definition of biography in biology

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A Dictionary of Biology (6 ed.)  

Elizabeth martin  and robert hine.

Fully revised and updated, the sixth edition of this dictionary provides comprehensive coverage of biology, biophysics, and biochemistry, as well as key terms from medicine and palaeontology. It includes biographies of key scientists, and feature articles on important topics, such as bioinformatics, genetically modified organisms, microarray technology, and RNA interference. The dictionary’s chronologies chart developments in major fields including cell biology, genetics, microscopy, and vitamins. A new feature is the inclusion of entry-level web links.

With over 5,500 clear and concise entries, over 400 of them new to this edition, this market-leading dictionary is the perfect guide for anyone studying biology, either at school or university.

Bibliographic Information

Affiliations are at time of print publication..

Elizabeth Martin, author

Robert Hine, author

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abiogenesis

Abiotic factor, abscisic acid, absolute refractory period, absorbed dose, absorption spectrum, abyssal zone, acceleration, accessory bud, accessory chromosome, accessory pigment, front matter, publishing information, general links for this work, simplified classification of the animal kingdom, simplified classification of land plants, geological time scale, model organisms and their genomes, major mass extinctions of species, nobel prizewinning contributions to biology.

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What is biology?

Biology is the study of everything that is, or was once, alive — whether it's a plant, animal or microorganism.

• Basic principles
• Branches of biology
• Multidisciplinary nature of biology

What do biologists do?

Additional resources, bibliography.

Biology is the study of life. The word "biology" is derived from the Greek words "bios" (meaning life) and "logos" (meaning "study"). In general, biologists study the structure, function, growth, origin, evolution and distribution of living organisms.

Biology is important because it helps us understand how living things work and how they function and interact on multiple levels, according to the Encyclopedia Britannica . Advances in biology have helped scientists do things such as develop better medicines and treatments for diseases, understand how a changing environment might affect plants and animals, produce enough food for a growing human population and predict how eating new food or sticking to an exercise regimen might affect our bodies.

The basic principles of modern biology

Four principles unify modern biology, according to the book " Managing Science " (Springer New York, 2010): 

• Cell theory is the principle that all living things are made of fundamental units called cells , and all cells come from preexisting cells.
• Gene theory is the principle that all living things have DNA , molecules that code the structures and functions of cells and get passed to offspring.
• Homeostasis is the principle that all living things maintain a state of balance that enables organisms to survive in their environment.
• Evolution is the principle that describes how all living things can change to have traits that enable them to survive better in their environments. These traits result from random mutations in the organism's genes that are "selected" via a process called natural selection. During natural selection, organisms that have traits better-suited for their environment have higher rates of survival, and then pass those traits to their offspring.

The many branches of biology

Although there are only four unifying principles, biology covers a broad range of topics that are broken into many disciplines and subdisciplines.

On a high level, the different fields of biology can each be thought of as the study of one type of organism, according to " Blackie's Dictionary of Biology " (S Chand, 2014). For example, zoology is the study of animals, botany is the study of plants and microbiology is the study of microorganisms.

Within those broader fields, many biologists specialize in researching a specific topic or problem. For example, a scientist may study behavior of a certain fish species, while another scientist may research the neurological and chemical mechanisms behind the behavior.

–   Science and the scientific method: Definitions and examples

– What is chemistry?

– What is a scientific theory?

– What is a scientific hypothesis?

There are numerous branches and subdisciplines of biology, but here is a short list of some of the more broad fields that fall under the umbrella of biology: 

Biochemistry: The study of the chemical processes that take place in or are related to living things, according to the Biochemical Society . For example, pharmacology is a type of biochemistry research that focuses on studying how drugs interact with chemicals in the body, as described in a 2010 review in the journal Biochemistry . 

Ecology: The study of how organisms interact with their environment. For example, an ecologist may study how honeybee behavior is affected by humans living nearby. 

Genetics: The study of heredity. Geneticists study how genes are passed down by parents to their offspring, and how they vary from person to person. For example, scientists have identified several genes and genetic mutations that influence human lifespan, as reported in a 2019 review published in the journal Nature Reviews Genetics .   

Physiology: The study of how living things work. Physiology, which is applicable to any living organism, "deals with the life-supporting functions and processes of living organisms or their parts," according to Nature . Physiologists seek to understand biological processes, such as how a particular organ works, what its function is and how it's affected by outside stimuli. For example, physiologists have studied how listening to music can cause physical changes in the human body , such as a slower or faster heart rate , according to the journal Psychological Health Effects of Musical Experiences . . 

The multidisciplinary nature of biology

Biology is often researched in conjunction with other fields of study, including mathematics , engineering and the social sciences. Here are a few examples:

Astrobiology is the study of the evolution of life in the universe, including the search for extraterrestrial life, according to NASA . This field incorporates principles of biology with astronomy. 

Bioarchaeologists are biologists who incorporate archaeological techniques to study skeletal remains and derive insights about how people lived in the past, according to George Mason University .

Bioengineering is the application of engineering principles to biology and vice versa, according to the University of California Berkeley . For example, a bioengineer might develop a new medical technology that better images the inside of the body, like an improved Magnetic Resonance Imaging (MRI) that scans the human body at a faster rate and higher resolution, or apply biological knowledge to create artificial organs, according to the journal Cell Transplant.

Biotechnology involves using biological systems to develop products, according to the Norwegian University of Science and Technology . For example, biotechnologists in Russia genetically engineered a better-tasting and more disease-resistant strawberry, which the researchers described in their 2007 study published in the journal Biotechnology and Sustainable Agriculture 2006 and Beyond .  

Biophysics employs the principles of physics to understand how biological systems work, according to the Biophysical Society . For example, biophysicists may study how genetic mutations leading to changes in protein structure impacts protein evolution, according to the Journal of the Royal Society

Biologists can work in many different fields, including research, healthcare, environmental conservation and art, according to the American Institute of Biological Sciences . Here are a few examples:

Research: Biologists can perform research in many types of settings. Microbiologists, for instance, may study bacterial cultures in a laboratory setting. Other biologists may perform field research, where they observe animals or plants in their native habitat. Many biologists may work in the lab and in the field — for example, scientists may collect soil or water samples from the field and analyze them further in the  lab, like at North Carolina University's Soil and Water Lab .

Conservation : Biologists can help with efforts in environmental conservation by studying and determining how to protect and conserve the natural world for the future. For example, biologists may help educate the public on the importance of preserving an animal's natural habitat and participate in endangered species recovery programs to stop the decline of an endangered species, according to the U.S. Fish & Wildlife Service .

Healthcare : People who study biology can go on to work in healthcare, whether they work as doctors or nurses, join a pharmaceutical company to develop new drugs and vaccines, research the efficacy of medical treatments or become veterinarians to help treat sick animals, according to the American Institute of Biological Sciences .

Art: Biologists who also have a background in art have both the technical knowledge and artistic skill to create visuals that will communicate complex biological information to a wide variety of audiences. One example of this is in medical illustration, in which an illustrator may perform background research, collaborate with experts, and observe a medical procedure to create an accurate visual of a body part, according to the Association of Medical Illustrators .

If you’re curious about just how wide-reaching biology is, The University of North Carolina at Pembroke has listed a number of biology subdisciplines on their website. Interested in a career in biology? Check out some options at the American Institute of Biological Sciences website.

Lornande Loss Woodruff, “History of Biology”, The Scientific Monthly, Volume 12, March 1921, http://www.jstor.org/stable/6836 .  

P.N. Campbell, “ Biology in Profile: A Guide to the Many Branches of Biology ”, Elsevier, October 2013. 

The University of North Carolina at Pembroke, “ Biology Sub-disciplines ”, October 2010. 

University of Minnesota Duluth, “ What is Biology? ”, January 2022. 

Eric J. Simon et al, “ Campbell Essential Biology ”, Pearson Education, January 2018. 

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Alane Lim holds a Ph.D. in materials science and engineering from Northwestern University and a bachelor's degrees in chemistry and cognitive science from Johns Hopkins University. She also has over five years of experience in writing about science for a variety of audiences. Her work has appeared on the science YouTube channel SciShow, the reference website ThoughtCo, and the American Institute of Physics.

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1 Definition of Life

Study guide, learn objectives.

• Identify the core characteristics that define “life.”
• Identify the commonalities and differences among various definitions of “life.”
• Discuss the challenges of settling on a single definition of life.

Key Concepts and Terms

• Sensitivity to stimuli

Reproduction

• Homeostasis
• Growth and development
• Energy processing

Biology is the science that studies life. What exactly is life? This may sound like a silly question with an obvious answer, but it is not easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. Although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life.

From its earliest beginnings, biology has wrestled with four questions: What are the shared properties that make something “alive”? How do those various living things function? When faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? Finally, what biologists ultimately seek to understand is how this diversity arises and how it continues. As new organisms are discovered every day, biologists continue to seek answers to these and other questions.

Properties of Life

All groups of living organisms share several key characteristics or functions: order, sensitivity or response to stimuli, reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing. When viewed together, these characteristics serve to define life.

Order (Cells)

Cells are considered the most basic units of life because they represent discrete units that can independently embody all of the other characteristics listed below. All life living things consist of one or more cells. Even very simple, single-celled organisms are remarkably complex. Inside each cell, atoms make up molecules. These in turn make up cell components or organelles. Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms in that their cells can be specialized to perform specific functions and even sacrificed in certain situations for the good of the organism as a whole. How these specialized cells come together to form organs such as the heart, lung, or skin in organisms like the toad shown in Figure 1  will be discussed later.

Sensitivity or Response to Stimuli

Organisms respond to diverse stimuli. For example, plants can grow toward a source of light or respond to touch ( Figure 2 ). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). The movement toward a stimulus is considered a positive response, while the movement away from a stimulus is considered a negative response.

CONCEPTS IN ACTION

Watch this video to see how the sensitive plant responds to a touch stimulus .

Single-celled organisms reproduce by first duplicating their DNA, which is the genetic material, and then dividing it equally as the cell prepares to divide to form two new cells. Many multicellular organisms (those made up of more than one cell) produce specialized reproductive cells that will form new individuals. When reproduction occurs, DNA, which encodes genes, is passed along to an organism’s offspring. These genes are the reason that the offspring will belong to the same species and will have characteristics similar to the parent, such as fur color and blood type.

Growth and Development

All organisms grow and develop according to specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young ( Figur e 3 ) will grow up to exhibit many of the same characteristics as its parents.

Regulation/Homeostasis

Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, such as the transport of nutrients, response to stimuli, and coping with environmental stresses. For example, organ systems such as the digestive or circulatory systems perform specific functions like carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body.

To function properly, cells require appropriate conditions such as proper temperature, pH, and concentrations of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through a process called homeostasis or “steady state”—the ability of an organism to maintain constant internal conditions. For example, many organisms regulate their body temperature in a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear ( Figure 4 ), have body structures that help them withstand low temperatures and conserve body heat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.

Energy Processing

All organisms (such as the California condor shown in Figure 5 ) use a source of energy for their metabolic activities. Some organisms capture energy from the Sun and convert it into chemical energy in food; others use chemical energy from molecules they take in.

The diversity of life on Earth is a result of mutations or random changes in hereditary material over time. These mutations allow the possibility for organisms to adapt to a changing environment. An organism that evolves characteristics fit for the environment will have greater reproductive success, subject to the forces of natural selection.

Evolution by natural selection results in adaptations . All living organisms exhibit a “fit” to their environment. Biologists refer to this fit as adaptation and it is a consequence of evolution by natural selection, which operates in every lineage of reproducing organisms. Examples of adaptations are as diverse as unique heat-resistant Archaea that live in boiling hot springs to the tongue length of a nectar-feeding moth that matches the size of the flower from which it feeds. All adaptations enhance the reproductive potential of the individual exhibiting them, including their ability to survive to reproduce. Adaptations are not constant. As an environment changes, natural selection causes the characteristics of the individuals in a population to track those changes.

Watch the following video to review the characteristics of life. Do the characteristics listed in the video differ from those listed above?

the study of living organisms and their interactions with one another and their environments

Introductory Biology: Evolutionary and Ecological Perspectives Copyright © by Various Authors - See Each Chapter Attribution is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Life n., plural: lives [laɪf] Definition: characteristic of a living organism; biota

Table of Contents

Life Definition

Life is a characteristic of a living organism that distinguishes the latter from a dead organism or a non-living thing, as specifically distinguished by the capacity to grow, metabolize, respond (to stimuli), adapt, and reproduce. Life may also pertain to the  biota of a particular region. Word origin: Old English līf (life, body).

Basic Characteristics of a Living Thing

When does life begin? There is no consensus about where life begins. Does it begin at the time of fertilization or the time before or after that? The origin of life is also contestable. Despite the irresolute answer for questions about life, the basic characteristics of a living thing are as follows:

• Organization . Living things have an organized structure to perform a specific function. In particular, a living thing is made up of a single cell or a group of cells. A cell is the basic structural and functional unit of any organism .
• Homeostasis . A life form would have the ability to keep up its existence, for instance, by regulating its internal environment to keep up a constant or favorable state.
• Metabolism . A living thing would be capable of converting energy from chemicals into cellular components through anabolic reactions. It would also be capable of decomposing organic matter through catabolism.
• Growth . A living thing grows, i.e. in size or in number.
• Response . An organism has the ability to respond to stimuli or to its environment, usually through a series of metabolic reactions.
• Reproduction . One of the hallmarks of life is the ability to reproduce, i.e. producing a new of its kind.
• Adaptation . An organism is capable of changing through time to adapt to its environment.

Evolutionary History of Life

Biologically, evolution is important because it drives biodiversity . Some traits will become predominant while others will become rare over the course of time. Without evolution, life may not be the way we know it. It will not be as diverse as it is now.

The Earth itself goes through a series of changes. At one point, the Earth was an inhabitable planet. The primitive condition of the Earth was hostile to life. It was presumed that only after about one billion years from the time that the Earth first came into being that life began. RNA-based, self-replicating entities are held as the descendants of all living things. Over a significant period of time, these life forms evolved into single-celled organisms. Multicellular forms came next. They first appeared about 600 million years ago.

Tracking the history of life at various geologic eras, one would find several mass extinctions occurring in between the bursts of life. For instance, during the Permian period of the Paleozoic era , the Earth had a supercontinent called Pangaea surrounded by Panthalassa ocean . This caused the inland to be very dry and arid. Because of this, reptiles flourished as they were able to thrive even in such habitats. A reptile group Dimetrodon evolved and gave rise to therapsids . The therapsids, in turn, evolved and gave rise to cynodonts , which were the early ancestors of animals . During this period, the early dinosaur ancestors, archosaurs , also appeared. Apparently, a mass extinction called “the Great Dying” occurred and wiped about 90% of life on Earth. The next era ( Mesozoic era ) is called “the Age of the dinosaurs”. These animals dominated the land, the seas, and the air of the Earth. However, a mass extinction occurred and caused the death of the dinosaurs as well as other large animals. Nevertheless, mammals took the open niche and expanded.

Evolution is crucial for life to persist on the ever-changing Earth. The organisms need to have the capacity to adapt genetically and phenotypically . Engaging in symbiotic relationships with other organisms could also help increase the propensity to survive and thrive. Along with evolution, speciation transpired. Species diverge into two or more descendant species throughout the course of evolution. Unfortunately, though, most of the species that lived on Earth already met their demise. 99% of the Earth’s species are now extinct. These organisms perished and their species entirely disappeared. Thus, it would seem that the extinction of species is inevitable.

A diagram, called an evolutionary tree , shows the evolutionary relationships of organisms. The grouping is based on the similarities and the differences in genetic and physical characteristics. The pattern of branching represents how species or entities evolved from a particular common ancestor. Tracking down the course of evolution of all living things that lived on Earth would altogether lead to the common ancestor, LUCA ( last universal common ancestor ). LUCA is the hypothetical ancestor of all living things and it is presumed to emerge some 3.5 to 3.8 billion years ago .

There is no consensus as yet as to how life originated on Earth. However, many believed that the RNA-based, self-replicating entities were likely the descendant of all living things. These entities evolved into single-celled organisms containing cytoplasmic structures but lacking internal compartmentalization. Single-celled organisms lacking membrane-bound organelles are referred to as prokaryotes .

Endosymbiotic theory

The prokaryotes emerged before the eukaryotes did. They were able to bear up the primitive hostile conditions of the Earth. Later on, single-celled eukaryotes appeared around 1.6 to 2.7 billion years ago . The endosymbiotic theory proposes that larger cells took in smaller cells, such as bacteria and cyanobacteria , for a cooperative association (endosymbiosis). Together, they underwent coevolution. In due course, the smaller prokaryotes evolved into semi-autonomic organelles. The bacteria evolved into mitochondria whereas the cyanobacteria, into chloroplasts . The presence of membrane-bound organelles inside the cell led to the advent of eukaryotes .

Multicellularity

In the Neoproterozoic era , particularly in the Ediacaran period (around 600 million years ago ), the first multicellular form emerged. How multicellularity came about is still a matter of debate until now. The most popular theory in this regard is that of Haeckel’s. According to his Gastraea Theory , multicellularity occurred when cells of the same species group together in a blastula-like colony, and gradually, certain cells in the colony underwent cell differentiation. Also in this period, sponge-like organisms evolved based on the recovered fossils of Ediacaran biota . They were presumed to be the first animals.

Cambrian explosion

The next era, the Paleozoic , is comprised of the geologic periods from Cambrian to Permian, each highlighted by major evolutionary events. In the Cambrian period (around 541 million years ago ), a sudden burst of life occurred. This geologic event was called the Cambrian explosion . Diverse plants and animals came into being. Plants and fungi spread to the land. Soon, animals such as arthropods ventured ashore, probably to mate and lay eggs.

Rise of invertebrates

In the Ordovician period ( 485 to 440 million years ago ), the invertebrates were the dominant animals. Primitive fish continue to evolve that in the next geologic period, Silurian , a mass evolution of fish occurred. Also in Silurian ( 440 to 415 million years ago ), arachnids and arthropods started to colonize the land, not just ventured it. Internal gas exchange systems, waterproof external layers, skeletal systems (endo- or exoskeletons), and a form of reproduction not involving water came about and helped life on land plausible.

“Age of the Fish”

Devonian period ( 415 to 360 million years ago ) is called the Age of the Fish . The fish became the dominant marine vertebrate species. On land, plants evolved and primitive plants, trees, and shrub-like forests served as new habitats. With the evolution of land plants, the animals, too, evolved and diversified. Amphibians were the first tetrapods to appear. They emerged around 364 million years ago .

The emergence of the amniotes

In the Carboniferous period (360 to 300 million years ago), a major evolutionary event occurred. Tetrapods that lay amniotic eggs emerged. The laying of amniotic eggs in a drier environment allowed the tetrapod amniotes to move farther away from the waterside and thereby dominate farther inland. Because of this, these early amniotes diversified greatly towards the end of this period.

Permian reptiles

In the Permian period ( 300 to 250 million years ago ), reptiles and synapsids flourished. Soon, a major evolutionary event occurred, which led to the emergence of beast-faced therapsids. These therapsids later gave rise to the cynodonts (the early ancestors of mammals). The first archosaurs (early ancestors of dinosaurs) also appeared in the Permian period.

“Age of the Dinosaurs”

Following the Paleozoic era is the Mesozoic era ( 252 to 66 million years ago ), which is referred to as “the Age of the Dinosaurs”. The dinosaurs roamed and dominated the Earth. However, a mass extinction event occurred. They perished together with the other large animals (>25 kg in weight) by the end of this era.

“New Life”

In the next era, Cenozoic ( 66 million years ago to the present day ) era is called the “New Life”. Mammals expanded and diversified. The great apes evolved and led to the evolution of hominids, which was the evolutionary line that led to the Homo species. The only extant species of the genus Homo is the Homo sapiens (anatomically modern humans).

• living thing
• homeostasis

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Biology: The Study of Life

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What is biology ? Simply put, it is the study of life, in all of its grandeur. Biology concerns all life forms, from the very small algae to the very large elephant. But how do we know if something is living? For example, is a virus alive or dead? To answer these questions, biologists have created a set of criteria called the "characteristics of life." 

The Characteristics of Life

Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses . On a basic level, we can say that life is ordered . Organisms have an enormously complex organization. We're all familiar with the intricate systems of the basic unit of life, the cell .

Life can "work." No, this doesn't mean all animals are qualified for a job. It means that living creatures can take in energy from the environment. This energy, in the form of food, is transformed to maintain metabolic processes and for survival.

Life grows and develops . This means more than just replicating or getting larger in size. Living organisms also have the ability to rebuild and repair themselves when injured.

Life can reproduce . Have you ever seen dirt reproduce? I don't think so. Life can only come from other living creatures.

Life can respond . Think about the last time you accidentally stubbed your toe. Almost instantly, you flinched back in pain. Life is characterized by this response to stimuli.

Finally, life can adapt and respond to the demands placed on it by the environment. There are three basic types of adaptations that can occur in higher organisms.

• Reversible changes occur as a response to changes in the environment. Let's say you live near sea level and you travel to a mountainous area. You may begin to experience difficulty breathing and an increase in heart rate as a result of the change in altitude. These symptoms go away when you go back down to sea level.
• Somatic changes occur as a result of prolonged changes in the environment. Using the previous example, if you were to stay in the mountainous area for a long time, you would notice that your heart rate would begin to slow down and you would begin to breath normally. Somatic changes are also reversible.
• The final type of adaptation is called genotypic (caused by genetic mutation ). These changes take place within the genetic makeup of the organism and are not reversible. An example would be the development of resistance to pesticides by insects and spiders .

In summary, life is organized, "works," grows, reproduces, responds to stimuli and adapts. These characteristics form the basis of the study of biology.

Basic Principles of Biology

The foundation of biology as it exists today is based on five basic principles. They are the cell theory, gene theory, evolution, homeostasis, and laws of thermodynamics.

• Cell Theory : all living organisms are composed of cells. The cell is the basic unit of life.
• Gene Theory : traits are inherited through gene transmission. Genes are located on chromosomes and consist of DNA .
• Evolution : any genetic change in a population that is inherited over several generations. These changes may be small or large, noticeable or not so noticeable.
• Homeostasis : ability to maintain a constant internal environment in response to environmental changes.
• Thermodynamics : energy is constant and energy transformation is not completely efficient.

Subdiciplines of Biology The field of biology is very broad in scope and can be divided into several disciplines. In the most general sense, these disciplines are categorized based on the type of organism studied. For example, zoology deals with animal studies, botany deals with plant studies, and microbiology is the study of microorganisms. These fields of study can be broken down further into several specialized sub-disciplines. Some of which include anatomy, cell biology , genetics , and physiology.

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