A child is diagnosed with rickets, a condition in which the bones become soft and weak. Explain why a lack of vitamin D and calcium in the diet leads to this condition.

Eduqas GCSE Biology — 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)

Calcium is required for the formation and hardening of bone tissue; it is the main mineral that gives bone strength.
Vitamin D is necessary for the absorption of calcium from the intestine.
If the diet lacks calcium, bone mineralisation is reduced and the bones remain soft.
If the diet lacks vitamin D, calcium absorption is impaired, so even normal dietary calcium cannot reach the bones, again leaving the bones soft and weak.

Examiner tips

  • Use the exact terms ‘calcium’, ‘vitamin D’, ‘absorption’, ‘bone mineralisation’, ‘soft/weak bones’.
  • Show the causal chain: vitamin D → calcium absorption → bone hardening.
  • Mention that both deficiencies give the same outcome – soft/weak bones.

Common mistakes

  • Confusing vitamin D with vitamin C or A.
  • Saying calcium is absorbed by the liver instead of the intestine.
  • Failing to link vitamin D deficiency to reduced calcium absorption.

Mark scheme (4 marks)

  1. Calcium is needed for the formation / hardening / mineralisation of bones (and teeth)
  2. Vitamin D is needed for the absorption of calcium (from the gut / intestine / food)
  3. Without sufficient calcium, bones do not harden / remain soft / have reduced strength
  4. Lack of vitamin D means less calcium is absorbed, so even if calcium is present in the diet it may not reach bones in sufficient amounts / linking deficiency of both to the same outcome of soft or weak bones

Key terms in this question

vitamin D · calcium · rickets

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