How does active transport differ from passive transport?

Active transport is characterized by the movement of molecules against their concentration gradient, meaning that substances move from areas of lower concentration to areas of higher concentration. This process is essential for maintaining cellular functions, such as nutrient uptake and waste removal, particularly when the substances need to enter or exit the cell in a manner that would not occur spontaneously due to diffusion.

In contrast, passive transport involves the movement of substances along their concentration gradient, from high to low concentration, and does not require energy input. Therefore, the distinction lies in the direction of movement and the energy requirements; active transport needs energy, typically in the form of ATP, to drive the process, reflecting the need to move substances against their natural flow.

The other options do not accurately describe the differences between active and passive transport. Active transport does not exclusively occur in plant cells; it is a mechanism present in various types of cells, including animal cells. Additionally, active transport requires energy, so the statement that it requires no energy is incorrect. Lastly, while the speed of transport can vary based on the circumstances and specific substances involved, the distinguishing factor remains whether energy is utilized and the direction of the concentration gradient.