Biology is the science of life and living processes.The living world comprises an amazing diversity of living organisms. However, living organisms show 'Fundamental Similarity' in many respects. The study of 'Life' involves a multidisciplinary approach, involving many of the principles of chemistry, physics and mathematics too at some places. Biological systems are the most 'complex chemical systems' on the Earth. The bodies of early organisms are at the 'cellular' level. However large an organism is, 'cells' of an organism are the 'Basic Units' of 'structure' and 'function'. Organisms constantly interact with their surrounding environment 'exchanging energy' and 'recycling minerals'. The intricate chemical processes of cells are based on the basic principles of chemistry. Every level of biological organization involves 'energy transactions' governed by the 'Laws of thermodynamics'. The fundamental source of energy for all biological systems is the 'Sun'. Green plants, over a period of several millions of years, evolved and have mastered the art of converting solar energy into chemical energy involving complex reactions and pass it on to other higher living organisms to keep LIFE.