Homeothermic To Hyperpolarization (Biology)

Homeothermic The process of maintaining a constant body temperature.

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. See also homeobox.

Hominoids A collective term used for humans and apes.

Homogamy The tendency for similar types to mate with similar types.

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.

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.

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.


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.

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.

Homonomy (serial homology) Organs that are identical or of similar construction within the same organism (e.g., segments in annelid worms).

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.

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.

Homosexual Having an affection for members of the same sex, i.e., male attracted to male or female attracted to female (lesbianism).

Homosporous Plants that produce a single type of spore that develops into a bisexual gametophyte and has both male and female sex organs.

homozygous Having two identical forms of a particular gene.

Hooke, Robert (1635-1703) 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 spiral 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.

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.

Hopkins, Frederick Gowland (1861-1947) 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.

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.

Houssay, Bernardo Alberto (1887-1971) Argentine Physiologist Bernardo Alberto Houssay was born in Buenos Aires, Argentina, on April 10, 1887, to Dr. Albert and Clara Houssay (nee Laffont), who had come to Argentina from France. His father was a barrister. Houssay’s early education was at a private school, the Colegio Britanico. 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.

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.

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."

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.

Hyaline A clear or transparent structure such as a wing of a dragonfly (e.g., Aeshna canadensis and Sym-petrum vicinum), or an amorphous texture due to accumulation of intra- or extracellular material.

Hybrid The offspring produced by genetically distinct different parents. Mating can be within species (intraspecific) as well as between species (interspecific).

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.

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.


Hybrid vigor Increased vitality or success of a hybrid over its inbred parents.

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.

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) ^ A (aqueous solution).

Hydrocarbon A compound made of only carbon and hydrogen.

Hydrocephalus A condition in which the head becomes enlarged and expanded beyond normal size due to congenital or other causes.

Hydrogenase An enzyme, dihydrogen acceptor oxi-doreductase, 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.

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.

Hydrogen ion (hydron) A single proton with a charge of +1.

Hydrolase An enzyme of EC class 3, also known as a hydro-lyase, that catalyzes the hydrolysis of a substrate.

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+.

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.

Hydrophilicity The tendency of a molecule to be sol-vated by water.

Hydrophobic A molecule or substance that does not associate, bond, or dissolve in water. Hydrophobic molecules dissolve easily in fats and oils.

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.

Hydrophobicity The association of nonpolar groups or molecules in an aqueous environment that arises from the tendency of water to exclude nonpolar molecules.

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.

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.

Hydroxyl ion (-OH). One atom each of oxygen and hydrogen bonded into an ion that carries a negative charge.

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.

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.

Hyperendemic Disease organisms that exist in a host population at very high rates. The human papillo-mavirus is a large group of viruses that are hyperen-demic in humans. They cause common warts, such as plantar and genital warts.

Science and the Spiritual Factor

By John McConnell

For the most part, the scientific community has avoided questions that cannot be measured, analyzed, and evaluated using their present tools and procedures. An example of this is the scientist who stated that she would consider the possible existence of a soul—as soon as they determined the part of the brain that provided communication with the soul.

Most people believe that they have a soul and consider the issues of life after death, the existence and nature of God, and the meaning of life. Religious beliefs and values enable them to relate to the unknown with benefit to their personal values, conduct, and happiness. However, most scientists by their indifference and skepticism have tended to undermine the value of faith and treat it as superstition.

In these matters, hypotheses that cannot be proved or disproved should be judged, or at least acknowledged of value, by the results in the lives of individuals who practice their faith.

The one belief that science has mathematically proved is the existence and benefit of love. (See Von Foerster, Heinz. Logical Structure of Environment and Its Internal Representation. Zeeland, Mich.: Herman Miller Inc., 1963.) Love can thus provide the test of hypotheses about phenomena of mind and spirit that presently defy explanation. So now ultimate questions about reality, which remain profound mysteries that cannot be approached by scientific measurements or methods, can nevertheless be recognized and pursued through articles of faith and practice. If reality is consistent, then the truth and the value of a faith or belief can be judged by the increase and depth of love—or creative altruism—in the lives of those who practice at belief.

Prayer to a personal God and practice of the Sermon on the Mount has inspired personal love and courage and led to great peaceful changes for social freedom and justice. (See This Freedom Whence by John Wesley Brady, and Communism and Christ by Charles Loury.)

Science must no longer negate the values of religious belief, but rather strengthen and support the importance of faith—of using the personal metaphor that increases the well-being of the individual, that deepens relationships with people and kinship with life on Earth.

The scientific approach can at the same time diminish religious intolerance by calling attention to the nature of metaphor or hypothesis. A hypothesis can be exciting and useful and obtain confidence from its supporters who may totally believe in its validity. Nevertheless, by its nature there must be, and can be, recognition and respect for people with a different hypothesis about reality. Where approval for a different religious or philosophical doctrine may be impossible, there still can be deep approval of the love that is motivated and demonstrated in connection with it.

The scientific community should also give importance to any phenomenon that greatly affects human values and potentials, even though scientific explanation eludes its grasp. There is overwhelming evidence of answered prayer in the lives of many people. The incidence of favorable coincidence in deeply dedicated people who pray with fervor and faith should be studied and compared with other people who practice a purely psychological approach to needs. The nature and extent of coincidences that run contrary to probability theory should be more thoroughly explored. Perhaps there is no satisfactory explanation possible. But this should not cause science to ignore the phenomenon or its causes and effects in the lives of people.

Of course, scientists would make a careful distinction between a phenomenon and its effects, on the other hand, explaining what it is and how it works. Great benefit could come from more attention to phenomenology and the many instances of its effects on the lives of people.

The nature and extent of spiritual healing should be more critically examined. While success seems a random effect that is rare, many proven cases defy medical explanation.

By its very nature, any effort to make Earth a healthy, peaceful planet must be achieved through a great spiritual awakening of a kind that will foster the nurture and care of Earth and a creative happy life for all its people.

Hyperparasitoid A parasitoid that lives on another parasitoid, e.g., members of the families Perilampidae, Signiphoridae, and Elasmidae.

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.

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.

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