Active transport mechanisms are collectively called pumps. What do they work against?

1. To move substances against a concentration or electrochemical gradient, the cell must use energy. 2. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. 3. That energy is harvested from ATP generated through the cell's metabolism. 4. Osmotic pressure, hydrostatic pressure and surface tension are real quantities, but none of them is what a pump is built to oppose. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 5 "Structure and Function of Plasma Membranes", section 5.3 Active Transport_