Factors influencing passive diffusion:
* Size: Smaller molecules diffuse more easily than larger ones.
* Lipid solubility: Molecules that are more soluble in lipids (like fats) can pass through the phospholipid bilayer more readily.
* Charge: Uncharged molecules generally diffuse more easily than charged ones.
* Concentration gradient: Molecules move from areas of high concentration to areas of low concentration.
Examples of molecules that diffuse passively:
* Oxygen (O2): Small, non-polar, and essential for cellular respiration.
* Carbon dioxide (CO2): Small, non-polar, and a byproduct of cellular respiration.
* Water (H2O): Small and polar, but its high concentration allows for significant passive diffusion.
* Steroid hormones: Lipid-soluble and can easily cross the membrane.
* Small, uncharged molecules: Like ethanol, urea, and glycerol.
It's important to note that:
* Some molecules require facilitated diffusion to cross the membrane, which involves protein channels or carriers. Examples include glucose, amino acids, and ions.
* Active transport moves molecules against their concentration gradient, requiring energy.
Let me know if you'd like to explore any of these topics in more detail!
