Final answer:
Carrier proteins are used in both active and passive transport to move substances across cell membranes. In passive transport, they facilitate movement down a concentration gradient without energy, while in active transport, energy in the form of ATP is required to move substances against a gradient.
Step-by-step explanation:
Both active transport and passive transport mechanisms can utilize transport proteins that span a cell's plasma membrane. A shared component in both types of transport is the use of carrier proteins, which serve to move substances across the membrane.
In passive transport, these proteins facilitate the movement of substances from areas of higher concentration to areas of lower concentration without the expenditure of cellular energy. This process includes methods such as osmosis and facilitated diffusion. Contrastingly, active transport requires energy, often derived from ATP (adenosine triphosphate), to move substances against their concentration gradient, from regions of lower concentration to higher concentration.
The sodium-potassium pump is an example of an active transport mechanism where ATP is used to move sodium and potassium ions across the membrane, against their respective concentration gradients. This establishes an electrochemical gradient necessary for various cellular processes.
A detailed mechanism like receptor-mediated endocytosis also involves active transport, where specific substances are ingested into the cell with the help of specific binding proteins and ATP.