Biology H
What is Haber-Weiss reaction ?
The Haber-Weiss cycle consists of the following two reactions:
H2O2 + OH. Ô H2O + O2– + H+ and
H2O2 + O2– Ô O2 + OH– + OH.
The second reaction achieved notoriety as a possible source of hydroxyl radicals. However, it has a negligible rate constant. It is believed that iron(III) complexes can catalyze this reaction: first Fe(III) is reduced by superoxide, followed by oxidation by dihydrogen peroxide.
What is habituation ?
Reaction to the repeated presentation of the same stimulus that has no special significance and that causes reduced attention to the stimulus. Shortterm habituation lasts for only minutes, while longerterm habituation could last for weeks.
What is Haeckelian recapitulation (embryonic recapitulation) ?
A clade goes through, in its development, an ontogenetic stage that is present in the adults of its sister group. Named for Ernst Haeckel (1834–1919), who promoted the idea that the development of the human embryo in the womb is a rerun (recapitulation) of the steps in humanity’s rise from a primitive creature. Haeckel’s views about evolution have been refuted by most scientists.
What is half-life ?
For a given reaction the half-life, t1/2, of a reactant is the time required for its concentration to reach a value that is the arithmetic mean of its initial and final (equilibrium) value. For a reactant that is entirely consumed, it is the time taken for the reactant concentration to fall to one-half of its initial value. For a first-order reaction, the half-life of the reactant can be called the half-life of the reaction. In nuclear chemistry, (radioactive) half-life is defined, for a simple radioactive decay process, as the time required for the activity to decrease to half its value by that process.
What is haloperoxidase ?
A PEROXIDASE that catalyzes the oxidative transformation of halides to XO– (X being Cl, Br, or I) or to organic halogen compounds. Most are HEME proteins, but some bromoperoxidases from algae are vanadium-containing ENZYMEs.
What is halophyte ?
A plant that has adapted to grow in saltrich soils or salt-rich air, e.g., glassworts (Salicornia virginica). Obligatory halophytes need salt, whereas facultative halophytes can live in freshwater conditions as well.
What is hansch analysis ?
The investigation of the quantitative relationship between the biological activity of a series of compounds and their physicochemical substituent or global parameters representing hydrophobic, electronic, steric, and other effects using multiple regression correlation methodology.
What is haploid cell ?
A cell containing one set of chromosomes. Sperm and egg cells are haploid.
What is haplozoans ?
Extinct echinoderms of the Cambrian era that include two classes, Cycloidea and Cyamoidea. Cyamoids have bilateral symmetry, and cycloids are dome-shaped with radial symmetry. They are quite uncharacteristic of echinoderms, although they have a skeletal structure that relates them. Otherwise, they have uncertain affinities to all other echinoderms and may provide a link between echinoderms and fish.
What is hapten ?
A molecule (usually a small organic molecule) that can be bound to an ANTIGENic determinant/epitope. Usually they are too small to give a response of their own. They become antigenic if they are coupled to a suitable macromolecule, such as a protein.
What is hapto ?
The hapto symbol, η (Greek eta), with numerical superscript, provides a topological description for the bonding of hydrocarbons or other π-electron systems to metals by indicating the connectivity between the LIGAND and the CENTRAL ATOM. The symbol is prefixed to the ligand name or to that portion of the ligand name most appropriate. The superscript numerical index on the right indicates the number of COORDINATING atoms in the ligand that bind to the metal. Examples:
[PtCl2(C2H4)(NH3)] amminedichloro (η2-ethene)platinum
[Fe(η5-C5H5)2] bis (η5-cyclopentadienyl)iron (ferrocene)
What is hard acid ?
A LEWIS ACID with an acceptor center of low polarizability. It preferentially associates with HARD BASEs rather than with soft bases, in a qualitative sense (sometimes called HSAB rule). Conversely, a soft acid possesses an acceptor center of high polarizability and exhibits the reverse preference for a partner for COORDINATION.
What is hard base ?
A LEWIS BASE with a donor center of low polarizability; the converse applies to soft bases.
What is hard drug ?
A nonmetabolizable compound, characterized either by high lipid solubility and accumulation in adipose tissues and organelles, or by high water solubility. In the lay press, the term hard drug refers to a powerful DRUG of abuse such as cocaine or heroin.
Who was Hardy-Weinberg theorem ?
A mathematical theorem that describes a population that is not evolving under certain conditions. First proposed in 1908 by G. H. Hardy, an English mathematician, and B. W. Weinberg, a German physician, although both were working independently of each other. The theory describes the frequencies of various genotypes in a population and the ability to predict how the frequencies will change in future generations based on certain assumptions not being violated, such as the absence of mutation, the absence of migration or selection, random mating, and an infinite population size. In other words, in the absence of any of these factors, the allele frequencies and the frequencies of the different genotypes will remain the same from one generation to the next, and genetic recombination due to sexual reproduction will not result in any changes in allele frequencies or genotype frequencies.
What is harelip (cleft lip) ?
A congenital (birth) deformity caused by a failure of developing tissues to fuse; a cleft in the upper lip, found on one or both sides of the midline. Often associated with a cleft palate.
What is haustorium ?
A specialized structure of a parasitic plant or entophyte, an organism that lives at least part of its life cycle within a host plant, that penetrates the living host and absorbs nutrients. In parasitic fungi, it is a hyphal tip that penetrates the host but not the cell membrane.
What is Haversian system (osteon) ?
A structural composition of compact bone that contains a Haversian canal, a longitudinally arranged vascular channel in the center of the osteon containing blood vessels and nerves; Haversian lamella, the circumferentially arranged layers of osteoid and osteocytes surrounding the canal; and the canaliculi, fine channels through the bone that provide a link between osteocytes.
What is heart ?
A muscular organ composed of cardiac muscle that pumps blood throughout the body.
What is heat ?
Kinetic energy in the process of being transferred from one object to another due to a temperature difference. It moves in one of three ways: radiation, conduction, or convection.
What is heath hen ?
Along with the passenger pigeon, the heath hen (Tympanuchus cupido cupido), a relative of the prairie chicken, is an example of extinction by human disturbance. Last observed on March 11, 1932, at James Green’s farm in West Tisbury, Martha’s Vineyard, Massachusetts, it became the victim of habitat conversion to crops and pastureland, as well as being hunted as game and for sport. It was a grounddwelling/nesting meadows seedeater ranging from Maine to Chesapeake Bay.
What is heat-shock proteins (HSPs) ?
A family of closely related proteins, widely distributed in virtually all organisms (plants, animals, microorganisms, and humans). Even though they are found in widely different sources, they show structural similarity. HSP expression increases in response to physiological stresses such as rise in temperature, pH changes, and oxygen deprivation. Many of these stresses can disrupt the three-dimensional structure, or folding, of a cell’s proteins, and so HSPs bind to those damaged proteins, helping them refold back into their proper shapes. They also help newly synthesized polypeptides fold and prevent premature interactions with other proteins. HSPs, also called chaperones, aid in the transport of proteins throughout the cell’s various compartments and aid in the destruction of peptides specific to tumors or pathogens.
What is hectare ?
A unit of land measurement. One hectare (ha) is equal to 2.5 acres.
What is helium ?
An inert gas; an element with atomic number 2. Helium is produced in stars and is the second most abundant element in the universe. Its atom contains two protons, two neutrons, and two electrons.
What is helix ?
A particular rigid left- or right-handed arrangement of a polymeric chain, characterized by the number of strands, the number (n) of units per turn, and its pitch (p), the distance the helix rises along its axis per full turn. Examples of single-stranded helices are the protein helices: α-helix: n = 3.6, p = 540 picometer; 310-helix: n = 3.0, p = 600 picometer; π-helix: n = 4.4, p = 520 picometer.
What is helminth ?
A worm or wormlike organism. Three major helminths exist that affect humans: the nematodes (roundworm), trematodes (flukes), and cestodes (tapeworms).
What is helper T cell ?
A type of T cell needed to turn on antibody production by activating cytotoxic T cells and causing other immune responses in the body. They aid in helping B cells to make antibodies against thymusdependent antigens. TH1 and TH2 helper T cells secrete materials (interleukins and gamma interferon) that help cell-mediated immune response.
What is heme ?
A near-planar COORDINATION complex obtained from iron and the dianionic form of PORPHYRIN. Derivatives are known with substitutes at various positions on the ring named a, b, c, d, etc. Heme b, derived from PROTOPORPHYRIN IX, is the most frequently occurring heme.
What is hemerythrin ?
A dioxygen-carrying protein from marine invertebrates, containing an oxo-bridged dinuclear iron center.
What is hemichordates ?
Consisting of only a few hundred species, the hemichordates include the acorn worms (e.g., Saccoglossus), which burrow in sand and mud, and pterobranchs (e.g., Rhabdopleura), tiny colonial animals. The hemichordates have a tripartite (threefold) division of the body, pharyngeal gill slit, a form of dorsal nerve cord, and a similar structure to a notochord. Graptolites, which comprise the class Graptolithina, are common fossils in Ordovician and Silurian rocks and are now considered hemichordates.
What is hemochromatosis ?
A genetic condition of massive iron overload leading to cirrhosis and/or other tissue damage attributable to iron.
What is hemocyanin ?
A dioxygen-carrying protein (from invertebrates, e.g., arthropods and mollusks), containing dinuclear TYPE 3 COPPER sites.
What is hemoglobin ?
A dioxygen-carrying heme protein of red blood cells, generally consisting of two alpha and two beta SUBUNITs, each containing one molecule of PROTOPORPHYRIN IX.
What is hemolymph ?
The body circulatory fluid found in invertebrates, functionally equivalent to the blood and lymph of the vertebrate circulatory system.
What is hemophilia ?
An inherited clotting problem that occurs, with few exceptions, in males. It delays coagulation of the blood, making hemorrhage difficult to control. Hemophilia A, called classical or standard hemophilia, is the most common form of the disorder and is due to a deficiency of a factor called factor VIII (FVIII). Hemophilia B, also called Christmas disease, is due to a deficiency of factor IX (FIX). A person with hemophilia does not bleed any faster than a normal person, but the bleeding continues for a much longer time.
What is hemorrhoids (piles) ?
Abnormally enlarged or dilated veins around the anal opening.adrenal gland. He shared with Edward C. Kendall and Tadeus REICHSTEIN the 1950 Nobel Prize in physiology or medicine for this pioneering work in the treatment of rheumatoid arthritis with cortisone and ACTH.
He authored many papers in the field of rheumatology, received numerous awards, and belonged to several scientific organizations throughout his life. He died on March 30, 1965, in Ocho Rios, Jamaica
What is hepatic portal vessel ?
A system of veins that delivers blood from glands and organs of the gastrointestinal tract (GIT) to the liver. A portal vein enters the liver at the porta hepatis and distributes venules and sinusoids, capillarylike vessels where blood becomes purified, before it goes into the inferior vena cava. The hepatic artery carries oxygen-rich blood to the liver from the heart and mixes with the portal vein in the sinusoids. Thus two filtering systems, the capillaries of the GIT and sinusoids of the liver, perform their tasks on the blood.
What is herb ?
Part of a plant that is used for medicinal, food, or aromatic properties.
What is herbivore ?
An animal that only eats plants to obtain its necessary nutrients for survival.
What is hermaphrodite ?
An individual with both male and female sexual reproductive organs and that functions as both male and female, producing both egg and sperm. The individual can be a simultaneous hermaphrodite, having both types of organs at the same time, or a sequential or successive hermaphrodite that has one type early in life and the other type later. If the female part forms first it is called protogynous hermaphroditism; it is called protandrous hermaphroditism if the male forms first.
Some examples of hermaphrodites are most flukes, tapeworms, gastrotriches, earthworms, and even some humans.
In plants, it is when male and female organs occur in the same flower of a single individual.
What is hernia ?
A protrusion of a tissue or organ or a part of one through the wall of the abdominal cavity or other area. A hiatal hernia has part of the stomach protruding through the diaphragm and up into the chest and affects about 15 percent of the human population.
Who was Herodotus ?
A Greek who lived ca. 400 B.C.E. and observed fossil seashells in the rocks of mountains. He interpreted these remains as once-living marine organisms and concluded that these areas must have been submerged in the past.
Who was Hess, Walter Rudolf ?
Hess, Walter Rudolf (1881–1973) was Swiss Physiologist Walter Rudolf Hess was born in Frauenfeld, in Aargau Canton, Switzerland, on March 17, 1881, to a teacher of physics. He received a doctor of medicine in 1906 from the University of Zurich.
Originally he began his career as an ophthalmologist for six years (1906–12), but dropped his practice and turned to the study of physiology at the University of Bonn. In 1917 he was nominated director of the Physiological Institute at Zurich, with corresponding teaching responsibilities, and later director of the Physiological Institute (1917–51) at the University of Zürich.
He spent most of his life investigating the responses of behavior, respiration, and blood pressure by stimulating the diencephalon of cats using his own techniques. He was awarded the Nobel Prize in 1949 for his work related to the diencephalon.
Among Hess’s books is The Biology of Mind (1964). He died on August 12, 1973.
What is heterochromatin ?
Most cell nuclei contain varying amounts of functional (active) and nonfunctional (inactive) DNA. Functional DNA is called euchromatin, while nonfunctional or inactive is called heterochromatin. The latter is DNA that is so tightly packaged it cannot transcript. Two forms exist: constitutive heterochromatin, where portions of the chromosome are always inactive, and facultative heterochromatin, where portions of the chromosome are active in some cells at one time but are inactive now (such as the Y chromosome and Barr bodies). A gene is closed or inaccessible and not expressed if it is heterochromatin.
What is heterochrony ?
An evolutionary change in developmental timing in the relative time or rate of appearance or development of a character. The morphological outcomes of changes in rates and timing of development are paedomorphosis (less growth) or peramorphosis (more growth). Peramorphosis is the extended or exaggerated shape of the adult descendant relative to the adult ancestor; its later ontogenetic stages retain characteristics from earlier stages of an ancestor. Paedomorphosis is where the adult descendant retains a more juvenile looking shape or looks more like the juvenile form of its adult ancestor; its development goes further than the ancestor and produces exaggerated adult traits. Paedomorphosis can happen as a result of beginning late (postdisplacement), ending early (progensis), or slowing in the growth rate (neoteny). Likewise, peramorphosis can result from starting early (predisplacement), ending late (hypermorphosis), or having a greater growth rate (acceleration).
What is heterocyst ?
A large, thick-walled, specialized cell working in anoxic (oxygen absent) conditions that engages in nitrogen fixation from the air on some filamentous cyanobacteria; an autotrophic organism.
What is heteroecious ?
A parasite that starts its life cycle on one organism and then affects a second host species to complete the cycle, e.g., peach-potato aphid (Myzus persicae).
What is heterogamy ?
Producing gametes of two different types from unlike individuals, e.g., egg and sperm. The tendency for unlike types to mate with unlike types.
What is heterolysis (heterolytic cleavage or heterolytic fission) ?
The cleavage of a bond so that both bonding electrons remain with one of the two fragments between which the bond is broken.
What is heteromorphic ?
Having different forms at different periods of the life cycle, as in stages of insect metamorphosis and the life cycle of modern plants, where the sporophyte and gametophyte generations have different morphology.
What is Heteroptera ?
A suborder known as true bugs. They have very distinctive front wings, called hemelytra. The basal half is leathery and the apical half is membranous. They have elongate, piercing-sucking mouthparts. Worldwide in distribution, there are more than 50,000 species. Two families are ectoparasites. The Cimicidae (bed bugs) live on birds and mammals including humans, and the Polyctenidae (bat bugs) live on bats.
What is heteroreceptor ?
A RECEPTOR regulating the synthesis and/or the release of mediators other than its own ligand.
What is heterosexual ?
Having an affection for members of the opposite sex, i.e., male attracted to female.
What is heterosis ?
Vigorous, productive hybrids that result from a directed cross between two pure-breeding plant lines.
What is heterosporous ?
Producing two types of spores differing in size and sex. Plant sporophytes that produce two kinds of spores that develop into either male or female gametophytes.
What is heterotrophic organisms ?
Organisms that are not able to synthesize cell components from carbon dioxide as a sole carbon source. Heterotrophic organisms use preformed oxidizable organic SUBSTRATEs such as glucose as carbon and energy sources, while energy is gained through chemical processes (chemoheterotrophy) or through light sources (photoheterotrophy).
What is heterozygote ?
A diploid organism or cell that has inherited different alleles, at a particular locus, from each parent (i.e., Aa individual); a form of polymorphism.
What is heterozygote advantage (overdominance) ?
The evolutionary mechanism that ensures that eukaryotic heterozygote individuals (Aa) leave more offspring than homozygote (AA or aa) individuals, thereby preserving genetic variation; condition in which heterozygotes have higher fitness than homozygotes.
What is heterozygous ?
Two different alleles of a particular gene present within the same cell; a diploid individual having different alleles of one or more genes producing gametes of different genotypes.
Who was Heymans, Corneille Jean-François ?
Heymans, Corneille Jean-François (1892–1968) was Belgian Physiologist Corneille Jean-François Heymans was born in Ghent, Belgium, on March 28, 1892, to J. F. Heymans, a former professor of pharmacology and rector of the University of Ghent, and who founded the J. F. Heymans Institute of Pharmacology and Therapeutics at the same university.
Corneille received his secondary education at the St. Lievens College (Ghent), St. Jozefs College (Turnhout), and St. Barbara College (Ghent). He pursued his medical education at the University of Ghent and received a doctor’s degree in 1920. After graduation he worked at various colleges until 1922, when he became lecturer in pharmacodynamics at the University of Ghent. In 1930 he succeeded his father as professor of pharmacology and was appointed head of the department of pharmacology, pharmacodynamics, and toxicology; at the same time he became director of the J. F. Heymans Institute, retiring in 1963.
His research was directed toward the physiology and pharmacology of respiration, blood circulation, metabolism, and pharmacological problems. He discovered chemoreceptors in the cardio-aortic and carotid sinus areas, and made contributions to knowledge of arterial blood pressure and hypertension. He was awarded the Nobel Prize in physiology or medicine in 1938 for his work on the regulatory effect of the cardio-aortic and the carotid sinus areas in the regulation of respiration.
He wrote more than 800 scientific papers, was active in a number of professional organizations, and was publisher and editor-in-chief of the Archives Internationales de Pharmacodynamie et de Thérapie, founded in 1895 by his father and Professor E. Gley in Paris. He died on July 18, 1968, in Knokke.
What is hibernation ?
A physiological state of dormancy, a sleeplike condition, that lowers body temperature, slows the heart and breathing, and reduces the need for food for extended periods of time, usually during periods of cold. Examples of hibernators are bears, bats, snakes, frogs, squirrels, turtles, and some birds.
Who was Hill, Archibald Vivian ?
Hill, Archibald Vivian (1886–1977) British Physiologist Archibald Vivian Hill was born in Bristol on September 26, 1886. After an early education at Blundell’s School, Tiverton, he entered Trinity College, Cambridge, with scholarships. He studied mathematics but was urged to go into physiology by one of his teachers, Walter Morley Fletcher.
In 1909 he began study on the nature of muscular contraction and the dependence of heat production on the length of muscle fiber. From 1911 to 1914, until the start of World War I, he continued his work on the physiology of muscular contraction at Cambridge as well as other studies on nerve impulse, hemoglobin, and calorimetry.
In 1926 he was appointed the Royal Society’s Foulerton research professor and was in charge of the biophysics laboratory at University College until 1952.
His work on muscle function, especially the observation and measurement of thermal changes associated with muscle function, was later extended to similar studies on the mechanism of the passage of nerve impulses. He coined the term oxygen debt to describe the process of recovery after exercise.
He discovered and measured heat production associated with nerve impulses and analyzed physical and chemical changes associated with nerve excitation, among other studies. In 1922 he won the Nobel Prize in physiology or medicine (with Otto MEYERHOF) for work on chemical and mechanical events in muscle contraction such as the production of heat in muscles. This research helped establish the origin of muscular force in the breakdown of carbohydrates while forming lactic acid in the muscle.
His important works include Muscular Activity (1926), Muscular Movement in Man (1927), Living Machinery (1927), The Ethical Dilemma of Science and Other Writings (1960), and Traits and Trials in Physiology (1965).
He was a member of several scientific societies and was elected a fellow of the Royal Society in 1918, serving as secretary for the period 1935–45, and foreign secretary in 1946. Hill died on June 3, 1977.
What is hill topping ?
A behavior exhibited by butterflies where males and females congregate at a high point in the landscape, increasing each individual butterfly’s chance of finding a mate.
What is hilum ?
The area where blood vessels, nerves, and ducts enter an organ.
What is HiPIP ?
Formerly used abbreviation for high-potential IRON–SULFUR PROTEIN, now classed as a FERREDOXIN. An ELECTRON TRANSFER PROTEIN from photosynthetic and other bacteria, containing a [4FE-4S] CLUSTER that undergoes oxidation-reduction between the [4Fe-4S]2+ and [4Fe-4S]3+ states.
What is hirudin ?
A nonenzymatic chemical secreted from the leech that prevents blood clotting. Today, the genetically engineered lepirudin and desirudin and the synthetic bivalirudin are used as anticoagulants.
What is histamine ?
A hormone and chemical transmitter found in plant and animal tissues. In humans it is involved in local immune response that will cause blood vessels to dilate during an inflammatory response; also regulates stomach acid production, dilates capillaries, and decreases blood pressure. It increases permeability of the walls of blood vessels by vasodilation when released from mast cells and causes the common symptoms of allergies such as running nose and watering eyes. It will also shut the airways in order to prevent allergens from entering, making it difficult to breath. Antihistamines are used to counteract this reaction.
What is histology ?
The study of the microscopic structure of plant and animal tissue.
What is histone ?
A basic unit of chromatin structure; several types of protein characteristically associated with the DNA in chromosomes in the cell nucleus of eukaryotes. They function to coil DNA into nucleosomes, which are a combination of eight histones (a pair each of H2A, H2B, H3, and H4) wrapped by two turns of a DNA molecule. A high number of positively charged amino acids bind to the negatively charged DNA.
What is holoblastic cleavage ?
A complete and equal division of the egg in an early embryo that has little yolk. Characteristic of amphibians, mammals, nonvertebrate chordates, echinoderms, most mollusks, annelids, flatworms, and nematodes.
What is holocene ?
The present epoch of geological time starting approximately 10,000 years ago to the present.
What is holoenzyme ?
An ENZYME containing its characteristic PROSTHETIC GROUP(s) and/or metal(s).
What is holotype ?
The exact specimen of a new animal or plant representing what is meant by the new name and designated so by publication. The holotype specimen does not have to be the first ever collected, but it is the official one with which all others are compared.
What is homeobox (HOX genes) ?
A short stretch of similar or identical 180-base-pair (nucleotide) sequences of DNA within a homeotic gene in most eukaryotic organisms that plays a major role in controlling body development by regulating patterns of differentiation. Homeotic genes create segments in an embryo that become specific organs or tissues. Homeoboxes determine positional cell differentiation and development. Mutations in these genes will cause one body part to convert into a totally different one.
What is homeosis ?
The replacement of one body part by another caused by mutations or environmental factors initiating developmental anomalies.
What is homeostasis ?
The ability of an organism to automatically maintain a constant internal condition regardless of the external environment.
What is homeothermic ?
The process of maintaining a constant body temperature.
What is homeotic gene ?
Controls the overall body plan of animals by controlling the developmental fate of groups of cells. A homeotic mutation results in the replacement of one type of body part in place of another.
What is hominoids ?
A collective term used for humans and apes.
What is homogamy ?
The tendency for similar types to mate with similar types.
What is homologous chromosomes ?
A pair of chromosomes (homologues); contains the same length, gene position, centromere location, and same characters at corresponding loci, with one homologue coming from the mother and another from the father. Homologous chromosomes line up with each other and then separate during meiosis.
What is homologous structures ?
Characteristics or parts in different animals that may have served the same general function and are shared with related species and inherited from a common ancestor. In related species, they may have the same evolutionary origin, but their functions may differ. Examples include the front fins of a whale, forelimb of a bat or horse, and human and chimp arm bones.
What is homologue ?
Used to describe a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene group, a peptide residue, etc. Also refers to one member of a chromosome pair.
What is homology ?
The similarity of characteristics that result from a shared ancestry; the relationship between structures in different organisms that are united by modification of the same structure, gene, or set of genes of a common ancestor.
What is homolysis (homolytic cleavage or homolytic fission) ?
The cleavage of a bond so that each of the molecular fragments between which the bond is broken retains one of the bonding electrons.
What is homonomy (serial homology) ?
Organs that are identical or of similar construction within the same organism (e.g., segments in annelid worms).
What is homoplasy ?
The possession by two or more species of a similar characteristic that has not evolved in those species from a common ancestor. Instead, these characteristics derive from convergent evolution, parallel evolution, or character reversal. An example is the wings of insects and the wings of the flying dinosaurs, the pterosaurs.
What is Homoptera ?
An order of insects with beaklike piercing-sucking mouthparts that include cicadas, aphids, tree and leaf hoppers, and scale insects. The forewings are either wholly membranous or wholly leathery. The wings rest on the back in the shape of a tent, e.g., cicadas, frog-hoppers, and aphids. They are found worldwide and are plant feeders.
What is homosexual ?
Having an affection for members of the same sex, i.e., male attracted to male or female attracted to female (lesbianism).
What is homosporous ?
Plants that produce a single type of spore that develops into a bisexual gametophyte and has both male and female sex organs.
What is homozygous ?
Having two identical forms of a particular gene.
Who was Hooke, Robert ?
Hooke, Robert (1635–1703) was English Physicist, Astronomer Considered one of the greatest scientists of the 17th century, and second only to Sir Isaac Newton, Robert Hooke was born in Freshwater, Isle of Wight, on July 18, 1635, the son of John Hooke, a clergyman.
He entered Westminster School in 1648 at the age of 13, and then attended Christ College, Oxford, in 1653, where many of the best English scientists were congregating, such as Robert Boyle, Christopher Wren (astronomer), John Wilkins (founder of the Royal Society), and William Petty (cartographer). He never received a bachelor’s degree, was nominated for the M.A. in 1663 by Lord Clarendon, the chancellor of the university, and given an M.D. at Doctors’ Commons in 1691, also by patronage.
Hooke’s first publication of his own work in 1661 was a small pamphlet on capillary action. Shortly after, in 1662, he was appointed the first curator of experiments at the newly founded Royal Society of London. The society, also known as The Royal Society of London for Improving Natural Knowledge, was founded on November 28, 1660, to discuss the latest developments in science, philosophy, and the arts. The founding fathers, consisting of 12 men, began after a lecture by Christopher Wren at Gresham College. The group included Wren, Boyle, John Wilkins, Sir Robert Moray, and William Brouncker. This position gave Hooke a unique opportunity to familiarize himself with the latest progress in science.
Part of Hooke’s job was to demonstrate and lecture on several experiments at the Royal Society at each weekly meeting. This led him to many observations and inventions in a number of fields, including astronomy, physics, and meteorology. He excelled at this job, and in 1663 Hooke was elected a fellow of the society, becoming not just an employee but on equal footing with the other members.
Hooke took advantage of his experience and position. He invented the first reflecting telescope, the spi ral spring in watches, an iris diaphragm for telescopes (now used in cameras instead), the universal joint, the first screw-divided quadrant, a compound microscope, an odometer, a wheel-cutting machine, a hearing aid, a new type of glass, and carriage improvements. Despite all of these accomplishments, he remains one of the most neglected scientists, due to his argumentative style and the apparent retribution by his enemies such as Newton.
Hooke became a professor of physics at Gresham College in 1665 and stayed there for his entire life. It was also where the Royal Society met until after his death. Hooke also served as the society’s secretary from 1677 to 1683.
The year 1665 is another milestone year for Hooke, since that is when he published his major work Micrographia, the first treatment on microscopy, and where he demonstrated his remarkable powers of observation and his skillful microscopic investigation in the fields of botany, chemistry, and meteorology. Within this work, he made many acute observations, illustrated with intricate drawings, and proposed several theories.
Hooke was the first to discover plant cells and he coined the word cell, which he attributed to the porous structure of cork, although he failed to realize that cells were the basic units of life. He made detailed observations, some of the first, on insects, sponges, bryozoans, foraminifera, and even birds. He was the first to examine fossils under a microscope and concluded that many fossils represented organisms that no longer existed on Earth.
Because of his controversies—he had competing claims with Christian Huyghens over the invention of the spring regulator and with Newton, first over optics (1672) and, second, over the formulation of the inverse square law of gravitation (1686)—Hooke fell out of favor in the scientific community. He died in London on March 3, 1703, and was buried in Bishopsgate. However, sometime in the 19th century his bones were removed, and no one knows where he is buried today.
What is hookworms ?
Tiny parasitic nematode worms belonging to the family Ancylostomatidae. They attach themselves to the intestinal walls of humans with hooked mouthparts. Hookworms (Necator and Ancylostoma spp.) are responsible for ancylostomiasis.
Who was Hopkins, Frederick Gowland ?
Hopkins, Frederick Gowland (1861–1947) was English Biochemist Frederick Gowland Hopkins was born on June 20, 1861, in Eastbourne, England, to a bookseller in Bishopsgate Street, London, who died when Frederick was an infant.
In 1871 he attended the City of London School, and at the early age of 17, he published a paper in The Entomologist on the bombardier beetle. He went to University College, London, where he became the assistant to Sir Thomas Stevenson, an expert on poisoning. In 1888 he became a medical student at Guy’s Hospital, London.
In 1894 he graduated in medicine and taught physiology and toxicology at Guy’s Hospital for four years, and in 1898 he moved to Cambridge. He was appointed fellow and tutor at Emmanuel College, Cambridge.
Hopkins established biochemistry as a field in Great Britain. He discovered how to isolate the amino acid tryptophan and identified its structure, discovered enzymes, and isolated glutathione. For his research on discovering growth-stimulating vitamin, which he called “accessory substances,” he was awarded the Nobel Prize in 1929 in medicine or physiology. He actually isolated vitamins C, A, and D.
Hopkins was knighted in 1925 and received the Order of Merit in 1935. Hopkins died in 1947 at the age of 86. The Sir Frederick Gowland Hopkins Memorial Lecture of the Biochemical Society, named in his honor, is presented by a lecturer to assess the impact of recent advances in his or her particular field on developments in biochemistry. The award is made every two to three years and the lecturer is presented with a medal and £1,000.
What is hormone ?
A substance produced by endocrine glands, released in very low concentration into the bloodstream, and which exerts regulatory effects on specific organs or tissues distant from the site of secretion.
Who was Houssay, Bernardo Alberto ?
Houssay, Bernardo Alberto (1887–1971) was Argentine Physiologist Bernardo Alberto Houssay was born in Buenos Aires, Argentina, on April 10, 1887, to Dr. Albert and Clara Houssay (née Laffont), who had come to Argentina from France. His father was a barrister. Houssay’s early education was at a private school, the Colegio Británico. He then entered the School of Pharmacy of the University of Buenos Aires at the age of 14, graduating in 1904. He had already begun studying medicine and, in 1907, before completing his studies, took up a post in the department of physiology and began research that resulted in his receiving an M.D. in 1911.
In 1910 he was appointed professor of physiology in the university’s school of veterinary medicine. In 1919 he became professor of physiology in the medical school at Buenos Aires University and also organized the Institute of Physiology at the medical school, making it a center with an international reputation. He remained professor and director of the institute until 1943, when the government then in power deprived him of his post, the result of his voicing the opinion that there should be effective democracy in the country. In 1955 a new government reinstated him in the university.
He demonstrated that a hormone secreted by the pituitary prevented metabolism of sugar and that injections of pituitary extract induced symptoms of diabetes. He was awarded the 1947 Nobel Prize in physiology or medicine for this work on the functions of the pituitary gland.
In 1949 he came to the United States as a special research fellow at the National Institutes of Health. During his lifetime, Houssay authored more than 500 papers and several books and won many scientific prizes and awards. He died on September 21, 1971.
Who was Human Genome Project ?
The Human Genome Project (HGP) is an international research effort to determine the DNA sequence of the entire human genome. Contributors to the HGP include the National Institutes of Health (NIH); the U.S. Department of Energy (DOE); numerous universities throughout the United States; and international partners in the United Kingdom, France, Germany, Japan, and China.
Begun in 1990, the U.S. Human Genome Project is a long-term effort coordinated by the Department of Energy and the National Institutes of Health. The goals of the project are to identify all of the approximately 30,000 genes in human DNA; determine the sequences of the 3 billion chemical base pairs that make up human DNA; store this information in databases; improve tools for data analysis; transfer related technologies to the private sector; and address the ethical, legal, and social issues (ELSI) that may arise from the project.
What is humoral immunity ?
A form of immune reaction that attacks bacteria and viruses found in body fluids using antibodies synthesized by the B lymphocytes that circulate in blood plasma and lymph. These fluids were once called “humors.”
Who was Huxley, T. H. ?
A 19th-century evolutionist who discovered the unbroken horse lineage from the Eocene to the Holocene (recent) epochs, perhaps the longest and most complete evolutionary sequence in the fossil record.
What is hyaline ?
A clear or transparent structure such as a wing of a dragonfly (e.g., Aeshna canadensis and Sympetrum vicinum), or an amorphous texture due to accumulation of intra- or extracellular material.
What is hybrid ?
The offspring produced by genetically distinct different parents. Mating can be within species (intraspecific) as well as between species (interspecific).
What is hybridization ?
Producing hybrids from interbreeding two species. In genetics, it is the annealing of two complementary strands of DNA, or an RNA strand to a complementary DNA strand.
What is hybridoma ?
The fusion of two different cells to create a hybrid cell that secretes a single specific antibody, e.g., the fusion of a spleen cell and a cancer cell, or a T lymphocyte with a lymphoma cell.
What is hybrid vigor ?
Increased vitality or success of a hybrid over its inbred parents.
What is hybrid zone ?
A geographical territory where previously isolated or genetically distinct populations make contact and form hybrids. Where two geographical races of a single species overlap, hybrids and intermediates can outnumber the pure forms in the overlap region. What determines whether there will be two species or one is the balance between gene flow and selection against hybrids.
What is hydration ?
Addition of water or the elements of water (i.e., H and OH) to a molecular entity. The term is also used in a more restricted sense for the process: A (gas) Ô A (aqueous solution).
What is hydrocarbon ?
A compound made of only carbon and hydrogen.
What is hydrocephalus ?
A condition in which the head becomes enlarged and expanded beyond normal size due to congenital or other causes.
What is hydrogenase ?
An ENZYME, dihydrogen acceptor OXIDOREDUCTASE, that catalyzes the formation or oxidation of H2. Hydrogenases are of various types. One class ([Fe]-hydrogenases) contains only IRON–SULFUR CLUSTERs. The other major class ([NiFe]-hydrogenases) has a nickel-containing center and iron–sulfur clusters; a variation of the latter type ([NiFeSe]-hydrogenases) contains selenocysteine.
What is hydrogen bond ?
A form of association between an electronegative atom and a hydrogen atom attached to a second, relatively electronegative atom. It is best considered as an electrostatic interaction, heightened by the small size of hydrogen, that permits proximity of the interacting dipoles or charges. Both electronegative atoms are usually (but not necessarily) from the first row of the periodic table, e.g., N, O, or F. Hydrogen bonds can be intermolecular or intramolecular. With a few exceptions, usually involving fluorine, the associated energies are less than 20–25 kJ mol–1 (5–6 kcal mol–1).
A type of bond formed when the partially positive hydrogen atom of a polar covalent bond in one molecule is attracted to the partially negative atom of a polar covalent bond in another.
What is hydrogen ion (hydron) ?
A single proton with a charge of +1.
What is hydrolase ?
An ENZYME of EC class 3, also known as a hydro-LYASE, that catalyzes the HYDROLYSIS of a SUBSTRATE.
What is hydron ?
General name for the ion H+, either in natural abundance or where it is not desired to distinguish between the isotopes, such as proton for 1H+, deuteron for 2H+, and triton for 3H+.
What is hydrophilic ?
“Water loving.” The capacity of a molecular entity or of a substituent to interact with polar solvents, in particular with water, or with other polar groups. Hydrophilic molecules dissolve easily in water, but not in fats or oils.
What is hydrophilicity ?
The tendency of a molecule to be solvated by water.
What is hydrophobic ?
A molecule or substance that does not associate, bond, or dissolve in water. Hydrophobic molecules dissolve easily in fats and oils.
What is hydrophobic interaction ?
The tendency of hydrocarbons (or of lipophilic hydrocarbonlike groups in solutes) to form intermolecular aggregates in an aqueous medium as well as analogous intramolecular interactions. The name arises from the attribution of the phenomenon to the apparent repulsion between water and hydrocarbons. Use of the misleading alternative term hydrophobic bond is discouraged.
What is hydrophobicity ?
The association of nonpolar groups or molecules in an aqueous environment that arises from the tendency of water to exclude nonpolar molecules.
What is hydrostatic skeleton ?
A skeletal system created by the pressure caused by fluid-filled closed areas that support rigidity in an organism or one of its parts. Many invertebrates have hydrostatic skeletons. Earthworms are an example.
What is hydroxyl group ?
A functional group that has a hydrogen atom joined to an oxygen atom by a polar covalent bond (–OH). When put in solution with water, they form alcohols.
What is hydroxyl ion ?
(–OH). One atom each of oxygen and hydrogen bonded into an ion that carries a negative charge.
What is Hymenoptera ?
A large order of insects having two pairs of membranous wings (hymen means “membrane”) coupled by a row of tiny hooks. Examples include ants, bees, sawflies, and wasps.
What is hyperactive ?
A state of excessive muscular activity or a condition when a particular portion of the body is excessively active, e.g., a gland that produces too much of its particular hormone. Often referred to in attention deficit hyperactivity disorder (ADHD) in children.
What is hyperendemic ?
Disease organisms that exist in a host population at very high rates. The human papillomavirus is a large group of viruses that are hyperendemic in humans. They cause common warts, such as plantar and genital warts.
What is hyperparasitoid ?
A parasitoid that lives on another parasitoid, e.g., members of the families Perilampidae, Signiphoridae, and Elasmidae.
What is hyperplasia ?
The enlargement of an organ or tissue due to an increase in the number of cells. An example is benign prostatic hyperplasia, a nonmalignant (non-cancerous) enlargement of the prostate gland, common in older men.
What is hyperpolarization ?
An electrical state where the inside of a cell is made more negative relative to the outside than was the case at its resting potential of about –70 mV.
What is hypertonic solution ?
A solution whose solute concentration is high enough to cause water to move out of cells via osmosis.
What is hypertrophy ?
A condition where an organ or tissue enlarges or overgrows due to an increase in the size of its cells, not the number of cells.
What is hyperventilate ?
The act of excessive breathing, causing a loss of carbon dioxide in the blood. Other symptoms include faintness or fainting and numbness around the mouth, fingertips, or toes.
What is hypha ?
The threadlike, filamentous, absorptive structures of fungi. When combined to form mats, they are called mycelia and are the main body of fungi.
What is hypogynous ovary (superior ovary)?
Ovaries that have the calyx, corolla, and androecium attached below the ovary to the receptacle
What is hypoosmotic solution ?
A solution whose osmotic pressure is less than that of another solution.
What is hypothalamus ?
An area in the posterior part of the brain beneath the thalamus that contains nerve cells and controls many autonomic functions. Controls the pituitary gland and is the control site for feeding, drinking, temperature regulation, emotion, and motivation.
What is hypothesis ?
The formal declaration of the possible explanation of a set of observations that needs to be tested and proved.
What is hypotonic solution ?
A solution where solute concentration is low enough to cause water to move into cells via osmosis.
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