Explain why glucose is the monomer used to build carbohydrate polymers, and describe what happens to the water molecules released when these polymers are formed.

AQA A-Level Biology (7402) — 3.1.2 Carbohydrates · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Carbohydrates are biological molecules made up of carbon, hydrogen, and oxygen. Simple sugars can be joined together to form long-chain polymers used for energy storage and structural support.

Model answer (5 marks)

1. Glucose is a simple sugar (monosaccharide) that can be transported freely in the bloodstream.
2. When two glucose molecules join, a condensation (dehydration) reaction occurs.
3. The reaction releases one water molecule for each bond formed.
4. The released water can be used in hydrolysis reactions to break the polymer back into glucose.
5. Glucose is small, soluble and provides energy when oxidised, making it an ideal monomer for carbohydrate polymers.

Examiner tips

  • Use the word "condensation" to show you know the reaction type.
  • Mention the release of one water molecule per glycosidic bond.
  • Explain the role of glucose in transport and energy.
  • Link hydrolysis to the water released.

Mark scheme (5 marks)

  1. Glucose is a simple sugar / monosaccharide
  2. Glucose molecules are joined together by condensation reactions
  3. A water molecule is released / produced each time two monomers are joined
  4. The water released can be used in hydrolysis reactions to break polymers back down into monomers
  5. Glucose is suited as a monomer because it is small / soluble and can be transported easily / provides energy when respired

Key terms in this question

monomer · polymer

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