Passive transport is a process that allows molecules to move across cell membranes without the need for energy input. This movement occurs along the concentration gradient, from an area of higher concentration to an area of lower concentration. Several types of molecules use passive transport, including:
- Oxygen (O2): Oxygen molecules are small and non-polar, allowing them to easily diffuse through the lipid bilayer of the cell membrane.
- Carbon Dioxide (CO2): Similar to oxygen, carbon dioxide is also small and non-polar, facilitating its diffusion across the membrane.
- Water (H2O): Water molecules can pass through the cell membrane via osmosis, a type of passive transport. They move through specialized channels called aquaporins.
- Lipids: Lipids, being hydrophobic, can easily pass through the lipid bilayer without the need for energy.
- Small Non-Polar Molecules: Molecules like ethanol and urea can also diffuse through the cell membrane due to their small size and non-polar nature.
These molecules rely on passive transport to maintain cellular homeostasis and ensure that essential substances are efficiently distributed within the cell.