatic habitats, this has implications for their ability to access CO2 for photosynthesis. CO2 diffuses 10,000 times slower in water than in air, is slow to equilibrate; the result of this is that water, as a medium, is easily depleted of CO2 and is slow to gain CO2 from the air. CO2 equilibrates with bicarbonate when dissolved in water, does so on a pH-dependent basis. In sea water for example, the pH is such that dissolved inorganic carbon is found in the form of HCO3−.
The net result of this is a low concentration of free CO2, sufficient for an algal RuBisCO to run at a quarter of its maximum velocity, thus, CO2 availability may sometimes represent a major limitation of algal photosynthesis. Pyrenoids were first described in 1803 by Vaucher; the term was first coined by Schmitz who observed how algal chloroplasts formed de novo during cell division, leading Schimper to propose that chloroplasts were autonomous, to surmise that all green plants had originated through the “unification of a colourless organism with one uniformly tinged with chlorophyll". From these pioneering observations, Mereschkowski proposed, in the early 20th century, the symbiogenetic theory and the genetic independence of chloroplasts. In the following half-century, phycologists used the pyrenoid as a taxonomic marker, but physiologists long failed to appreciate the importance of pyrenoids in aquatic photosynthesis; the classical paradigm, which prevailed until the early 1980s, was that the pyrenoid was the site of starch synthesis.
Microscopic observations were misleading as a starch sheath encloses pyrenoids. The discovery of pyrenoid deficient mutants with normal starch grains in the green alga Chlamydomonas reinhardtii, as well as starchless mutants with formed pyrenoids discredited this hypothesis, it was not before the early 1970s that the proteinaceous nature of the pyrenoid was elucidated, when pyrenoids were isolated from a green alga, showed that up to 90% of it was composed of biochemically active RuBisCO. In the following decade and more evidence emerged that algae were capable of accumulating intracellular pools of DIC, converting these to CO2, in concentrations far exceeding that of the surrounding medium. Badger and Price first suggested the function of the pyrenoid to be analogous to that of the carboxysome in cyanobacteria, in being associated with CCM activity. CCM activity in algal and cyanobacterial photobionts of lichen associations was identified using gas exchange and carbon isotope isotopes and associated with the pyrenoid by Palmqvist and Badger et al.
The Hornwort CCM was characterized by Smith and Griffiths. From there on, the pyrenoid was studied in the wider context of carbon acquisition in algae, but has yet to be given a precise molecular definition. There is substantial diversity in pyrenoid morphology and ultrastructure between algal species. In the unicellular red alga Porphyridium purpureum and in the green alga Chlamydomonas reinhardtii, there is a single conspicuous pyrenoid in a single chloroplast, visible using light microscopy. By contrast, in diatoms and dinoflagellates, there can be multiple pyrenoids; when examined with transmission electron microscopy, pyrenoids appear as electron dense structures. The pyrenoid matrix, composed of RuBisCO, is traversed by thylakoids, which are in continuity with stromal thylakoids. In Porphyridium, these transpyrenoidal thylakoids are naked. Unlike carboxysomes, pyrenoids are not delineated by a protein shell. A starch sheath is formed or deposited at the periphery of pyrenoids when that starch is synthesised in the cytosol rather than in the chloroplast.
In Chlamydomonas, a high-molecular weight complex of two proteins forms an additional concentric layer around the pyrenoid, outside the starch sheath, this is hypothesised to act as a barrier to CO2-leakage or to recapture CO2 that escapes from the pyrenoid. The entire protein diversity and composition of the pyrenoid has yet to be elucidated, but thus far, a number of proteins other than RuBisCO have been shown to localise to the pyrenoid; however it is not yet known how the pyrenoid forms during cell division. Mutagenic work on Chlamydomonas has shown that the RuBisCO small subunit is important for pyrenoid assembly, that two solvent exposed alpha-helices of the RuBisCO small subunit are key to the process. Whether RuBisCO self-assembles into pyrenoids or requires additional chaperones is at present not known; the confinement of the CO2-fixing enzyme into a subcellular micro-compartment, in association with a mechanism to deliver CO2 to that site, is believed to enhance the efficacy of photosynthesis in an aqueous environment.
Having a CCM favours carboxylation over wasteful oxygenation by RuBisCO. The molecular basis of the pyrenoid and the CCM have been characterised to some detail in the model green alga Chlamydomonas reinhardtii; the current model of the biophysical CCM reliant upon a pyrenoid considers act
Algae is an informal term for a large, diverse group of photosynthetic eukaryotic organisms that are not closely related, is thus polyphyletic. Including organisms ranging from unicellular microalgae genera, such as Chlorella and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 m in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata and phloem, which are found in land plants; the largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example and the stoneworts. No definition of algae is accepted. One definition is that algae "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells". Although cyanobacteria are referred to as "blue-green algae", most authorities exclude all prokaryotes from the definition of algae.
Algae constitute a polyphyletic group since they do not include a common ancestor, although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, the roots and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy; some unicellular species of green algae, many golden algae, euglenids and other algae have become heterotrophs, sometimes parasitic, relying on external energy sources and have limited or no photosynthetic apparatus.
Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery derived from cyanobacteria that produce oxygen as a by-product of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago. The singular alga retains that meaning in English; the etymology is obscure. Although some speculate that it is related to Latin algēre, "be cold", no reason is known to associate seaweed with temperature. A more source is alliga, "binding, entwining"; the Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it. The Latinization, fūcus, meant the cosmetic rouge; the etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך, "paint", a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean.
It could be any color: black, green, or blue. Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used; the name Fucus appears in a number of taxa. The algae contain chloroplasts. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events; the table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members; some retain plastids, but not chloroplasts. Phylogeny based on plastid not nucleocytoplasmic genealogy: Linnaeus, in Species Plantarum, the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are considered among algae.
In Systema Naturae, Linnaeus described the genera Volvox and Corallina, a species of Acetabularia, among the animals. In 1768, Samuel Gottlieb Gmelin published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus, it included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey and Lamouroux were the first to divide macroscopic algae into four divisions based on their pigmentation; this is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae, brown algae, green algae, Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers studying the Infusoria. Unlike macroalgae, which were viewed as plants, microalgae were considered animals because they are motile; the nonmotile microalgae were sometimes seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-D