What is the difference between a protein channel and a concentration gradient?

This is like comparing apples to oranges. A protein channel is a channel in the membrane of a cell, made of protein, that allows some solute to go through it. For example, you could have a sodium channel, and when open, sodium ions would flow through, but when closed, no sodium could move through. A concentration gradient means that there is more of the solute on one side of the membrane, than on the other, and if the membrane is permeable to this solute, then with time, the concentrations on each side will equalize via diffusion.

face creams

plumping lip gloss

powder

cooking oil