Chemical Composition

How to Analyse Chemical Composition?

All the carbon (organic) compounds that are present in the living things are called 'Biomolecules'. As organic molecules, biomolecules consist primarily of carbon, hydrogen, nitrogen, oxygen and to a smaller extent, phosphorus and sulfur. Other elements sometimes are incorporated but are much less common.

However, living organisms also have inorganic elements and compounds in them. How do we know this? A slightly different but destructive experiment has to be done. Weigh a small amount of a living tissue (leaf, liver etc.,) and dry it, so all the water evaporates. The remaining material gives dry weight. Now if the tissue is fully burnt, all the carbon compounds are oxidised to gaseous form (CO₂, water vapour) and are removed. What is remaining is called 'ash'. This ash contains inorganic elements (calcium, magnesium etc.). Inorganic compounds like sulphate, phosphate, etc., are also seen in the acid-soluble fraction.

Therefore, elemental analysis gives the elemental composition of living tissues in the form of hydrogen, oxygen, chlorine, carbon etc., while analysis for compounds gives an idea of the kind of organic and inorganic constituents present in living tissues. But, from a biological point of view, they are classified into amino acids, nucleotide bases, fatty acids etc.

Inorganic Constituents of Living Tissues

Component	Formula
Sodium	Na^+
Potassium	K^+
Calcium	Ca^++
Magnesium	Mg^++
Water	H2O
Compounds	NaCl, CaCO3, P, S

Diagrammatic representation of small molecular weight organic compounds in living tissues