How does facilitated transport differ from active transport regarding energy usage?

Facilitated transport and active transport are two mechanisms used by cells to move substances across membranes, and they differ significantly in how they utilize energy. Active transport specifically requires energy to move substances against their concentration gradient, meaning it moves molecules from an area of lower concentration to an area of higher concentration. This process often relies on the hydrolysis of ATP or other energy sources, ensuring that the cell can accumulate nutrients or maintain ion concentrations crucial for its function.

In contrast, facilitated transport operates without the direct use of energy. It takes advantage of existing concentration gradients, allowing molecules to move from areas of higher concentration to lower concentration through specific transport proteins in the cell membrane. This type of transport is essential for substances that cannot easily diffuse through the lipid bilayer, such as ions and polar molecules.

B captures the essence of active transport by emphasizing its reliance on energy to move substances against their gradient. This distinction is fundamental in understanding cellular transport mechanisms and their respective roles in maintaining homeostasis within biological systems.