Explain why inorganic ions are important for the production of haemoglobin and for the synthesis of DNA in a human body cell.

AQA A-Level Biology (7402) — 3.1.8 Inorganic Ions · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Iron ions are required to form the heme group of haemoglobin, enabling the protein to bind oxygen.
Phosphate ions are essential for building the sugar‑phosphate backbone of DNA.
Without iron, haemoglobin cannot transport oxygen, causing anaemia.
Without phosphate, DNA synthesis and stability are impaired, leading to genetic defects.
Thus, correct inorganic ions are vital for haemoglobin function and DNA integrity, and their deficiency causes health problems.

Examiner tips

  • Use the exact terms "iron ions" and "phosphate ions". Explain the functional role (oxygen binding, backbone formation). Show cause–effect (deficiency leads to disease).

Common mistakes

  • Confusing iron with other metals. Forgetting to mention the heme group. Saying phosphate is only a nutrient, not part of the backbone.

Mark scheme (5 marks)

  1. Iron ions are needed / used to make haemoglobin
  2. Iron ions allow haemoglobin to carry / bind oxygen
  3. Phosphate ions are needed for the synthesis / formation of DNA
  4. Phosphate ions form / are part of the sugar-phosphate backbone of DNA
  5. Without the correct inorganic ions the molecules cannot be made / function correctly, leading to health problems

Key terms in this question

inorganic ions · haemoglobin · DNA

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