Which transport processes require energy?

• A. Active transport and bulk transport
• B. Facilitated diffusion only
• C. Osmosis only
• D. Simple diffusion only

Answer: (A)

The concept being tested is when energy is needed for moving substances across membranes. Energy is required when a cell moves substances against their concentration gradient or moves large amounts of material in vesicles.

Active transport uses energy to push substances through a membrane even when they would move the other way along their gradient, often using ATP. An example is the sodium–potassium pump, which moves Na+ and K+ against their gradients.

Bulk transport also needs energy because it involves forming vesicles and moving them within the cell, which relies on ATP and motor proteins to drive endocytosis and exocytosis.

In contrast, facilitated diffusion, osmosis, and simple diffusion do not require cellular energy. They occur passively, driven by concentration or pressure gradients, with facilitated diffusion using membrane proteins to help substances move down their gradient, while osmosis and simple diffusion move water or small nonpolar molecules down their respective gradients.

So, processes that require energy are active transport and bulk transport.