The big idea: Hydrolysis breaks a bond between two monomers by splitting a water molecule. Its -H and -OH end up in the two monomers.
The points to remember
- Hydrolysis splits a polymer into its monomers: the reverse of condensation.
- One water molecule is used for every bond broken.
- The water is split into -H and -OH.
- The -H joins one monomer and the -OH joins the other, so both become complete.
- That is the name: hydro = water, lysis = splitting.
Remember it as: Water in, bond broken, monomers out.
Real example: lactose in milk: The enzyme lactase hydrolyses lactose, the sugar in milk, into glucose and galactose, which are small enough to be absorbed.
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The big idea: Digestion uses hydrolysis to turn every big food molecule back into the monomers it was built from.
The points to remember
- Digestion is hydrolysis: big food molecules are split into monomers that can be absorbed.
- Starch and glycogen → glucose; proteins → amino acids; DNA and RNA → nucleotides.
- A disaccharide → two monosaccharides (lactose → glucose + galactose).
- A triglyceride → glycerol + three fatty acids, using three water molecules.
- Enzymes speed up hydrolysis; the water is what is split.
| Food molecule | Hydrolysed into | Water used |
|---|---|---|
| Starch | many glucose | one per bond |
| Protein | amino acids | one per peptide bond |
| Lactose | glucose + galactose | one |
| Triglyceride | glycerol + 3 fatty acids | three |
Remember it as: Built by condensation, broken by hydrolysis.
Condensation
- Joins monomers into a polymer
- Water is released
- A bond is made
Hydrolysis
- Splits a polymer into monomers
- Water is used and split
- A bond is broken
Water is used, not made: The products of hydrolysing a triglyceride are glycerol and fatty acids. Water is a reactant, so it is never one of the products.
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How it is asked: A one-mark State on the reaction that digests a sugar, and multiple-choice items on the role of water and on the products of hydrolysis.
Sucrose, table sugar, is digested in the small intestine into glucose and fructose. State the type of reaction that produces monosaccharides from disaccharides.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
And a multiple-choice item on the role of water:
What is the role of water in the digestion of a polymer?
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.