Question

What causes concentration gradient?

Answer 1

A concentration gradient occurs when over a particular range, the concentration of a substance gets progressively smaller. Substances will tend to move from where they are most concentrated to where they are least concentrated, i.e. along their concentration gradient.

Answer 2

in biology, concentration gradients are used to power chemical reactions. they are "produced" by active ion pumps, which are membrane proteins. also, during photosynthesis, protons are pumped into an extra compartiment by sheer electromagnetic force. those are the two causes for concentration gradients.