# Diffusion and Osmosis **Diffusion:** Movement from a high to low concentration without the use of energy. **Osmosis:** A type of diffusion, specifically the diffusion of a [[Solutions & Concentrations|solvent]] across a *selectively permeable* membrane. ## Principles of Diffusion **Osmotic Pressure** **Types of Tonicity** - *Isotonic* (equilibrium) - *Hypotonic:* Lower solute concentration - If a microorganism - *Hypertonic:* Higher osmotic concentration > [!info]- Types of Tonicity Visualized > > ![[Pasted image 20230914034413.png|675]] > > --- > > ![[Pasted image 20231003175413.png|700]] > > ## Diffusion (Passive Transport) In all types of passive transport, molecules/ions are traveling *down their concentration gradient* There are two main types of diffusion: - **Passive Diffusion:** Transportation of small molecules which cross the plasma membrane independently (Ex: H2O, O2, CO2) - **Facilitated Diffusion:** Transport of typically larger molecules across the plasma membrane by traveling through *permease* proteins ![[Passive vs Active Transport.png|300]] saturation (space on the highway vs volume of traffic)