Glossary of Scientific Terms

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D

Darwinian fitness
The true measure of evolutionary change of an organism. Darwinian fitness refers to the numerical advantage of having offspring. The individual with the most offspring has the higher fitness. The reasons can be chance or natural selection and are not important to measure fitness. It is often equated with survival of the fittest, which is often meant to be the strongest or best adapted individual. However, this interpretation is wrong, if it does not explain why a certain individual has the most offspring. Overall, the genetic variation of the individuals with the most offspring will dominate the genepool of a population. The change in genetic variability in a population from generation to generation is the true measure of (micro-)evolution.

Degree of freedom
A degree of freedom accounts for an independent variable in a system. Independent variables allow for changes within a system. For instance, the movement of two atoms in a gas is independent of each other assigning the distance between two atoms one degree of freedom. Two atoms covalently linked together within a molecule (a chemical bond) are also described by the same degree of freedom, also their movements are usually coupled. While this is true for the movement of the entire molecule, the length of the chemical bond is not static, but vibrates at very short time ranges measured in femto seconds to pico seconds (one trillionth to one billionth of a second). How many degrees of freedom a system has depends on the number of components and their interactions.

Depolarization
A process of changing the membrane potential from negative to more positive values. The sign of the potential refers to the inside of the cell. Depolarization causes action potentials in neurons and muscle cells. (See also hyperpolarization; op.). Depolarization is the result of inward currents carried by Na+ and Ca++ ions.

Designer foods
Foods that are enriched with nutraceuticals, antioxidants, and secondary metabolites to improve the physical performance of the body.

Diffusion coefficient D
The diffusion coefficient D describes the relationship between a concentration gradient DC/Dx and the flow of matter per unit area (flux rate J)

DNA (see also RNA)
Short for Deoxy-Ribonucleic Acid; makes up the genetic component of each cell. DNA is a linear polymer of four building blocks called nucleotides. Nucleotides are distinguished by their base structures known as adenine (A), guanine (G), thymine (T), and cytosine (C). The structure of DNA is the double helix and in all organisms contains only two forms of base pair combinations  -  AT (TA) and GC (CG)  -  which determine and control the accurate copying of the nucleotide sequence during cell division or protein biosynthesis.

Driving Force
A terminology used in thermodynamics expressing the availability of energy to 'drive' a process such as mechanical work or chemical synthesis. Driving forces exist where a potential gradient exist. A potential gradient can be in form of a temperature gradient causing heat to flow, an electrical gradient causing electrons or ions to flow, or a concentration gradient causing diffusion.
 

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Copyright  © 2000-2008 Lukas K. Buehler