Lewis/Life - Glossary

H

habitat HAB-eh-tat The physical and living surroundings of a species. 830

habituation ha-BIT-ju-AY-shun The simplest form of learning, in which an animal learns not to respond to certain irrelevant stimuli. 815

hair follicle hayr fol-i-kul An epidermal structure anchored in the dermis from which a hair grows. 599

half-life The time it takes for half the isotopes in a sample of an element to decay into a second isotope. 393

halophiles HAL-o-files Archaea that tolerate extremely salty surroundings. 451

haploid cell HAP-loid SEL A cell with one copy of each chromosome. Also called 1n. 192

hardwood Wood in dicots, such as oak, maple, and ash. 551

Hardy-Weinberg equilibrium HAR-dee WINE-berg EE-kwah-LIB-ree-um Maintenance of the proportion of genotypes in a population from one generation to the next. 405

heart valves Flaps in the heart that keep blood flow in one direction. 720

heartwood Wood in the center of a tree, where wastes collect. 551

heat capacity The amount of heat necessary to raise the temperature of a substance. 42

heat of vaporization HEET of VA-por-i-ZA-shun The amount of heat required to convert a liquid to vapor (gas). 42

heavy chains The two larger polypeptides of an antibody subunit. 795

helper T cell Lymphocyte that produces cytokines and stimulates activities of other immune system cells. 794

heme group HEEM GROOP An iron-containing complex that forms the oxygen-binding part of hemoglobin. 715

hemizygous HEM-ee-ZY-gus A gene on the Y chromosome in humans. 291

hemocoel HEEM-o-seal The body cavity of an arthropod. 522

hemocyanin heem-o-SI-a-nin A respiratory pigment in mollusks that carries oxygen. 710

hemoglobin HEEM-o-GLO-bin The iron-binding protein that carries oxygen in mammals. 710

hemolymph HEEM-o-limf The blood in arthropods. 522

hepatic portal system heh-PAH-tik POR-tel SIS-tum A division of the circulatory system that enables the liver to rapidly harness chemical energy in digested food. 725

heritability herr-it-a-BILL-it-ee The proportion of a trait attributable to heredity. 278

heterochromatin het-er-o-KROME-a-tin Dark-staining genetic material. 296

heterogametic sex HET-er-o-gah-MEE-tik SEX The sex with two different sex chromosomes. 290

heterotherm HET-er-o-therm An animal with variable body temperature. 771

heterotroph(ic) HET-er-o-TROFE An organism that obtains nourishment from another organism. 14, 146, 751

heterozygous HET-er-o-ZI-gus Possessing two different alleles for a particular gene. 265

highly conserved A protein or nucleic acid sequence that is very similar in different species. 395

hindbrain HIND-brayne The lower portion of the vertebrate brain, which includes the brain stem and controls vital functions. 620

hirudinea hear-EW-din-ay A class of annelids that includes the leeches. 521

histamine HIS-tah-meen An allergy mediator that dilates blood vessels and causes allergy symptoms. 791

holozoic HOLE-o-ZO-ik A protozoan that takes in food through phagocytic vacuoles. 459

homeostasis HOME-ee-o-STA-sis The ability of an organism to maintain constant body temperature, fluid balance, and chemistry. 9

homeotherm HOME-e-o-therm An animal with constant body temperature. 771

homeotic home-ee-OT-ik A mutant in which body parts form in the wrong places. 215

hominid HOM-eh-nid Animals ancestral to humans only. 367

hominoid HOM-eh-noid Animals ancestral to apes and humans. 367

homogametic sex HO-mo-gah-MEE-tik SEX The sex with two identical sex chromosomes. 290

homologous pairs ho-MOL-eh-gus PAIRZ Chromosome pairs that have the same sequence of genes. 198

homologous structures ho-MOL-eh-gus STRUK-churs Similar structures in different species that have the same general function, indicating descent from a common ancestor. 393

homozygous HO-mo-ZI-gus Possessing two identical alleles for a particular gene. 265

hornwort HORN-wart A type of bryophyte. 493

horsetail Seedless vascular plant of genus Equisetum. 497

human chorionic gonadotropin YU-man KOR-ee-on-ik go-NAD-o-TRO-pin (hCG) A hormone secreted by the preembryo and embryo that prevents menstruation. 218, 674

humoral immune response HUME-er-al IM-mune ree-SPONZ Secretion of antibodies by B cells in response to detecting a foreign antigen. 795

hybridoma hi-bri-DOME-ah An artificial cell created by fusing a B cell with a cancer cell that secretes a particular antibody. It mass-produces the antibody. 804

hydrocarbon HI-dro-kar-bon A molecule containing carbon and hydrogen. 38

hydrogen bond HI-dro-gen BOND A weak chemical bond between negatively charged portions of molecules and hydrogen ions. 39

hydrolysis hi-DROL-eh-sis Splitting a molecule by adding water. 43

hydrophilic HI-dro-FILL-ik Attracted to water. 39

hydrophobic HI-dro-FOBE-ik Repelled by water. 39

hydrostatic skeleton Hi-dro-STAT-ik SKEL-eh-ten The simplest type of skeleton, consisting of flexible tissue surrounding a constrained liquid. 683

hydroxide ion hi-DROX-ide I-on (OH{neg}) A molecule consisting of one oxygen and one hydrogen. 40

hyperthermophiles hi-per-THERM-o-files Archaea that use sulfur and tolerate extreme heat. 451

hypertonic hi-per-TON-ik The solution on one side of a membrane where the solute concentration is greater than on the other side. 89

hypertrophy hi-PER-tro-fee Increase in muscle mass, usually due to exercise. 701

hypha HI-fa A fungal thread, the basic structural unit of a multicellular fungus. 477

hypocotyl hi-po-COT-ul Stemlike region beneath seed leaves. 568

hypodermis hi-po-DERM-is An outer layer of a roundworm that secretes a protective cuticle. 519 The outermost protective layer of the cortex of a plant. 547

hypothalamus Hi-po-THAL-eh-mus A small structure beneath the thalamus that controls homeostasis and links the nervous and endocrine systems. 627

hypothesis hy-POTH-eh-sis An educated guess based on prior knowledge. 21

hypotonic hi-po-TON-ic The solution on one side of a membrane where the solute concentration is less than on the other side. 89

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