Final answer:
Active transport is a true energy-expending process necessary for moving substances against a concentration gradient or for transporting large molecules across a cell membrane, using ATP as the energy source.
Step-by-step explanation:
Active transport proceeds when energy is expended, which is true. This critical biological process involves the movement of molecules and ions across a cell’s plasma membrane. Unlike passive transport, active transport requires the cell to use its energy, mainly in the form of adenosine triphosphate (ATP), to move substances against their concentration gradient – from areas of lower concentration to areas of higher concentration – or to transport large molecules that cannot pass through the membrane easily.
Two common examples of active transport include the sodium-potassium pump, which plays a significant role in nerve transmission and muscle contraction, and vesicle transport, which is used to move large particles such as proteins and polysaccharides into or out of the cell. Both mechanisms are essential for maintaining cellular homeostasis.
Active transport processes are vital because they allow cells to maintain concentration gradients of certain substances, which are crucial for various physiological functions. For instance, cells can uptake nutrients even when they are in lower concentrations outside the cell or expel waste products against their concentration gradient. Therefore, active transport is indispensable in sustaining life at the cellular level.