Answer:
Involves the transport of ions
Step-by-step explanation:
Cells need certain substances in form of ions to function. These ions /solutes dissolve in a solvent (usually water) and move in and out of the cell. This movement is propelled by the osmotic/electrochemical gradient formed between the cell's membrane and the extracellular content. In nature, this dissolved solutes move down the concentration gradient.
However, in case whereby the concentration gradient is not favorable for the solute to move into the cell, the cell brings them in against concentration gradient using energy in form of ATP. This process is known as ACTIVE TRANSPORT. Active transport is the movement of ions/substances across a membrane against concentration gradient with the use of ATP.
An important example is the sodium-pottasium pump that moves sodium (Na+) into the cell and pottasium (K+) out of the cell.