Biology is the study of living organisms. Before the 19th century, biology was known as natural history (the study of all living things). Gottfried Reinhold Treviranus was the first person to coin the term biology. Biology comes from the Greek words bios (meaning “life”) and logia (meaning “study of”). It is a common science that is a standard subject in schools and universities around the world. Over a million papers are published annually in biology and medicinal journals.

Not just a study of living organisms, biology also deals with the structure, function, growth, origin, evolution, distribution and classification of all living things. There are five defining principles of modern biology: cell theory, evolution, gene theory, energy, and homeostasis. There are also three specialized disciplines of modern biology. These are generally grouped by the type of organism being studied. These disciplines are botany (the study of plants), zoology (the study of animals), and microbiology (the study of microorganisms). These disciplines can be further divided into sub-disciplines that are based on the level and scale at which an organism is being studied. These sub-disciplines include biochemistry, molecular biology, cellular biology, physiology, and ecology.

One area of biology, physiology, deals with the study of mechanical, physical, and biochemical processes of living organisms by trying to understand how all the structures function as a whole. The term “structure to function” is central to all of biology. Although physiology is divided into either plant physiology, animal physiology, or human physiology, the principles are universal. What is learned in plant physiology can sometimes apply to animal physiology and vice versa. Animal physiology also extends the tools and methods to human physiology. Plant physiology also borrows techniques from both fields. Anatomy is an important part of physiology. It deals with how organ systems (such as nervous, immune, endocrine, respiratory, and circulatory systems) function and interact. These systems are studied also medically with the disciplines of neurology and immunology.

The classification of biological systems is divided into two disciplines (systematics and taxonomy). Taxonomy places organisms into groups called taxa, while systematics defines the relationships with each other. Historically, living things have been divided into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. The five-kingdom system is considered outdated by many scientists and a modern three-domain system was developed: Archaea, Bacteria, and Eukarya (which includes protists, fungi, plants and animals). These new domains reflect whether the cells have nuclei or not, and other differences in cell exteriors.

Each kingdom is broken down further until each species can be separately classified. The order of classification is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. Scientific names of organisms are obtained from its genus and species. For example, humans would be listed as Homo sapiens. Homo is the genus and sapiens is the species. When writing a scientific name of an organism, it is proper to capitalize the first letter of the genus name and put all species in lowercase. The entire term should always be italicized or underlined.

The dominant classification system is known as Linnaean taxonomy. This system includes ranks and binomial nomenclature. How organisms become named is based on international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB). A fourth draft known as BioCode was published in 1997 to prompt naming standards within the three areas. This publication has yet to be formally adopted.

Ecology is another important part of biology. It is based on the distribution and abundance of living organisms, and the interactions between organisms and their environment. Environment can refer to both the habitat of the organism, and the organisms that share its habitat. Ecology is studied at several different levels, from individual organisms and populations to ecosystems and the biosphere. Population ecology is often synonymous with population biology, although population biology is more readily used when studying diseases, viruses, and microbes. Population ecology is used mainly when studying plants and animals.

Ethology is the study of animal behavior among social animals such as primates and canids. Ethology is sometimes considered a branch of zoology. Ethologists are particularly concerned with the evolution of behavior and the understanding of natural selection. Charles Darwin could be considered the first modern ethologist, because of his book “The Expression of the Emotions in Man and Animals” influenced many ethologists.

Biogeography is the study of spatial distribution among organisms on the Earth. It focuses on topics such as plate tectonics, climate change, dispersal and migration, and cladistics. Every living thing interacts with and reacts to other organism in its environment. One reason why biogeography can be difficult to study is that there are possibly billions and billions of different interactions between organisms and the environment. Matters can become even more complex and extreme to study when two or more different organisms interact in an ecosystem. Studies of this type are epic to ecology.