Answer:
From their region of high concentration to their region of low concentration.
Explanation:
A substance that moves across a cell membrane without using the cells energy tends to move from their region of high concentration to their region of low concentration. A good example of such a process would be Osmosis.
On the other hand if the substance moves across a cell membrane and requires the use of energy then it tends to move against a concentration gradient, as is the case with Active transport.
