Within the bonds of their molecules
I believe the second answer is correct.
A toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
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.'
