Vital Scientific Terms (H)

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Habitat
The natural conditions and environment, for example, forest, desert, or wetlands, in which a plant or animal leaves.
Hackle
Any of the long slender feathers on the neck or lower back of a male bird, especially a fowl.
Hafnium (Hf)
A bright silvery metallic chemical element found in zirconium ores.
Hair
Any of the narrow threadlike outgrowths from the skin of mammals, consisting of dead cells containing large amounts or horny keratin (a protein) and granules of pigment.
Hair Follicle
A small cavity in the epidermis and corium of the skin, from which a hair develops.
Half-Cell
A single electrode immersed in a container filled with an electrolyte, and having a specific electrical potential for a given combination of electrode and electrolyte.
Half-Life
The interval of time required for half of the remaining quantity of a radioactive material to disintegrate.
Halobiont
An organism that lives in a salty environment, especially the sea.
Halophyte
A plant that grows in soils with a high concentration of salt.
Hamstring
A powerful group of muscles at the back of the thigh that arise in the hip and pelvis and insert as strong tendons behind the knee.
Hand
The part of the human arm below the wrist, consisting of a thumb, four fingers, and a palm and capable of holding and manipulating things.
Hansen's Disease
Also known as leprosy.
Hantavirus
Any of a group of viruses of the genus Hantavirus, carried by rodents, that cause severe respiratory infections in humans, and in some cases, hemorrhaging, kidney disease, and death.
Haploid
Having a single set of unpaired chromosomes.
Haptaglobin
A plasma protein that is a normal constituent of blood serum and functions in the binding of free hemoglobin in the bloodstream.
Hard Copy
An information which is printed on to paper. It usually comes from a computer or from a fax machine.
Hard Disk
One or more rigid magnetic disks fixed within a disk drive rotating about a central axle with associated read/write heads and electronics, used to store computer data.
Hardware
The mechanical, magnetic, electronic, and electrical devices comprising a computer system, as the CPU, disk drives, keyboard, or screen.
Hard Water
Water that contains magnesium, calcium, or iron salts and therefore forms a soap lather with difficulty.
Harem
A group of female animals of the same species associated for breeding purposes with one male.
Hassium (Hs)
A synthetic, radioactive element that is produced by bombarding lead with iron ions.
Haustorium
A specialized absorbing structure of a parasitic plant, such as the rootlike outgrowth of the dodder, that obtains food from a host plant.
Haversian Canals
Refers to a series of fine interconnecting canals that run usually longitudinally through dense bone of vertebrates.
Hay
Grass or other plants that are cut, dried, and then often used as fodder.
Hay Fever
Form of seasonal rhinitis caused by allergy to pollens and symptoms are intense seizures of sneezing, inflammation of nose and eye membranes and wheezing.
Head
The topmost part of a vertebrate body, where the brain, eyes, nose, ears, mouth, and jaws are situated.
Heal
To be repaired and restored naturally, for example, by the formation of scar tissue.
Health
The general condition of the body or mind, especially in terms of the presence or absence of illnesses, injuries, or impairments.
Heart
The chambered muscular organ in vertebrates that pumps blood received from the veins into the arteries, thereby maintaining the flow of blood through the entire circulatory system.
Heartbeat
A vigorous contraction of the lower chambers of the heart that drives blood through the body.
Heartburn
A burning sensation, usually centered in the middle of the chest near the sternum, caused by the reflux of acidic stomach fluids that enter the lower end of the esophagus.
Heartwood
The hard central region of a tree trunk made up of xylem vessels that are no longer involved in water transport.
Heat
A form of energy associated with the motion of atoms or molecules and capable of being transmitted through solid, fluid, and empty space; the transfer of energy from one body to another as a result of a difference in temperature or a change in phase.
Heat Conductor
Substance that conducts heat more effectively than other substance.
Heat Energy
A form of energy that is transferred by a difference in temperature.
Heat Engine
Machine that changes heat energy into mechanical energy in order to do work.
Heat of Crystallization
The quantity of heat released when a unit mass of a liquid turns to solid at constant temperature.
Heat of Reaction
The quantity of heat liberated or absorbed during a chemical change.
Heat of Vaporization
Amount of heat needed to change a substance from the liquid phase to gas phase.
Heel
The back part of a person's foot immediately below the ankle, or the same part of an animal's foot or paw.
Heliophyte
A plant that grows best in full sunlight.
Helium (He)
An inert, gaseous element present in the sun's atmosphere and in natural gas, and also occurring as a radioactive decomposition product, used as a substitute for flammable gases in dirigible balloons.
Helminth
A worm, usually a parasitic one.
Helminthology
Study of parasitic worms.
Hematite
A mineral that is an important iron ore and occurs as black, brown, or red crystals or in a massive uncrystallized form, often in very large deposits.
Hemichordata
A small phylum of marine invertebrates.
Hemipode
A small round-bodied ground-dwelling bird of the grasslands of Africa, Australia, and Southern Europe and Asia.
Hemisphere
One half of the Earth, especially a half North or South of the Equator or West or East of the Prime Meridian.
Hemoglobin
An iron-containing protein in red blood cells that combines reversibly with oxygen and transports it from the lungs to body tissues.
Hemolymph
A fluid in certain invertebrates that functions like the blood in vertebrates.
Hemophilia
A disorder linked to a recessive gene on the X-chromosome and occurring almost exclusively in men and boys, in which the blood clots much more slowly than normally, resulting in extensive bleeding from even minor injuries.
Hemorrhage
The loss of blood from a ruptured blood vessel, either internally or externally.
Hemostasis
The stoppage of bleeding or hemorrhaging in an organ or body part; the stoppage of the circulation of blood in a part of the body.
Hemp
A tall, coarse plant that is native to Asia and is the source of a valuable fiber as well as drugs such as marijuana and hashish.
Heparin
An acidic glycosaminoglycan found in lung and liver tissue that prevents the clotting of blood and is used intravenously in the treatment of thrombosis and embolism.
Hepatitis
A disease of the liver which usually comes from a virus spread by direct or indirect contact with an infected person.
Hepatocyte
Any of the epithelial cells of the liver that secrete bile; also called hepatic cell or liver cell.
Heptane
An isomeric form of an organic chemical obtained from petroleum; especially a colorless flammable liquid alkane hydrocarbon used as a solvent and anesthetic and to determine octane ratings.
Herb
A low -growing aromatic plant used fresh or dried for seasoning in cooking, for its medicinal properties, or in perfumes.
Herbaceous
Used to describe plants or plant parts that are fleshy and wither after each growing season, as opposed to plants such as trees that grow woody stems and are persistent.
Herbaceous Stem
Composed of vascular bundles (xylem and phloem) arranged in a circle around a central core of spongy tissue.
Herbicide
A chemical preparation designed to kill plants, especially weeds, or to inhibit their growth.
Heredity
Passing of characteristics from parent to children.
Hermaphrodite
One who has both male and female elements of genital structure and both male and female secondary sexual characteristics.
Hernia
A condition in which part of an internal organ projects abnormally through the wall of the cavity that contains it, especially the projection of the intestine from the abdominal cavity.
Herpes
A viral infection causing small painful blisters and inflammation, most commonly at the junction of skin and mucous membrane in the mouth or nose or in the genitals.
Hertz
A unit of measurement which measures the frequency of vibration such as sound and of waves such as radio.
Hess's Law
When a reaction can be expressed as the algebraic sum of two or more other reactions, then the heat of the reaction is the algebraic sum of the heats of other reactions.
Heterodont
Having teeth of different kinds, as in most mammals, which have incisors, canines, and molars.
Heterogeneous
Having parts with different properties.
Heterogeneous Matter
Matter that has parts with different properties.
Heterogeneous Mixture
A mixture in which the ingredients are not uniformly dispersed.
Heterogeneous Reaction
A reaction that involves reactants in more than one phase.
Heterokaryon
A cell that has two or more genetically different nuclei.
Heterokaryosis
The presence in a cell of two or more nuclei of different genetic origin.
Heterosporous
Producing two types of spore, microspores and megaspores, on the same plant.
Heterospory
The production of two different sizes of spore, microspore and megaspore.
Heterotrophic
Obtaining nourishment by digesting plant or animal matter, as animals do, as opposed to photosynthesizing food, as plants do.
Heterozygous
Having different alleles at one or more corresponding chromosomal loci; of or relating to a heterozygote.
Hexane
A voltaile hydrocarbon found in petroleum that is a major ingredient in gasoline and is commonly used as a solvent.
Hi-Fi
Is an abbreviation for high fidelity.
High Fidelity
The electronic reproduction of sound with little or no distortion.
Hilum
A scar on the testa of a seed marking the point at which it was attached to the ovary well by the funicle.
High Tide
The tide at its fullest, when the water reaches its highest level.
Hinge Joints
Allow movement in only one direction.
Histamine
Amine formed from histidine that stimulates gastric secretions and dilates blood vessels; released by the human immune system during allergic reactions.
Histone
A protein whose molecules organize and pack the DNA in chromosomes into the greatly condensed form (chromatin) it normally adopts.
Hive
A shelter in which a colony of social bees, especially honeybees, build its nest.
Holmium (Ho)
A silvery-white metallic chemical element of the rare-earth group often found with yttrium in gadolinite and monazite.
Hologram
A negative produced by exposing a high-resolution photographic plate, without camera or lens, near a subject illuminated by monochromatic, coherent radiation, as from a laser; when it is placed in a beam of coherent light a true three-dimensional image of the subject is formed.
Homeostasis
A state of equilibrium, or a tendency to reach equilibrium.
Homeotherm
An organism whose stable body temperature is generally independent of the temperature of its surrounding environment.
Homo Erectus
An extinct species of the human lineage having upright stature and a well-evolved postcranial skeleton, but with a smallish brain, low forehead, and protruding face. They lived during Pleistocene Epoch from about 1.6 million years ago to 250,000 years ago.
Homogeneous
Having similar properties throughout.
Homogeneous Matter
Matter that has identical properties throughout.
Homogeneous Mixture
A uniform intermixture of particles. Samples from different parts of this mixture show the same composition.
Homogeneous Reaction
A reaction in which all the reactants are in the same phase.
Homogenization
The act of making something homogeneous or uniform in composition.
Homo Habilis
An extinct species of humans considered to be an ancestor of modern humans and the earliest hominid to make tools; existed between 1.5 and 2 million years ago.
Homologous Series
Organic compounds with a similar general formula, possessing similar chemical properties, and show a gradation in physical properties in molecular size and mass.
Homology
Similar characteristics in two animals that are a product of descent from a common ancestor rather than from a similar environment.
Homo Sapiens
The modern species of humans; probably evolved around 300,000 years ago or earlier in Africa; bipedal primate having language and ability to make and use complex tools; brain volume at least 1400 cc.
Hooke's Law
The principle that within the elastic limit, the stress applied to a solid is proportional to the strain produced.
Horizon
The apparent intersection of the Earth and sky as seen by an observer; in Geology, a specific position in a stratigraphic column, such as the location of one or more fossils, that serves to identify the stratum with a particular period.
Hormone
A substance, usually a peptide or steroid, produced by one tissue and conveyed by the bloodstream to another to effect physiological activity, such as growth or metabolism.
Horsepower
A unit of power equivalent to 550 foot-pounds per second, or 746.7 watts.
Horticulture
Science and art of gardening and of cultivating fruits, vegetables, flowers, and ornamental plants.
Hospital
An institution where people receive medical, surgical, or psychiatric treatment and nursing care.
Host
Organism in which another organism lives.
Humerus
The long bone of the human upper arm; a corresponding bone, structure, or region in the forelimbs of other animals or in the wings of birds or insects.
Humus
A dark brown organic component of soil that is derived from decomposed plant and animal remains and animal excrement.
Hurricane
A severe tropical storm with torrential rain and winds above 119 km/hr or 74 mi/hr.
Hybrid
An offspring of two animals or plants of different races, breeds, varieties, species, or genera.
Hybridization
The act of mixing different species or varieties of animals or plants and thus to produce hybrids.
Hydrate
A solid compound containing water molecules combined in a definite ratio as an integral part of the crystal.
Hydraulic Machine
Operated by the pressure created by forcing water, oil, or another liquid through a comparatively narrow pipe or orifice.
Hydrocarbon
Chemical substance and it can be solid, liquid, or gas; molecules which contain atoms of carbon and hydrogen.
Hydrochloric Acid
A solution of hydrogen chloride in water, forming a very strong, poisonous, corrosive acid with a sharp odor. It is used in food processing, metal cleaning, and dyeing.
Hydrocortisone
Also known as cortisol, it is a steroid hormone produced by the adrenal cortex that regulates carbohydrate metabolism and maintains blood pressure.
Hydroelectric Plant
Plant that uses energy from moving water to produce electricity.
Hydroelectric Power
Electricity which is generated by flowing water. Inside a hydroelectric power station, the water spins a turbine which drives on electric generator.
Hydrogen (H)
A highly reactive colorless gas, the lightest chemical element and the most abundant in the universe, occurring mainly in water and in most organic compounds.
Hydrogen Bond
The bond formed between a hydrogen atom in one molecule and a highly electronegative atom in another molecule.
Hydrogen Chloride (HCl)
A colorless pungent poisonous gas that fumes in moist air and yields hydrochloric acid when dissolved in water.
Hydrogen Ion
A positively charged atom of hydrogen.
Hydrogenation
The addition of hydrogen to a compound, especially to solidify an unsaturated fat or fatty acid.
Hydrolase
An enzyme that catalyses the hydrolysis of a substrate through the addition of water.
Hydrologic Cycle
The cycle of evaporation and condensation that controls the distribution of the Earth's Water as it evaporates from bodies of water, condenses, precipitates, and returns to those bodies of water.
Hydrometer
An instrument for determining specific gravities of liquids and hence the strength (as of alcoholic liquors or battery acids).
Hydrotropism
The response of plants to water. The influence of water is stronger than gravity.
Hygiene
The science that deals with the promotion and preservation of health.
Hygrometer
Any instrument for measuring the water vapor content of the atmosphere.
Hygroscope
An instrument that indicates the approximate humidity of the air.
Hyperparasite
The organism which lives parasitically in or on another parasite.
Hypertension
Elevation of the blood pressure, especially the diastolic pressure.
Hyperthyroidism
An abnormality of the thyroid gland characterized by excessive production of the thyroid hormone, which can result in an increase basal metabolic rate, causing weight loss, heart palpitations, and tremors.
Hypertonia
A condition marked by an abnormal increase in the tightness of muscle tone and a reduced ability of a muscle to stretch, i.e. an increased stiffness.
Hypocotyl
Part of an embryo plant lying between its cotyledons and its radicle.
Hypoglycemia
The medical condition of having an abnormally low level of sugar in the blood.
Hypotension
Decreased or lowered blood pressure.
Hypothesis
A formula derived by inference from scientific data that explains a principle operating in nature.
Hypothyroidism
An abnormality of the thyroid gland characterized by insufficient production of thyroid hormone, which can result in a decreased basal metabolic rate, causing weight gain and fatigue.
Hysteria
A mental disorder characterized by emotional excitability and sometimes by amnesia or a physical deficit, such as paralysis, or a sensory deficit, without an organic cause.
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