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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 chemical potential .
Motile animals can disperse themselves by their spontaneous and independent locomotive powers. For example, dispersal distances across bird species depend on their flight capabilities. [24] On the other hand, small animals utilize the existing kinetic energies in the environment, resulting in passive movement.
This high concentration of urea creates a diffusion gradient which permits the shark to absorb water in order to equalize the concentration difference. [4] The crab-eating frog , or Rana cancrivora, is an example of a vertebrate osmoconformer.
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 ...
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment.
[40] [2]: 405 In the absence of blood vessels, oxygen, nutrients, and waste products would need to diffuse across the interface, a process that would be greatly limited by the available partial pressure and surface area, in accordance with Fick's law of diffusion. [41]: 48 For large multicellular animals, diffusion would be insufficient. [27]
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes (salts in solution which in this case is represented by body fluid) to keep the body fluids from becoming too diluted or concentrated.
The kinesis strategy controlled by the locally and instantly evaluated well-being can be described in simple words: Animals stay longer in good conditions and leave bad conditions more quickly. If the well-being is measured by the local reproduction coefficient then the minimal reaction-diffusion model of kinesis can be written as follows: [ 3 ]