These are the three main disciplines of science.
PHYSICS : this is derived from the Greek word 'physis', which means 'nature'. It is basically, in simple words, the study of the abiotic, i.e. non-living components of nature and its varied processes, which is divided into basic sub-divisions and their specific study- motion(mechanics), light(optics), subatomic particles(quantum), sound(sonics),etc.
CHEMISTRY : this is derived from words originating in either ancient Egyptian or Arabic. It is the study of various elements, compounds and mixtures existing in nature, or artificially obtained. It may have been originated from the word 'alchemist'.
BIOLOGY : this is derived from the Greek word 'bios', which means 'life'. It is the study of nature's biotic, i.e. living components of nature and its various ecosystems. It can be divided into three main subtopics: botany(plants), zoology(animals) and physiology(function of living systems).
Chemistry is the "scientific study of matter, its properties, and interactions with other matter and with energy". Its procedures are systematic and reproducible and its hypotheses are tested using the scientific method. The broadest, most important and conventional, and still widely observed division of chemistry is into its physical, organic and inorganic branches.
Physics is the science of matterand energyand the relationships between them. Branches of physics include classical mechanics, electromagnetism, optics, relativity, astrophysics, thermodynamics, and quantum mechanics as well as the modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics, and plasma physics. It is an experimental science in which theories are developed and tested against observations. The goals of physics include explaining and predicting how the universe works.
Biology is the study of life. It is defined as the science of life and living organisms. Aspects of biological science range from the study of molecular mechanisms in cells, to the classification and behaviour of organisms, how species evolve and interaction between ecosystems. The field of biology is very broad in scope and can be divided into several disciplines like anatomy, cell biology, genetics,physiology etc.