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 organisation 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.