Life is exposed at a atomic and molecular scale in molecular biology, biochemistry, and molecular genetics. At a level of the cell, it is exposed inside cell biology, and at multicellular scales, it is examined inside physiology, anatomy, and histology. Developmental biology studies life at the level of the development or even ontogeny of an individual organism.

Moving higher a shell towards supplementary than of these organism, genetics considers how heredity works between parent and offspring. Ethology considers group behavior of supplementary than 1 single. Population genetics looks at the level of an entire population, and systematics considers the multi-species shell of lineages. Mutualist populations & their habitats are examined in ecology and evolutionary biology. The speculative newly field is astrobiology (or xenobiology) which examines a possibility of life beyond a Globe.

Principles of biology

When biology is unlike physics around that it does not commonly describe biological systems in terms of objects which obey changeless physical laws described by mathematics, it is however characterized by many major information & conception which include: catholicity, evolution, diversity, continuity, homeostasis & interactions.

Universality: Biochemistry, cells and the genetic code

Independent articles: Life

Tons organisms (viruses not involved) consist of cells, which in turn, come according to the most common carbon-based biochemistry. 100% parasites pass in their heredity via the genetic material which is based upon a nucleic acids such as DNA using a about universal genetic code. Around development the theme of universal processes is also present, for instance within virtually all metazoan organisms the basic steps of the early embryo development share similar morphological stages & include similar genes.

Evolution: The central principle of biology
Independent article: Evolution

One of the exchange, organizing conception inside biology is that a lot life has descended from either a common origin through a run of evolution. Indeed, these are one of a reasons that biological parasites exhibit a striking similarity of units & processes discussed in the former part. Charles Darwin established evolution as a viable theory by articulating its driving force: natural selection. (Alfred Russell Wallace is commonly recognized when a co-discoverer of this conception). Genetic drift was embraced as an additional mechanism in the and then-supposed modern synthesis. the evolutionary history of a species—which tells the characteristics of the various mintage from either which it descended—together sustaining its genealogic relationship to each more coinage is known as its phylogeny. Widely varied approaches to biology generate tools all about evolution. These include a comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient parasites around paleontology. Life scientist organize & analyze evolutionary relationships across various methods, including phylogenetics, phenetics, and cladistics. Major cases in the evolution of life, when life scientist presently realize the two, come summarized on this evolutionary timeline.

Diversity: The variety of living organisms
A all living things, based on rRNA gene data, showing the separation of the three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.]]

Despite a underlying unity, life exhibits an astonishing wide diversity within morphology, behavior and life histories. Sequentially to grapple by using this diversity, life scientist attempt to classify whole animate thing. This scientific classification should reflect a evolutionary trees (phylogenetic trees) of the different organisms. Such classifications come a province of the disciplines of systematics and taxonomy. Taxonomy puts parasites inside groups known as taxa, while systematics tries their relationships.

Traditionally, animate thing were divided into 5 kingdoms:

Still, this 5-kingdom models is okay, considered by numbers of to exist as superannuated. Supplementary modern option typically lead off using a three-domain system:

These domains reflect whether cells stand nuclei or even non too when differences inside cell exteriors. There exists besides the series of intracellular "parasites" that are more and more less alive inside terms of existence metabolically active:

Continuity: The common descent of life
Independent article: Common descent

The class action of parasites is said to keep close at hand most common descent whenever it have a most common ancestor. Completely existent organisms on Earth are descended from the most common antecedent or even transmissible gene pool. This "last universal common ancestor, that is, the most recent common ancestor of all organisms, is believed to have appeared about 3.5 billion years ago (see: origin of life).

The notion that "a lot life [is] from either [an] egg" (from the Latin "Omne vivum ex ovo") is a foundational concept of modern biology, it means that there has been an unbroken continuity of life from the initial origin of life to the present time. Up into the 19th century it was commonly believed that life forms can appear spontaneously under certain conditions (see abiogenesis). The universality of the genetic code is generally regarded by biologists as definitive evidence in favor of the theory of universal common descent (UCD) for all bacteria, archaea, and eukaryotes (see Three domain system).

Homeostasis: Adapting to change
Main article: Homeostasis

Homeostasis is the property of an open system to regulate its internal environment so as to maintain a stable condition, by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular exhibit homeostasis. Homeostasis can manifest itself at the cellular level through the maintenance of a stable internal acidity (pH); at the organismal level warm-blooded animals maintain a constant internal body temperature; and at the level of the ecosystem, for example when atmospheric carbon dioxide levels rise, plants are theoretically able to grow healthier and thus remove more carbon dioxide from the atmosphere. Tissues and organs can also maintain homeostasis.

Interactions: Groups and environments

Mutual symbiosis between clownfish of the genus Amphiprion that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protects the anemone fish from its predators

Every living thing interacts with other organisms and its environment. One of the reasons that biological systems can be difficult to study is that there are so many different possible interactions with other organisms and the environment. A microscopic bacterium responding to a local gradient in sugar is as much responding to its environment as a lion is responding to its environment when it is searching for food in the African savannah. Within a particular species behaviors can be co-operative, aggressive, parasitic or symbiotic. Matters become more complex still when two or more different species interact in an ecosystem, and is the province of ecology.

Scope of biology
Main article: List of biology disciplines

Biology has become such a vast research enterprise that it is not generally studied as a single discipline, but as a number of clustered sub-disciplines. We consider four broad groupings here. The first broad group consists of disciplines that study the basic structures of living systems: cells, genes etc., a second grouping considers the operation of these structures at the level of tissues, organs and bodies; a third grouping considers organisms and their histories; a final constellation of disciplines focuses on the interactions. It is important to note, however, that these boundaries and groupings and descriptions are a simplified description of biological research. In reality the boundaries between disciplines are very fluid and most disciplines borrow techniques from each other frequently. For example evolutionary biology leans heavily on techniques from molecular biology to determine DNA sequences which assist in understanding the genetic variation of a population; and physiology borrows extensively from cell biology in describing the function of organ systems.

Structure of life
cell depicting the various organelles and structures]]

Main articles: Molecular biology, Cell biology, Genetics, Developmental biology

Molecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology, particularly genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA and protein synthesis and learning how these interactions are regulated.

Cell biology studies the physiological properties of cells, as well as their behaviors, interactions, and environment; this is done both on a microscopic and molecular level. Cell biology researches both single-celled organisms like bacteria and specialized cells in multicellular organisms like humans.

Understanding the composition of cells and how cells work is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology. These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types.

Genetics is the science of genes, heredity, and the variation of organisms. In modern research, genetics provides important tools in the investigation of the function of a particular gene, e.g. analysis of genetic interactions. Within organisms, genetic information generally is carried in chromosomes, where it is represented in the chemical structure of particular DNA molecules.

Genes encode the information necessary for synthesizing proteins, which in turn play a large role in influencing the final phenotype of the organism, although in many instances do not completely determine it.

Developmental biology studies the process by which organisms grow and develop. Originating in embryology, today developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy. Model organisms for developmental biology include the round worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, the zebrafish Brachydanio rerio, the mouse Mus musculus, and the weed Arabidopsis thaliana.

Physiology of organisms
Main articles: Physiology, Anatomy

Physiology studies the mechanical, physical, and biochemical processes of living organisms, by attempting to understand how all the structures function as a whole. The theme of 'structure to function' is central to biology. Physiology studies have traditionally been divided into plant physiology and animal physiology but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cell can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human animal species. Plant physiology also borrows techniques from both fields.

Anatomy is an important part of physiology and considers how organ systems in animals such as the nervous, immune, endocrine, respiratory and circulatory systems function and interact. The study of these systems is shared with the medically oriented disciplines of neurology, immunology and the like.

Diversity and evolution of organisms

Main articles: Evolutionary biology, Botany, Zoology

Evolutionary biology is concerned with the origin and descent of species, as well as their change over time, i.e. their evolution. Evolutionary biology is an inclusive field because it includes scientists from many traditional taxonomically-oriented disciplines. For example, it generally includes scientists who may have a specialist training in particular organisms such as mammalogy, ornithology, or herpetology but use those organisms as systems to answer general questions in evolution. It also generally includes paleontologists who use fossils to answer questions about the mode and tempo of evolution, as well as theoreticians in areas such as population genetics and evolutionary theory. In the 1990s developmental biology made a re-entry into evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields which are often considered part of evolutionary biology are phylogenetics, systematics and taxonomy.

The two major traditional taxonomically-oriented disciplines are botany and zoology. Botany is the scientific study of plants. Botany covers a wide range of scientific disciplines that study the growth, reproduction, metabolism, development, diseases, and evolution of plant life. Zoology is the discipline which involves the study of animals, which includes the physiology of animals is studied under various fields including anatomy and embryology. The common genetic and developmental mechanisms of animals and plants is studied in molecular biology, molecular genetics and developmental biology. The ecology of animals is covered under behavioral ecology and other fields.

Classification of life

The dominant classification system is called Linnaean taxonomy, which includes ranks and binomial nomenclature. How organisms are named is governed by 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 BioCode was published in 1997 in an attempt to standardize naming in the three areas, but it does not appear to have yet been formally adopted. The International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.

Interactions of organisms
Main articles: Ecology, Ethology, Behavior, Biogeography

Ecology studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. The environment of an organism includes both its habitat, which can be described as the sum of local abiotic factors like climate and geology, as well as the other organisms which share its habitat. Ecological systems are studied at several different levels from individuals and populations to ecosystems and biosphere level. Ecology is a multi-disciplinary science, drawing on many other branches of science.

Ethology studies animal behavior (particularly of social animals such as primates and canids), and is sometimes considered as a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense the first modern ethologist was Charles Darwin, whose book The expression of the emotions in animals and men influenced many ethologists.

Biogeography studies the spatial distribution of organisms on the Earth, focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics.

History of the word "biology"
Formed by combining the Greek βίος (bios), meaning 'life', and λόγος (logos), meaning 'study of', the word "biology" in its modern sense seems to have been introduced independently by Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and by Jean-Baptiste Lamarck (Hydrogéologie, 1802). The word itself is sometimes said to have been coined in 1800 by Karl Friedrich Burdach, but it appears in the title of Volume 3 of Michael Christoph Hanov's Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia, phytologia generalis et dendrologia, published in 1766.

History
Main articles: History of biology, History of medicine, History of genetics

Major discoveries in biology include: Cell theory Germ theory of disease Genetics Evolution DNA