Passive Transport: Diffusion and Osmosis

Ever wonder how your cells get what they need without working hard? That's passive transport - the natural movement of molecules from areas where there's more of them to areas with less. No energy required!

There are two main types of passive transport. Diffusion is when molecules spread across a cell membrane from high to low concentration. Think about how a drop of food coloring spreads through water - that's diffusion in action! The material being dissolved (like salt or sugar) is called the solute, while the liquid doing the dissolving (usually water in living things) is the solvent.

Osmosis is simply the diffusion of water molecules across a membrane. Water always moves from areas with more water to areas with less water. This movement is described using three important terms: hypertonic (high solute concentration), hypotonic (low solute concentration), and isotonic (equal concentration).

💡 Remember: In a hypertonic environment, water moves OUT of the cell. In a hypotonic environment, water moves INTO the cell. In an isotonic environment, water moves equally in and out.

Some molecules are too large to pass through the membrane directly but still need to move from high to low concentration. They use facilitated diffusion - hitching a ride through special channel proteins or carrier proteins in the membrane. Like regular diffusion, this still doesn't require energy!