Physiology examines the biological mechanisms that sustain animal existence and seeks to better understand how animals function. Many different levels of the organisation, from the membranes to the organelles to the cells to the organs to the organ systems to the complete animal, are all amenable to the study of these processes. Animal physiology is the study of biological processes, including how they are controlled and integrated and how they respond to different environmental situations. Animal physiology relies heavily on the study of anatomy (the study of the connection between form and function) and the fundamental physical & chemical principles that place limits on living and also nonliving systems. All creatures have to operate under the same fundamental physical and chemical limits, but the strategies and procedures they use to do so are somewhat varied. Animal biochemistry is the scientific study of the composition, function, and regulation of the cellular components in animals, including proteins, carbohydrates, lipids, nucleic acids, and other biomolecules. These days, biochemists pay a lot of attention to the chemical processes that take place in enzymes and the properties of proteins. Biochemical studies of cellular metabolism are also rather prevalent in modern academia. In addition to DNA and RNA chemistry, protein synthesis, transport across cell membranes, and signal transduction are all subfields of biochemistry.