Question

What types of molecules can pass through a membrane without the aid of a membrane protein? What types of molecules use a membrane protein in order to cross the membrane?

Answer 1

the plasma membrane is made of the lipid bilayer, lipid bilayer has amphipathic lipid molecules having a polar head and hydrophobic tail arranged into two layers such that the lipids of both layers face each other.

since lipid bilayer has the hydrophobic region, hydrophilic molecules cannot pass through the membrane without the help of proteins but hydrophobic lipid-soluble molecules can move through the plasma membrane into the cell.

types of molecules can pass through a membrane without the aid of a membrane protein are hydrophobic, fat-soluble molecules.

types of molecules use a membrane protein in order to cross the membrane: hydrophilic molecules ( small hydrophilic molecules can pass through the lipid bilayer at low rates)