Passive Transport

Did you know that cells can move molecules in and out without using energy? This process is called passive transport.

A common example is simple diffusion, where small, uncharged molecules like oxygen and carbon dioxide move from areas of high concentration to low concentration.

For instance, when we breathe, the oxygen in the lungs rises and becomes greater than the oxygen in the blood. This concentration difference allows oxygen molecules to diffuse from the lungs into the bloodstream.

However, carbon dioxide moves from the bloodstream to the lungs, where its concentration is lower. This natural movement helps maintain essential gas exchange in the body.

But what about larger or charged molecules like glucose or sodium ions? They need extra help to cross the membrane and rely on another form of passive transport called facilitated diffusion.

Here, special proteins known as channel proteins create open passageways for ions, while carrier proteins bind to molecules and carry them across the membrane.

Both types of passive transport, simple and facilitated diffusion, allow molecules to flow down their concentration gradient without energy.