What Role Do Inorganic Ions Play in Biology?

Inorganic ions help control pH, transport oxygen, absorb nutrients and form parts of essential molecules such as ATP and DNA. For AQA A-level Biology, the key examples are hydrogen, iron, sodium and phosphate ions. An inorganic ion is a charged particle that is not itself an organic molecule. Its charge and chemical properties help determine its role in living organisms.

What does each ion do?

• Hydrogen ions affect pH. A change in pH can disrupt bonds that maintain an enzyme’s shape, altering its active site and reducing its activity.
• Iron ions are part of haemoglobin, the protein in red blood cells that binds and transports oxygen. Each haem group contains an iron ion that binds oxygen reversibly, allowing oxygen to be loaded in the lungs and unloaded at respiring tissues.
• Sodium ions help glucose and amino acids enter cells lining the ileum, where digested nutrients are absorbed. Sodium ions move into these cells down their concentration gradient through co-transport proteins, carrying glucose or amino acids with them. ATP is used to maintain the sodium ion gradient.
• Phosphate ions are needed to make ATP, which transfers energy to energy-requiring processes. Phosphate groups also form part of the sugar–phosphate backbone of DNA. There, they link neighbouring sugars to form each DNA strand: this is a structural role, not direct energy transfer.

A quick application

Suppose a cell lining the ileum can no longer maintain its sodium ion gradient. Fewer sodium ions would move into the cell through co-transport proteins, so less glucose would be absorbed by this route. This shows why naming an ion alone is not enough: explain how it enables the process.

Common exam mistake: Do not say that sodium ions provide the energy for co-transport. ATP maintains the sodium ion gradient; the movement of sodium ions down that gradient then drives glucose or amino acid uptake.