Some metals such as sodium, potassium, calcium, magnesium, iron and copper play a vital role in the living systems.

(i) Sodium and potassium are the most common cations in biological fluids. These ions are involved in the electrical activity in nerves and in muscle contraction.

(ii) Calcium ions occur in animal bones in combination with phosphate. Calcium ions also play an important role in muscle contraction.

(iii) Copper and zinc are the constituents of enzymes.

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(iv) Iron is a constituent of haemoglobin, which transports oxygen in man and other animals.

(v) Magnesium is present in chlorophyll, the main pigment responsible for the absorption of sunlight in plants.