CBSE Class 9 Answered

Active transport is an energy utilising process, in which the cell transports molecules against a concentration gradient ( i.e. from regions of low concentration to regions of high concentration). ATP or other form of metabolic energy is utilised in active transport. This process is usually carried out with the aid of proteins in the cell membrane. An example of this process is the sodium-potassium pump that maintains the sodium and potassium ion gradients across nerve cell membranes.