What is a concentration gradient?

A concentration gradient occurs when you have a solute, like salt, dissolved in a solution, like water. Most of the time there won't be the same amount of salt through out all of the water - there will be more in some areas (a higher concentration) and less in others (a lower concentration). From the highest concentration areas, the concentration gradually decreases to the lowest - this is called a concentration gradient and it is very important in biology.