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Fick's first law relates the diffusive flux to the gradient of the concentration. It postulates that the flux goes from regions of high concentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient (spatial derivative), or in simplistic terms the concept that a solute will move from a region of high concentration to a region of low ...
A morphogen spreads from a localized source and forms a concentration gradient across a developing tissue. [7] In developmental biology, 'morphogen' is rigorously used to mean a signalling molecule that acts directly on cells (not through serial induction) to produce specific cellular responses that depend on morphogen concentration.
is the gradient, i.e., rate of change with position, of the logarithm of the salt concentration, which is equivalent to the rate of change of the salt concentration, divided by the salt concentration – it is effectively one over the distance over which the concentration decreases by a factor of e. The above equation is approximate, and ...
For example, oxygen can diffuse through cell membranes so long as there is a higher concentration of oxygen outside the cell. However, because the movement of molecules is random, occasionally oxygen molecules move out of the cell (against the concentration gradient).
where is the diffusion coefficient and can be obtained by the Stokes-Einstein equation, and the second term is the gradient of the chemical potential with respect to position. Note that [B] refers to the average concentration of B in the solution, while [B](r) is the "local concentration" of B at position r.
μ is the growth rate of a considered microorganism, μ max is the maximum growth rate of this microorganism, [S] is the concentration of the limiting substrate S for growth, K s is the "half-velocity constant"—the value of [S] when μ/μ max = 0.5. μ max and K s are empirical (experimental) coefficients to the Monod equation. They will ...
The mole fraction, the molar concentration, and the partial pressure of both gases involved in equimolar counterdiffusion vary linearly. These relationships can be found in the following equations expressing the molar flow rates for each species, A and B, for a one-dimensional flow through a channel with no homogeneous chemical reactions:
The first term corresponds to Fick's law of diffusion, which gives the flux due to diffusion down the concentration gradient, i.e., from high to low concentration. The constant D A is the diffusion constant of the ion A.