Science / Biology Glossary

Inheritance Of Acquired Characteristics: Lamarcks view that features acquired during an organisms lifetime would be passed on to succeeding generations, leading to inheritable change in species over time.

Initiation: The first step in translation; occurs when a messenger RNA molecule, a ribosomal subunit, and a transfer RNA molecule carrying the first amino acid bind together to form a complex; begins at . . . View Full Definition

Initiation Codon (AUG): Three-base sequence on the messenger RNA that codes for the amino acid methionine; the start command for protein synthesis.

Insertion: A type of mutation in which a new DNA base is inserted into an existing sequence of DNA bases. This shifts the reference frame in protein synthesis, resulting (sometimes) in altered amino ac . . . View Full Definition

Insulin: A hormone secreted by the pancreas that stimulates the uptake of glucose by body cells. Insulin works antagonistically with glucagon to control blood sugar levels.

Integration: The process of combining incoming information; one of the functions of the nervous system.

Integument: Something that covers or encloses, e.g., the skin.

Integumentary System: The skin and its derivatives (hair, nails, feathers, horns, antlers, and glands), which in multicellular animals protect against invading foreign microorganisms and prevent the loss or excha . . . View Full Definition

Interferons: Proteins released by cells in response to viral infection; activate the synthesis and secretion of antiviral proteins.

Internal Environment: In multicellular organisms, the aqueous environment that is outside the cells but inside the body.

Interneurons: Neurons that process signals from one or more sensory neurons and relay signals to motor neurons. Aka connector neurons.

Internodes: The stem regions between nodes in plants.

Interphase: The period between cell divisions when growth and replacement occur in preparation for the next division; consists of gap 1 (G1), synthesis (S), and gap 2 (G2).

Interstitial: Being situated within a particular organ or tissue.

Interstitial Fluid: Fluid surrounding the cells in body tissues; provides a path through which nutrients, gases, and wastes can travel between the capillaries and the cells.

Intracellular Digestion: A form of digestion in which food is taken into cells by phagocytosis; found in sponges and most protozoa and coelenterates.

Intracellular Parasites: Viruses that enter a host cell and take over the hosts cellular machinery to produce new viral particles.

Intracellular Route: Path taken by water through the cells of the root between the epidermis and the xylem, moving through plasmodesmata.

Intron: In eukaryotes, bases of a gene transcribed but later excised from the mRNA prior to exporting from the nucleus and subsequent translation of the message into a polypeptide.

Inversion: A reversal in the order of genes on a chromosome segment.

Ion: An atom that has lost or gained electrons from its outer shell and therefore has a positive or negative charge, respectively; symbolized by a superscript plus or minus sign and sometimes a n . . . View Full Definition

Ionic Bond: A chemical bond in which atoms of opposite charge are held together by electrostatic attraction.

Isotonic: Term applied to two solutions with equal solute concentrations.

Isotopes: Atoms with the same atomic number but different numbers of neutrons; indicated by adding the mass number to the elements name, e.g., carbon 12 or 12C.

Jejunum: The second portion of the small intestine. Also, a popular month for weddings!

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