Lesson 3.1.2.3

3.1.2.3 Biochemical tests for sugars and starch Quiz: AQA Biology, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.2.3, Biochemical tests for sugars and starch: 20 multiple choice questions for the AQA Biology (7402), Unit 1: Biological molecules, written with Revision Ninja.

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The 20 questions

  1. Which reagent is used to test a sample for reducing sugars?

    • Ethanol emulsion
    • Biuret reagent
    • Benedict's reagent
    • Iodine solution

  2. Which reagent is added to a sample to test for the presence of starch?

    • Biuret solution
    • Iodine solution
    • Benedict's solution
    • DCPIP solution

  3. What colour is a positive starch test with iodine in potassium iodide solution?

    • Blue-black
    • Brick-red
    • Green
    • Purple

  4. What colour precipitate indicates a high concentration of reducing sugar in a Benedict's test?

    • Lilac
    • Blue
    • Green
    • Brick-red

  5. What colour does Benedict's solution stay if no reducing sugar is present?

    • Brick-red
    • Blue
    • Green
    • Yellow-orange

  6. Which sugar is a non-reducing sugar?

    • Glucose
    • Lactose
    • Maltose
    • Sucrose

  7. Why must a Benedict's test mixture be heated in a water bath?

    • Evaporates excess water
    • Denatures enzyme molecules
    • Hydrolyses glycosidic bonds
    • Provides activation energy

  8. Which process must be performed first to test sucrose with Benedict's reagent?

    • Alcohol extraction
    • Lipid emulsification
    • Alkaline precipitation
    • Acid hydrolysis

  9. Why is sodium hydrogencarbonate added to hydrolysed sucrose before the Benedict's test?

    • To neutralise acid
    • To provide alkali
    • To denature enzyme
    • To precipitate sugar

  10. A colorimeter reading of a standard glucose solution of 0.5 g/dm3 gives an absorbance of 0.20, and 1.0 g/dm3 gives 0.40. An unknown gives 0.30. What is its concentration?

    • 1.50 g/dm3
    • 0.50 g/dm3
    • 0.60 g/dm3
    • 0.75 g/dm3

  11. A 10 cm3 sample of a 2.0 mol/dm3 sugar solution is diluted with water to a final volume of 50 cm3. What is the new concentration?

    • 10.0 mol/dm3
    • 0.4 mol/dm3
    • 0.2 mol/dm3
    • 1.0 mol/dm3

  12. What does an orange-brown colour result in an iodine test indicate?

    • Starch is present
    • Reducing sugar present
    • Starch is absent
    • Non-reducing sugar present

  13. A sample gives a brick-red Benedict's result and an orange-brown iodine result. What is present?

    • Non-reducing sugar only
    • Sugar and starch
    • Reducing sugar only
    • Starch only

  14. Sample A produces a green Benedict's precipitate while Sample B produces brick-red. What is concluded?

    • Contains starch only
    • Lower sugar concentration
    • Higher sugar concentration
    • Contains non-reducing sugar

  15. Which piece of apparatus is used to measure the colour intensity in a quantitative Benedict's test?

    • A Bunsen burner
    • A pipette filler
    • A water bath
    • A colorimeter

  16. Why is distilled water used as a control in a Benedict's test?

    • Hydrolyses non-reducing sugars
    • Calibrates water bath
    • Ensures reaction completion
    • Shows baseline colour

  17. A student uses a colorimeter to measure the absorbance of a diluted sugar solution. The diluted solution was prepared by 1 in 5 dilution. Its calibrated concentration is 0.6 mg/cm3. What was the concentration of the original sample?

    • 0.12 mg/cm3
    • 0.6 mg/cm3
    • 3.0 mg/cm3
    • 5.6 mg/cm3

  18. What type of result does a Benedict's test colour change provide about reducing sugar concentration?

    • Fully quantitative
    • Semi-quantitative
    • Qualitative only
    • Absolute quantitative

  19. Why does iodine solution produce a blue-black colour with starch?

    • Trapped in amylose
    • Denatures amylopectin branches
    • Breaks glycosidic bonds
    • Reduces copper ions

  20. Which chemical treatment is needed before testing a non-reducing sugar with Benedict's reagent?

    • Alkalis addition
    • Acid hydrolysis
    • Thermal boiling
    • Enzyme digestion

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