What is active transport? Use an example to demonstrate when active transport is used.

Active transport is a process where particles move from an area of low concentration to an area of high concentration against a concentration gradient. In order for particles to move against a concentration gradient, energy is required in the form of ATP. Carrier proteins use ATP to move particles across cell membranes.
An example of where active transport is used is in the root hair cells of plants. These cells need essential minerals to move from an area of low concentration in the soil, to an area of high concentration in the cell. Root hair cells are adapted to carry out active transport as they contain high numbers of mitochondria. Mitochondria produce the ATP needed to move particles against the concentration gradient.