Final answer:
Active transport requires energy to move substances against their concentration gradient, whereas passive transport does not. Examples of passive transport include simple diffusion, facilitated diffusion, and osmosis, while active transport examples include the sodium-potassium pump.
Step-by-step explanation:
The primary difference between active and passive transport across the plasma membrane is the need for energy. Passive transport requires no energy as substances move down their concentration gradient from an area of higher concentration to one of lower concentration. Examples of passive transport methods include simple diffusion, facilitated diffusion, and osmosis. For instance, carbon dioxide can cross the membrane directly by simple diffusion due to its small size and nonpolar nature.
On the other hand, active transport requires energy in the form of ATP (adenosine triphosphate) when substances need to be moved against their concentration gradient, from an area of lower concentration to one of higher concentration. The sodium-potassium pump is a well-known example of active transport, as it uses ATP to move sodium ions out of the cell and potassium ions into the cell, both against their respective concentration gradients.
Understanding these transport processes is essential for maintaining the homeostasis of a cell, ensuring that the cell's internal environment remains stable despite changes in the external environment. Active and passive transport are critical mechanisms by which cells regulate the concentration of various substances, thereby maintaining equilibrium.