Re: i dont understand how alcohols make the tonoplast more permeable

Your second idea is the more correct, though the first contributes. The primary reason that alcohol (and most any organic solvent) destroys a cell membrane is that it is either solubilizing the phospholipid and cholesterol or other lipids, or, with some solvents, causing a phase change (reorganization of the lipids into another structure) that makes the membrane very, very leaky (effectively it pokes holes in the membrane rather than just dissolving them). A third reason is that alcohol desiccates cells by drawing the water out. In fact, 70% alcohol is better for the latter than 95%-100%. The latter actually almost seals the membrane and not as much water exchanges.

Alcohols and organic solvents will also denature some, though not all, proteins. This probably happens when a cell is hit with alcohol but it is not the major factor in generating cell death or leakiness.