Explain why a balanced diet must include both water and dietary fibre, even though neither provides the body with energy.

WJEC GCSE Biology (Wales) — 1.3.1 Diet and nutrition · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Water is essential because it acts as a solvent for the chemical reactions that occur in the body and it transports dissolved substances such as nutrients, hormones and waste products throughout the body.
Dietary fibre, although it gives no energy, adds bulk to the diet, helps food move through the intestines and promotes peristalsis. Without enough fibre a person can develop constipation and other bowel problems.

Examiner tips

  • Use the word "acts as a solvent" and "transports" to hit the key points about water. Mention "adds bulk" and "promotes peristalsis" for fibre. Keep the answer concise – 4 marks can be earned with two short sentences.

Common mistakes

  • Writing that fibre provides energy, or that water is only a drink. Omitting the transport function of water. Forgetting to link fibre to constipation or bowel problems.

Mark scheme (4 marks)

  1. Water is needed as a solvent / for chemical reactions to take place in the body
  2. Water is needed to transport dissolved substances around the body
  3. Dietary fibre adds bulk to food / helps food move through the intestines / aids peristalsis
  4. Without sufficient dietary fibre a person may suffer from constipation / bowel problems

Key terms in this question

balanced diet · dietary fibre

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