Final answer:
Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient. It is an important mechanism for maintaining homeostasis in cells. ATP is commonly used as the energy source for active transport.
Step-by-step explanation:
Active transport is the energy-requiring process of pumping molecules and ions across membranes against a concentration gradient. Unlike passive transport, which moves particles down a concentration gradient, active transport moves particles against the concentration gradient. It requires the expenditure of energy, usually in the form of ATP.
One example of active transport is the sodium-potassium pump, which exchanges sodium ions for potassium ions. By actively pumping these ions against their concentration gradients, the sodium-potassium pump helps to maintain homeostasis.
In summary, active transport is the process of moving particles against their concentration gradient, requiring the input of energy. ATP is commonly used as the energy source for active transport.