Inorganic Ions (AQA A Level Biology): Revision Note

Inorganic ions

• An ion is an atom (or sometimes a group of atoms) that has an electrical charge

  • An ion that has a positive charge is known as a cation

  • An ion that has a negative charge is known as an anion

• An inorganic ion is an ion that does not contain carbon

• Inorganic ions occur in solution in the cytoplasm and body fluids of organisms

  • The concentration of certain ions can fluctuate and can be used in cell signalling and neuronal transmission

Properties & roles of inorganic ions

Hydrogen ions

• Hydrogen ions (H⁺) are protons

• The concentration of H⁺ in a solution determines the pH

• There is an inverse relationship between the pH value and the hydrogen ion concentration

  • The more H⁺ ions present, the lower the pH (the more acidic the solution)

  • The fewer H⁺ ions present, the higher the pH (the more alkaline the solution)

• The concentration of H⁺ is therefore very important for enzyme-controlled reactions, which are all affected by pH

  • The fluids in the body normally have a pH value of approximately 7.4

  • The maintenance of this normal pH is essential for many of the metabolic processes that take place within cells

  • Changes in pH can affect enzyme structure

Iron ions

• There are two versions of iron ions (known as oxidation states)

  • Iron (II) ions, also known as ferrous ions (Fe²⁺)

  • Iron (III) ions, also known as ferric ions (Fe³⁺)

• Iron ions are essential as they can bind oxygen

  • Haemoglobin is the large protein in red blood cells that is responsible for transporting oxygen around the body

  • Haemoglobin is made up of four polypeptide chains that each contain one Fe²⁺

  • This Fe²⁺ is a key component in haemoglobin as it binds to oxygen

Sodium ions

• Sodium ions (Na⁺) are required for the transport of glucose and amino acids across cell-surface membranes (e.g. in the small intestine)

  • Glucose and amino acid molecules can only enter cells (through carrier proteins) alongside Na⁺ in a process known as co-transport

• Na⁺ is also required for the transmission of nerve impulses

Phosphate ions

• Phosphate ions (PO₄^3-) attach to other molecules to form phosphate groups, which are an essential component of DNA, RNA and ATP

• In DNA and RNA, the phosphate groups allow individual nucleotides tobond to form polynucleotides

• In ATP, the bonds between phosphate groups store energy

  • These phosphate groups can be easily attached or detached

  • When the bonds between phosphate groups are broken, they release a large amount of energy, which can be used for cellular processes

• Phosphates are also found in phospholipids, which are key components of the phospholipid bilayer of cell membranes