imtoken钱包安卓官方版|biology

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Biology | Definition, History, Concepts, Branches, & Facts | Britannica

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1History

2Chemical basis

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2.1Atoms and molecules

2.2Water

2.3Organic compounds

2.4Macromolecules

3Cells

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3.1Cell structure

3.2Metabolism

3.3Cellular respiration

3.4Photosynthesis

3.5Cell signaling

3.6Cell cycle

4Genetics

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4.1Inheritance

4.2Genes and DNA

4.3Gene expression

4.4Gene regulation

4.5Genes, development, and evolution

5Evolution

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5.1Evolutionary processes

5.2Speciation

5.3Phylogeny

5.4History of life

6Diversity

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6.1Bacteria and Archaea

6.2Eukaryotes

6.3Viruses

7Ecology

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7.1Ecosystems

7.2Populations

7.3Communities

7.4Biosphere

7.5Conservation

8See also

9References

10Further reading

11External links

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Biology

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AfrikaansAlemannischአማርኛАԥсшәаالعربيةAragonésԱրեւմտահայերէնArmãneashtiArpetanঅসমীয়াAsturianuअवधीAvañe'ẽАварAzərbaycancaتۆرکجهবাংলাBanjarBân-lâm-gúBasa BanyumasanБашҡортсаБеларускаяБеларуская (тарашкевіца)भोजपुरीBikol CentralBislamaБългарскиBoarischབོད་ཡིགBosanskiBrezhonegБуряадCatalàЧӑвашлаCebuanoČeštinaChamoruChiShonaCorsuCymraegDagbanliDanskالدارجةDeutschދިވެހިބަސްEestiΕλληνικάЭрзяньEspañolEsperantoEstremeñuEuskaraفارسیFiji HindiFøroysktFrançaisFryskFurlanGaeilgeGaelgGàidhligGalegoГӀалгӀайGĩkũyũگیلکیગુજરાતી客家語/Hak-kâ-ngîХальмг한국어HausaHawaiʻiՀայերենहिन्दीHornjoserbsceHrvatskiIdoIlokanoBahasa IndonesiaInterlinguaInterlingueᐃᓄᒃᑎᑐᑦ / inuktitutИронIsiXhosaIsiZuluÍslenskaItalianoעבריתJawaKabɩyɛKalaallisutಕನ್ನಡKapampanganქართულიकॉशुर / کٲشُرKaszëbscziҚазақшаKernowekKiswahiliKotavaKreyòl ayisyenKriyòl gwiyannenKurdîКыргызчаLadinLadinoລາວLatinaLatviešuLëtzebuergeschЛезгиLietuviųLigureLimburgsLingálaLingua Franca NovaLivvinkarjalaLa .lojban.LugandaLombardMagyarMadhurâМакедонскиMalagasyമലയാളംMaltiमराठीმარგალურიمصرىBahasa Melayuꯃꯤꯇꯩ ꯂꯣꯟMinangkabau閩東語 / Mìng-dĕ̤ng-ngṳ̄MirandésМонголမြန်မာဘာသာNāhuatlNa Vosa VakavitiNederlandsNedersaksiesनेपालीनेपाल भाषा日本語NapulitanoߒߞߏНохчийнNordfriiskNorfuk / PitkernNorsk bokmålNorsk nynorskNouormandNovialOccitanОлык марийଓଡ଼ିଆOromooOʻzbekcha / ўзбекчаਪੰਜਾਬੀPälzischپنجابیပအိုဝ်ႏဘာႏသာႏPapiamentuپښتوPatoisភាសាខ្មែរPiemontèisTok PisinPlattdüütschPolskiPortuguêsQaraqalpaqshaQırımtatarcaRomânăRumantschRuna SimiРусиньскыйРусскийСаха тылаGagana Samoaसंस्कृतम्سرائیکیSarduScotsSeelterskSesothoSesotho sa LeboaShqipSicilianuසිංහලSimple EnglishسنڌيSiSwatiSlovenčinaSlovenščinaŚlůnskiSoomaaligaکوردیСрпски / srpskiSrpskohrvatski / српскохрватскиSundaSuomiSvenskaTagalogதமிழ்TaclḥitTaqbaylitТатарча / tatarçaతెలుగుTetunไทยThuɔŋjäŋትግርኛТоҷикӣತುಳುTürkçeTürkmençeУдмуртBasa UgiУкраїнськаاردوئۇيغۇرچە / UyghurcheVahcuenghVènetoVepsän kel’Tiếng ViệtVolapükVõroWalon文言West-VlamsWinaray吴语Xitsongaייִדיש粵語ZazakiZeêuwsŽemaitėška中文Tolışiⵜⴰⵎⴰⵣⵉⵖⵜ ⵜⴰⵏⴰⵡⴰⵢⵜ

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From Wikipedia, the free encyclopedia

Science that studies life

For other uses, see Biology (disambiguation).

"Biological" redirects here. For other uses, see Biological (disambiguation).

Biology is the science of life. It spans multiple levels from biomolecules and cells to organisms and populations.

Part of a series onBiologyScience of life

Index

Outline

Glossary

History (timeline)

Key components

Cell theory

Ecosystem

Evolution

Phylogeny

Properties of life

Adaptation

Energy processing

Growth

Order

Regulation

Reproduction

Response to environment

Domains and Kingdoms of life

Archaea

Bacteria

Eukarya (Animals, Fungi, Plants, Protists)

Branches

Abiogenesis

Aerobiology

Agronomy

Agrostology

Anatomy

Astrobiology

Bacteriology

Biochemistry

Biogeography

Biogeology

Bioinformatics

Biological engineering

Biomechanics

Biophysics

Biosemiotics

Biostatistics

Biotechnology

Botany

Cell biology

Cellular microbiology

Chemical biology

Chronobiology

Cognitive biology

Computational biology

Conservation biology

Cryobiology

Cytogenetics

Dendrology

Developmental biology

Ecological genetics

Ecology

Embryology

Epidemiology

Epigenetics

Evolutionary biology

Freshwater biology

Genetics

Genomics

Geobiology

Gerontology

Herpetology

Histology

Human biology

Ichthyology

Immunology

Lipidology

Mammalogy

Marine biology

Mathematical biology

Microbiology

Molecular biology

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Biology is the scientific study of life.[1][2][3] It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field.[1][2][3] For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life.[1][2][3] Energy processing is also important to life as it allows organisms to move, grow, and reproduce.[1][2][3] Finally, all organisms are able to regulate their own internal environments.[1][2][3][4][5]

Biologists are able to study life at multiple levels of organization,[1] from the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations.[1][6] Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use.[7][8][9] Like other scientists, biologists use the scientific method to make observations, pose questions, generate hypotheses, perform experiments, and form conclusions about the world around them.[1]

Life on Earth, which emerged more than 3.7 billion years ago,[10] is immensely diverse. Biologists have sought to study and classify the various forms of life, from prokaryotic organisms such as archaea and bacteria to eukaryotic organisms such as protists, fungi, plants, and animals. These various organisms contribute to the biodiversity of an ecosystem, where they play specialized roles in the cycling of nutrients and energy through their biophysical environment.

History

Main article: History of biology

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

The earliest of roots of science, which included medicine, can be traced to ancient Egypt and Mesopotamia in around 3000 to 1200 BCE.[11][12] Their contributions shaped ancient Greek natural philosophy.[11][12][13][14] Ancient Greek philosophers such as Aristotle (384–322 BCE) contributed extensively to the development of biological knowledge. He explored biological causation and the diversity of life. His successor, Theophrastus, began the scientific study of plants.[15] Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dīnawarī (828–896), who wrote on botany,[16] and Rhazes (865–925) who wrote on anatomy and physiology. Medicine was especially well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew heavily on Aristotelian thought.

Biology began to quickly develop with Anton van Leeuwenhoek's dramatic improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and helped to develop techniques of microscopic dissection and staining.[17] Advances in microscopy had a profound impact on biological thinking. In the early 19th century, biologists pointed to the central importance of the cell. In 1838, Schleiden and Schwann began promoting the now universal ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, although they opposed the idea that (3) all cells come from the division of other cells, continuing to support spontaneous generation. However, Robert Remak and Rudolf Virchow were able to reify the third tenet, and by the 1860s most biologists accepted all three tenets which consolidated into cell theory.[18][19]

Meanwhile, taxonomy and classification became the focus of natural historians. Carl Linnaeus published a basic taxonomy for the natural world in 1735, and in the 1750s introduced scientific names for all his species.[20] Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent.[21]

In 1842, Charles Darwin penned his first sketch of On the Origin of Species.[22]

Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck, who presented a coherent theory of evolution.[23] The British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Malthus's writings on population growth, and his own morphological expertise and extensive natural observations, forged a more successful evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel Wallace to independently reach the same conclusions.[24][25]

The basis for modern genetics began with the work of Gregor Mendel in 1865.[26] This outlined the principles of biological inheritance.[27] However, the significance of his work was not realized until the early 20th century when evolution became a unified theory as the modern synthesis reconciled Darwinian evolution with classical genetics.[28] In the 1940s and early 1950s, a series of experiments by Alfred Hershey and Martha Chase pointed to DNA as the component of chromosomes that held the trait-carrying units that had become known as genes. A focus on new kinds of model organisms such as viruses and bacteria, along with the discovery of the double-helical structure of DNA by James Watson and Francis Crick in 1953, marked the transition to the era of molecular genetics. From the 1950s onwards, biology has been vastly extended in the molecular domain. The genetic code was cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain codons. The Human Genome Project was launched in 1990 to map the human genome.[29]

Chemical basis

Atoms and molecules

Further information: Chemistry

All organisms are made up of chemical elements;[30] oxygen, carbon, hydrogen, and nitrogen account for most (96%) of the mass of all organisms, with calcium, phosphorus, sulfur, sodium, chlorine, and magnesium constituting essentially all the remainder. Different elements can combine to form compounds such as water, which is fundamental to life.[30] Biochemistry is the study of chemical processes within and relating to living organisms. Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms, and interactions.

Water

Model of hydrogen bonds (1) between molecules of water

See also: Planetary habitability, Circumstellar habitable zone, and Water distribution on Earth

Life arose from the Earth's first ocean, which formed some 3.8 billion years ago.[31] Since then, water continues to be the most abundant molecule in every organism. Water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. Once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life.[31] In terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen (H) atoms to one oxygen (O) atom (H2O).[31] Because the O–H bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge.[31] This polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive.[31] Surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid.[31] Water is also adhesive as it is able to adhere to the surface of any polar or charged non-water molecules.[31] Water is denser as a liquid than it is as a solid (or ice).[31] This unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above.[31] Water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol.[31] Thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor.[31] As a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again.[31] In pure water, the number of hydrogen ions balances (or equals) the number of hydroxyl ions, resulting in a pH that is neutral.

Organic compounds

Further information: Organic chemistry

Organic compounds such as glucose are vital to organisms.

Organic compounds are molecules that contain carbon bonded to another element such as hydrogen.[31] With the exception of water, nearly all the molecules that make up each organism contain carbon.[31][32] Carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules.[31][32] For example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide (CO2), or a triple covalent bond such as in carbon monoxide (CO). Moreover, carbon can form very long chains of interconnecting carbon–carbon bonds such as octane or ring-like structures such as glucose.

The simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other elements such as oxygen (O), hydrogen (H), phosphorus (P), and sulfur (S), which can change the chemical behavior of that compound.[31] Groups of atoms that contain these elements (O-, H-, P-, and S-) and are bonded to a central carbon atom or skeleton are called functional groups.[31] There are six prominent functional groups that can be found in organisms: amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group.[31]

In 1953, the Miller-Urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early Earth, thus suggesting that complex organic molecules could have arisen spontaneously in early Earth (see abiogenesis).[33][31]

Macromolecules

Main article: Macromolecule

The (a) primary, (b) secondary, (c) tertiary, and (d) quaternary structures of a hemoglobin protein

Macromolecules are large molecules made up of smaller subunits or monomers.[34] Monomers include sugars, amino acids, and nucleotides.[35] Carbohydrates include monomers and polymers of sugars.[36]

Lipids are the only class of macromolecules that are not made up of polymers. They include steroids, phospholipids, and fats,[35] largely nonpolar and hydrophobic (water-repelling) substances.[37]

Proteins are the most diverse of the macromolecules. They include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. The basic unit (or monomer) of a protein is an amino acid.[34] Twenty amino acids are used in proteins.[34]

Nucleic acids are polymers of nucleotides.[38] Their function is to store, transmit, and express hereditary information.[35]

Cells

Main article: Cell (biology)

Cell theory states that cells are the fundamental units of life, it a unity of Protoplasm made of cytoplasm and nucleus surrounded by a cell membrane.[39] that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division.[40] Most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope.[41] There are generally two types of cells: eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. Prokaryotes are single-celled organisms such as bacteria, whereas eukaryotes can be single-celled or multicellular. In multicellular organisms, every cell in the organism's body is derived ultimately from a single cell in a fertilized egg.

Cell structure

Structure of an animal cell depicting various organelles

Every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space.[42] A cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. Cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions.[43] Cell membranes also contains membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell.[44] Cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton.

Structure of a plant cell

Within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids.[45] In addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units.[46] These organelles include the cell nucleus, which contains most of the cell's DNA, or mitochondria, which generates adenosine triphosphate (ATP) to power cellular processes. Other organelles such as endoplasmic reticulum and Golgi apparatus play a role in the synthesis and packaging of proteins, respectively. Biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. Plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds.[46] Eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles.[46] In terms of their structural composition, the microtubules are made up of tubulin (e.g., α-tubulin and β-tubulin whereas intermediate filaments are made up of fibrous proteins.[46] Microfilaments are made up of actin molecules that interact with other strands of proteins.[46]

Metabolism

Further information: Bioenergetics

Example of an enzyme-catalysed exothermic reaction

All cells require energy to sustain cellular processes. Metabolism is the set of chemical reactions in an organism. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conversion of food/fuel to monomer building blocks; and the elimination of metabolic wastes. These enzyme-catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolic reactions may be categorized as catabolic—the breaking down of compounds (for example, the breaking down of glucose to pyruvate by cellular respiration); or anabolic—the building up (synthesis) of compounds (such as proteins, carbohydrates, lipids, and nucleic acids). Usually, catabolism releases energy, and anabolism consumes energy. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts—they allow a reaction to proceed more rapidly without being consumed by it—by reducing the amount of activation energy needed to convert reactants into products. Enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell's environment or to signals from other cells.

Cellular respiration

Main article: Cellular respiration

Respiration in a eukaryotic cell

Cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.[47] The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. Respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. The overall reaction occurs in a series of biochemical steps, some of which are redox reactions. Although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions.

Sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. Cellular respiration involving oxygen is called aerobic respiration, which has four stages: glycolysis, citric acid cycle (or Krebs cycle), electron transport chain, and oxidative phosphorylation.[48] Glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of ATP being produced at the same time.[48] Each pyruvate is then oxidized into acetyl-CoA by the pyruvate dehydrogenase complex, which also generates NADH and carbon dioxide. Acetyl-Coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. At the end of the cycle, the total yield from 1 glucose (or 2 pyruvates) is 6 NADH, 2 FADH2, and 2 ATP molecules. Finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. Oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from NADH and FADH2 that is coupled to the pumping of protons (hydrogen ions) across the inner mitochondrial membrane (chemiosmosis), which generates a proton motive force.[48] Energy from the proton motive force drives the enzyme ATP synthase to synthesize more ATPs by phosphorylating ADPs. The transfer of electrons terminates with molecular oxygen being the final electron acceptor.

If oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD+ so it can be re-used in glycolysis. In the absence of oxygen, fermentation prevents the buildup of NADH in the cytoplasm and provides NAD+ for glycolysis. This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by NADH. During anaerobic glycolysis, NAD+ regenerates when pairs of hydrogen combine with pyruvate to form lactate. Lactate formation is catalyzed by lactate dehydrogenase in a reversible reaction. Lactate can also be used as an indirect precursor for liver glycogen. During recovery, when oxygen becomes available, NAD+ attaches to hydrogen from lactate to form ATP. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate-level phosphorylation, which does not require oxygen.

Photosynthesis

Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.

Main article: Photosynthesis

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism's metabolic activities via cellular respiration. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water.[49][50][51] In most cases, oxygen is released as a waste product. Most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth.[52]

Photosynthesis has four stages: Light absorption, electron transport, ATP synthesis, and carbon fixation.[48] Light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. The absorbed light energy is used to remove electrons from a donor (water) to a primary electron acceptor, a quinone designated as Q. In the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a final electron acceptor, which is usually the oxidized form of NADP+, which is reduced to NADPH, a process that takes place in a protein complex called photosystem I (PSI). The transport of electrons is coupled to the movement of protons (or hydrogen) from the stroma to the thylakoid membrane, which forms a pH gradient across the membrane as hydrogen becomes more concentrated in the lumen than in the stroma. This is analogous to the proton-motive force generated across the inner mitochondrial membrane in aerobic respiration.[48]

During the third stage of photosynthesis, the movement of protons down their concentration gradients from the thylakoid lumen to the stroma through the ATP synthase is coupled to the synthesis of ATP by that same ATP synthase.[48] The NADPH and ATPs generated by the light-dependent reactions in the second and third stages, respectively, provide the energy and electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate (RuBP) in a sequence of light-independent (or dark) reactions called the Calvin cycle.[53]

Cell signaling

Main article: Cell signaling

Cell signaling (or communication) is the ability of cells to receive, process, and transmit signals with its environment and with itself.[54][55] Signals can be non-chemical such as light, electrical impulses, and heat, or chemical signals (or ligands) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell.[56][55] There are generally four types of chemical signals: autocrine, paracrine, juxtacrine, and hormones.[56] In autocrine signaling, the ligand affects the same cell that releases it. Tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self-division. In paracrine signaling, the ligand diffuses to nearby cells and affects them. For example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. In juxtacrine signaling, there is direct contact between the signaling and responding cells. Finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. Once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. For instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. Other types of receptors include protein kinase receptors (e.g., receptor for the hormone insulin) and G protein-coupled receptors. Activation of G protein-coupled receptors can initiate second messenger cascades. The process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction

Cell cycle

In meiosis, the chromosomes duplicate and the homologous chromosomes exchange genetic information during meiosis I. The daughter cells divide again in meiosis II to form haploid gametes.

Main article: Cell cycle

The cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division.[57] In eukaryotes (i.e., animal, plant, fungal, and protist cells), there are two distinct types of cell division: mitosis and meiosis.[58] Mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA is replicated) and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of mitosis all together define the mitotic phase of an animal cell cycle—the division of the mother cell into two genetically identical daughter cells.[59] The cell cycle is a vital process by which a single-celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. After cell division, each of the daughter cells begin the interphase of a new cycle. In contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions.[60] Homologous chromosomes are separated in the first division (meiosis I), and sister chromatids are separated in the second division (meiosis II). Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor.

Prokaryotes (i.e., archaea and bacteria) can also undergo cell division (or binary fission). Unlike the processes of mitosis and meiosis in eukaryotes, binary fission takes in prokaryotes takes place without the formation of a spindle apparatus on the cell. Before binary fission, DNA in the bacterium is tightly coiled. After it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. Growth of a new cell wall begins to separate the bacterium (triggered by FtsZ polymerization and "Z-ring" formation)[61] The new cell wall (septum) fully develops, resulting in the complete split of the bacterium. The new daughter cells have tightly coiled DNA rods, ribosomes, and plasmids.

Genetics

Inheritance

Main article: Classical genetics

Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms

Genetics is the scientific study of inheritance.[62][63][64] Mendelian inheritance, specifically, is the process by which genes and traits are passed on from parents to offspring.[27] It has several principles. The first is that genetic characteristics, alleles, are discrete and have alternate forms (e.g., purple vs. white or tall vs. dwarf), each inherited from one of two parents. Based on the law of dominance and uniformity, which states that some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the phenotype of that dominant allele. During gamete formation, the alleles for each gene segregate, so that each gamete carries only one allele for each gene. Heterozygotic individuals produce gametes with an equal frequency of two alleles. Finally, the law of independent assortment, states that genes of different traits can segregate independently during the formation of gametes, i.e., genes are unlinked. An exception to this rule would include traits that are sex-linked. Test crosses can be performed to experimentally determine the underlying genotype of an organism with a dominant phenotype.[65] A Punnett square can be used to predict the results of a test cross. The chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by Thomas Morgans's experiments with fruit flies, which established the sex linkage between eye color and sex in these insects.[66]

Genes and DNA

Bases lie between two spiraling DNA strands.

Further information: Gene and DNA

A gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid (DNA) that carries genetic information that controls form or function of an organism. DNA is composed of two polynucleotide chains that coil around each other to form a double helix.[67] It is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell is collectively known as its genome. In eukaryotes, DNA is mainly in the cell nucleus.[68] In prokaryotes, the DNA is held within the nucleoid.[69] The genetic information is held within genes, and the complete assemblage in an organism is called its genotype.[70]

DNA replication is a semiconservative process whereby each strand serves as a template for a new strand of DNA.[67] Mutations are heritable changes in DNA.[67] They can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical (e.g., nitrous acid, benzopyrene) or radiation (e.g., x-ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes).[67] Mutations can lead to phenotypic effects such as loss-of-function, gain-of-function, and conditional mutations.[67]

Some mutations are beneficial, as they are a source of genetic variation for evolution.[67] Others are harmful if they were to result in a loss of function of genes needed for survival.[67]

Gene expression

The extended central dogma of molecular biology includes all the processes involved in the flow of genetic information.

Main article: Gene expression

Gene expression is the molecular process by which a genotype encoded in DNA gives rise to an observable phenotype in the proteins of an organism's body. This process is summarized by the central dogma of molecular biology, which was formulated by Francis Crick in 1958.[71][72][73] According to the Central Dogma, genetic information flows from DNA to RNA to protein. There are two gene expression processes: transcription (DNA to RNA) and translation (RNA to protein).[74]

Gene regulation

Main article: Regulation of gene expression

The regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, RNA splicing, translation, and post-translational modification of a protein.[75] Gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the DNA sequence close to or at a promoter.[75] A cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes (e.g., Caenorhabditis elegans).[75][76] In positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. Negative regulation occurs when another transcription factor called a repressor binds to a DNA sequence called an operator, which is part of an operon, to prevent transcription. Repressors can be inhibited by compounds called inducers (e.g., allolactose), thereby allowing transcription to occur.[75] Specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active.[75] In contrast to both, structural genes encode proteins that are not involved in gene regulation.[75] In addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of DNA and protein found in eukaryotic cells.[75]

Genes, development, and evolution

Main article: Evolutionary developmental biology

Development is the process by which a multicellular organism (plant or animal) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle.[77] There are four key processes that underlie development: Determination, differentiation, morphogenesis, and growth. Determination sets the developmental fate of a cell, which becomes more restrictive during development. Differentiation is the process by which specialized cells from less specialized cells such as stem cells.[78][79] Stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell.[80] Cellular differentiation dramatically changes a cell's size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself.[81] Thus, different cells can have very different physical characteristics despite having the same genome. Morphogenesis, or the development of body form, is the result of spatial differences in gene expression.[77] A small fraction of the genes in an organism's genome called the developmental-genetic toolkit control the development of that organism. These toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. Differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. Among the most important toolkit genes are the Hox genes. Hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva.[82]

Evolution

Evolutionary processes

Main article: Evolutionary biology

Natural selection for darker traits

Evolution is a central organizing concept in biology. It is the change in heritable characteristics of populations over successive generations.[83][84] In artificial selection, animals were selectively bred for specific traits.

[85] Given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, Darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits.[85] Darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals.[85] He further inferred that this would lead to the accumulation of favorable traits over successive generations, thereby increasing the match between the organisms and their environment.[86][87][88][85][89]

Speciation

Main article: Speciation

A species is a group of organisms that mate with one another and speciation is the process by which one lineage splits into two lineages as a result of having evolved independently from each other.[90] For speciation to occur, there has to be reproductive isolation.[90] Reproductive isolation can result from incompatibilities between genes as described by Bateson–Dobzhansky–Muller model. Reproductive isolation also tends to increase with genetic divergence. Speciation can occur when there are physical barriers that divide an ancestral species, a process known as allopatric speciation.[90]

Phylogeny

Main article: Phylogenetics

Phylogenetic tree showing the domains of bacteria, archaea, and eukaryotes

A phylogeny is an evolutionary history of a specific group of organisms or their genes.[91] It can be represented using a phylogenetic tree, a diagram showing lines of descent among organisms or their genes. Each line drawn on the time axis of a tree represents a lineage of descendants of a particular species or population. When a lineage divides into two, it is represented as a fork or split on the phylogenetic tree.[91] Phylogenetic trees are the basis for comparing and grouping different species.[91] Different species that share a feature inherited from a common ancestor are described as having homologous features (or synapomorphy).[92][93][91] Phylogeny provides the basis of biological classification.[91] This classification system is rank-based, with the highest rank being the domain followed by kingdom, phylum, class, order, family, genus, and species.[91] All organisms can be classified as belonging to one of three domains: Archaea (originally Archaebacteria); bacteria (originally eubacteria), or eukarya (includes the protist, fungi, plant, and animal kingdoms).[94]

History of life

Main article: History of life

The history of life on Earth traces how organisms have evolved from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago and all life on Earth, both living and extinct, descended from a last universal common ancestor that lived about 3.5 billion years ago.[95][96] Geologists have developed a geologic time scale that divides the history of the Earth into major divisions, starting with four eons (Hadean, Archean, Proterozoic, and Phanerozoic), the first three of which are collectively known as the Precambrian, which lasted approximately 4 billion years.[97] Each eon can be divided into eras, with the Phanerozoic eon that began 539 million years ago[98] being subdivided into Paleozoic, Mesozoic, and Cenozoic eras.[97] These three eras together comprise eleven periods (Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary).[97]

The similarities among all known present-day species indicate that they have diverged through the process of evolution from their common ancestor.[99] Biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes.[100][10][101][102] Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean epoch and many of the major steps in early evolution are thought to have taken place in this environment.[103] The earliest evidence of eukaryotes dates from 1.85 billion years ago,[104][105] and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions.[106]

Algae-like multicellular land plants are dated back even to about 1 billion years ago,[107] although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 billion years ago.[108] Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician period. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event.[109]

Ediacara biota appear during the Ediacaran period,[110] while vertebrates, along with most other modern phyla originated about 525 million years ago during the Cambrian explosion.[111] During the Permian period, synapsids, including the ancestors of mammals, dominated the land,[112] but most of this group became extinct in the Permian–Triassic extinction event 252 million years ago.[113] During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates;[114] one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods.[115] After the Cretaceous–Paleogene extinction event 66 million years ago killed off the non-avian dinosaurs,[116] mammals increased rapidly in size and diversity.[117] Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify.[118]

Diversity

Bacteria and Archaea

Further information: Microbiology

Bacteria – Gemmatimonas aurantiaca (-=1 Micrometer)

Bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. Typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste,[119] and the deep biosphere of the Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory.[120]

Archaea – Halobacteria

Archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), a term that has fallen out of use.[121] Archaeal cells have unique properties separating them from the other two domains, Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla. Archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of Haloquadratum walsbyi.[122] Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes,[123] including archaeols. Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria, no known species of Archaea form endospores.

The first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. Improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet.

Archaea are a major part of Earth's life. They are part of the microbiota of all organisms. In the human microbiome, they are important in the gut, mouth, and on the skin.[124] Their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles: carbon fixation; nitrogen cycling; organic compound turnover; and maintaining microbial symbiotic and syntrophic communities, for example.[125]

Eukaryotes

Main article: Eukaryote

Euglena, a single-celled eukaryote that can both move and photosynthesize

Eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria (or symbiogenesis) that gave rise to mitochondria and chloroplasts, both of which are now part of modern-day eukaryotic cells.[126] The major lineages of eukaryotes diversified in the Precambrian about 1.5 billion years ago and can be classified into eight major clades: alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals.[126] Five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals.[126] While it is likely that protists share a common ancestor (the last eukaryotic common ancestor),[127] protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. Like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience.[126][128] Most protists are unicellular; these are called microbial eukaryotes.[126]

Plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom Plantae, which would exclude fungi and some algae. Plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts.[129] The first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related.[129] Algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of Plantae.[129] Unlike glaucophytes, the other algal clades such as red and green algae are multicellular. Green algae comprise three major clades: chlorophytes, coleochaetophytes, and stoneworts.[129]

Fungi are eukaryotes that digest foods outside their bodies,[130] secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. Many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems.[130]

Animals are multicellular eukaryotes. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. They have complex interactions with each other and their environments, forming intricate food webs.[131]

Viruses

Main article: Virus

Bacteriophages attached to a bacterial cell wall

Viruses are submicroscopic infectious agents that replicate inside the cells of organisms.[132] Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.[133][134] More than 6,000 virus species have been described in detail.[135] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.[136][137]

The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction.[138] Because viruses possess some but not all characteristics of life, they have been described as "organisms at the edge of life",[139] and as self-replicators.[140]

Ecology

Main article: Ecology

Ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment.[141]

Ecosystems

Main article: Ecosystem

The community of living (biotic) organisms in conjunction with the nonliving (abiotic) components (e.g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil) of their environment is called an ecosystem.[142][143][144] These biotic and abiotic components are linked together through nutrient cycles and energy flows.[145] Energy from the sun enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one another, animals move matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.[146]

Populations

Main article: Population ecology

Reaching carrying capacity through a logistic growth curve

A population is the group of organisms of the same species that occupies an area and reproduce from generation to generation.[147][148][149][150][151] Population size can be estimated by multiplying population density by the area or volume. The carrying capacity of an environment is the maximum population size of a species that can be sustained by that specific environment, given the food, habitat, water, and other resources that are available.[152] The carrying capacity of a population can be affected by changing environmental conditions such as changes in the availability resources and the cost of maintaining them. In human populations, new technologies such as the Green revolution have helped increase the Earth's carrying capacity for humans over time, which has stymied the attempted predictions of impending population decline, the most famous of which was by Thomas Malthus in the 18th century.[147]

Communities

Main article: Community (ecology)

A (a) trophic pyramid and a (b) simplified food web. The trophic pyramid represents the biomass at each level.[153]

A community is a group of populations of species occupying the same geographical area at the same time. A biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or of different species (interspecific interactions). These effects may be short-term, like pollination and predation, or long-term; both often strongly influence the evolution of the species involved. A long-term interaction is called a symbiosis. Symbioses range from mutualism, beneficial to both partners, to competition, harmful to both partners.[154] Every species participates as a consumer, resource, or both in consumer–resource interactions, which form the core of food chains or food webs.[155] There are different trophic levels within any food web, with the lowest level being the primary producers (or autotrophs) such as plants and algae that convert energy and inorganic material into organic compounds, which can then be used by the rest of the community.[52][156][157] At the next level are the heterotrophs, which are the species that obtain energy by breaking apart organic compounds from other organisms.[155] Heterotrophs that consume plants are primary consumers (or herbivores) whereas heterotrophs that consume herbivores are secondary consumers (or carnivores). And those that eat secondary consumers are tertiary consumers and so on. Omnivorous heterotrophs are able to consume at multiple levels. Finally, there are decomposers that feed on the waste products or dead bodies of organisms.[155]

On average, the total amount of energy incorporated into the biomass of a trophic level per unit of time is about one-tenth of the energy of the trophic level that it consumes. Waste and dead material used by decomposers as well as heat lost from metabolism make up the other ninety percent of energy that is not consumed by the next trophic level.[158]

Biosphere

Main article: Biosphere

Fast carbon cycle showing the movement of carbon between land, atmosphere, and oceans in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. Effects of the slow carbon cycle, such as volcanic and tectonic activity, are not included.[159]

In the global ecosystem or biosphere, matter exists as different interacting compartments, which can be biotic or abiotic as well as accessible or inaccessible, depending on their forms and locations.[160] For example, matter from terrestrial autotrophs are both biotic and accessible to other organisms whereas the matter in rocks and minerals are abiotic and inaccessible. A biogeochemical cycle is a pathway by which specific elements of matter are turned over or moved through the biotic (biosphere) and the abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. There are biogeochemical cycles for nitrogen, carbon, and water.

Conservation

Main article: Conservation biology

Conservation biology is the study of the conservation of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions.[161][162][163] It is concerned with factors that influence the maintenance, loss, and restoration of biodiversity and the science of sustaining evolutionary processes that engender genetic, population, species, and ecosystem diversity.[164][165][166][167] The concern stems from estimates suggesting that up to 50% of all species on the planet will disappear within the next 50 years,[168] which has contributed to poverty, starvation, and will reset the course of evolution on this planet.[169][170] Biodiversity affects the functioning of ecosystems, which provide a variety of services upon which people depend. Conservation biologists research and educate on the trends of biodiversity loss, species extinctions, and the negative effect these are having on our capabilities to sustain the well-being of human society. Organizations and citizens are responding to the current biodiversity crisis through conservation action plans that direct research, monitoring, and education programs that engage concerns at local through global scales.[171][164][165][166]

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Biology

What is Biology?

“Biology is defined as the study of living organisms, their origins, anatomy, morphology, physiology, behaviour, and distribution.”

Life is teeming in every corner of the globe – from the frozen Arctics to the searing Sahara. And with over 8.7 million species documented till date, the earth is the only planet in the universe where life is known to exist.

Advancements in technology have opened up even more insights about life and its constituents. For instance, discoveries such as viruses have scrutinized traditional definitions and pushed scientists to look at life from a whole new perspective.

Branches of Biology

Biology caters to these intriguing aspects through various sub-disciplines or branches. Some branches are intertwined with other disciplines of science.

For instance, theoretical biology is a branch of biology that encompasses mathematical models to investigate certain principles that affect life.

Quantum Biology deals with biological processes that are quantum mechanical in nature – such as the conversion of energy into more usable forms. Other branches of biology are as follows:

Divisions of Biology

Anatomy

Biotechnology

Botany

Ecology

Genetics

Immunology

Microbiology

Physiology

Zoology

Important Topics in Biology

Properties of Carbon

Did you know, carbon is the second most abundant element in humans (about 18% of mass) after oxygen? Explore more about this element and the reason behind its importance in biological elements.

Carbon cycle

Human Biology

The human body is an amazing system as it is made up of a group of organs called the organ system. Explore more about the organ systems starting from the circulatory system to the nervous system and much more.

Human Brain

Immunology

Human Anatomy

Circulatory System

Human nervous system

Human Circulatory System

Regulation of Kidney Function

Macro Molecules

Food provides the body with the nutrients it needs to survive. Many of these critical nutrients are biological macromolecules, or large molecules, necessary for life. Four main types of macromolecules such as proteins, carbohydrates, nucleic acids and lipids control all activities. Explore the types of macromolecules, their importance in human life, and how they build up.

What are macromolecules?

Proteins

Nucleic Acid

Lipids

Carbohydrates

Energy and Enzymes

Several chemical reactions are taking place in the body of a living organism, and surprisingly all of them are mediated by enzymes. Read more about how energy transfers occur in the human body and how biological energy transfers work and much more.

Energy in metabolism

ATP and reaction coupling

Introduction to enzymes

Structure of a Cell

Do you know, humans have about 100 trillion cells in their body! All the living organisms that exist in this whole universe – like mushrooms, plants, humans, elephants etc. are made up of lots and lots of cells! Learn more about different types of cells, their structure and much more.

Cell Structure

Introduction to Cells

Types of Cell – Prokaryotic and Eukaryotic Cells

Cell Structure and Function

Membranes and Transport

This topic is all about how cells protect themselves from the surrounding with a barrier. Explore more about what this barrier is made up of? How it works and how the molecules are transported across the membrane?

Cell Wall and Cell Membrane

Diffusion

Reverse Osmosis

Passive Transport

Active Transport

Cellular Respiration

Respiration is one of an essential process carried out by all living organism to survive. Explore more about how it extracts energy from food for the human body? How respiration occurs at the cellular level, its types and much more.

Oxygen Cycle

Introduction to cellular respiration

Types of Respiration – aerobic and anaerobic

Stages of Respiration

Photosynthesis

Did you know photosynthesis is the single most important chemical process on the earth? Learn more about how plants utilize sunlight to convert light energy into chemical energy, Calvin Cycle, light-dependent reactions and much more.

Introduction to Photosynthesis

Light Dependent Reactions

Calvin Cycle

Photorespiration – C3, C4 plants

Cell Division

Did you know in an average human body, almost 2 trillion cell divisions occur daily? Every organism goes through the cell division process. So let’s study about how cell division occurs and how the problem in cell cycle control is responsible for causing cancer.

Introduction to Cell Division

Cell cycle

Mitosis

Meiosis Stage 1 and Meiosis stage 2

Classical and Molecular Genetics

Know about the reason behind the resemblance of children to their parents, the impact of genetics on the next generation and explore more about Mendel’s model of inheritance, it’s disorders and much more.

Introduction to genetics

Mendelian genetics

Mendel’s law of inheritance

Mendelian Disorders

Chromosomes

Genes

DNA as the Genetic Material

Did you know your DNA could stretch from the earth to the sun and back approximately 600 times? Explore more facts about DNA, its structure and much more.

DNA Structure

Central Dogma

The central dogma of molecular biology explains the flow of genetic information, from DNA to RNA, to make a functional product, a protein. Explore more about this amazing process and much more.

Introduction to Central Dogma

Transcription of DNA to RNA

Translation Protein Synthesis

Gene Regulation

Did you know we have tens of thousands of genes in our genome? Read more about what is gene regulation and how it controls the manner and rate of gene expression.

Introduction to gene regulation

Biotechnology

Did you know humans have unknowingly used biotechnology practices for thousands of years, specifically in pharmaceuticals and farming? Explore more facts about biotechnology, its application and its scope in agriculture.

Introduction to biotechnology

Biotechnology in agriculture

Application of biology in medicine

Bacteria and Archaea

At about 5 million trillion strong, bacteria and their cousins, the archaea, vastly outnumber all other life forms on earth! Read about the difference between bacteria and archaea and much more.

Difference between Archaea and Bacteria

What is Bacteria?

Viruses

Viruses are neither dead nor alive! Yes, it is quite surprising, so learn more facts about these fascinating particles that occupy a “grey area” between living and nonliving things.

All about viruses

Virology

Evolution and the Tree of life

Discover the diversity of life on earth and the forces that help to shape it! Explore more about evolution, natural selection and biological evolution and much more.

Evolution

Darwin’s theory of evolution

Natural Selection and Genetic Drift

History of life on Earth

The first life on Earth developed in the oceans through a process called abiogenesis or biopoesis. This is a natural process in which life grows from non-living matter like simple organic compounds! Explore more about life on earth.

Origin of life on earth

Evolution of life on earth

Ecology

Ecology encompasses all living things, from single-cellular and acellular organisms, through to the most complex of all living creatures. Read more about ecology, population ecology, types of biogeochemical cycles and much more.

What is Ecology?

Population Ecology

Ecosystem

Food Web

Energy flow in the ecosystem

Biogeochemical Cycles

Water Cycle

Nitrogen Cycle

Population growth

Population control

Human population

Ecological succession

Binomial Nomenclature

Biodiversity and Conservation

Biodiversity is critical to an ecosystem because each species plays a different role in the maintenance of the ecosystem. Discover more about the ecosystem, ecosystem services and much more.

Biodiversity

Biodiversity Process

Biodiversity Conservation

Importance of Biodiversity

Biodiversity Pattern in Species

Biodiversity in plants and animals

Plant Biology

Did you know pineapple is a berry? Explore more facts and information about plants like parts of plants, classification of plants and much more.

Parts of plants

The Plant Kingdom

Classification of plants

Transportation in plants

History of Biology

Origin of the Term “Biology”

Before the term biology was adapted, other terms existed which described the study of plants and animals. For instance, the term Natural History was used to explain animals, plants, fungi and other lifeforms in their natural environment.

Furthermore, it was observational rather than an experimental field of study. Hence, a person who would study natural history is termed as a natural historian or a naturalist. Other terms that came before biology included Natural Theology and Natural philosophy.

The term “Biology”, in the modern sense, was introduced through the works of Michael Christoph Hanow in 1766. However, it was introduced independently four more times through the works of Thomas Beddoes (1799), Karl Friedrich Burdach (1800), Gottfried Reinhold Treviranus (1802) and Jean-Baptiste Lamarck (1802).

Origins as a Field of Study

For the very first humans, knowledge about plants and animals meant the difference between life or death. As a result, cumulative knowledge about species, behaviour and anatomy were passed down for many generations.

However, the most significant development in biological knowledge came when humans transitioned from hunters and foragers to farmers, cultivating crops and perfecting agriculture.

Traditions of medicine, collective knowledge from physicians, works of prominent historical figures such as Aristotle eventually coalesced into the field of study we know today as biology.

The most significant revolutions in biology came during the 19th century, with a host of discoveries and technological innovations.

Biology - Definition & Meaning, Examples, Branches and Principles

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Dictionary > Biology

Biology

n., [baɪˈɑlədʒi]

Definition: scientific study of life

Table of Contents

ToggleBiology DefinitionEtymologyIntroduction to BiologyModern Principles and Concepts of BiologyCell theoryGene theoryEvolutionary theoryHomeostasisEnergyImportance of BiologyResearchBranches of BiologyHuman Biology – DefinitionQuizSend Your Results (Optional)See AlsoReferencesRecommended Source

Biology Definition

Biology is the branch of science that primarily deals with the structure, function, growth, evolution, and distribution of organisms. As a science, it is a methodological study of life and living things. It determines verifiable facts or formulates theories based on experimental findings on living things by applying the scientific method. An expert in this field is called a biologist.

Some of the common objectives of their research include understanding the life processes, determining biological processes and mechanisms, and how these findings can be used in medicine and industry. Thus, biological research settings vary, e.g. inside a laboratory or in the wild.

Biology is a wide-ranging field. It encompasses various fields in science, such as chemistry, physics, mathematics, and medicine. Biochemistry, for instance, is biology and chemistry combined. It deals primarily with the diverse biomolecules (e.g. nucleic acids, proteins, carbohydrates, and lipids), studying biomolecular structures and functions. Biophysics is another interdisciplinary field that applies approaches in physics to understand biological phenomena.

Mathematics and biology have also gone hand in hand to come up with theoretical models to elucidate biological processes using mathematical techniques and tools. Medical biology or biomedicine is another major integration where medicine makes use of biological principles in clinical settings. These are just a few of the many biology examples wherein its fundamental tenets are integrated into other scientific fields.

Etymology

Biology is the study of all living things. From top left to bottom right: archaeon, bacterium, protist, fungus, plant, and animal.

The term biology comes from the Greek βίος (bios), meaning “life” and from the Greek λογία (logia), meaning “study of”. Abbreviation: biol. Synonyms: biological science; life science.

Introduction to Biology

A typical cell of an animal. Inside the cell are organelles (e.g. nucleus, mitochondrion, endoplasmic reticulum, and Golgi apparatus) and many other cytoplasmic structures.

A basic biology definition would be is that it is the study of living organisms. It is concerned with all that has life and living. (Ref.1) In contrast to inanimate objects, a living matter is one that demonstrates life. For instance, a living thing would be one that is comprised of a cell or a group of cells.

Each of these cells can carry out processes, e.g. anabolic and catabolic reactions, in order to sustain life. These reactions may be energy-requiring. They are also regulated through homeostatic mechanisms. A living matter would also be one that is capable of reacting to stimuli, adapt to its environment, reproduce, and grow.

The major groups of living things are animals, plants, fungi, protists, bacteria, and archaea. Biology studies their structure, function, distribution, evolution, and taxonomy.

Recommended: BLASTing through the kingdom of life – a guide for teachers, from Digitalworldbiology.com.

Modern Principles and Concepts of Biology

The fundamental principles of biology that are acceptable to this day include cell theory, gene theory, evolutionary theory, homeostasis, and energy.

Cell theory

Cell theory is a scientific theory proposed by the scientists, Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. It is formulated to refute the old theory, Spontaneous generation. It suggests the following tenets: (1) All living things are made up of one or more cells, (2) the cell is the structural and functional unit, (3) cells come from a pre-existing process of division, (4) all cells have the same chemical composition, and (5) energy flow occurs within the cell. (Ref.2)

Gene theory

In Gene theory, the gene is the fundamental unit of heredity. In this chart (called Punnett Square), it shows how a particular phenotype of an offspring depends on the inherited alleles from the parents. In this example, the dominant trait (yellow color) is expressed on offspring inheriting the Y allele. In contrast, the offspring lacking the dominant allele and inherits yy will express the recessive trait (green color).

In Gene theory, the gene is considered as the fundamental, physical, and functional unit of heredity. (Ref.3) It is located on the chromosome and contains DNA. The gene stores the genetic code, i.e. a sequence of nucleotides that determines the structure of a protein or RNA. A gene is a unit of heredity because it is transmitted across generations. It is through which the phenotypic trait of an organism is based upon.

Gregor Johann Mendel was one of the main pioneers that established the science of genetics. As such, he is regarded as the father of the said field. He was able to determine the occurrence of unit factors (now referred to as genes) that were passed down from one generation to the next. He described these unit factors as occurring in pairs. One of the pairs will be dominant over the other (recessive). He formulated the Mendelian laws to elucidate how heredity occurs.

These laws include Law of Segregation, Law of Independent Assortment, and Law of Dominance. The inheritance pattern that follows these laws is referred to as Mendelian inheritance. Conversely, an inheritance pattern that does not conform to these laws is described as Non-Mendelian.

Evolutionary theory

This diagram shows how mutation and selection work as key factors in evolution.

Evolution pertains to the genetic changes in a population over successive generations driven by natural selection, mutation, hybridization, or inbreeding. (Ref.4) Charles Darwin is one of the major contributors to the theory of evolution. He is known for his work Origin of Species by Natural Selection after his Beagle voyage.

He was able to observe different plant and animal species. Based on his analysis, he postulated that living things have an inherent tendency to produce offspring of the same kind. Thus, the survival of the species becomes dependent on the available food and space. As a result, organisms compete as the carrying capacity of the habitat would not be able to sustain a massive population. (Ref.5) Survival or struggle for existence, thus, becomes an individual feat.

Homeostasis

Homeostasis is the tendency of an organism to maintain optimal internal conditions. It entails a system of feedback controls so as to stabilize and keep up with the normal homeostatic range despite the changing external conditions. For instance, it employs homeostatic mechanisms to regulate temperature, pH, and blood pressure.

The homeostatic system is comprised of three main components: a receptor, a control center, and an effector. The receptor of the homeostatic system includes the various sensory receptors that can detect external and internal changes. The information is sent to the control center to process it and to produce a signal to incite an appropriate response from the effector. The concept of homeostasis is credited to Claude Bernard in 1865.

Energy

In biology, energy is essential to drive various biological processes, especially anabolic reactions. Adenosine triphosphate (ATP) is the main energy carrier of the cell. It is released from carbohydrates through glycolysis, fermentation, and oxidative phosphorylation. Lipids are another group of biomolecules that store energy.

Importance of Biology

Biology is the scientific way to understand life. Knowing the biological processes and functions of life is essential to gain a deeper knowledge and appreciation in life. Furthermore, it opens an avenue of resources for use in medicine and industry. How a biological process proceeds, its regulatory systems, and its components can lead to better awareness. For example, conservation efforts could begin to save a species that has been classified as endangered, i.e. on the verge of extinction.

Research

A specialist or an expert in the field of biology is called a biologist. Biologists look upon the biophysical, biomolecular, cellular, and systemic levels of an organism. They attempt to understand the mechanisms at play in various biological processes that govern life. They are also interested in coming up with innovations to create and improve life. Some of them have advocacies and are concerned with the conservation of species. Depending on the nature and objectives of their research, they may be found conducting research inside a laboratory. Others carry out their scientific pursuits outside, such as in diverse habitats where an organism or a population of organisms thrive.

The biological study can be traced back to early times. Aristotle, for instance, was a Greek philosopher in Athens known for his contributions to philosophy and biology. He was the first person to study biology systematically. Some of his popular works include the History of Animals, Generation of Animals, Movement of Animals, Parts of Animals. Much of his botanical studies, though, were lost. Because of his many pioneering studies, he is regarded by many as the “Father of Biology”.

At present, biologists are now seeking the potential use of biology in other fields, such as medicine, agriculture, and industry. One of the most recent breakthroughs is CRISPR — a gene-hacking tool used by scientists to splice specific DNA targets and then replace them with a DNA that would yield the desired effect. One of its promises is that it can correct physiological anomalies due to mutated or defective gene mutations. (Ref.6)

Authors can now submit preprints to bioRxiv — an online archive and distribution service for preprints in the life sciences. More details here: BioTechniques Welcomes Preprints – BioTechniques (BioTechniques: https://www.biotechniques.com/general-interest/biotechniques-welcomes-preprints/).

Branches of Biology

Biology encompasses various sub-disciplines or branches. Some of the branches of biology are as follows:

Anatomy – the study of the animal form, particularly the human body

Astrobiology – the branch of biology concerned with the effects of outer space on living organisms and the search for extraterrestrial life

Biochemistry – the study of the structure and function of cellular components, such as proteins, carbohydrates, lipids, nucleic acids, and other biomolecules, and of their functions and transformations during life processes

Bioclimatology – a science concerned with the influence of climates on organisms, for instance, the effects of climate on the development and distribution of plants, animals, and humans

Bioengineering – or biological engineering, a broad-based engineering discipline that deals with bio-molecular and molecular processes, product design, sustainability, and analysis of biological systems

Biogeography – a science that attempts to describe the changing distributions and geographic patterns of living and fossil species of plants and animals

Bioinformatics – information technology as applied to the life sciences, especially the technology used for the collection, storage, and retrieval of genomic data

Biomathematics – mathematical biology or biomathematics, an interdisciplinary field of academic study which aims at modeling natural, biological processes using mathematical techniques and tools. It has both practical and theoretical applications in biological research

Biophysics – or biological physics, interdisciplinary science that applies the theories and methods of physical sciences to questions of biology

Biotechnology – applied science concerned with biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use

Botany – the scientific study of plants

Cell biology – the study of cells at the microscopic or at the molecular level. It includes studying the cells’ physiological properties, structures, organelles, interactions with their environment, life cycle, cell division, and apoptosis

Chronobiology – a science that studies time-related phenomena in living organisms

Conservation Biology – concerned with the studies and schemes of habitat preservation and species protection for the purpose of alleviating extinction crisis and conserving biodiversity

Cryobiology – the study of the effects of low temperatures on living organisms

Developmental Biology – the study of the processes by which an organism develops from a zygote to its full structure

Ecology – the scientific study of the relationships between plants, animals, and their environment

Ethnobiology – a study of the past and present human interactions with the environment, for instance, the use of diverse flora and fauna by indigenous societies

Evolutionary Biology – a subfield concerned with the origin and descent of species, as well as their change over time, i.e. their evolution

Freshwater Biology – a science concerned with the life and ecosystems of freshwater habitats

Genetics – a science that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited characteristics among similar or related organisms

Geobiology – a science that combines geology and biology to study the interactions of organisms with their environment

Immunobiology – a study of the structure and function of the immune system, innate and acquired immunity, the bodily distinction of self from non-self, and laboratory techniques involving the interaction of antigens with specific antibodies

Marine Biology – the study of ocean plants and animals and their ecological relationships

Medicine – the science which relates to the prevention, cure, or alleviation of disease

Microbiology – the branch of biology that deals with microorganisms and their effects on other living organisms

Molecular Biology – the branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, and especially with their role in cell replication and the transmission of genetic information

Mycology – the study of fungi

Neurobiology – the branch of biology that deals with the anatomy, physiology, and pathology of the nervous system

Paleobiology – the study of the forms of life existing in prehistoric or geologic times, as represented by the fossils of plants, animals, and other organisms

Parasitology – the study of parasites and parasitism

Pathology – the study of the nature of the disease and its causes, processes, development, and consequences

Pharmacology – the study of preparation and use of drugs and synthetic medicines

Physiology – the biological study of the functions of living organisms and their parts

Protistology – the study of protists

Psychobiology – the study of mental functioning and behavior in relation to other biological processes

Toxicology – the study of how natural or man-made poisons cause undesirable effects in living organisms

Virology – the study of viruses

Zoology – The branch of biology that deals with animals and animal life, including the study of the structure, physiology, development, and classification of animals

Ethology – the study of animal behavior

Entomology – the scientific study of insects

Ichthyology – the study of fishes

Herpetology – the science of reptiles and amphibians

Ornithology – the science of birds

Mammalogy – the study of mammals

Primatology – the science that deals with primates

Human Biology – Definition

Human biology is the branch of biology that focuses on humans in terms of evolution, genetics, anatomy and physiology, ecology, epidemiology, and anthropology. It can be a subfield of Primatology since humans belong to the group of primates, particularly of the family Hominidae (tribe Hominini). Since human biology is a course that deals mainly with humans, it is a viable option for use as a preparatory course in medicine.

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1. What is biology? Scientific study of earth's physical structure Branch of science that deals with living things An investigation of the composition of matter

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3. A principle in biology stating that all living things are made up of a cell or group of cells Cell theory Gene theory Evolutionary theory

4. A concept in biology that is defined as the tendency of an organism to maintain optimal internal conditions Evolution Reproduction Homeostasis

5. A biological energy Cell DNA ATP

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By Alane Lim, Scott Dutfield published 2 February 2022

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

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Biology is the study of all living organisms, including this adorable jewel bug and the plant it's perched on.

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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 biologyFour 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 biologyAlthough 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.A botanist is a biologist who studies plants. (Image credit: Shutterstock)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.Related Links– 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 biologyBiology 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 SocietyA 3d Illustration of the chain of amino acids that make up protein. (Image credit: Getty Images)What do biologists do?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.An ecologist taking a water samples from a creek. (Image credit: Getty Images)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.Additional resourcesIf 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.Bibliography 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 LimSocial Links NavigationContributorAlane 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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imtoken钱包安卓官方版|biology

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Biology | Definition, History, Concepts, Branches, & Facts | Britannica

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Biology -What is Biology, Branches of Biology, History, Concepts & Facts

Biology - Definition & Meaning, Examples, Branches and Principles

What Is Biology? | Live Science

502 Bad Gateway

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Biology and its branches | Britannica

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