A double bond is stored reactivity. Alkenes meet hydrogen, a halogen, a hydrogen halide or water, and the pi bond opens so the incoming atoms add across the two carbons - one molecule in, one molecule out, every atom kept. Alkanes have no such open door: force bromine onto an alkane and it needs ultraviolet light and swaps a hydrogen instead, spitting the leftover out as hydrogen bromide. Addition against substitution is the cleanest fingerprint saturated and unsaturated chemistry has. This is the real knowscape from knowhere, not a picture of one. Drag it. Watch what actually changes.
Every reaction here is just carbon changing partners, and only two moves exist: swap something in where a bond breaks, or add something across a double bond. Name the starting material's bond and you've already named which move is possible — the product is forced from there.
One whole pizza sits on the plate — the big joined-up molecule, all in one piece.
Add water and cut it — hydrolysis slices the ester back into two separate parts.
Two pieces now, split evenly — the alcohol and acid you started from.
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