Which transport process moves substances against their concentration gradient and requires energy?

Which transport process moves substances against their concentration gradient and requires energy?

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

Answer: (C)

Moving substances against their concentration gradient requires energy because you’re pushing them from a region of low concentration to a region of higher concentration, which is not spontaneous. In cells, this energy comes from ATP directly or from the energy stored in another gradient, and it’s delivered by pumps that move ions or molecules uphill. This is what defines active transport: it uses energy to move substances uphill, such as the Na+/K+ pump or a glucose/Na+ cotransporter that relies on a preexisting ion gradient. By contrast, passive processes like diffusion, osmosis, and facilitated diffusion move substances down their gradient without using cellular energy, so they do not require energy.

Moving substances against their concentration gradient requires energy because you’re pushing them from a region of low concentration to a region of higher concentration, which is not spontaneous. In cells, this energy comes from ATP directly or from the energy stored in another gradient, and it’s delivered by pumps that move ions or molecules uphill. This is what defines active transport: it uses energy to move substances uphill, such as the Na+/K+ pump or a glucose/Na+ cotransporter that relies on a preexisting ion gradient. By contrast, passive processes like diffusion, osmosis, and facilitated diffusion move substances down their gradient without using cellular energy, so they do not require energy.