In chemistry in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, either saturated or unsaturated. Most occurring fatty acids have an unbranched chain of an number of carbon atoms, from 4 to 28. Fatty acids are not found in organisms, but instead as three main classes of esters: triglycerides and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells; the concept of fatty acid was introduced by Michel Eugène Chevreul, though he used some variant terms: graisse acide and acide huileux. Fatty acids are classified in many ways: by length, by saturation vs unsaturation, by vs odd carbon content, by linear vs branched. Short-chain fatty acids are fatty acids with aliphatic tails of five or fewer carbons. Medium-chain fatty acids are fatty acids with aliphatic tails of 6 to 12 carbons, which can form medium-chain triglycerides. Long-chain fatty acids are fatty acids with aliphatic tails of 13 to 21 carbons.

Long chain fatty acids are fatty acids with aliphatic tails of 22 or more carbons. Saturated fatty acids have no C=C double bonds, they have the same formula CH3nCOOH, with variations in "n". An important saturated fatty acid is stearic acid, which when neutralized with lye is the most common form of soap. Unsaturated fatty acids have one or more C=C double bonds; the C=C double bonds can give either cis or trans isomers. Cis A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain; the rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has; when a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend.

Α-Linolenic acid, with three double bonds, favors a hooked shape. The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be packed, therefore can affect the melting temperature of the membrane or of the fat. Trans A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain; as a result, they do not cause the chain to bend much, their shape is similar to straight saturated fatty acids. In most occurring unsaturated fatty acids, each double bond has three, six, or nine carbon atoms after it, all double bonds have a cis configuration. Most fatty acids in the trans configuration are not found in nature and are the result of human processing; some trans fatty acids occur in the milk and meat of ruminants. They are produced, in the rumen of these animals, they are found in dairy products from milk of ruminants, may be found in breast milk of women who obtained them from their diet.

The differences in geometry between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, in the construction of biological structures. Most fatty acids are even-chained, e.g. stearic and oleic, meaning that an number of carbon atoms comprise them. Some fatty acids have odd numbers of carbon; the most common OCFA are the saturated C15 and C17 derivatives pentadecanoic acid and heptadecanoic acid, which are found in dairy products. On a molecular level, OCFAs are biosynthesized and metabolized differently from the even-chained relatives. Most occurring fatty acids have an unbranched chain of carbon atoms, with a carboxyl group at one end, a methyl group at the other end; the carbon next to the carboxyl group is labeled as carbon α, using the first letter of the Greek alphabet. The next is labeled as β, so forth. Although fatty acids can be of different lengths, the last position is always labelled as ω, the last letter in the Greek alphabet.

The position of the carbon atoms in the backbone of a fatty acid can be indicated by numbering them, either from the −COOH end or from the −CH3 end of the carbon chain. If the position is counted from the −COOH end the C-x notation is used, with x=1, 2, 3, etc.. If the position is counted from the −CH3 end it is represented by the ω-x notation, or equivalently, by the n-x notation; the positions of the double bonds in a fatty acid chain can, therefore, be indicated in two ways, using the C-x or the ω-x notation. Thus, in an 18 carbon fatty acid, a double bond between C-12 and C-13 is reported either as Δ12 if counted from the −COOH end, or as ω-6 if counting from the −CH3 end. In both cases, only the “beginning” of the double bond is indicated; the "Δ" is the Greek letter delta. Omega is the last letter in the Greek alphabet, is therefore used to indicate the “last” carbon atom in the fatty acid chain; the ω-x notation i

Poland is part of two global ecoregions as defined by the World Wide Fund for Nature, an international non-governmental organization with a branch in Poland. The two global habitat types extending into the country are the European-Mediterranean Montane Mixed Forests, as well as the Northeast Atlantic Shelf Marine ecoregion, encircling all of Continental Europe. Most of Poland is covered by the deciduous woodlands, known as the temperate broadleaf and mixed forests, it is identified as one of three Palearctic ecoregion zones of the European continent present in the country. The geographic range of the continental mixed forest biozone, spans all the way from Lithuania to Romania, from Germany to western Russia; the north-western part of Poland is in the Palearctic Northern European temperate broadleaf and mixed forests ecoregion known as the Baltic mixed forests. This ecoregion includes the coastal regions of north Germany and southern Sweden. Part of Poland's habitat is made up of the Temperate coniferous forest as well, but only around the mountains.

It is known as the Carpathian montane conifer forest. In total, the temperate broadleaf and mixed forest of Europe is 282,300 square miles in size, with a status of the critical/endangered ecoregion featuring one of the last herds of European bison known as wisent, the heaviest surviving wild land animal on the continent, grazing the protected Białowieża Forest of north-eastern Poland; the wisent's range encompassed all lowlands of Europe, extending from the Massif Central to the Caucasus. Its range decreased; the European bison became extinct in southern Sweden in the 11th century, southern England in the 12th century. The species survived in the Ardennes and the Vosges until the 15th century before being hunted to extinction. In mid-16th century King Sigismund II Augustus of Poland pronounced a death penalty for poaching a European bison in Białowieża. Despite these measures, its population continued to decline. During World War I, occupying German troops killed 600 wisent for food and horns.

The last wild European bison in Poland was killed in 1919. They were reintroduced from captivity. There are pockets of the Western European broadleaf forests in Poland centered around the Upper Rhine. A branch of the World Wide Fund has operated in Poland since the early 1990s. In 1993, the WWF Polska succeeded in the creation of the Biebrza National Park followed in 1998 by the opening of its first permanent office in Białystok, which led to the creation of additional protected areas including Ujście Warty Landscape Park, Krzesin Landscape Park and the Muskau Park. In 2000, the new permanent office in Warsaw became the headquarters of the foundation. An additional branch was set up in Wrocław which helped create the Ujście Warty National Park in 2001; the next year, WWF Poland petitioned the government into signing the Kyoto Protocol. In 2004 it organized a campaign against the illegal trade in endangered species resulting in new laws enacted by Polish Parliament, in 2008 caused the cancellation of the Via Baltica expressway across the Rospuda valley.

In recent years, WWF Polska volunteers removed the estimated 20 tons of abandoned nets from the Baltic sea, among numerous other projects. List of ecoregions in Europe Media related to Palearctic SVG maps of WWF ecoregions at Wikimedia Commons

Anton Wachter is the protagonist of eight novels by Dutch author Simon Vestdijk. The life of Wachter is captured in eight semi-autobiographical novels considered central to Vestdijk's oeuvre; the first four volumes are set in the town of Lahringen, meaning Harlingen, where Vestdijk was born and raised. The last four volumes are set in Amsterdam and describe the life of Wachter/Vestdijk as a medical student. Sint Sebastiaan Surrogaten voor Murk Tuinstra Terug tot Ina Damman De Andere School De Beker van de Min De Vrije Vogel en Zijn Kooien De Rimpels van Esther Ornstein De Laatste Kans The first three novels originate from Vestdijk's ambitious debut novel, Kind tussen vier vrouwen. Written in 1933, it was rejected by the publisher, but published posthumously in 1972; the first novel in the cycle's chronology, Sint Sebastiaan, derived its name from a painting of the saint by Alonso Cano Vestdijk admired in the Rijksmuseum in Amsterdam. From an early age Vestdijk spent vacations in Amsterdam, returned there during his studies in Utrecht and after he moved to Doorn to enjoy "the pool of sinful and forbidden things".

A statue of Anton Wachter by Suze Boschma-Berkhout, in Harlingen's Voorstraat, was unveiled in 1973