What is the difference between passive and active transport?

Passive transport moves substances down their concentration gradient without energy, while active transport requires energy to move substances against their gradient.

Passive transport and active transport are two fundamental methods by which cells move substances across their membranes. Passive transport, as the name suggests, is a process that does not require any energy input from the cell. It involves the movement of substances from an area of higher concentration to an area of lower concentration, following the concentration gradient. This process continues until equilibrium is reached, where the concentrations of the substances are equal on both sides of the membrane. Examples of passive transport include simple diffusion, facilitated diffusion, and osmosis.

On the other hand, active transport is a process that requires energy, usually in the form of ATP (adenosine triphosphate), to move substances against their concentration gradient. This means substances are moved from an area of lower concentration to an area of higher concentration. Active transport is essential for maintaining the cell's internal environment, allowing it to keep the concentrations of certain substances at levels different from their surroundings. Examples of active transport include the sodium-potassium pump, endocytosis, and exocytosis.

The key difference between these two types of transport lies in the direction of the movement of substances and the requirement of energy. Passive transport is driven by the natural tendency of substances to spread out evenly, while active transport is driven by cellular energy to maintain specific concentration gradients.

In terms of their roles in the cell, both passive and active transport are crucial for the cell's survival and function. Passive transport allows necessary substances like water and oxygen to enter the cell easily, and waste products to leave. Active transport, however, allows the cell to control the movement of ions and large molecules, which is essential for various cellular functions such as nerve impulse transmission and muscle contraction.

In summary, while both passive and active transport are essential for cellular function, they differ in their energy requirements and the direction of substance movement.