• Living organism is formed of many types of inorganic as well as organic biomolecules.
• Inorganic compounds include water, minerals etc. and are always micro-biomolecules (small sized, low molecular weight, readily soluble in water and diffusible) while organic molecules may be micro (e.g., monosugars, amino acids etc.) or macro-biomolecules (large sized, high molecular weight, insoluble or slightly soluble and non-diffusible e.g., proteins, fats, nucleic acids, etc.). These both types of biomolecules play important roles in metabolism.
• Role of Water : Water forms 70-90% of the cellular pool. It forms 65% (about two-thirds) of human body. It is formed of H and O in the ratio of 2:1. 95% of water is found in free state and 5% in combined form in the cell. Water helps in sustaining the life processes.
• Role of Oxygen : Oxygen is mainly utilized in aerobic respiration of the nutrients inside the mitochondria to produce energy-rich ATP molecules, so it is essential for life. In the absence of oxygen, only 5% of energy available is released.
• Role of Carbohydrates : Carbohydrates are organic compounds formed of C, H and O generally in the ratio
  of 1:2:1. These are commonly called saccharides (Gk. saccharon = sugar). Carbohydrates are the main storage molecules and most organisms use carbohydrates, as an important fuel, by breaking these bonds and releasing energy to sustain life.
• Role of Proteins : Proteins are polymeric compounds formed by interlinking of amino acids (monomers) by peptide bonds. Out of about 100 types of amino acids, only 20 types
  of amino acids are of biological importance, so are called Magic-20. Proteins play a vital role in the formation of structures in living organisms. Like carbohydrate and fat, protein can be broken down with the release of energy. Protein is not stored as such in the body and it is only used as a substantial source of energy in condition of starvation.
• Role of lipids : Lipids comprise a major group of insoluble hydrocarbons having many functions. These are polymers of alcohols (e.g., glycerol) and fatty acids interlinked by ester bonds.

Complex lipids such as true fats are important organic molecules that are used to provide energy.

• Role of Nucleic acid : These are polymers of nucleotides interlinked by phosphodiester bonds called polynucleotides. Each nucleotide is formed of 3 components: a pentose sugar (e.g., ribose in RNA and deoxyribose in DNA), a phosphate group and an inorganic nitrogen-base (a purine or a pyrimidine).
  DNA acts as genetic material in most organisms and controls the synthesis of structural and functional proteins. RNA also act as genetic material in all plant viruses e.g., TMV and helps in protein synthesis.