Q. What is the relationship between concentration gradient and passive and active transport?

Passive transport is the movement of substances across membranes in favour of their concentration gradient that is from a more concentrated region to a less concentrated region. Active transport, on the other hand, is the transport of substances across membranes against their concentration gradient, from a fewer concentrated to a more concentrated region. In passive transport, because it is spontaneous, there is no energy spent the active transport though requires energy (work) to occur.

Active transport works to increase or maintain the concentration gradient of a substance between two regions while passive transport acts in a manner to reduce the concentration gradient.