Hi,here is a text I saw on the Internet

"The membrane is highly permeable to non-polar (fat-soluble) molecules. The permeability of the membrane to polar (water soluble) molecules is very low. The permeability to charged molecular species (ions) is very low.

Surely i know cell membrane is lipid bilayer so that lipid soluble molecules can pass through easily BUT can anyone tell me the reason why water cannot across the membrane? (in the chemical point of view)

And,what is the reason that ion (charged) molecules are difficult to move through cell membrane?

Thank you very much for your detailed explanation

Push

The lipid bilayer of the cell membrane is primarily composed of hydrophobic (water-repelling) fatty acid chains. This hydrophobic interior of the membrane acts as a barrier to the movement of polar and charged molecules, such as water and ions, respectively.

1. Why can't water cross the cell membrane?
Water is a polar molecule, meaning it has a partial positive charge on one end (hydrogen) and a partial negative charge on the other (oxygen). The hydrophobic interior of the lipid bilayer repels water molecules. The charged ends of the water molecules are attracted to each other and form hydrogen bonds, which stabilize the molecules and prevent them from easily passing through the hydrophobic regions of the membrane. As a result, water molecules have difficulty crossing the cell membrane on their own.

2. Why are ion molecules difficult to move through the cell membrane?
Charged molecules, like ions, cannot easily pass through the cell membrane due to their interactions with the hydrophobic environment. The hydrophobic interior repels the charged ions, which prefer to interact with water molecules. Additionally, the cell membrane contains protein channels and transporters that selectively regulate the movement of ions across the membrane. These channels and transporters are responsible for the controlled movement of ions in and out of the cell.

In summary, the lipid bilayer of the cell membrane acts as a barrier to the movement of polar and charged molecules. Water molecules are unable to easily cross the membrane due to their polarity and the hydrophobic nature of the lipid bilayer. Charged molecules, like ions, face similar challenges and require specialized transporters or channels to pass through the membrane.