Important Cations

Cations are positively charged ions. Like anions, they are needed in small amounts but have very specific jobs.Calcium (Ca²⁺). Calcium phosphate gives bones and teeth their strength. Ca²⁺ ions trigger the release of neurotransmitter at synapses, allow muscle contraction by exposing binding sites on actin, and are needed for blood clotting. In plants, calcium pectate helps to hold neighbouring cell walls together.Sodium (Na⁺). Sodium ions are pumped out of cells by the sodium–potassium pump. The resulting gradient is used for nerve impulses and to absorb glucose and amino acids in the small intestine by co-transport. Sodium also affects the water potential of body fluids.Potassium (K⁺). Potassium ions are pumped into cells and help to set up the resting potential of neurones. In plants, K⁺ moving into guard cells lowers their water potential, water follows by osmosis, and the stomata open.Hydrogen (H⁺). The concentration of H⁺ ions determines pH, which affects the shape of enzymes and other proteins. H⁺ gradients also drive ATP synthesis in mitochondria and chloroplasts.Magnesium (Mg²⁺) and iron (Fe²⁺). Magnesium is at the centre of every chlorophyll molecule, so a lack of it causes yellow leaves. Iron is part of the haem group in haemoglobin, which binds oxygen, so iron deficiency causes anaemia.Ammonium (NH₄⁺) is produced when decomposers break down proteins and is converted to nitrate by nitrifying bacteria in the soil.