Which substances do you think will diffuse across the lipid bilayer most quickly? most slowly?

Ans.

Lipid bilayer is made up of two layers of phospholipids, which show polar, hydrophilic (polar) phosphate groups on surface of cell membrane and non-polar, hydrophobic (non-polar) tails on inner sides. The hydrophobic nature of cell membrane allows transport of small, hydrophobic molecules more quickly than larger, hydrophilic molecules.

Thus, 'the non-polar, uncharged or small molecules, such as water, oxygen and other gases, will diffuse across the lipid membrane most quickly, while the polar, charged or large molecules, such as ions, proteins, and salts, will diffuse most slowly.'