1. Presence of a Hydrophobic Core:
* Cell membranes are composed of a phospholipid bilayer.
* The phospholipids have hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
* The hydrophobic tails face inwards, creating a hydrophobic core within the membrane.
* Liquid-soluble molecules, which are also hydrophobic, can easily pass through this hydrophobic core.
2. Selectively Permeable:
* The cell membrane acts as a barrier, regulating what enters and leaves the cell.
* This is achieved by its selective permeability.
* While liquid-soluble molecules can easily pass through, larger molecules and charged molecules may need assistance (e.g., through protein channels).
3. Fluid Mosaic Model:
* The membrane is not a rigid structure but a fluid mosaic.
* This means the phospholipids can move laterally within the membrane, and proteins are embedded within it.
* This fluidity allows for the passage of small, hydrophobic molecules.
4. Possible Facilitated Diffusion:
* While liquid-soluble molecules may pass through the membrane directly, some may require the assistance of membrane proteins.
* This process is called facilitated diffusion, where a protein acts as a carrier to help the molecule cross the membrane.
In summary: The ability of liquid-soluble molecules to move across a cell membrane indicates a hydrophobic core within the membrane, which facilitates the passage of such molecules. However, the membrane still maintains its selective permeability, ensuring only specific molecules can enter and leave the cell.
