Explain the importance of phosphate ions and calcium ions in the human body.

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)

Phosphate ions are a component of DNA and RNA nucleotides, providing the backbone of genetic material.
Phosphate ions are a component of ATP, the main energy currency of the cell.
Phosphate ions are a component of phospholipids, which form the lipid bilayer of cell membranes.
Calcium ions stimulate muscle contraction by triggering the release of calcium from the sarcoplasmic reticulum.
Calcium ions are a component of bone and tooth mineral, forming calcium phosphate (hydroxyapatite).

Examiner tips

Use the exact phrases from the mark scheme – e.g. "component of DNA" and "stimulate muscle contraction".
Show the five points in separate sentences or numbered list to match the 5 marks.

Common mistakes

Confusing phosphate with other ions such as chloride; not mentioning DNA/RNA. For calcium, forgetting the role in bone mineralisation or mixing up muscle contraction with nerve conduction.

Mark scheme (5 marks)

Phosphate ions are a component of / needed to form DNA (and RNA) / nucleotides
Phosphate ions are a component of / needed to form ATP
Phosphate ions are a component of phospholipids (which form cell membranes)
Calcium ions are needed for / stimulate muscle contraction
Calcium ions are a component of / needed to form bones and teeth (as calcium phosphate / hydroxyapatite)

Key terms in this question

phosphate ions · calcium ions