| endosymbiosis theory | The scientific theory that the organelles of eukaryotic cells arose when free-living procaryotic cells began living within other, larger free-living procaryotic cells and formed mutualistic symbiotic relationships with them. (09 Oct 1997) |
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| enzyme inhibition theory of narcosis | That narcotics inhibit respiratory enzymes by suppression of the formation of high energy phosphate bonds within the cell. (05 Mar 2000) |
| James-Lange theory | That bodily changes, such as tachycardia or sweating, precede rather than follow the conscious perception of an emotion and by themselves evoke the emotional feeling. (05 Mar 2000) |
| two-sympathin theory | A theory, now obsolete, advanced by Cannon and Rosenblueth that two different types of substances (sympathin E and I) diffuse into circulation when adrenergic nerves are stimulated, although the mediator itself is the same. (05 Mar 2000) |
| jungian theory | A theoretical psychoanalytical system centreed around symbols of the unconscious with the unconscious material derived from two sources - the personal unconscious (repressed or forgotten experiences, thoughts and feelings) and the collective or objective unconscious (the universal inherited qualities which dispose the individual to behave as his ancestors). (12 Dec 1998) |
| Young-Helmholtz theory of colour vision | A theory that there are three colour-perceiving elements in the retina: red, green, and blue. Perception of other colours arises from the combined stimulation of these elements; deficiency or absence of any one of these elements results in inability to perceive that colour and a misperception of any other colour of which it forms a part. Synonym: Helmholtz theory of colour vision. (05 Mar 2000) |
| kern-plasma relation theory | A theory enunciated by Hertwig (1903) that a definite relation as to size normally exists in every cell between the mass of nuclear material and that of the protoplasm. Origin: Ger. Kern, kernel, nucleus (05 Mar 2000) |
| kinetic molecular theory | <chemistry> This theory assumes that molecules must collide in order to react. The more collisions the more likely it is for a reaction to occur. However, depending on the conditions, only a small fraction of the collisions are effective in producing a reaction. There are several constraints. In order for a reaction to occur, bonds initially are broken, which requires energy. This energy depends on the type of the reaction and comes from the kinetic energies that the molecules possess before the collision. It is called the activation energy. Increasing the temperature increases the kinetic energies and more collisions will occur. In adition, at a higher temperature a greater number of the reacting molecules might possess an energy equal to or greater than the activation energy. However the molecules must also collide in a specific orientation, called the steric factor in order for a reaction to occur. A reaction will only be successful, if the collision has enough energy to be either equal to or greater than the activation energy and if the orientation of the collision allows for correct bond formation. These factors are in the Arrhenius equation: k = zp The rate constant k is proportional to the Arrhenius factor A. A is the product of the collision frequency z, and the steric factor p. The fraction of collisions with sufficient energy to produce a reaction are in the term of the equation. (09 Jan 1998) |
| unineme theory | <cell biology> Theory that proposes that each chromosome (before S phase) consists of a single strand of DNA. Now generally accepted and being noncontroversial the term has fallen into disuse. (18 Nov 1997) |
| Knoop's theory | That the catabolism of fatty acids occurs in stages in each of which there is a loss of two carbon atoms as a result of oxidation at the beta-carbon atom, e.g. (05 Mar 2000) |
| Flourens' theory | That thought is a process depending upon the action of the entire cerebrum. (05 Mar 2000) |
| Ladd-Franklin theory | A theory, pertaining to colour vision, that gray is the earliest of colour sensations, from which are derived, by molecular change, two paired substances that, respectively, detect yellow and blue, and that the yellow gives rise to paired substances for detection of red and green. Synonym: Ladd-Franklin theory. (05 Mar 2000) |
| lamarckian theory | That acquired characteristics may be transmitted to the descendants and that experience, and not biology alone, can change and thereby influence genetic transmission. (05 Mar 2000) |
| Frerichs' theory | That uraemia represents a toxic condition caused by ammonium carbonate, which is formed as the result of the action of a plasma enzyme on the increased amounts of urea. (05 Mar 2000) |
| learning theory | Any of several prominent theories designed to explain learning, especially those promulgated by Pavlov, Thorndike, Guthrie, Hull, Kohler, Spence, Miller, Skinner, and their modern followers. See: conditioning. (05 Mar 2000) |