The kind of passive absorption of anions against the concentration gradient, in order to neutralize the effect of fixed cations in the cell, is called ____.

Donnan equilibrium is a passive process that accounts for the accumulation of ions against their concentration gradient without the expenditure of metabolic energy (ATP).

When a cell contains fixed, non-diffusible ions (such as proteins or organic molecules with a net charge), it creates an electrical imbalance. To neutralize the effect of these fixed cations or anions, diffusible ions of the opposite charge from the external medium passively diffuse into the cell.

This movement occurs against the concentration gradient but along the electrical gradient, eventually reaching an equilibrium state known as the Donnan equilibrium.

Answer: Donnan equilibrium