Dr. Paul's Virtually Biology Show.

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Imprinting.. Imprinting is a kind of learning that takes place during certain critical periods of an organism's life during which rapid and often irreversible fixation on presented stimuli happens. For instance many birds respond to the first organism they see upon hatching as they would to their mother with often comical results.

Incomplete dominance. A mode of inheritance in which the heterozygote has a phenotype that is intermediate between the phenotypes of either homozygotes. For instance for snap dragon flowers, if one homozygote is red, the other white, then the heterozygote will be pink. Incomplete dominance usually arises if one gene does not express a product and its other allele expresses an insufficient amount of product to mask the first allele.
Independent assortment. The random alignment and subsequent separation of pairs of homologous chromosomes at the equator of the cell during metaphase I and anaphase I of meiosis. This process is important in recombination of the genetic material found in the gamete or spore producing organism.

Induced fit model. The induced fit model says that the sites on enzymes or receptor molecules where substrate molecules will alter their shape slightly to accommodate the substrate molecules. This is in contrast to the old lock and key model of enzyme activity which held that the enzyme active site had a set and rigid shape. The induced fit model is important because it suggests that enzymes don't have to perfectly "fit" with the substrate in order to operate and thus evolution has plenty of leeway in terms of new enzyme variants evolving.

Inductive reasoning.Reasonong from a series of specific observations to a set of one or more general principles.For example, Darwin used sets of observations of the fossil record, the distribution of organisms, and the structure of organisms to infer natural selection that natural selection is a general concept helping to explain the diversity of life on Earth.

Ingestion. The taking of food into the organism and physical processing before digestion.

Inner compartment of mitochondrion. The central area of the mitochondrion, sometimes called the matrix and where the Kreb's cycle happens.

Insight learning. Modification of an organism's behavior brought about by combining information received from the environment in new ways to solve problems. Supposedly characteristic of human beings and a relatively small group of other vertebrates.

Instinct(Instinctive behavior).. An instinct is a simple or complex set of behaviors that are innate rather than learned.

Insulin. A protein hormone produced by the beta cells of the pancreas' islets of Langerhorns and that is involved with the regulation of blood glucose levels. Specifically insulin promotes the uptake of glucose and the formation of glycogen in the liver and muscles.
Interleukins. A series of local chemical signals involved in the immune system and that activate the production of cytotoxic T cells and promote the increased production of helper T cells.
Intermembrane space. The region in the mitochondrion that is between the outer and inner membranes of the organelle. The intermembrane space is important because the mitochondrion concentrates hydrogen ions in this area as part of electron transport phosphorylation.

Interneuron. A neuron that transmits information from at least one neuron to at least one other neuron. Interneurons in humans are characteristic of the central nervous system.
Internode. In plants, the region of the stem between where the leaves are attached.
Interphase. That part of the eukaryotic cell life when the chromosomes are not visible using a light microscope and when the cell is doing its every day function. The DNA actually duplicates during interphase and thus the chromosomes go from being unduplicated to duplicated.

Interstitial fluid. Fluid that is in the tissues: more literally, in the spaces that are in between the cells.

Intron. A segment of RNA transcript that is edited out by the cell and that stays in the nucleus. Introns appear to have a role in controlling gene expression in eukaryotes. Prokaryotes do not have introns. Contrast exon.
Ion. An atom or molecule with an unequal number of protons and electrons. Thus the atom or molecule has either a net positive or a negative charge.

Ionic bond. A bond between two atoms involving a complete transfer of electrons. Usually ionic bonds involve atoms of elements on the far left hand side of the periodic table and atoms of elements near the right hand column of the periodic table.

Isomers. Two molecules that have the same molecular formula (e.g. C6 H12 O6) but a different structure. Glucose and fructose are isomers of each other.
Isotonic. Two aqueous solutions are considered isotonic is they have the same concentration of solutes. Contrast hypertonic.
Isotope. An atom with a different number of neutrons but the same number of protons than another atom. Isotopes, thus can be said to have the same atomic number but different mass number. All isotopes of the same element have the same chemical properties. However some are radioactive. Isotopes are useful in medicine, biochemistry and in paleontology.