Explain the importance of calcium ions and sodium ions to the human body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
1. Calcium ions are essential for the formation and maintenance of bone and teeth, providing structural strength.
2. Calcium ions act as a key signalling ion in muscle cells, triggering contraction.
3. Sodium ions are crucial for generating and propagating action potentials in nerve cells.
4. Sodium ions drive the co‑transport of glucose and amino acids into cells via the sodium–glucose and sodium–amino acid symporters.
5. Both ions are required only in trace amounts, yet they perform vital physiological functions as inorganic ions.
2. Calcium ions act as a key signalling ion in muscle cells, triggering contraction.
3. Sodium ions are crucial for generating and propagating action potentials in nerve cells.
4. Sodium ions drive the co‑transport of glucose and amino acids into cells via the sodium–glucose and sodium–amino acid symporters.
5. Both ions are required only in trace amounts, yet they perform vital physiological functions as inorganic ions.
Examiner tips
- Use the exact terms ‘bone and teeth’, ‘muscle contraction’, ‘nerve impulses’, ‘co‑transport’, and note the trace‑quantity requirement.
- Structure answer with numbered points matching the mark scheme to show clear coverage of each point.
Common mistakes
- Confusing sodium with potassium as the main ion for nerve impulses.
- Failing to mention the trace‑quantity aspect or the role of calcium in bone structure.
Mark scheme (5 marks)
- Calcium ions are needed for bone (and teeth) formation/structure
- Calcium ions are needed for muscle contraction
- Sodium ions are involved in the transmission of nerve impulses
- Sodium ions are involved in the co-transport of glucose (and amino acids) into cells
- Both ions are needed in low concentrations / as trace amounts and are examples of inorganic ions that have important functions despite being present in small quantities
Key terms in this question
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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