Final answer:
Passive transport moves substances from high to low concentration without energy, while active transport moves molecules against their concentration gradient using energy.
Explanation:
Passive transport is a process where substances move from an area of higher concentration to lower concentration without requiring energy input from the cell. In contrast, active transport involves the movement of substances against their concentration gradient, requiring energy usually in the form of ATP.
Active transport mechanisms utilize protein carriers and energy to transport molecules uphill across membranes. An example is the sodium-potassium pump that moves sodium out and potassium into cells against their concentration gradients.
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