Chemistry • Year 12 • Module 7 • Lesson 15b
Carbohydrate Biomolecules
Lock in the core vocabulary: monosaccharide types, glycosidic bond formation, the three key disaccharides, and the starch–cellulose distinction before tackling harder questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: monosaccharide, disaccharide, polysaccharide, glycosidic bond, condensation, hydrolysis, aldose, ketose, starch, cellulose. 10 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | A single sugar unit with the general formula CₐH₲Oₘ for hexoses; the monomer of carbohydrates. | |
| 1.2 | A carbohydrate formed from two monosaccharides joined by a glycosidic bond with loss of water. | |
| 1.3 | A large carbohydrate polymer made from many monosaccharide monomers; examples include starch and cellulose. | |
| 1.4 | The C–O–C covalent bond that links monosaccharide units in disaccharides and polysaccharides; formed by condensation. | |
| 1.5 | A reaction in which two molecules join together with the release of a small molecule (water), forming a larger molecule. | |
| 1.6 | A reaction in which a bond is broken by the addition of water; the reverse of condensation. | |
| 1.7 | A monosaccharide with a carbonyl group at the terminal carbon (C1); glucose is an example. | |
| 1.8 | A monosaccharide with a carbonyl group within the chain (usually C2); fructose is an example. | |
| 1.9 | A polysaccharide of glucose linked by α-1,4-glycosidic bonds; forms a coiled helix and is used for energy storage. | |
| 1.10 | A polysaccharide of glucose linked by β-1,4-glycosidic bonds; forms straight chains and provides structural support in plant cell walls. |
2. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
2.1 Glucose and fructose are structural isomers because they have the same molecular formula (C⁶H₁₂O₆) but different structural arrangements. T / F
2.2 Hydrolysis releases water as a by-product. T / F
2.3 Cellulose and starch have different monomers; starch is made from glucose and cellulose is made from fructose. T / F
2.4 Sucrose is a disaccharide formed from glucose and fructose by a condensation reaction that releases one molecule of water. T / F
2.5 The molecular formula of maltose is C₁₂H₂₄O₁₂ because it is formed by joining two glucose molecules (2 × C⁶H₁₂O₆). T / F
2.6 Starch uses α-1,4-glycosidic bonds which produce a coiled helix structure that human amylase can recognise and cleave. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 8 marks (1 per blank)
Word bank:
glycosidic · condensation · hydrolysis · monosaccharides · cellulose · α-1,4 · β-1,4 · water
Carbohydrates are assembled from ___________ monomers such as glucose, fructose, and galactose. When two monosaccharides react, a ___________ reaction forms a covalent ___________ bond and releases one molecule of ___________. The reverse reaction, ___________, breaks this bond by adding water across it. In starch, glucose units are linked by ___________ bonds, which produce a coiled helix. In ___________, glucose units are linked by ___________ bonds, which produce straight, rigid chains.
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 What is the defining difference between an aldose and a ketose monosaccharide?
4.2 Name the three key disaccharides and state the two monosaccharides that make up each one.
4.3 Why does the molecular formula of maltose (C₁₂H₂₂O₁₁) contain fewer hydrogen and oxygen atoms than simple doubling of glucose (which would give C₁₂H₂₄O₁₂)?
4.4 State the type of bond found in each of the three biomolecule classes: fats, proteins, and carbohydrates.
5. Complete the disaccharide summary table
Fill in all blank cells. 12 marks (1 per cell)
| Disaccharide name | Monomer 1 | Monomer 2 | Common name / where found |
|---|---|---|---|
| Maltose | Malt sugar; produced when starch is partially hydrolysed | ||
| Glucose | Fructose | ||
| Lactose |
6. Complete the biomolecule comparison table from memory
Fill in all blank cells without looking at the lesson. 9 marks (1 per cell)
| Biomolecule class | Monomer(s) | Bond type (linkage) | Hydrolysis products |
|---|---|---|---|
| Fats (triglycerides) | |||
| Proteins | |||
| Carbohydrates |
Q1 — Term–definition match
1.1 monosaccharide • 1.2 disaccharide • 1.3 polysaccharide • 1.4 glycosidic bond • 1.5 condensation • 1.6 hydrolysis • 1.7 aldose • 1.8 ketose • 1.9 starch • 1.10 cellulose.
Q2 — True / false with correction
2.1 True. Glucose and fructose both have the formula C⁶H₁₂O₆ but different structural arrangements (glucose is an aldose; fructose is a ketose), so they are structural isomers.
2.2 False. Hydrolysis consumes water as a reactant — it uses H₂O to break bonds. Condensation releases water as a by-product.
2.3 False. Both cellulose and starch are made entirely from glucose (C⁶H₁₂O₆) monomers. The difference is the orientation of the glycosidic bond: α-1,4 in starch, β-1,4 in cellulose.
2.4 True. Sucrose = glucose + fructose joined by a glycosidic bond via condensation, releasing H₂O.
2.5 False. The correct formula of maltose is C₁₂H₂₂O₁₁, not C₁₂H₂₄O₁₂. One water molecule (H₂O) is lost in the condensation reaction that forms the glycosidic bond, so the formula is 2 × C⁶H₁₂O₆ − H₂O = C₁₂H₂₂O₁₁.
2.6 True.
Q3 — Cloze paragraph
In order: monosaccharides / condensation / glycosidic / water / hydrolysis / α-1,4 / cellulose / β-1,4.
Q4.1 — Aldose vs ketose
An aldose has a carbonyl group (C=O) at the terminal carbon (C1), making it an aldehyde. A ketose has a carbonyl group within the chain (usually at C2), making it a ketone. Glucose is an aldose; fructose is a ketose despite having the same molecular formula.
Q4.2 — Three disaccharides
Maltose = glucose + glucose. Sucrose = glucose + fructose. Lactose = glucose + galactose.
Q4.3 — Why maltose formula is C₁₂H₂₂O₁₁
During the condensation reaction that joins two glucose molecules, one water molecule (H₂O) is released as a by-product. The disaccharide formula is therefore 2 × C⁶H₁₂O₆ − H₂O = C₁₂H₂₂O₁₁. One H and one OH are lost to form the glycosidic bond, reducing the formula by H₂O.
Q4.4 — Bond types in biomolecule classes
Fats: ester bond. Proteins: peptide (amide) bond. Carbohydrates: glycosidic bond.
Q5 — Disaccharide table
Maltose: glucose + glucose. Sucrose: glucose + fructose; table sugar / found in sugar cane and sugar beet. Lactose: glucose + galactose; milk sugar / found in mammalian milk.
Q6 — Biomolecule comparison table
Fats: glycerol + fatty acids | ester bond | glycerol + 3 fatty acids.
Proteins: amino acids | peptide (amide) bond | amino acids.
Carbohydrates: monosaccharides | glycosidic bond | monosaccharides.