Final answer:
Active transport mechanisms require the cell's energy, usually in the form of adenosine triphosphate (ATP), to move substances into the cell against their concentration gradient.
Step-by-step explanation:
Active transport mechanisms require the use of the cell's energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient—that is, if the concentration of the substance inside the cell is greater than its concentration in the extracellular fluid—the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane.