∞ generated and posted on 2016.12.04 ∞
Movement from a region of high substance density or prevalence to a region of low density or prevalence.
| Down a Concentration Gradient refers to going from regions of high concentration of some entity to regions of low concentration, and such movement generally occurs spontaneously, that is, if allowed to happen it happens. |
Concentration gradients can be either gradual or instead abrupt. Gradual occurs during diffusion within a homogeneous environment, at least until the diffusion has eliminated the concentration gradient. Abrupt can be going from one side to the other side of a lipid bilayer, i.e., a membrane, and particularly as cell membrane.
Movement down a concentration gradient is movement towards equilibrium and as a consequence such movement releases energy, that is, the free energy of a system declines in the course of such movement and, therefore, movement down a concentration gradient is said to spontaneous.
Figure legend: The dashed line represents a barrier that is permeable to the stars, though actually having a permeable barrier is superfluous to the concept of down a concentration gradient. That is, a permeable barrier is not a requirement for movement down a concentration gradient… What matters is the difference in concentration going from one place to the other, that is, that there is a concentration gradient to go down. Net movement is from the region of high star concentration, here on the left, to the region of low star concentration, as found to the right. Any given star has the same potential to move in either direction. Nonetheless, because there are more stars on one side than the other, there simply is more moving in the region of high concentration than the region of low concentration, resulting in more movement to the region of low concentration than to the region of high concentration.
Down a concentration gradient can also be stated as movement that occurs 'with' a concentration gradient. Contrast with up a concentration gradient.