Simple diffusion

Definition

Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy input. It occurs across biological membranes and is driven by the concentration gradient.

5 Must Know Facts For Your Next Test

1. Simple diffusion does not require energy (ATP).
2. It can occur in both prokaryotic and eukaryotic cells.
3. Only small, nonpolar molecules like O2 and CO2 can easily diffuse through the lipid bilayer.
4. The rate of simple diffusion increases with a steeper concentration gradient.
5. Temperature and membrane permeability can affect the rate of simple diffusion.

Review Questions

• What types of molecules typically move through membranes by simple diffusion?
• How does temperature affect the rate of simple diffusion?
• Why does simple diffusion not require energy?

Related terms

Facilitated Diffusion: Passive transport process using carrier proteins or channels.

Active Transport: Movement of molecules against their concentration gradient, requiring ATP.

Osmosis:

Diffusion of water molecules across a selectively permeable membrane.