Organs are groups of tissues with similar functions. Plant and animal life relies on many organs. Organs are composed of main tissue, "sporadic" tissues, stroma; the main tissue is that, unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, connective tissues. The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer. Functionally-related organs cooperate to form whole organ systems. Organs exist in most multicellular organisms. In single-celled organisms such as bacteria, the functional analogue of an organ is known as an organelle. In plants there are three main organs. A hollow organ is an internal organ that forms a hollow tube, or pouch such as the stomach, intestine, or bladder. In the study of anatomy, the term viscus is used to refer to an internal organ, viscera is the plural form. 79 organs have been identified in the human body. In biology, tissue is a cellular organizational level between complete organs.
A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant morphology. Classical tools for studying tissues include the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis. Two or more organs working together in the execution of a specific body function form an organ system called a biological system or body system.
The functions of organ systems share significant overlap. For instance, the nervous and endocrine system both operate via the hypothalamus. For this reason, the two systems are studied as the neuroendocrine system; the same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems. Common organ system designations in plants includes the differentiation of root. All parts of the plant above ground, including the functionally distinct leaf and flower organs, may be classified together as the shoot organ system. Animals such as humans have a variety of organ systems; these specific systems are widely studied in human anatomy. Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart and blood vessels. Digestive system: digestion and processing food with salivary glands, stomach, gallbladder, intestines, colon and anus. Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid and adrenals, i.e. adrenal glands.
Excretory system: kidneys, ureters and urethra involved in fluid balance, electrolyte balance and excretion of urine. Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, adenoids and spleen. Integumentary system: skin and nails of mammals. Scales of fish and birds, feathers of birds. Muscular system: movement with muscles. Nervous system: collecting and processing information with brain, spinal cord and nerves. Reproductive system: the sex organs, such as ovaries, fallopian tubes, vulva, testes, vas deferens, seminal vesicles and penis. Respiratory system: the organs used for breathing, the pharynx, trachea, bronchi and diaphragm. Skeletal system: structural support and protection with bones, cartilage and tendons; the study of plant organs is referred to as plant morphology, rather than anatomy – as in animal systems.
Organs of plants can be divided into reproductive. Vegetative plant organs include roots and leaves; the reproductive organs are variable. In flowering plants, they are represented by the flower and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions of plants, the reproductive organs are called strobili, in Lycopodiophyta, or gametophores in mosses; the vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis, while the reproductive organs are essential in reproduction. However, if there is asexual vegetative reproduction, the vegetative organs are those that create the new generation of plants. Many societies have a system for organ donation, in which a living or deceased donor's organ is transplanted into a person with a failing organ; the transplantation of larger solid organs requires immunosuppression to prevent organ rejection or graft-versus-host disease.
There is considerable interest throughout the world in creating laboratory-grown or artificial organs. The English word "organ" dates back in reference to any musical instrument. By the late 14th
A bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusk. In life, the shell of this class of mollusks is composed of valves. Bivalves are common in all aquatic locales, including saltwater, brackish water, freshwater; the shells of bivalves wash up on beaches and along the edges of lakes and streams. Bivalves by definition possess two shells or valves, a "right valve" and a "left valve", that are joined by a ligament; the two valves articulate with one another using structures known as "teeth" which are situated along the hinge line. In many bivalve shells, the two valves are symmetrical along the hinge line— when symmetrical, such an animal is said to be equivalved. If symmetrical front-to-back, the valves are said to be equilateral, are otherwise considered inequilateral; this exoskeleton serves not only for muscle attachment, but for protection from predators and from mechanical damage. The shell has several layers, is made of calcium carbonate precipitated out into an organic matrix.
It is secreted by a part of the molluscan body known as the mantle. The shells of bivalves are equal sides connected by a hinge. Bivalve shells are collected by professional and amateur conchologists and are sometimes harvested for commercial sale in the international shell trade or for use in glue, chalk, or varnish to the detriment of the local ecology; the bivalve shell is composed of two calcareous valves. The mantle, a thin membrane surrounding the body, secretes the shell valves and hinge teeth; the mantle lobes secrete the valves, the mantle crest creates the other parts. The mantle itself is attached to the shell by numerous small mantle retractor muscles, which are arranged in a narrow line along the length of the interior of the shell; the position of this line is quite visible on the inside of each valve of a bivalve shell, as a shiny line, the pallial line, which runs along a small distance in from the outer edge of each valve joining the anterior adductor muscle scar to the posterior adductor muscle scar.
The adductor muscles are. In some bivalves the mantle edges fuse to form siphons, which take in and expel water during suspension feeding. Species which live buried in sediment have long siphons, when the bivalve needs to close its shell, these siphons retract into a pocket-like space in the mantle; this feature of the internal anatomy of a bivalve is indicated on the interior of the shell surface as a pallial sinus, an indentation in the pallial line. The valves of the shell are made of either calcite or both calcite and aragonite with the aragonite forming an inner layer, as is the case with the Pterioida which have this layer in the form of nacre or mother of pearl; the outermost layer of the shell is known as the periostracum and is composed of a horny organic substance. This sometimes forms a brownish "skin" on the outside of the shell; the periostracum may start to peel off of a shell when the shell is allowed to dry out for long periods. The shell is added to, increases in size, in two ways - by increments added to the open edge of the shell, by a gradual thickening throughout the animal's life.
The two shell valves are held together at the animal's dorsum by the ligament, composed of the tensilium and resilium. In life the ligament opens the shell, the adductor muscle or muscles close the shell; when a bivalve dies, its adductor muscle relax and the resilium pushes the valves open. A few groups of bivalves are active swimmers like the scallops. In many species of cemented bivalves, the lower valve is more cupped than the upper valve, which tends to be rather flat. In some groups of cemented bivalves the lower or cemented valve is the left valve, in others it is the right valve; the oldest point of a bivalve shell is called the beak, the raised area around it is known as the umbo. The hinge area is the back of the shell; the lower, curved margin is the ventral side. The anterior or front of the shell is where the byssus and foot are located and the posterior or back of the shell is where the siphon is located. Without being able to view these organs, determining anterior and posterior can be rather more difficult.
In those animals with a siphon, the pallial sinus of the siphon, which will be present on both the left and right valves, will point towards the animal's posterior— such valves are called sinopalliate. Shells without a pallial sinus are termed integripalliate— such animals have a byssal notch present on the anterior end of the right valve, the anterior auricles or "wings" of both valves will be either larger than, or equal to, the posterior ones; such valves may have a distinctive "comb" or ctinoleum within the byssal notch on the right valve. If a valve has neither notch nor comb nor sinus, and
The pallial line is a mark on the interior of each valve of the shell of a bivalve mollusk. This line shows. In clams with two adductor muscles the pallial line joins the marks known as adductor muscle scars, which are where the adductor muscles attach; the position of the pallial line is quite visible as a shiny line on the more dull interior surface of the bivalve shell
Walter Garstang FLS FZS, a Fellow of Lincoln College and Professor of Zoology at the University of Leeds, was one of the first to study the functional biology of marine invertebrate larvae. His best known works on marine larvae were his poems which were published together after his death as Larval Forms and Other Zoological Verses, which describe the form and function of several marine larvae as well as illustrating some controversies in evolutionary biology of the time. Garstang was known for his vehement opposition to Ernst Haeckel's Biogenetic Law, now discredited, he is noted for his hypothesis on chordate evolution, known as Garstang's theory, which suggests an alternative route for chordate evolution from echinoderms. Holland, in Walter Garstang: a Retrospective summarizes Garstang’s more important publications with special attention to his evolutionary thoughts—their source, their relation to the biology of his times, their fate in the twenty-first century. Walter Garstang was born on 9 February 1868 as the eldest son of Dr Walter Garstang of Blackburn and his wife Matilda Mary Wardley, older brother of the archaeologist John Garstang.
In 1895 he married Lucy Ackroyd. In 1884 at the age of 16, he was awarded a scholarship to Jesus College and was going to study medicine. Under the guidance of Henry Nottidge Moseley, he joined the school of Zoology and graduated in 1888 at the age of 20. Before graduation, Garstang was offered a position as secretary and assistant to Gilbert C Bourne, the new resident director of the Marine Biological Association of the United Kingdom in Plymouth. There he met Ray Lankester. In 1891 he left Plymouth and was a Berkley Research Fellow under Milnes Marshall at Owens College, Manchester. A year Garstang returned to Plymouth as Assistant Naturalist, only to be elected a Fellow of Lincoln College, Oxford, in 1893. In 1894, while Ray Lankester held the Linacre Chair, he became a lecturer at Lincoln College and in 1895 he started the series of Easter classes in which he took students on week-long field courses to Plymouth. Between 1902 and 1907 Garstang was employed by the MBA as the principle investigator working on North Sea fisheries.
He helped to establish a fisheries laboratory in Lowestoft, to become the Centre for Environment and Aquaculture Science, part of the Ministry of Agriculture and Food. Garstang instigated a series of detailed fisheries surveys throughout the southern North Sea aboard the RV Huxley, under the auspices of the newly formed International Council for the Exploration of the Sea. Garstang was Professor of Zoology at the University of Leeds from 1907 to 1933; the Garstang Building at the university is named in his honour. In 1912 in cooperation with Professor Alfred Denny of the University of Sheffield he established the Robin Hood's Bay Marine Laboratory; the minutes of Sheffield's Faculty of Pure Science on 12 March 1912 record the following resolution, carried unanimously: That the Faculty approves of the proposal to extend the work of the Department of Zoology by co-operating with the University of Leeds in establishing a small marine Zoological Laboratory at Robin Hood's Bay. Garstang noted from study of marine animals that both echinoderms and chordates are deuterostomes, while most other possible ancestors of Chordates are protostomes.
This inspired Garstang to suggest an alternate route of evolution: from echinoderms to chordates. There are many important differences between echinoderms. Most adult echinoderms show little likeness to chordates: echinoderms are radially symmetric, possess calcium carbonate plates in their skin and have tube feet. Garstang made the radical suggestion that it was echinoderm larvae, not adults, which had given rise to chordates. Echinoderm larvae, like chordates, are bilaterally symmetric. Notable are their similarities to larvae of hemichordates, which are a step closer to chordates as they share two of the five most noted chordate characteristics, namely a hollow neural tube and pharyngeal slits. Garstang's idea is supported by many lines of evidence. Most interesting and compelling is the fact that some amphibians can stay in larval form and still reach sexual maturity—this shows that echinoderm larvae could, have become sexually mature and stopped morphing into adults, instead evolving into chordate ancestors.
Species that show this refusal to leave the larval stage include mud puppies and other salamanders, which either or show neoteny: retention of juvenile traits or phenotypes after sexual maturity. Garstang's Hypothesis was revolutionary for both its time and idea: it suggests that not only may single species evolve, but that single life stages of species may evolve into separate organisms; the hypothesis, which Garstang proposed in the early 20th century, seemed far-fetched at the time of its conception and did not receive support until after Garstang's death. First published in 1951, two years after his death, Larval Forms and Other Zoological Verses is a compilation of 26 poems by Garstang on the form and development of various larval invertebrates. Although they were published posthumously, Garstang had had a desire to publish them for many years and never did because he always thought he would add to them. Except for the introduction written by Sir Alister Hardy, everything in the final publication, including the title and order of the poems, was his own work.
The zebra mussel is a small freshwater mussel. This species was native to the lakes of southern Russia and Ukraine. However, the zebra mussel has been accidentally introduced to numerous other areas, has become an invasive species in many countries worldwide. Since the 1980s, they have invaded the Hudson River; the species was first described in 1769 by the German zoologist Peter Simon Pallas in the Ural and Dnieper rivers. Zebra mussels get their name from a striped pattern seen on their shells, though it is not universally present, they are about the size of a fingernail, but can grow to a maximum length of nearly 2 in. Shells are D-shaped, attached to the substrate with strong byssal fibers, which come out of their umbo on the dorsal side. Zebra mussel and the related and ecologically similar quagga mussels are filter-feeding organisms, they remove particles from the water column. The zebra mussels process up to one liter of water per mussel; some particles are consumed as food, feces are deposited on the lake floor.
Nonfood particles are combined with mucus and other matter and deposited on lake floors as pseudofeces. Since the zebra mussel has become established in Lake Erie, water clarity has increased from 6 inches to up to three feet in some areas; this improved water clarity allows sunlight to penetrate deeper, enabling growth of submerged macrophytes. These plants, when decaying, wash up on shorelines, fouling beaches and cause water quality problems. Lake floor food supplies are enriched by zebra mussels; this biomass becomes available to the fish that feed on them. The catch of yellow perch increased 5 fold after the invasion of zebra mussels into Lake St. Clair. Zebra mussels attach to most substrates including sand and harder substrates, but juvenile mussels prefer harder, rockier substrates to which to attach. Other mussel species represent the most stable objects in silty substrates, zebra mussels attach to, kill these mussels, they build colonies on native unionid clams, reducing their ability to move and breed leading to their deaths.
This has led to the near extinction of the unionid clams in Lake St. Clair and the western basin of Lake Erie; this pattern is being repeated in Ireland, where zebra mussels have eliminated the two freshwater mussels from several waterways, including some lakes along the River Shannon in 1997. In 2012, the National University of Ireland, said "The discovery of zebra mussels in Lough Derg and the lower Shannon region in 1997 has led to considerable concern about the potential ecological and economic damage that this invasive aquatic nuisance species can cause." The lifespan of a zebra mussel is four to five years. A female zebra mussel begins to reproduce within 6–7 weeks of settling. An adult female zebra mussel can produce 30,000 to 40,000 eggs in each reproductive cycle, over 1 million each year. Free-swimming microscopic larvae, called veligers, drift in the water for several weeks and settle onto any hard surface they can find. Zebra mussels can tolerate a wide range of environmental conditions and adults can survive out of water for about 7 days.
Research on natural enemies, both in Europe and North America, has focused on predators birds and fish. The vast majority of the organisms that are natural enemies in Europe are not present in North America. Ecologically similar species do exist, but these species are unlikely to be able to eliminate those mussels established and will have a limited role in their control. Crayfish could have a significant impact on the densities of 1- to 5-mm-long zebra mussels. An adult crayfish consumes around about 6000 mussels in a season. Predation rates are reduced at lower water temperatures. Fish do not seem to limit the densities of zebra mussels in European lakes. Smallmouth bass are a predator in the zebra mussels' adopted North American Great Lakes habitat. On June 4, 2014, Canadian conservation authorities announced that a test using liquid fertilizer to kill invasive zebra mussels was successful; this test was conducted in a lakefront harbor in the western province of Manitoba. However, there continue to be outbreaks in Lake Winnipeg.
Similar tests were run in Illinois and Michigan, using Zequanox, a biopesticide. Researchers have found that Niclosamide proves effective in killing invasive zebra mussels in cool waters; the native distribution of the species is in the Black Caspian Sea in Eurasia. Zebra mussels have become an invasive species in North America, Great Britain, Italy and Sweden, they disrupt the ecosystems by monotypic colonization, damage harbors and waterways and boats, water treatment and power plants. Water treatment plants are most affected because the water intakes bring the microscopic free-swimming larvae directly into the facilities. Zebra mussels cling to pipes under the water and clog them. Grossinger reported it in Hungary in 1794. Kerney and Morton described the rapid colonization of Britain by the zebra mussel, first in Cambridgeshire in the 1820s, London in 1824, in the Union Canal near Edinburgh in 1834. In 1827, zebra mussels were seen in the Netherlands at Rotterdam. Canals that artificially link many European waterways facilitated their early dispersal.
It is nonindigenous in the Czech Republic in the Elbe River in Bohemia since 1893. Around 1920 the mussels reached Lake Mälaren in Sweden. Th
Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters, they provide a crucial source of food to many large aquatic organisms, such as fish and whales. These organisms include bacteria, algae and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification. Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish. Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim in the water, which are called nekton; the name plankton is derived from the Greek adjective πλαγκτός, meaning errant, by extension, wanderer or drifter, was coined by Victor Hensen in 1887.
While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day, their horizontal position is determined by the surrounding water movement, plankton flow with ocean currents. This is in contrast to nekton organisms, such as fish and marine mammals, which can swim against the ambient flow and control their position in the environment. Within the plankton, holoplankton spend their entire life cycle as plankton. By contrast, meroplankton are only planktic for part of their lives, graduate to either a nektic or benthic existence. Examples of meroplankton include the larvae of sea urchins, crustaceans, marine worms, most fish; the amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton. The study of plankton is termed planktology and a planktonic individual is referred to as a plankter; the adjective planktonic is used in both the scientific and popular literature, is a accepted term.
However, from the standpoint of prescriptive grammar, the less-commonly used planktic is more the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending is dropped, using only the root of the word in the derivation. Plankton are divided into broad functional groups: Phytoplankton, autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria and coccolithophores. Zooplankton, small protozoans or metazoans that feed on other plankton; some of the eggs and larvae of larger nektonic animals, such as fish and annelids, are included here. Bacterioplankton and archaea, which play an important role in remineralising organic material down the water column. Mycoplankton and fungus-like organisms, like bacterioplankton, are significant in remineralisation and nutrient cycling; this scheme divides the plankton community into broad producer and recycler groups.
However, determining the trophic level of many plankton is not always straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species perform both roles. In this mixed trophic strategy — known as mixotrophy — organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. For instance, relying on photosynthesis for growth when nutrients and light are abundant, but switching to predation when growing conditions are poor. Recognition of the importance of mixotrophy as an ecological strategy is increasing, as well as the wider role this may play in marine biogeochemistry. Plankton are often described in terms of size; the following divisions are used: However, some of these terms may be used with different boundaries on the larger end. The existence and importance of nano- and smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.
The microplankton and smaller groups are microorganisms and operate at low Reynolds numbers, where the viscosity of water is much more important than its mass or inertia. Plankton inhabit oceans, lakes, ponds. Local abundance varies horizontally and seasonally; the primary cause of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy, confining primary production to surface waters, to geographical regions and seasons having abundant light. A secondary variable is nutrient availability. Although large areas of the tropical and sub-tropical oceans have abundant light, they experience low primary production because they offer limited nutrients such as nitrate and silicate; this results from large-scale ocean water column stratification. In such regions, primary production occurs at greater depth, although at a reduced level. Despite significant macronutrient concentrations, some ocean regions are unproductive; the micronutrient iron is deficient in these reg
A hinge ligament is a crucial part of the anatomical structure of a bivalve shell, i.e. the shell of a bivalve mollusk. The shell of a bivalve has two valves and these are joined together by the ligament at the dorsal edge of the shell; the ligament is made of a strong and elastic, proteinaceous material, pale brown, dark brown or black in color. In life, the shell needs to be able to open a little and close again; as well as connecting the two bivalve shells together at the hinge line, the ligament functions as a spring which automatically opens the valves when the adductor muscle or muscles relax. The ligament is an uncalcified elastic structure comprised in its most minimal state of two layers: a lamellar layer and a fibrous layer; the lamellar layer consists of organic material, is brown in color, is elastic in response to both compressional and tensional stresses. The fibrous layer is made of aragonite fibers and organic material, is lighter in color and iridescent, is elastic only under compressional stress.
The protein responsible for the elasticity of the ligament is abductin, which has enormous elastic resiliency: this resiliency is what causes the valves of the bivalve mollusk to open when the adductor muscles relax. Ligaments that are simple morphologically have a central fibrous layer between the anterior and posterior lamellar layers. Repetitive ligaments are morphologically more complex, display additional, repeated layers. A recent study using scanning electron microscopy, X-ray diffraction, infrared spectroscopy, found that some bivalve mollusks have a third type of fibrous layer in the ligament which has a unique spring-like protein fiber structure, stretching continuously from the left to right valve; when the adductor muscles of a bivalve mollusk contract, the valves close, which compresses the ligament. When the adductor muscles relax again, the elastic resiliency of the ligament reopens the shell. Scallops swim through the water column by and clapping their valves. An interesting fact about scallops swimming in this manner is that they recover a greater percentage of the work performed through the elasticity of their abductin than do other bivalves.
The hinge ligament of a bivalve shell can be either internal, external, or both, is an example of complex development. Various types of hinge ligaments have been found in living species, the ligaments can be reconstructed in most fossil bivalves based on their sites of attachment on the shell; the taxonomic distribution of ligament types among families of bivalves has been used by paleontologists and malacologists as a means of inferring phylogenic evolution. External hinge ligaments may be described as having an "orientation", amphidetic, opisthodetic, or prosodetic. There are four main "structural types": alivincular, duplivincular and planivincular. An internal ligament is called a resilium and is attached to a resilifer or chrondophore, a depression or pit inside the shell near the umbo. E. R. Trueman, General features of Bivalvia. In: Moore R. C. editor. Bivalvia. Ligament. In: Treatise on invertebrate paleontology. Vol. 2. Geological Society of America and University of Kansas Press. P. N58-N64.
Part N - Mollusca, Bivalvia Vol. 6. T. R. Waller, The evolution of ligament systems in the Bivalvia. In: Morton B. editor. Proceedings of a Memorial Symposium in Honour of Sir Charles Maurice Yonge, Edinburgh, 1986. Hong Kong: Hong Kong University Press. P. 49-71. J. G. Carter, Evolutionary significance of shell microstructure in the Paleotaxodonta and Isofilibranchia. In: Carter J. G. editor. Skeletal biomineralization: patterns and evolutionary trends. New York: Van Nostrand Reinhold. P. 135-296