Simple diffusion is a type of passive transport where molecules move across a cell membrane from an area of high concentration to an area of low concentration, without the assistance of membrane proteins or energy input.
Examples of Simple Diffusion Across Cell Membranes
Several molecules utilize simple diffusion to move in and out of cells. According to the provided reference, these include:
- Water
- Oxygen
- Carbon dioxide
- Ethanol
- Urea
These substances are able to pass directly through the cell membrane, following the concentration gradient, without requiring any energy expenditure by the cell. The movement continues until equilibrium is reached.
Table Summarizing Examples of Simple Diffusion
| Molecule | Characteristics | Role in the Cell |
|---|---|---|
| Water | Small, polar molecule | Essential for cellular processes; solvent for many biochemical reactions. |
| Oxygen | Small, nonpolar molecule | Necessary for cellular respiration and energy production. |
| Carbon Dioxide | Small, nonpolar molecule | Waste product of cellular respiration; removed from the cell. |
| Ethanol | Small, amphipathic molecule | Can cross membranes relatively easily due to its partial solubility in lipids. |
| Urea | Small, polar molecule | Waste product of protein metabolism; excreted from the body. |
