In general, flux in

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

relates to movement of a substance between compartments. There are several cases where the concept of flux is important. * The movement of molecules across a membrane: in this case, flux is defined by the rate of

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemica ...

or transport of a substance across a permeable

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

. Except in the case of active transport, net flux is directly proportional to the

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...

difference across the membrane, the surface area of the membrane, and the membrane permeability constant. * In

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

, flux is often considered at the

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

level – for instance, accurate determination of

carbon flux The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...

es using techniques like

eddy covariance The eddy covariance (also known as eddy correlation and eddy flux) is a key atmospheric measurement technique to measure and calculate vertical turbulent fluxes within atmospheric boundary layers. The method analyses high-frequency wind and scal ...

(at a regional and global level) is essential for modeling the causes and consequences of

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

. * Metabolic flux refers to the rate of flow of metabolites through a biochemical network, along a linear metabolic pathway, or through a single enzyme. A calculation may also be made of carbon flux or flux of other elemental components of biomolecules (e.g. nitrogen). The general unit of flux is chemical mass /time (e.g., micromole/minute; mg/kg/minute). Flux rates are dependent on a number of factors, including: enzyme concentration; the concentration of precursor, product, and intermediate metabolites;

post-translational modification Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...

of enzymes; and the presence of metabolic activators or repressors. Metabolic flux in biologic systems can refer to biosynthesis rates of polymers or other macromolecules, such as proteins, lipids, polynucleotides, or complex carbohydrates, as well as the flow of intermediary metabolites through pathways.

Metabolic control analysis Metabolic control analysis (MCA) is a mathematical framework for describing metabolic, signaling, and genetic pathways. MCA quantifies how variables,elastsuch as fluxes and species concentrations, depend on network parameters. In particular, it is a ...

and

flux balance analysis Flux balance analysis (FBA) is a mathematical method for simulating metabolism in genome-scale reconstructions of metabolic networks. In comparison to traditional methods of modeling, FBA is less intensive in terms of the input data required for c ...

provide frameworks for understanding metabolic fluxes and their constraints.

Measuring movement

Flux is the net movement of particles across a specified area in a specified period of time. The particles may be ions or molecules, or they may be larger, like insects, muskrats or cars. The units of time can be anything from milliseconds to millennia. Flux is not the same as velocity or speed nor is it the same as density or concentration. Movement itself is not enough.

References

Biology terminology {{biology-stub