Symbiosis is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic. The organisms, each termed a symbiont, may be of different species. In 1879, Heinrich Anton de Bary defined it as "the living together of unlike organisms"; the term was subject to a century-long debate about whether it should denote mutualism, as in lichens. Symbiosis can be obligatory, which means that one or both of the symbionts depend on each other for survival, or facultative when they can live independently. Symbiosis is classified by physical attachment; when one organism lives on the surface of another, such as head lice on humans, it is called ectosymbiosis. The definition of symbiosis was a matter of debate for 130 years. In 1877, Albert Bernhard Frank used the term symbiosis to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms".
The definition has varied among scientists, with some advocating that it should only refer to persistent mutualisms, while others thought it should apply to all persistent biological interactions, in other words mutualisms, commensalism, or parasitism, but excluding brief interactions such as predation. Current biology and ecology textbooks use the latter "de Bary" definition, or an broader one where symbiosis means all interspecific interactions. In 1949, Edward Haskell proposed an integrative approach, proposing a classification of "co-actions" adopted by biologists as "interactions". Biological interactions can involve individuals of the same species or individuals of different species; these can be further classified by either the mechanism of the interaction or the strength and direction of their effects. Relationships can be obligate, meaning that one or both of the symbionts depend on each other for survival. For example, in lichens, which consist of fungal and photosynthetic symbionts, the fungal partners cannot live on their own.
The algal or cyanobacterial symbionts in lichens, such as Trentepohlia, can live independently, their symbiosis is, facultative. Endosymbiosis is any symbiotic relationship in which one symbiont lives within the tissues of the other, either within the cells or extracellularly. Examples include diverse microbiomes, nitrogen-fixing bacteria that live in root nodules on legume roots. Ectosymbiosis is any symbiotic relationship in which the symbiont lives on the body surface of the host, including the inner surface of the digestive tract or the ducts of exocrine glands. Examples of this include ectoparasites such as lice. Competition can be defined as an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both facilitates this type of interaction, although the competition may exist over other'amenities', such as females for reproduction. Mutualism or interspecies reciprocal altruism is a long-term relationship between individuals of different species where both individuals benefit.
Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both. A large percentage of herbivores have mutualistic gut flora to help them digest plant matter, more difficult to digest than animal prey; this gut flora is made up of cellulose-digesting protozoans or bacteria living in the herbivores' intestines. Coral reefs are the result of mutualisms between coral organisms and various types of algae which live inside them. Most land plants and land ecosystems rely on mutualisms between the plants, which fix carbon from the air, mycorrhyzal fungi, which help in extracting water and minerals from the ground. An example of mutualism is the relationship between the ocellaris clownfish that dwell among the tentacles of Ritteri sea anemones; the territorial fish protects the anemone from anemone-eating fish, in turn the stinging tentacles of the anemone protect the clownfish from its predators. A special mucus on the clownfish protects it from the stinging tentacles.
A further example is a fish which sometimes lives together with a shrimp. The shrimp cleans up a burrow in the sand in which both the shrimp and the goby fish live; the shrimp is blind, leaving it vulnerable to predators when outside its burrow. In case of danger, the goby touches the shrimp with its tail to warn it; when that happens both the shrimp and goby retreat into the burrow. Different species of gobies clean up ectoparasites in other fish another kind of mutualism. A non-obligate symbiosis is seen in encru
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton. A coral "group" is a colony of myriad genetically identical polyps; each polyp is a sac-like animal only a few millimeters in diameter and a few centimeters in length. A set of tentacles surround a central mouth opening. An exoskeleton is excreted near the base. Over many generations, the colony thus creates a large skeleton characteristic of the species. Individual heads grow by asexual reproduction of polyps. Corals breed sexually by spawning: polyps of the same species release gametes over a period of one to several nights around a full moon. Although some corals are able to catch small fish and plankton using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues.
These are known as zooxanthellae. Such corals require sunlight and grow in clear, shallow water at depths less than 60 metres. Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia. Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,300 metres; some have been found on the Darwin Mounds, northwest of Cape Wrath and others as far north as off the coast of Washington State and the Aleutian Islands. Aristotle's pupil Theophrastus described the red coral, korallion, in his book on stones, implying it was a mineral, but he described it as a deep-sea plant in his Enquiries on Plants, where he mentions large stony plants that reveal bright flowers when under water in the Gulf of Heroes. Pliny the Elder stated boldly that several sea creatures including sea nettles and sponges "are neither animals nor plants, but are possessed of a third nature".
Petrus Gyllius copied Pliny, introducing the term zoophyta for this third group in his 1535 book On the French and Latin Names of the Fishes of the Marseilles Region. Gyllius further noted, following Aristotle, how hard it was to define what was a plant and what was an animal; the Persian polymath Al-Biruni classified sponges and corals as animals, arguing that they respond to touch. People believed corals to be plants until the eighteenth century, when William Herschel used a microscope to establish that coral had the characteristic thin cell membranes of an animal. Presently, corals are classified as certain species of animals within the sub-classes Hexacorallia and Octocorallia of the class Anthozoa in the phylum Cnidaria. Hexacorallia includes the stony corals and these groups have polyps that have a 6-fold symmetry. Octocorallia includes blue coral and soft corals and species of Octocorallia have polyps with an eightfold symmetry, each polyp having eight tentacles and eight mesenteries.
Fire corals are not true corals. Corals are sessile animals and differ from most other cnidarians in not having a medusa stage in their life cycle; the body unit of the animal is a polyp. Most corals are colonial, the initial polyp budding to produce another and the colony developing from this small start. In stony corals known as hard corals, the polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism; this is deposited by the coenosarc, the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are variable in appearance. In soft corals, there is no stony skeleton but the tissues are toughened by the presence of tiny skeletal elements known as sclerites, which are made from calcium carbonate. Soft corals are variable in form and most are colonial. A few soft corals are stolonate. In some species this is thick and the polyps are embedded; some soft corals are form lobes. Others have a central axial skeleton embedded in the tissue matrix.
This is composed either of a fibrous protein called gorgonin or of a calcified material. In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and cnidocytes for defence against predators, soft corals relying on chemical defences in the form of toxic substances present in the tissues known as terpenoids; the polyps of stony corals have six-fold symmetry. The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance. In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow water species of both stony and soft corals can be zooxanthellate, the corals supplementing their plankton diet with t
Chlorella is a genus of single-celled green algae belonging to the division Chlorophyta. It is spherical in shape, about 2 to 10 μm in diameter, is without flagella. Chlorella contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. Through photosynthesis, it multiplies requiring only carbon dioxide, sunlight, a small amount of minerals to reproduce; the name Chlorella is taken from the Greek χλώρος, meaning green, the Latin diminutive suffix ella, meaning small. German biochemist and cell physiologist Otto Heinrich Warburg, awarded with the Nobel Prize in Physiology or Medicine in 1931 for his research on cell respiration studied photosynthesis in Chlorella. In 1961, Melvin Calvin of the University of California received the Nobel Prize in Chemistry for his research on the pathways of carbon dioxide assimilation in plants using Chlorella. Many people believe Chlorella can serve as a potential source of food and energy because its photosynthetic efficiency can, in theory, reach 8%, which exceeds that of other efficient crops such as sugar cane.
Chlorella is a potential food source. Mass-production methods are now being used to cultivate it in large man-made circular ponds, it is used as a'superfood' and can be found as an ingredient in certain liquid-based cocktails. When first harvested, Chlorella was suggested as an inexpensive protein supplement to the human diet. Advocates sometimes focus on other supposed health benefits of the algae, such as claims of weight control, cancer prevention, immune system support. According to the American Cancer Society, "available scientific studies do not support its effectiveness for preventing or treating cancer or any other disease in humans". Under certain growing conditions, Chlorella yields oils that are high in polyunsaturated fats—Chlorella minutissima has yielded eicosapentaenoic acid at 39.9% of total lipids. Following global fears of an uncontrollable human population boom during the late 1940s and the early 1950s, Chlorella was seen as a new and promising primary food source and as a possible solution to the then-current world hunger crisis.
Many people during this time thought hunger would be an overwhelming problem and saw Chlorella as a way to end this crisis by providing large amounts of high-quality food for a low cost. Many institutions began to research the algae, including the Carnegie Institution, the Rockefeller Foundation, the NIH, UC Berkeley, the Atomic Energy Commission, Stanford University. Following World War II, many Europeans were starving, many Malthusians attributed this not only to the war, but to the inability of the world to produce enough food to support the increasing population. According to a 1946 FAO report, the world would need to produce 25 to 35% more food in 1960 than in 1939 to keep up with the increasing population, while health improvements would require a 90 to 100% increase; because meat was costly and energy-intensive to produce, protein shortages were an issue. Increasing cultivated area alone would go only so far in providing adequate nutrition to the population; the USDA calculated that, to feed the U.
S. population by 1975, it would have to add 200 million acres of land, but only 45 million were available. One way to combat national food shortages was to increase the land available for farmers, yet the American frontier and farm land had long since been extinguished in trade for expansion and urban life. Hopes rested on new agricultural techniques and technologies; because of these circumstances, an alternative solution was needed. To cope with the upcoming postwar population boom in the United States and elsewhere, researchers decided to tap into the unexploited sea resources. Initial testing by the Stanford Research Institute showed Chlorella could convert 20% of solar energy into a plant that, when dried, contains 50% protein. In addition, Chlorella contains vitamins; the plant's photosynthetic efficiency allows it to yield more protein per unit area than any plant—one scientist predicted 10,000 tons of protein a year could be produced with just 20 workers staffing a 1000-acre Chlorella farm.
The pilot research performed at Stanford and elsewhere led to immense press from journalists and newspapers, yet did not lead to large-scale algae production. Chlorella seemed like a viable option because of the technological advances in agriculture at the time and the widespread acclaim it got from experts and scientists who studied it. Algae researchers had hoped to add a neutralized Chlorella powder to conventional food products, as a way to fortify them with vitamins and minerals; when the preliminary laboratory results were published, the scientific community at first backed the possibilities of Chlorella. Science News Letter praised the optimistic results in an article entitled "Algae to Feed the Starving". John Burlew, the editor of the Carnegie Institution of Washington book Algal Culture-from Laboratory to Pilot Plant, stated, "the algae culture may fill a real need," which Science News Letter turned into "future populations of the world will be kept from starving by the production of improved or educated algae related to the green scum on ponds."
The cover of the magazine featured Arthur D. Little's Cambridge laboratory, a supposed future food factory. A few years the magazine published an article entitled "Tomorrow's Dinner", which stated, "There is no doubt in the mind of scientists that the farms of the future will be factories." Science Digest reported, "common pond scum would soon bec
Chemotaxis is the movement of an organism in response to a chemical stimulus. Somatic cells and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment; this is important for bacteria to find food by swimming toward the highest concentration of food molecules, or to flee from poisons. In multicellular organisms, chemotaxis is critical to early development and subsequent phases of development as well as in normal function and health. In addition, it has been recognized that mechanisms that allow chemotaxis in animals can be subverted during cancer metastasis; the aberrant chemotaxis of leukocytes and lymphocytes contribute to inflammatory diseases such as atherosclerosis and arthritis. Positive chemotaxis occurs if the movement is toward a higher concentration of the chemical in question. Chemically prompted. Although migration of cells was detected from the early days of the development of microscopy by Leeuwenhoek, a Caltech lecture regarding chemotaxis propounds that'erudite description of chemotaxis was only first made by T. W. Engelmann and W. F. Pfeffer in bacteria, H. S. Jennings in ciliates'.
The Nobel Prize laureate I. Metchnikoff contributed to the study of the field during 1882 to 1886, with investigations of the process as an initial step of phagocytosis; the significance of chemotaxis in biology and clinical pathology was accepted in the 1930s, the most fundamental definitions underlying the phenomenon were drafted by this time. The most important aspects in quality control of chemotaxis assays were described by H. Harris in the 1950s. In the 1960s and 1970s, the revolution of modern cell biology and biochemistry provided a series of novel techniques that became available to investigate the migratory responder cells and subcellular fractions responsible for chemotactic activity; the availability of this technology led to the discovery of C5a, a major chemotactic factor involved in acute inflammation. The pioneering works of J. Adler represented a significant turning point in understanding the whole process of intracellular signal transduction of bacteria; some bacteria, such as E. coli, have several flagella per cell.
These can rotate in two ways: Counter-clockwise rotation aligns the flagella into a single rotating bundle, causing the bacterium to swim in a straight line. The directions of rotation are given for an observer outside the cell looking down the flagella toward the cell; the overall movement of a bacterium is the result of alternating swim phases. If one watches a bacterium swimming in a uniform environment, its movement will look like a random walk with straight swims interrupted by random tumbles that reorient the bacterium. Bacteria such as E. coli are unable to choose the direction in which they swim, are unable to swim in a straight line for more than a few seconds due to rotational diffusion. By evaluating their course, adjusting if they are moving in the wrong direction, bacteria can direct their motion to find favorable locations with high concentrations of attractants and avoid repellents. In the presence of a chemical gradient bacteria will chemotax, or direct their overall motion based on the gradient.
If the bacterium senses that it is moving in the correct direction, it will keep swimming in a straight line for a longer time before tumbling. In other words, bacteria like E. coli use temporal sensing to decide whether their situation is improving or not, in this way, find the location with the highest concentration of attractant quite well. Under high concentrations, it can still distinguish small differences in concentration, fleeing from a repellent works with the same efficiency; this biased random walk is a result of choosing between two methods of random movement. In fact, chemotactic responses such as forgetting direction and choosing movements resemble the decision-making abilities of higher life-forms with brains that process sensory data; the helical nature of the individual flagellar filament is critical for this movement to occur, the protein that makes up the flagellar filament, flagellin, is quite similar among all flagellated bacteria. Vertebrates seem to have taken advantage of this fact by possessing an immune receptor designed to recognize this conserved protein.
As in many instances in biology, there are bacteria. Many bacteria, such as Vibrio, are monoflagellated and have a single flagellum at one pole of the cell, their method of chemotaxis is different. Others possess a single flagellum, kept inside the cell wall; these bacteria move by spinning the whole cell, shaped like a corkscrew. Chemical gradients are sensed through multiple transmembrane receptors, called methyl-accepting chemotaxis proteins, which vary in the molecules that they detect; these receptors may bind attractants or repellents directly or indirectly through interaction with prot
The dinoflagellates are a classification subgroup of protista. They are a large group of flagellate eukaryotes. Most are marine plankton, but they are common in freshwater habitats, their populations are distributed depending on salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey. In terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, although this group is smaller than diatoms; some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are unpigmented predators on other protozoa, a few forms are parasitic; some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their lifecycles. Dinoflagellates are considered to be protists, with Dinoflagellata. About 1,555 species of free-living marine dinoflagellates are described. Another estimate suggests about 2,000 living species, of which more than 1,700 are marine and about 220 are from fresh water.
The latest estimates suggest a total of 2,294 living dinoflagellate species, which includes marine and parasitic dinoflagellates. A bloom of certain dinoflagellates can result in a visible coloration of the water colloquially known as red tide, which can cause shellfish poisoning if humans eat contaminated shellfish; some dinoflagellates exhibit bioluminescence—primarily emitting blue-green light. In 1753, the first modern dinoflagellates were described by Henry Baker as "Animalcules which cause the Sparkling Light in Sea Water", named by Otto Friedrich Müller in 1773; the term derives from the Greek word δῖνος, meaning whirling, Latin flagellum, a diminutive term for a whip or scourge. In the 1830s, the German microscopist Christian Gottfried Ehrenberg examined many water and plankton samples and proposed several dinoflagellate genera that are still used today including Peridinium and Dinophysis; these same dinoflagellates were first defined by Otto Bütschli in 1885 as the flagellate order Dinoflagellida.
Botanists treated them as a division of algae, named Pyrrophyta or Pyrrhophyta after the bioluminescent forms, or Dinophyta. At various times, the cryptomonads and ellobiopsids have been included here, but only the last are now considered close relatives. Dinoflagellates have a known ability to transform from noncyst to cyst-forming strategies, which makes recreating their evolutionary history difficult. Dinoflagellates are unicellular and possess two dissimilar flagella arising from the ventral cell side, they have a ribbon-like transverse flagellum with multiple waves that beats to the cell's left, a more conventional one, the longitudinal flagellum, that beats posteriorly. The transverse flagellum is a wavy ribbon in which only the outer edge undulates from base to tip, due to the action of the axoneme which runs along it; the axonemal edge has simple hairs. The flagellar movement produces forward propulsion and a turning force; the longitudinal flagellum is conventional in appearance, with few or no hairs.
It beats with two periods to its wave. The flagella lie in surface grooves: the transverse one in the cingulum and the longitudinal one in the sulcus, although its distal portion projects behind the cell. In dinoflagellate species with desmokont flagellation, the two flagella are differentiated as in dinokonts, but they are not associated with grooves. Dinoflagellates have a complex cell covering called an amphiesma or cortex, composed of a series of membranes, flattened vesicles called alveolae and related structures. In armoured dinoflagellates, these support overlapping cellulose plates to create a sort of armor called the theca, as opposed to athecate dinoflagellates; these occur in various shapes and arrangements, depending on the species and sometimes on the stage of the dinoflagellate. Conventionally, the term tabulation has been used to refer to this arrangement of thecal plates; the plate configuration can be denoted with the plate tabulation formula. Fibrous extrusomes are found in many forms.
Together with various other structural and genetic details, this organization indicates a close relationship between the dinoflagellates, the Apicomplexa, ciliates, collectively referred to as the alveolates. Dinoflagellate tabulations can be grouped into six "tabulation types": gymnodinoid, gonyaulacoid–peridinioid, nannoceratopsioid and prorocentroid; the chloroplasts in most photosynthetic dinoflagellates are bound by three membranes, suggesting they were derived from some ingested algae. Most photosynthetic species contain chlorophylls a and c2, the carotenoid beta-carotene, a group of xanthophylls that appears to be unique to dinoflagellates peridinin and diadinoxanthin; these pigments give many dinoflagellates their typical golden brown color. However, the dinoflagellates Karenia brevis, Karenia mikimotoi, Karlodinium micrum have acquired other pigments through endosymbiosis, including fucoxanthin; this suggests their chloroplasts were incorporated by several endosymbiotic events involving colored or secondarily colorless forms.
The discovery of plastids in the Apicomplexa has led some to suggest they were inherited from an ancestor common to the two groups, b
An autotroph or primary producer, is an organism that produces complex organic compounds from simple substances present in its surroundings using energy from light or inorganic chemical reactions. They are the producers such as plants on land or algae in water, they do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and create a store of chemical energy. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide; some autotrophs, such as green plants and algae, are phototrophs, meaning that they convert electromagnetic energy from sunlight into chemical energy in the form of reduced carbon. Autotrophs can be chemoautotrophs. Phototrophs use light as an energy source, while chemotrophs use electron donors as a source of energy, whether from organic or inorganic sources; such chemotrophs are lithotrophs. Lithotrophs use inorganic compounds, such as hydrogen sulfide, elemental sulfur and ferrous iron, as reducing agents for biosynthesis and chemical energy storage.
Photoautotrophs and lithoautotrophs use a portion of the ATP produced during photosynthesis or the oxidation of inorganic compounds to reduce NADP+ to NADPH to form organic compounds. The Greek term autotroph was coined by the German botanist Albert Bernhard Frank in 1892, it stems from the ancient Greek word τροφή, meaning "nourishment" or "food". Some organisms rely on organic compounds as a source of carbon, but are able to use light or inorganic compounds as a source of energy; such organisms are not defined rather as heterotrophic. An organism that obtains carbon from organic compounds but obtains energy from light is called a photoheterotroph, while an organism that obtains carbon from organic compounds but obtains energy from the oxidation of inorganic compounds is termed a chemoheterotroph, chemolithoheterotroph, or lithoheterotroph. Evidence suggests that some fungi may obtain energy from radiation; such radiotrophic fungi were found growing inside a reactor of the Chernobyl nuclear power plant.
Autotrophs are fundamental to the food chains of all ecosystems in the world. They take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates; this mechanism is called primary production. Other organisms, called heterotrophs, take in autotrophs as food to carry out functions necessary for their life. Thus, heterotrophs — all animals all fungi, as well as most bacteria and protozoa — depend on autotrophs, or primary producers, for the energy and raw materials they need. Heterotrophs obtain energy by breaking down organic molecules obtained in food. Carnivorous organisms rely on autotrophs indirectly, as the nutrients obtained from their heterotroph prey come from autotrophs they have consumed. Most ecosystems are supported by the autotrophic primary production of plants that capture photons released by the sun. Plants can only use a fraction of this energy for photosynthesis 1% is used by autotrophs; the process of photosynthesis splits a water molecule, releasing oxygen into the atmosphere, reducing carbon dioxide to release the hydrogen atoms that fuel the metabolic process of primary production.
Plants convert and store the energy of the photon into the chemical bonds of simple sugars during photosynthesis. These plant sugars are polymerized for storage as long-chain carbohydrates, including other sugars and cellulose; when autotrophs are eaten by heterotrophs, i.e. consumers such as animals, the carbohydrates and proteins contained in them become energy sources for the heterotrophs. Proteins can be made using nitrates and phosphates in the soil. Electrolithoautotroph Organotroph Electrotroph Primary nutritional groups Heterotrophic nutrition