Active and passive transport are two fundamental processes that cells use to move substances across their membranes, and both are influenced by the concentration gradient.
Passive Transport: This process occurs when substances move across a cell membrane without the need for energy because they move along the concentration gradient—from an area of higher concentration to an area of lower concentration. Think of it like a ball rolling down a hill; it naturally moves to the lower point without any push. Common examples of passive transport include diffusion and osmosis.
Active Transport: In contrast, active transport requires energy (usually from ATP) because it involves moving substances against their concentration gradient—from an area of lower concentration to an area of higher concentration. This can be likened to pushing a ball uphill; it needs an external force to move it in that direction. An example of active transport is the sodium-potassium pump, which helps maintain essential gradients of sodium and potassium ions across the cell membrane.
In summary, the concentration gradient directly influences how substances are transported in and out of cells. Passive transport relies on this gradient and does not require energy, while active transport does require energy to move substances against the gradient.