- Specification route
- 3.1.2
- Question bank
- 30 questions
- Course stage
- AS / Year 12
Sample questions
A student carries out a Benedict's test on a sample of sucrose. What steps must be taken to produce a positive result?
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Sucrose is a non-reducing sugar, so its glycosidic bond must be broken before the test can work.
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Answer: Boil the sample with dilute hydrochloric acid, neutralise with an alkali, then heat with Benedict's solution.
Sucrose is a non-reducing sugar. It must first be hydrolysed into its constituent monosaccharides (glucose and fructose) by boiling with acid, then neutralised, before testing with Benedict's solution to yield a positive result.
How does the structure of cellulose relate to its function in plant cell walls?
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Plant cell walls require high tensile strength rather than energy storage capability.
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Answer: It is composed of long, unbranched chains of $\beta$-glucose linked by hydrogen bonds to form strong microfibrils.
Cellulose is formed by the condensation of $\beta$-glucose. These form long, unbranched chains that run parallel to each other, allowing hydrogen bonds to form cross-linkages between chains, creating strong microfibrils.
Which feature makes glycogen an efficient storage molecule in animal cells?
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Animals often require rapid bursts of energy.
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Answer: It is highly branched, allowing for rapid hydrolysis to release glucose for respiration.
Glycogen is formed by the condensation of $\alpha$-glucose. Its highly branched structure means it has more ends that can be acted on simultaneously by enzymes, allowing rapid hydrolysis into glucose.
A student tests a solution with iodine in potassium iodide, and it remains yellow-brown. They then heat the solution with Benedict's reagent, and a brick-red precipitate forms. What can be concluded about the solution?
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Iodine tests for starch; Benedict's (without prior acid hydrolysis) tests for a specific type of sugar.
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Answer: It contains a reducing sugar but no starch.
A negative iodine test (remains yellow-brown) indicates no starch. A positive Benedict's test (brick-red precipitate upon heating) indicates the presence of reducing sugars.
Glucose is described as a hexose sugar and has the formula $C_{6}H_{12}O_{6}$. What makes $\alpha$-glucose an isomer of $\beta$-glucose?
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The definition of an isomer relates to the formula and structural arrangement.
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Answer: They have the same molecular formula but a different structural arrangement of atoms.
Glucose has two isomers, alpha-glucose and beta-glucose. Isomers are molecules that have the same molecular formula ($C_{6}H_{12}O_{6}$) but a different structural arrangement of atoms in space (the position of the hydroxyl group on carbon 1).
Which two monosaccharides condense to form a molecule of sucrose?
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Sucrose is common table sugar, produced heavily by plants.
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Answer: Glucose and fructose
Sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule.
Which of the following disaccharides is formed by the condensation of two glucose molecules?
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This sugar is often found in germinating seeds and malt.
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Answer: Maltose
Maltose is a disaccharide formed by condensation of two glucose molecules.
Which polymer is formed by the condensation of $\beta$-glucose units?
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This polymer provides structural support in plant cell walls.
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Answer: Cellulose
Cellulose is formed by the condensation of beta-glucose. Glycogen and starch are formed by the condensation of alpha-glucose.
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