Question

Why bacteria cells prefer active transport rather than facilitated diffusion? Why do they want energy to diffuse substances than letting the molecules go through protein channels ?

Answer 1

I am not so sure it is a matter of preferring, but rather that there isn't much a choice.
Assume you have a molecule A that can exist in the cellular and extracellular environment. the equilibrium between the amount of molecule A in the cellular and extracellular environment is given by some equilibrium constant and thereby free energy.

Facilitated diffusion:
The facilitated diffusion will go towards equilibrium (for now assume the constant is 1 meaning 50/50 on each side). The thermodynamics would still remain the same as no energetics has changed through a transporter. The kinetics would however be elevated to faster reach equilibrium than would it be left to diffusion alone.

Active transport:
The active transport will add an additional equilibrium into the consideration. Let's still assume that molecule A got a equilibrium constant of 1, this means that ideally there would be 50/50 on each side, but as you now got an additional equilibrium which is having an equilibrium constant different from 1, this would be multiplied to the first equilibrium constant to describe the full reaction to thus obtain an equilibrium constant different from 0 of the full reaction and change the energetics of the reaction.


If we are talking anti and co-transport it follows the same principle as active transport (the "driving" equilibrium), but transport by simply using a protein channel does not change the thermodynamics, but the kinetics (exactly like enzymes!)

Answer 2

If you want a source I can provide you with a compendium in electrophysiology which attempts to describe the thermodynamics of ion transport in neurons.

Answer 3

That makes sense. Thank you!