In botany, a peduncle is a stem supporting an inflorescence, or after fecundation, an infructescence. The peduncle is a stem green, though some peduncles are more or less florally colored or neutral in color, having no particular pigmentation. In some species, peduncles are leafless, though others bear small leaves, or cataphylls, at nodes; the peduncle is the inflorescence base without flowers. When an unbranched peduncle has no obvious nodes, rises directly from a bulb or stem, if it rises directly from the ground, it is referred to as a scape; the acorns of the pedunculate oak are borne on hence the name of the tree. Pedicel Scape
Anthozoa is a class of marine invertebrates which includes the sea anemones, stony corals, soft corals and gorgonians. Adult anthozoans are all attached to the seabed, while their larvae can disperse as part of the plankton; the basic unit of the adult is the polyp. Sea anemones are solitary, but the majority of corals are colonial, being formed by the budding of new polyps from an original, founding individual. Colonies are strengthened by calcium carbonate and other materials and take various massive, plate-like, bushy or leafy forms. Anthozoa is included within the phylum Cnidaria, which includes the jellyfish, box jellies and parasitic Myxozoa and Polypodiozoa; the two main subclasses of Anthozoa are the Hexacorallia, members of which have six-fold symmetry and includes the stony corals, sea anemones, tube anemones and zoanthids. The smaller subclass, consists of the tube-dwelling anemones; some additional species are included as incertae sedis until their exact taxonomic position can be ascertained.
Anthozoans are carnivores. Many species supplement their energy needs by making use of photosynthetic single-celled algae that live within their tissues; these species live in shallow water and many are reef-builders. Other species lack the zooxanthellae and, having no need for well-lit areas live in deep-water locations. Unlike other members of this phylum, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs into the water. After fertilisation, the planula larvae form part of the plankton; when developed, the larvae settle on the seabed and attach to the substrate, undergoing metamorphosis into polyps. Some anthozoans can reproduce asexually through budding or by breaking in pieces. More than 16,000 species have been described; the name "Anthozoa" comes from the Greek words άνθος and ζώα, hence ανθόζωα = "flower animals", a reference to the floral appearance of their perennial polyp stage. Anthozoans are marine, include sea anemones, stony corals, soft corals, sea pens, sea fans and sea pansies.
Anthozoa is the largest taxon of cnidarians. They range in size from small individuals less than half a centimetre across to large colonies a metre or more in diameter, they include species with a wide range of forms that build and enhance reef systems. Although reefs and shallow water environments exhibit a great array of species, there are in fact more species of coral living in deep water than in shallow, many taxa have shifted during their evolutionary history from shallow to deep water and vice versa. Anthozoa is subdivided into three subclasses: Octocorallia and Ceriantharia, which form monophyletic groups and show differentiating reflections on symmetry of polyp structure for each subclass; the relationships within the subclasses are unresolved. The "Ceriantipatharia" was thought to be a separate subclass but, of the two orders it comprised, Antipatharia is now considered part of Hexacorallia and Ceriantharia is now considered an independent subclass; the extant orders are shown to the right.
Hexacorallia includes coral reef builders: the stony corals, sea anemones, zoanthids. Genetic studies of ribosomal DNA has shown Ceriantharia to be a monophyletic group and the oldest, or basal, order among them. Classification according to the World Register of Marine Species: subclass Hexacorallia order Actiniaria — sea anemones order Antipatharia — black coral order Corallimorpharia — corallimorphs order Rugosa † order Scleractinia — stony corals order Zoantharia — zoanthids subclass Octocorallia order Alcyonacea — soft corals and gorgonians order Helioporacea — blue corals order Pennatulacea — pennatules, sea feathers, sea pens, sea pansies subclass Ceriantharia — ceriantharians, tube-dwelling anemones order Penicillaria order Spirularia Anthozoa incertae sedis genus Aiptasiodes order Auloporida † genus Sarcinula †Octocorallia comprises the sea pens, soft corals, blue coral. Sea whips and sea fans, known as gorgonians, are part of Alcyonacea and were divided into separate orders. Ceriantharia comprises the related tube-dwelling anemones.
Tube-dwelling anemones or cerianthids look similar to sea anemones, but belong to an different subclass of anthozoans. They are solitary. Tube anemones live and can withdraw into tubes, which are made of a fibrous material, made from secreted mucus and threads of nematocyst-like organelles, known as ptychocysts; the basic body form of an anthozoan is the polyp. This consists of a tubular column topped by the oral disc, with a central mouth. In solitary individuals, the base of the polyp is the foot or pedal disc, which adheres to the substrate, while in colonial polyps, the base links to other polyps in the colony; the mouth leads into a tubular pharynx which descends for some distance into the body before opening into the coelenteron, otherwise known as the gastrovascular cavity, that occupies the interior of the body. Internal tensions pull the mouth into a slit-shape, the ends of the slit lead into two grooves in the pharynx wall called siphonoglyphs; the coelenteron is subdivided by a number of vertical partitions, known as mesenteries or septa.
Some of these extend from th
The littoral zone or nearshore is the part of a sea, lake or river, close to the shore. In coastal environments the littoral zone extends from the high water mark, inundated, to shoreline areas that are permanently submerged, it always includes this intertidal zone and is used to mean the same as the intertidal zone. However, the meaning of "littoral zone" can extend well beyond the intertidal zone. There is no single definition. What is regarded as the full extent of the littoral zone, the way the littoral zone is divided into subregions, varies in different contexts; the use of the term varies from one part of the world to another, between different disciplines. For example, military commanders speak of the littoral in ways that are quite different from marine biologists; the adjacency of water gives a number of distinctive characteristics to littoral regions. The erosive power of water results in particular types of landforms, such as sand dunes, estuaries; the natural movement of the littoral along the coast is called the littoral drift.
Biologically, the ready availability of water enables a greater variety of plant and animal life, the formation of extensive wetlands. In addition, the additional local humidity due to evaporation creates a microclimate supporting unique types of organisms; the word "littoral" is used both as an adjective. It derives from the Latin noun litus, meaning "shore". In oceanography and marine biology, the idea of the littoral zone is extended to the edge of the continental shelf. Starting from the shoreline, the littoral zone begins at the spray region just above the high tide mark. From here, it moves to the intertidal region between the high and low water marks, out as far as the edge of the continental shelf; these three subregions are called, in order, the supralittoral zone, the eulittoral zone and the sublittoral zone. The supralittoral zone is the area above the spring high tide line, splashed, but not submerged by ocean water. Seawater penetrates these elevated areas only during storms with high tides.
Organisms here must cope with exposure to fresh water from rain, cold and predation by land animals and seabirds. At the top of this area, patches of dark lichens can appear as crusts on rocks; some types of periwinkles and detritus feeding Isopoda inhabit the lower supralittoral. The eulittoral zone is the intertidal zone known as the foreshore, it extends from the spring high tide line, inundated, to the spring low tide line, not inundated. The wave action and turbulence of recurring tides shapes and reforms cliffs and caves, offering a huge range of habitats for sedentary organisms. Protected rocky shorelines show a narrow homogenous eulittoral strip marked by the presence of barnacles. Exposed sites show a wider extension and are divided into further zones. For more on this, see intertidal ecology; the sublittoral zone starts below the eulittoral zone. This zone is permanently covered with seawater and is equivalent to the neritic zone. In physical oceanography, the sublittoral zone refers to coastal regions with significant tidal flows and energy dissipation, including non-linear flows, internal waves, river outflows and oceanic fronts.
In practice, this extends to the edge of the continental shelf, with depths around 200 meters. In marine biology, the sublittoral refers to the areas where sunlight reaches the ocean floor, that is, where the water is never so deep as to take it out of the photic zone; this results in high primary production and makes the sublittoral zone the location of the majority of sea life. As in physical oceanography, this zone extends to the edge of the continental shelf; the benthic zone in the sublittoral is much more stable than in the intertidal zone. Sublittoral corals do not have to deal with as much change as intertidal corals. Corals can live in both zones. Within the sublittoral, marine biologists identify the following: The infralittoral zone is the algal dominated zone to maybe five metres below the low water mark; the circalittoral zone is the region beyond the infralittoral, that is, below the algal zone and dominated by sessile animals such as oysters. Shallower regions of the sublittoral zone, extending not far from the shore, are sometimes referred to as the subtidal zone.
In freshwater situations, littoral zones occur on the edge of large lakes and rivers with extensive areas of wetland. Hence, they are sometimes referred to as fringing wetlands. Here, the effects of tides are minimal. For example, the Minnesota Department of Natural Resources defines littoral as that portion of the lake, less than 15 feet in depth; the littoral zone may form a narrow or broad fringing wetland, with extensive areas of aquatic plants sorted by their tolerance to different water depths. Four zones are recognized, from higher to lower on the shore: wooded wetland, wet meadow and aquatic vegetation; the relative areas of these four types depends not only on the profile of the shoreline, but upon past water levels. The area of wet meadow is dependent upon past water levels.
The blue mussel known as the common mussel, is a medium-sized edible marine bivalve mollusc in the family Mytilidae, the mussels. Blue mussels are subject to intensive aquaculture. Systematically blue mussels consist of a group of three related taxa of mussels, known as the Mytilus edulis complex. Collectively they occupy both coasts of the North Atlantic and of the North Pacific in temperate to polar waters, as well as coasts of similar nature in the Southern Hemisphere; the distribution of the component taxa has been modified as a result of human activity. The taxa can hybridise with each other. Mytilus edulis sensu stricto: Native to the North Atlantic. Mytilus galloprovincialis, the Mediterranean mussel: Native in the Mediterranean, the Black Sea and Western Europe. Introduced in the temperate North Pacific, South Africa and elsewhere in the Southern Hemisphere. Mytilus planulatus, a distinct lineage native to the Southern Hemisphere along the southern coast of Australia and New Zealand Mytilus platensis, the Montevideo mussel: Temperate and sub-Antarctic waters of South America and the Kerguelen Islands.
Mytilus trossulus: North Pacific, northern parts of the North Atlantic, Baltic Sea. The Atlantic blue mussel is native on the North American Atlantic coast, but is found intermixed with M. trossulus north of Maine. In Atlantic Canada, M. trossulus was found to have smaller shell growth values than M. edulis and contain less meat than M. edulis. Keeping this in mind, M. edulis, under raft culture conditions, is estimated to have an economic value of 1.7 times M. trossulus. In Europe it is found from French Atlantic coast northwards to Novaya Zemlya and Iceland, but not in the Baltic Sea. In France and in the British Isles, it makes hybrid zones with M. galloprovincialis, is sometimes intermixed with M. trossulus. A genetically distinct lineage of M. edulis is present in the Southern Hemisphere, has been attributed to subspecies Mytilus edulis platensis. This includes the Chilean mussel. Blue mussels are boreo-temperate invertebrates that live in intertidal areas attached to rocks and other hard substrates by strong thread-like structures called byssal threads, secreted by byssal glands located in the foot of the mussel.
The shape of the shell is elongate with rounded edges. The shell is smooth with a sculpturing of fine concentric growth lines but no radiating ribs; the shells of this species are purple, blue or sometimes brown in color with radial stripes. The outer surface of the shell is covered by the periostracum which as eroded, exposes the colored prismatic calcitic layer. Blue Mussels are semi-sessile, having the ability to detach and reattach to a surface allowing the mollusk to reposition itself relative to the water position. Mussels have separate sexes. Once the sperm and eggs are developed they are released into the water column for fertilization. Although there are about 10,000 sperm per egg, large proportions of eggs deposited by blue mussel are never fertilized; as few as 1% of larvae that do mature reach adulthood, the majority are eaten by predators before completing metamorphosis. The reproductive strategy seen in blue mussels is characteristic of planktotrophs, by minimizing nutrients in egg production to the bare minimum they are able to maximize the number of gametes produced.
If the adult mussels are stressed during the beginning of gametogenesis, the process is terminated. When stressed while fresh gametes are present, adult mussels reabsorb gametes. Larvae viability is affected by the condition of parents: high water temperatures and scarcity of food, during gamete production; the reduction in viability is due to the lack of lipid reserves distributed to the eggs. Larval development can last from 15 to 35 days depending environmental conditions including salinity and temperature, as well as location. Larvae originating from Connecticut mature at 15–20 °C, though at 15 °C normal development occurs at salinities between 15 and 35 ppt and 20 at 35 ppt at 20 °C; the first stage of development is the ciliated embryo, which in 24-hours for fertilization form the trochophore. At this point although mobile, it is still reliant on the yolk for nutrients. Characterized by a functional mouth and alimentary canal the veliger stage has cilia which are used for filtering food as well as propulsion.
A thin translucent shell is secreted by the shell gland forming the notable straight hinge of the prodissoconch I shell. The veliger continues to mature forming the prodissoconch II shell. In the end stage of veliger development photosensitive eye spots and elongated foot with a byssal gland are formed. Once the pediveliger is developed, its foot extends and makes contact with substrate; the initial contact with the substrate is loose. If the substrate is suitable, the larva will metamorphoses into the juvenile form and attach byssus threads; the mussel will remain in that state until reaching 1-1.5mm in length. This attachment is the prerequisite for the foundation for the blue mussel population. In sheltered environments large masses sometimes form beds which offer shelter and food for other invertebrates. Byssal thread are secreted by byssal glands located in the foot of the mussel, are made up of polyphenolic proteins are proteins which serve as a bioadhesive. Blue mussels form clumps, or aggregates, of individuals when population density is low.
The mussels attach to one another via collagenous protein strands called byssal threads. The aggregates are observed
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals. Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that protect the coral. Most reefs grow best in warm, clear and agitated water. Called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems, they occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, worms, echinoderms, sponges and other cnidarians. Coral reefs flourish in ocean waters, they are most found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas. Coral reefs deliver ecosystem services for tourism and shoreline protection.
The annual global economic value of coral reefs is estimated between US$30–375 billion and 9.9 trillion USD. Coral reefs are fragile because they are sensitive to water conditions, they are under threat from excess nutrients, rising temperatures, oceanic acidification, sunscreen use, harmful land-use practices, including runoff and seeps. Most coral reefs were formed after the last glacial period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old; as communities established themselves, the reefs grew pacing rising sea levels. Reefs that rose too could become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls; the majority of these islands are volcanic in origin. Others have tectonic origins. In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle.
He theorized that subsidence of the Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the ocean floor subsides; as the subsidence continues, the fringing reef becomes a barrier reef and an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, can grow to become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land.
A barrier reef can encircle an island, once the island sinks below sea level a circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not form complete circles, but are broken in places by storms. Like sea level rise, a subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure; the two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, the history of the change in sea level relative to that substrate. The 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was 120 m lower than in the 21st century; as sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain.
By 13,000 years ago, sea level had risen to 60 m lower than at present, many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands; the corals could overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed in the last 6,000 years; the age of living reef structure is estimated to be between 8,000 years. Although the Great Barrier Reef formed along a continental shelf, not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, it formed 300 -- 1,000 m from shore, stretching for 2,000 km. Healthy tropical coral reefs grow horizontally from 1 to 3 cm per year, grow vertically anywhere from 1 to 25 cm per year; as the name implies, coral reefs are made up of coral skeletons from intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However
Sponges, the members of the phylum Porifera, are a basal Metazoa clade as a sister of the Diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells; the branch of zoology that studies sponges is known as spongiology. Sponges have unspecialized cells that can transform into other types and that migrate between the main cell layers and the mesohyl in the process. Sponges do not have digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges were first to branch off the evolutionary tree from the common ancestor of all animals, making them the sister group of all other animals; the term sponge derives from the Ancient Greek word σπόγγος. Sponges are similar to other animals in that they are multicellular, lack cell walls and produce sperm cells.
Unlike other animals, they lack true organs. Some of them are radially symmetrical; the shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine species, ranging from tidal zones to depths exceeding 8,800 m. While most of the 5,000–10,000 known species feed on bacteria and other food particles in the water, some host photosynthesizing microorganisms as endosymbionts and these alliances produce more food and oxygen than they consume. A few species of sponge that live in food-poor environments have become carnivores that prey on small crustaceans. Most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the "mother".
The fertilized eggs form larvae to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding; when conditions deteriorate, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules, "survival pods" of unspecialized cells that remain dormant until conditions improve and either form new sponges or recolonize the skeletons of their parents. The mesohyl functions as an endoskeleton in most sponges, is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More the mesohyl is stiffened by mineral spicules, by spongin fibers or both. Demosponges use spongin, in many species, silica spicules and in some species, calcium carbonate exoskeletons. Demosponges constitute about 90% of all known sponge species, including all freshwater ones, have the widest range of habitats. Calcareous sponges, which have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to shallow marine waters where production of calcium carbonate is easiest.
The fragile glass sponges, with "scaffolding" of silica spicules, are restricted to polar regions and the ocean depths where predators are rare. Fossils of all of these types have been found in rocks dated from 580 million years ago. In addition Archaeocyathids, whose fossils are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge; the single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals; some studies have shown that sponges do not form a monophyletic group, in other words do not include all and only the descendants of a common ancestor. Recent phylogenetic analyses suggest that comb jellies rather than sponges are the sister group to the rest of animals; the few species of demosponge that have soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools.
By the 1950s, these had been overfished so that the industry collapsed, most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging. Sponges constitute the phylum Porifera, have been defined as sessile metazoans that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella. However, a few carnivorous sponges have lost the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another. If a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such a mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass.
This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy. Like cnidarians (jellyfish, e
In biology, an organism is any individual entity that exhibits the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into specified groups such as the multicellular animals and fungi. All types of organisms are capable of reproduction and development, some degree of response to stimuli. Humans are multicellular animals composed of many trillions of cells which differentiate during development into specialized tissues and organs. An organism may be either a eukaryote. Prokaryotes are represented by two separate domains -- archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus and contain additional membrane-bound compartments called organelles. Fungi and plants are examples of kingdoms of organisms within the eukaryotes. Estimates on the number of Earth's current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to over five billion species, that lived are estimated to be extinct.
In 2016, a set of 355 genes from the last universal common ancestor of all organisms was identified. The term "organism" first appeared in the English language in 1703 and took on its current definition by 1834, it is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to Immanuel Kant's 1790 Critique of Judgment. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, fungus or bacterium, capable of growth and reproduction". Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction. A superorganism is an organism consisting of many individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism and indeed about whether or not such a definition is necessary.
Several contributions are responses to the suggestion that the category of "organism" may well not be adequate in biology. Viruses are not considered to be organisms because they are incapable of autonomous reproduction, growth or metabolism; this controversy is problematic because some cellular organisms are incapable of independent survival and live as obligatory intracellular parasites. Although viruses have a few enzymes and molecules characteristic of living organisms, they have no metabolism of their own; this rules out autonomous reproduction: they can only be passively replicated by the machinery of the host cell. In this sense, they are similar to inanimate matter. While viruses sustain no independent metabolism and thus are not classified as organisms, they do have their own genes, they do evolve by mechanisms similar to the evolutionary mechanisms of organisms; the most common argument in support of viruses as living organisms is their ability to undergo evolution and replicate through self-assembly.
Some scientists argue. In fact, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible; this is not true for cells. If viruses did not exist, the direction of cellular evolution could be different, but cells would be able to evolve; as for the reproduction, viruses rely on hosts' machinery to replicate. The discovery of viral metagenomes with genes coding for energy metabolism and protein synthesis fueled the debate about whether viruses belong in the tree of life; the presence of these genes suggested. However, it was found that the genes coding for energy and protein metabolism have a cellular origin. Most these genes were acquired through horizontal gene transfer from viral hosts. Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival; the same laws that govern non-living chemistry govern the chemical processes of life.
It is the phenomena of entire organisms that determine their fitness to an environment and therefore the survivability of their DNA-based genes. Organisms owe their origin and many other internal functions to chemical phenomena the chemistry of large organic molecules. Organisms are complex systems of chemical compounds that, through interaction and environment, play a wide variety of roles. Organisms are semi-closed chemical systems. Although they are individual units of life, they are not closed to the environment around them. To operate they take in and release energy. Autotrophs produce usable energy using light from the sun or inorganic compounds while heterotrophs take in organic compounds from the environment; the primary chemical element in these compounds is carbon. The chemical properties of this element such as its grea