What type of transport requires carrier molecules and energy?

Active transport is the correct answer because it involves the movement of molecules across a cell membrane against their concentration gradient, which requires energy. This process is typically powered by adenosine triphosphate (ATP). Carrier molecules, which are specific proteins embedded in the cell membrane, play a crucial role in this transport process by binding to the molecules that need to be moved, aiding in their passage across the membrane despite the unfavorable concentration gradient. Unlike passive transport methods, such as diffusion and facilitated diffusion, which rely on the natural kinetic energy of molecules and do not require additional energy, active transport enables cells to maintain necessary concentrations of various ions and molecules, essential for processes like nutrient uptake and waste removal. This energy-dependent mechanism is vital for maintaining homeostasis within cells.