Online Biology Dictionary I–K

I (1) iodine; (2) isolucine.

Iapetus Ocean An ocean that once existed (Late Precambrian to Devonian) between the former continents of Avalonia, Baltica, and Laurentia.   SEE MAP

iatric /eye-AT-rick/ Medical.

iatrology /eye-uh-TRAWL-uh-jee/ Medical science.

An ichnite (a Neanderthal footprint) Photo: Magnus Manske

ichnite (also ichnolite) /IK-nite, IK-nuh-lite/ A fossil footprint.

ichnology /ik-NAWL-uh-gee/ The scientific study of the traces of animal activity, such as footprints, burrows, trails, and borings.

ichthyic /ik-THEE-ick/ Of or pertaining to fish.

ichthyology /IK-thee-AWL-luh-gee/ The scientific study of fish.

icteritious /IK-ter-RISH-us/ Yellowed with jaundice.

icterohematuria /IK-ter-oh-HEEM-uh-TER-ee-uh/ A disease of sheep caused by the protozoan blood parasite Babesia ovis; a jaundiced condition results from the destruction of erythrocytes.

identical twins Genetically identical individuals that develop from a single zygote. See also: fraternal twins.

idiopathic /id-ee-oh-PATH-ick/ Pertaining to disease without known cause.

IDL Intermediate-density lipoprotein.

IF Initiation factor.

Ig Immunoglobulin.

igneous rock Rock formed from the cooling and solidification of magma. Because igneous deposits can be accurately dated, they are useful for determining the age of fossils (the approximate age of a fossiliferous deposit can often be determined by evaluating the age of beds of igneous rock that over- or underlie the deposit).

IHP Inositol hexaphosphate.

ile Isolucine.

ileal /ILL-ee-uhl/ Of or pertaining to the ileum.

ileocecal valve /ill-ee-oh-CEE-cuhl/ A one-way valve between the ileum and the cecum, which prevents the contents of the large intestine from returning to the ileum.

Intestine Diagram (click to enlarge)

ileum (pl ilea) /ILL-ee-uhm/ The lower, third portion of the small intestine, lying between the jejunum and the cecum. It is about 4 meters in length.

ilium (pl ilia) /ILL-ee-uhm/ The wide upper portion of the hipbone or innominate bone.

immune system The system that defends an organism against infection. The cellular components of this system are all derived from the same cells (hematopoietic stem cells), residing in the bone marrow, that can alternatively mature into erythrocytes. MORE ABOUT THE IMMUNE SYSTEM

immunoglobulins (Ig) /im-MYOON-uh-GLAWB-yuh-lins/ See antibodies.

immunotherapy /im-MYOON-oh-THAIR-uh-pee/ (1) use of the immune system to treat or prevent disease (e.g. vaccines); (2) therapy of diseases caused by the immune system.

IMP Inosine monophosphate.

imprinting /IM-print-ing/ (1) a genetic phenomenon in which phenotype is dependent on the parent that passed on the gene; (2) sexual preferences determined by exposure to stimuli at an early stage of development (for example, if a duckling is spends the time of its early development with chickens, it will later prefer to mate with a chickens instead of other ducks.

incision /in-SISH-uhn/ A cut made with a knife.

incisor /in-SIZE-er/ One of the slicing teeth at the front of the mouth.

incubator /in-cyuh-BAIT-er, cyoo/ (1) An apparatus for maintaining eggs at a constant temperature; (2) An apparatus, for rearing premature babies, in which such factors as temperature and oxygen levels can be closely controlled; (3) A device for culturing bacteria.

incubation /in-cyuh-BAY-shun, cyoo/ (1) in reptiles and birds: the maintenance of a constant egg temperature; (2) in premature human infants: the time spent in an incubator; (3) in disease: the time between first infection and emergence of symptoms; (4) in bacteriology: the period of culture development.

independent assortment The random distribution into gametes during meiosis of genes on different chromosomes. See also: linkage.

indeterminate growth Growth that continues throughout life (characteristic of plants), as opposed to determinate growth.

inflorescence /in-fluh-RESS-ehns/ A cluster of flowers.

infraclass /IN-fruh-CLASS/ See: subphylum.

infraorder /IN-fruh-ORE-der/ See: subclass.

infraorbital /IN-fruh-ORB-uh-tuhl/ Beneath the orbit.

ingestion /in-JEST-shun/ Swallowing (in order to introduce something into the digestive tract). The term ingestion can also refer a cell engulfing or surrounding food or some other material. Compare: absorption.

inoculate /in-KNOCK-yuh-late/ To inject or introduce a pathogenic (usually weakened) microorganism into the body in order to stimulate the production of antibodies.

inorganic (1) in chemistry, refers to compounds lacking carbon; (2) not fom living things.

in situ hybridization Use of a DNA or RNA probe to detect complementary DNA sequences cultured eukaryotic cells or bacterial clones.

insertion A chromosome abnormality in which a piece of DNA is incorporated into a gene and thereby disrupts the gene's normal function. See also: chromosome, DNA, gene, mutation.

InsP₃ Inositol 1,4,5-trisphosphate.

insulin A hormone that causes blood sugar levels to fall. Individuals with diabetes melitus have a deficiency of this hormone. It is normally produced by the islets of Langerhans in the pancreas.

integrin In animals, an adhesive extracellular matrix protein.

interbedded Refers to layers (beds) of rock alternating with layers of a different type of rock.

internode The portion of a plant stem between two nodes.

interference See: negative interference, positive interference.

interphase The period in the eukaryotic cell cycle when cell growth occurs and DNA is replicated in the nucleus; alternates with mitosis. MORE INFORMATION

interspecific hybridization Hybridization between forms treated as distinct species. MORE INFORMATION

intertidal zone The zone between the high and low tide marks, which is subject to alternating flooding and drying.

intestine (also intestines) The portion of the digestive tract lying between the pylorus and the anus.

Intestine Diagram (click to enlarge)

intestine, large The large intestine, or colon, is the portion of the digestive tract leading from the ileum to the anus. It functions primarily in extracting moisture from digested matter so as to convert it to solid feces. The large intestine begins with the cecum, which is attached to the vermiform appendix (see picture). To see the various other regions of the large intestine, click on the figure at right. The colon is usually from 1.5 to 2.0 meters in length.

intestine, small The portion of the digestive tract lying between the stomach and large intestine. It functions in the extraction of nutrients from digested matter. The small intestine is composed of the duodenum, jejunum, and ileum.

intramuscular Within a muscle. <~ injection>

intron A portion of a gene that is transcribed into mRNA but cut out of the mRNA before it is translated into protein. See also: exon.

intrusion Rock formed from cooled magma that forced its way into preexisting rock.

inversion A chromosome segment that has been reversed with respect to the remainder of the chromosome.

invertebrates Animals lacking a backbone. Invertebrates do not develop a notochord during embryogenesis.

in vitro Refers to studies performed outside a living organism such as in a laboratory.

in vivo Refers to studies carried out in living organisms.

ion An atom or small molecule with a negative or positive charge.

ionize (British: ionise) To change into ions.

IP₁ Inositol-1-phosphate.

IP₃ Inositol 1,4,5-triphosphate.

IPTG Isopropylthiogalactoside.

iridescence The quality of changing color depending on the angle of observation.

IS Insertion sequence.

isoelectric point The pH at which there is a zero net negative and positive charge on a protein.

isoenzyme An isozyme.

isogeneic graft A graft involving a genetically identical donor and host.

isoleucine (I or ile) An essential-amino acid. CODONS | MOLECULAR STRUCTURE | BIOSYNTHESIS PATHWAY

isomers Chemical compounds with the same molecular formula that differ in structure.

isometry (or isometric growth) Growth of a part at the rate as that of some other part. Compare: allometry.

isotopes /EYE-suh-topes/ Variants of the same chemical element, differing with respect to the number of neutrons present (different isotopes always have the same number of protons).

isozymes /EYE-suh-zimes/ An enzyme performing the same function as another enzyme but having a different amino acid sequence. They catalyze the same reactions, but differ in molecular structure and with respect to other characteristics such as isoelectric point and molecular weight.

ITP Inosine triphosphate.

iteroparity The condition of producing offspring repeatedly during the lifetime of an individual. Compare: semelparity

J (1) joule; (2) Jurassic Period.

A jaglion - lioness x jaguar Photo: Sarah Hartwell

jaglion /JAG-lie-uhn/ (also jaguon /JAG-wan/) hybrid produced by the mating of a lioness and a jaguar.

jarovization Vernalization.

jaundice /JAWN-duhs/ A condition resulting from excess bilirubin in the blood. It is characterized by yellowness of the skin, mucous membranes, and the whites of the eyes. Often a sign of liver malfunction, although it can also result from obstruction of the bile duct, or from excessive destruction of erythrocytes.

Java man A name used for a representative of the hominid Homo erectus discovered on the island of Java; formerly Pithecanthropus erectus.

jejunum /juh-JOON-uhm/ The second portion of the small intestine; lying between the duodenum and the ileum. It is a little over 2 meters in length.

JH Juvenile hormone.

joule 10⁷ ergs.

jugum A connecting bar or ridge.

jumping genes An informal name for transposons.

junk DNA (also non-coding DNA) Regions of the genome not coding for genes, especially those composed of repetitive sequences; in most organisms a majority of the genome consists of so-called junk DNA which may have regulatory and other functions.

juvenile hormones (JHs) also allatum hormones Hormones regulating many aspects of insect physiology; particularly important in controlling the metamorphosis of holometabolous insects; secreted by the corpora allata.

k Kilo-, one thousand.

K (1) lysine; (2) potassium.

Human karyotype colored to show pairing (click to enlarge)

karyotypic /kare-ee-uh-TIP-ick/ Of or pertaining to a karyotype or karyotypes.

Kcat The maximum number of moles of substrate that an enzyme can convert to product per catalytic site per unit time.

kDa Kilodalton.

keratin /KARE-uh-tin/ A structural protein found in hair, nails, and the tough outer layer of skin (stratum corneum). Keratin is used as a coating on pills that should pass through the stomach intact.

keratoconjunctivitis Inflammation of the cornea and conjunctiva of the eye.

Ketone

ketone /KEE-tone/ A molecule containing the carbonyl group (CO) with general formula as shown in the figure at left.

kg kilogram.

KHCO₃ Potassium carbonate.

KHSO₄ Potassium bisulfate.

KI Potassium iodide.

Interior structure of human kidney (click to enlarge)

kidneys /KID-neez/ Organs present in vertebrates, usually near the spine, that function in cleansing the blood of uric acid, urea, and other metabolic wastes. In humans, they are bean shaped. The interior surface of the kidney is lined with the pelvis renalis or renal pelvis, which is continuous with the lining of the ureter. LOCATION OF KIDNEYS

kilobase (kb) /KILL-uh-base/ Unit of length for DNA fragments equal to 1000 nucleotides.

kilodalton (kDa) /KILL-uh-DAWL-tuhn/ 1000 dalton units.

kinesialgia Pain resulting from movement of the muscles.

kinesiology /kuh-neez-ee-AWL-uh-jee/ The study of the movement of muscles.

kinetochores /kuh-NET-uh-kores/ The regions on centromeres to which the microtubules of the spindle apparatus attach.

kingdom /KING-duhm/ In taxonomy, a division of a domain that itself contains one or more phyla. CHART OF RELATIVE TAXONOMIC RANKS

kinocilium The motile cilium of one of the hair cells of the inner ear.

km Kilometer.

kM Michaelis constant.

KMnO₄ Potassium permanganate.

kolypeptic Interfering with digestion.

koniology (also coniology) The study of dust in relation to its effects on health.

koniometer A measurement device for estimation of atmospheric dust loads.

krypton (Kr) Rare gaseous element; Atomic weight 83.80, atomic number 36. PERIODIC TABLE

KT Cretaceous-Tertiary.

KT extinction See: Cretaceous-Tertiary mass extinction

kyogenic /KIGH-oh-GEHN-ik/ Causing pregnancy.

kyphosis /kigh-FOE-suhs/ A curvature of the upper spine; commonly known as hunchback or hump back.

kysthitis /kiss-THIGH-tuhs/ Vaginal inflammation.