Passive transport and active transport are fundamental processes that cells use to move substances across their membranes. The correct distinction between these two processes is that passive transport moves substances along their concentration gradient, meaning from an area of higher concentration to an area of lower concentration, without the expenditure of energy. This occurs naturally due to the inherent tendency of molecules to spread out and reach equilibrium.
On the other hand, active transport involves moving substances against their concentration gradient, which requires energy, typically in the form of ATP. This process enables cells to accumulate substances in concentrations that are higher than those in the surrounding environment, which is essential for various cellular functions, including nutrient uptake and waste removal.
The other options do not accurately convey the relationship between passive and active transport, as they either mix up the descriptions of how energy is used or misrepresent the direction relative to the concentration gradient, or inaccurately state the involvement of proteins in these processes. Understanding the correct definitions helps clarify the critical roles these transport mechanisms play in maintaining cellular homeostasis and function.