What process requires energy (ATP) to move substances from low to high concentration?

• A. Facilitated Diffusion
• B. Passive Transport
• C. Active Transport
• D. Osmosis

Answer: (C)

Active transport is the process that requires energy in the form of ATP to move substances against their concentration gradient, which means from an area of lower concentration to an area of higher concentration. This is essential for maintaining cellular homeostasis and allowing cells to acquire necessary nutrients or ions that may be present in lower concentrations outside the cell.

In contrast, facilitated diffusion, passive transport, and osmosis do not require energy. Facilitated diffusion moves substances down their concentration gradient with the help of transport proteins. Passive transport refers to any movement of molecules across a membrane that does not require energy, while osmosis is a specific type of passive transport referring to the movement of water across a semipermeable membrane. None of these processes involve the input of ATP as active transport does.