ACTIVE TRANSPORT
 Active transport is the movement of molecules across a cell membrane from a region of their lower concentration to a region of their higher concentration in the direction against some gradient or other obstructing factor (often a concentration gradient). Unlike passive transport, which uses the kinetic energy and natural entropy of molecules moving down a gradient, active transport uses cellular energy to move them against a gradient, polar repulsion, or other resistance. Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants

Electrochemical gradients

 

We have already discussed simple concentration gradients, in which a substance is found in different concentrations over a region of space or on opposite sides of a membrane. However, because atoms and molecules can form ions and carry positive or negative electrical charges, there may also be an electrical gradient, or difference in charge, across a plasma membrane. In fact, living cells typically have what’s called a membrane potential, an electrical potential difference (voltage) across their cell membrane.