A mycorrhiza is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in its root system. Mycorrhizae play important roles in soil biology and soil chemistry. In a mycorrhizal association, the fungus colonizes the host plant's root tissues, either intracellularly as in arbuscular mycorrhizal fungi, or extracellularly as in ectomycorrhizal fungi; the association is mutualistic, but in particular species or in particular circumstances, mycorrhizae may be variously parasitic in the host plants. A mycorrhiza is a symbiotic association between a fungus; the plant makes organic molecules such as sugars by photosynthesis and supplies them to the fungus, the fungus supplies to the plant water and mineral nutrients, such as phosphorus, taken from the soil. Mycorrhizas are located in the roots of vascular plants, but mycorrhiza-like associations occur in bryophytes and there is fossil evidence that early land plants that lacked roots formed arbuscular mycorrhizal associations.
Most plant species form mycorrhizal associations, though some families like Brassicaceae and Chenopodiaceae cannot. Different forms for the association are detailed in the next section; the most common is the arbuscular type, present in 70% of plant species, including many crop plants such as wheat and rice. Mycorrhizas are divided into ectomycorrhizas and endomycorrhizas; the two types are differentiated by the fact that the hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root, while the hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane. Endomycorrhiza includes arbuscular and orchid mycorrhiza, while arbutoid mycorrhizas can be classified as ectoendomycorrhizas. Monotropoid mycorrhizas form a special category. Ectomycorrhizas, or EcM, are symbiotic associations between the roots of around 10% of plant families woody plants including the birch, eucalyptus, oak and rose families and fungi belonging to the Basidiomycota and Zygomycota.
Some EcM fungi, such as many Leccinum and Suillus, are symbiotic with only one particular genus of plant, while other fungi, such as the Amanita, are generalists that form mycorrhizas with many different plants. An individual tree may have 15 or more different fungal EcM partners at one time. Thousands of ectomycorrhizal fungal species hosted in over 200 genera. A recent study has conservatively estimated global ectomycorrhizal fungal species richness at 7750 species, although, on the basis of estimates of knowns and unknowns in macromycete diversity, a final estimate of ECM species richness would be between 20,000 and 25,000. Ectomycorrhizas consist of a hyphal sheath, or mantle, covering the root tip and a Hartig net of hyphae surrounding the plant cells within the root cortex. In some cases the hyphae may penetrate the plant cells, in which case the mycorrhiza is called an ectendomycorrhiza. Outside the root, ectomycorrhizal extramatrical mycelium forms an extensive network within the soil and leaf litter.
Nutrients can be shown to move between different plants through the fungal network. Carbon has been shown to move from paper birch trees into Douglas-fir trees thereby promoting succession in ecosystems; the ectomycorrhizal fungus Laccaria bicolor has been found to lure and kill springtails to obtain nitrogen, some of which may be transferred to the mycorrhizal host plant. In a study by Klironomos and Hart, Eastern White Pine inoculated with L. bicolor was able to derive up to 25% of its nitrogen from springtails. When compared to non-mycorrhizal fine roots, ectomycorrhizae may contain high concentrations of trace elements, including toxic metals or chlorine; the first genomic sequence for a representative of symbiotic fungi, the ectomycorrhizal basidiomycete L. bicolor, has been published. An expansion of several multigene families occurred in this fungus, suggesting that adaptation to symbiosis proceeded by gene duplication. Within lineage-specific genes those coding for symbiosis-regulated secreted proteins showed an up-regulated expression in ectomycorrhizal root tips suggesting a role in the partner communication.
L. bicolor is lacking enzymes involved in the degradation of plant cell wall components, preventing the symbiont from degrading host cells during the root colonisation. By contrast, L. bicolor possesses expanded multigene families associated with hydrolysis of bacterial and microfauna polysaccharides and proteins. This genome analysis revealed the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots; this type of mycorrhiza involves plants of the Ericaceae subfamily Arbutoideae. It is however different from ericoid mycorrhiza and resembles ectomycorrhiza, both functionally and in terms of the fungi involved; the difference to ectomycorrhiza is that some hyphae penetrate into the root cells, making this type of mycorrhiza an ectendomycorrhiza. Endomycorrhizas are variable and have been further classified as arbuscular, arbutoid and orchid mycorrhizas. Arbuscular mycorrhizas, or AM, are mycorrhizas whose hyphae penetrate plant cells, producing structures that are either balloon-like or dichotomously branching invaginations as a means of nutrient exchange.
The fungal hyphae invaginate the cell membrane. The struct
Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, crayfish, krill and barnacles. The crustacean group is treated as a subphylum, because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, comprises all animals in the Pancrustacea clade other than hexapods; some crustaceans are more related to insects and other hexapods than they are to certain other crustaceans. The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm, to the Japanese spider crab with a leg span of up to 3.8 m and a mass of 20 kg. Like other arthropods, crustaceans have an exoskeleton, they are distinguished from other groups of arthropods, such as insects and chelicerates, by the possession of biramous limbs, by their larval forms, such as the nauplius stage of branchiopods and copepods. Most crustaceans are free-living aquatic animals, but some are terrestrial, some are parasitic and some are sessile; the group has an extensive fossil record, reaching back to the Cambrian, includes living fossils such as Triops cancriformis, which has existed unchanged since the Triassic period.
More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimp and prawns. Krill and copepods are not as fished, but may be the animals with the greatest biomass on the planet, form a vital part of the food chain; the scientific study of crustaceans is known as carcinology, a scientist who works in carcinology is a carcinologist. The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, the pereon or thorax, the pleon or abdomen; the head and thorax may be fused together to form a cephalothorax, which may be covered by a single large carapace. The crustacean body is protected by the hard exoskeleton, which must be moulted for the animal to grow; the shell around each somite can be divided into a dorsal tergum, ventral sternum and a lateral pleuron. Various parts of the exoskeleton may be fused together; each somite, or body segment can bear a pair of appendages: on the segments of the head, these include two pairs of antennae, the mandibles and maxillae.
The abdomen bears pleopods, ends in a telson, which bears the anus, is flanked by uropods to form a tail fan. The number and variety of appendages in different crustaceans may be responsible for the group's success. Crustacean appendages are biramous, meaning they are divided into two parts, it is unclear whether the biramous condition is a derived state which evolved in crustaceans, or whether the second branch of the limb has been lost in all other groups. Trilobites, for instance possessed biramous appendages; the main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum. Malacostraca have haemocyanin as the oxygen-carrying pigment, while copepods, ostracods and branchiopods have haemoglobins; the alimentary canal consists of a straight tube that has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food. Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, a collection of major ganglia is found below the gut.
In many decapods, the first pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans return to the sea to release the eggs. Others, such as woodlice, lay their eggs on land, albeit in damp conditions. In most decapods, the females retain the eggs; the majority of crustaceans are aquatic, living in either marine or freshwater environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs, woodlice. Marine crustaceans are as ubiquitous in the oceans; the majority of crustaceans are motile, moving about independently, although a few taxonomic units are parasitic and live attached to their hosts, adult barnacles live a sessile life – they are attached headfirst to the substrate and cannot move independently. Some branchiurans are able to withstand rapid changes of salinity and will switch hosts from marine to non-marine species. Krill are the bottom layer and the most important part of the food chain in Antarctic animal communities.
Some crustaceans are significant invasive species, such as the Chinese mitten crab, Eriocheir sinensis, the Asian shore crab, Hemigrapsus sanguineus. The majority of crustaceans have separate sexes, reproduce sexually. A small number are hermaphrodites, including barnacles and Cephalocarida; some may change sex during the course of their life. Parthenogenesis is widespread among crustaceans, where viable eggs are produced by a female without needing fertilisation by a male; this occurs in many branchiopods, some os
Wilting is the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells; the rate of loss of water from the plant is greater than the absorption of water in the plant. The process of wilting modifies the leaf angle distribution of the plant towards more erectophile conditions. Lower water availability may result from: drought conditions, where the soil moisture drops below conditions most favorable for plant functioning. Wilting diminishes the plant's ability to transpire and grow. Permanent wilting leads to plant death. Symptoms of wilting and blights resemble one another. In woody plants, reduced water availability leads to cavitation of the xylem. Wilting occurs in plants such as tulasi/tulsi. Wilting is an effect of the plant growth inhibiting hormone, abscisic acid. With Cucurbits, wilting can be caused by the Squash vine borer
Asclepias is a genus of herbaceous, flowering plants known as milkweeds, named for their latex, a milky substance containing cardiac glycosides termed cardenolides, exuded where cells are damaged. Most species are toxic; the genus contains over 200 species distributed broadly across Africa, North America, South America. It belonged to the family Asclepiadaceae, now classified as the subfamily Asclepiadoideae of the dogbane family Apocynaceae; the genus was formally described by Carl Linnaeus in 1753, who named it after Asclepius, the Greek god of healing. Members of the genus Asclepias produce some of the most complex flowers in the plant kingdom, comparable to orchids in complexity. Five petals reflex backwards revealing a gynostegium surrounded by a five-membrane corona; the corona is composed of a five paired hood and horn structure with the hood acting as a sheath for the inner horn. Glands holding pollinia are found between the hoods; the size and color of the horns and hoods are important identifying characteristics for species in the genus Asclepias.
Pollination in this genus is accomplished in an unusual manner. Pollen is grouped into complex structures called pollinia, rather than being individual grains or tetrads, as is typical for most plants; the feet or mouthparts of flower-visiting insects such as bees and butterflies, slip into one of the five slits in each flower formed by adjacent anthers. The bases of the pollinia mechanically attach to the insect, so that a pair of pollen sacs can be pulled free when the pollinator flies off, assuming the insect is large enough to produce the necessary pulling force. Pollination is effected by the reverse procedure, in which one of the pollinia becomes trapped within the anther slit. Large-bodied hymenopterans are the most common and best pollinators, whereas monarch butterflies are not good pollinators of milkweed. Asclepias species produce their seeds in pods termed follicles; the seeds, which are arranged in overlapping rows, bear a cluster of white, filament-like hairs known as the coma. The follicles ripen and split open, the seeds, each carried by its coma, are blown by the wind.
Some, but not all, milkweeds reproduced by clonal reproduction. American milkweeds are an important nectar source for native bees and other nectar-seeking insects, though non-native honey bees get trapped in the stigmatic slits and die. Milkweeds are the larval food source for monarch butterflies and their relatives, as well as a variety of other herbivorous insects specialized to feed on the plants despite their chemical defenses. Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves, cardenolide toxins, latex fluids. Data from a DNA study indicate that more evolved milkweed species use these preventative strategies less but grow faster than older species regrowing faster than caterpillars can consume them. Milkweed is not grown commercially in large scale, but the plant has had many uses throughout human history; the milkweed filaments from the coma are hollow and coated with wax, have good insulation qualities. During World War II, more than 5,000 t of milkweed floss was collected in the United States as a substitute for kapok.
Milkweed is grown commercially as a hypoallergenic filling for pillows and as insulation for winter coats. A study of the insulative properties of various materials found that milkweed floss was outperformed by other materials in terms of insulation and lumpiness, but it scored well when mixed with down feathers. Milkweed fibers are used to clean up oil spills; the bast fibers of some species can be used for rope. Milkweed latex contains about two percent latex and was attempted as a source of natural rubber by both Nazi Germany and the United States during World War II. No record has been found of large-scale success. Asclepias is known as "Silk of America", a strand of common milkweed gathered in the valley of the Saint Lawrence River in Canada; the silk is used in thermal insulation, acoustic insulation, oil absorbents. Milkweed contains cardiac glycoside poisons that inhibit animal cells from maintaining a proper K+, Ca+ concentration gradient; as a result, many natives of South America and Africa used arrows poisoned with these glycosides to fight and hunt more effectively.
Milkweed may cause death when animals consume large quantities of the plant. Milkweed causes mild dermatitis in some who come in contact with it. Nonetheless, it can be made edible; the leaves of Asclepias species are a food source for monarch butterfly larvae and some other milkweed butterflies. These plants are used in butterfly gardening; some Asclepias species: There are 12 species of Asclepias in South America, among them: A. barjoniifolia, A. boliviensis, A. curassavica, A. mellodora, A. candida, A. flava, A. pilgeriana. Species classified under the genus Asclepias include: Calotropis gigantea W. T. Aiton Calotropis procera W. T. Aiton Cynanchum louiseae Kartesz & Gandhi Cynanchum thesioides K. Schum. Funastrum clausum Schltr. Gomphocarpus cancellatus Bruyns Gomphocarpus fruticosus W. T. Aiton Marsdenia macrophylla E. Fourn. (as A. macrophylla Humb. &
Peptides are short chains of amino acid monomers linked by peptide bonds. The covalent chemical bonds are formed when the carboxyl group of one amino acid reacts with the amino group of another; the shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, etc. A polypeptide is a long and unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids and polysaccharides, etc. Peptides are distinguished from proteins on the basis of size, as an arbitrary benchmark can be understood to contain 50 or fewer amino acids. Proteins consist of one or more polypeptides arranged in a biologically functional way bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule, or to complex macromolecular assemblies. While aspects of the lab techniques applied to peptides versus polypeptides and proteins differ, the size boundaries that distinguish peptides from polypeptides and proteins are not absolute: long peptides such as amyloid beta have been referred to as proteins, smaller proteins like insulin have been considered peptides.
Amino acids that have been incorporated into peptides are termed "residues" due to the release of either a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both, as a water molecule is released during formation of each amide bond. All peptides except cyclic peptides have an N-terminal and C-terminal residue at the end of the peptide. Many kinds of peptides are known, they have been categorized according to their sources and function. According to the Handbook of Biologically Active Peptides, some groups of peptides include plant peptides, bacterial/antibiotic peptides, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, endocrine peptides, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides, opiate peptides, neurotrophic peptides, blood–brain peptides; some ribosomal peptides are subject to proteolysis.
These function in higher organisms, as hormones and signaling molecules. Some organisms produce peptides as antibiotics, such as microcins. Peptides have posttranslational modifications such as phosphorylation, sulfonation, palmitoylation and disulfide formation. In general, peptides are linear. More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom. Nonribosomal peptides are assembled by enzymes, not the ribosome. A common non-ribosomal peptide is glutathione, a component of the antioxidant defenses of most aerobic organisms. Other nonribosomal peptides are most common in unicellular organisms and fungi and are synthesized by modular enzyme complexes called nonribosomal peptide synthetases; these complexes are laid out in a similar fashion, they can contain many different modules to perform a diverse set of chemical manipulations on the developing product. These peptides are cyclic and can have complex cyclic structures, although linear nonribosomal peptides are common.
Since the system is related to the machinery for building fatty acids and polyketides, hybrid compounds are found. The presence of oxazoles or thiazoles indicates that the compound was synthesized in this fashion. Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein; these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can be forensic or paleontological samples that have been degraded by natural effects. Use of peptides received prominence in molecular biology for several reasons; the first is that peptides allow the creation of peptide antibodies in animals without the need of purifying the protein of interest. This involves synthesizing antigenic peptides of sections of the protein of interest; these will be used to make antibodies in a rabbit or mouse against the protein. Another reason is that techniques such as mass spectrometry enable the identification of proteins based on the peptide masses and sequence that result from their fragmentation.
Peptides have been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to see where protein-peptide interactions occur- see the page on Protein tags. Inhibitory peptides are used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases. For example, one of the most promising application is through peptides that target LHRH; these particular peptides act as an agonist, meaning that they bind to a cell in a way that regulates LHRH receptors. The process of inhibiting the cell receptors suggests that peptides could be beneficial in treating prostate cancer, but additional investigations and experiments are required before their cancer-fighting attributes can be considered definitive; the peptide families in this section are ribosomal peptides with hormonal activity. All of these peptides are synthesized by cells as longer "propeptides" or "proproteins" and truncated prior to exiting the cell.
They are released into the bloodstream. Magainin family Cecropin famil
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India and the 1st century BC book On Agriculture by Marcus Terentius Varro. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Antonie van Leeuwenhoek. In the 1850s, Louis Pasteur found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s, Robert Koch discovered that microorganisms caused the diseases tuberculosis and anthrax. Microorganisms include all unicellular organisms and so are diverse. Of the three domains of life identified by Carl Woese, all of the Archaea and Bacteria are microorganisms; these were grouped together in the two domain system as Prokaryotes, the other being the eukaryotes. The third domain Eukaryota includes all multicellular organisms and many unicellular protists and protozoans.
Some protists are related to some to green plants. Many of the multicellular organisms are microscopic, namely micro-animals, some fungi and some algae, but these are not discussed here, they live in every habitat from the poles to the equator, geysers and the deep sea. Some are adapted to extremes such as hot or cold conditions, others to high pressure and a few such as Deinococcus radiodurans to high radiation environments. Microorganisms make up the microbiota found in and on all multicellular organisms. A December 2017 report stated that 3.45-billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel and other bioactive compounds, they are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora.
They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. The possible existence of microorganisms was discussed for many centuries before their discovery in the 17th century. By the fifth century BC, the Jains of present-day India postulated the existence of tiny organisms called nigodas; these nigodas are said to be born in clusters. According to the Jain leader Mahavira, the humans destroy these nigodas on a massive scale, when they eat, breathe and move. Many modern Jains assert that Mahavira's teachings presage the existence of microorganisms as discovered by modern science; the earliest known idea to indicate the possibility of diseases spreading by yet unseen organisms was that of the Roman scholar Marcus Terentius Varro in a 1st-century BC book titled On Agriculture in which he called the unseen creatures animalcules, warns against locating a homestead near a swamp: … and because there are bred certain minute creatures that cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and they cause serious diseases.
In The Canon of Medicine, Avicenna suggested that tuberculosis and other diseases might be contagious. Akshamsaddin mentioned the microbe in his work Maddat ul-Hayat about two centuries prior to Antonie Van Leeuwenhoek's discovery through experimentation: It is incorrect to assume that diseases appear one by one in humans. Disease infects by spreading from one person to another; this infection occurs through seeds that are so small they are alive. In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or without contact over long distances. Antonie Van Leeuwenhoek is considered to be the father of microbiology, he was the first in 1673 to discover, describe and conduct scientific experiments with microoorganisms, using simple single-lensed microscopes of his own design. Robert Hooke, a contemporary of Leeuwenhoek used microscopy to observe microbial life in the form of the fruiting bodies of moulds.
In his 1665 book Micrographia, he made drawings of studies, he coined the term cell. Louis Pasteur exposed boiled broths to the air, in vessels that contained a filter to prevent particles from passing through to the growth medium, in vessels without a filter, but with air allowed in via a curved tube so dust particles would settle and not come in contact with the broth. By boiling the broth beforehand, Pasteur ensured that no microorganisms survived within the broths at the beginning of his experiment. Nothing grew in the broths in the course of Pasteur's experiment; this meant that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. Thus, Pasteur supported the germ theory of disease. In 1876, Robert Koch established, he found that the blood of cattle which were infected with anthrax always had large numbers of Bacillus anthracis. Koch found that he could transmit anthrax from one animal to another by taking a small sample of blood from the infected animal and injecting it into a healthy one, this caused the healthy animal to become sick.
He found that he could grow the bacteria in a nutrient broth inject it into a heal