What does "fishing down the food web" mean?​

Fishing down the food web is the cycle whereby fisheries in a given environment, "having drained the enormous savage fish on top of the food web, go to progressively more modest species, at last winding up with recently scorned little fish and spineless creatures".

Explanation:

this protocol provides a detailed procedure for agarose-based ip to purify and enrich the protein of interest.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.