This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology, Glossary of environmental science and Glossary of scientific naming, or any of the organism-specific glossaries in Category:Glossaries of biology.
A
absorption (physiology) A process in which one substance permeates another. A fluid permeates or is dissolved by a liquid or solid. Skin absorption is a route by which substances can enter the body through the skin.
acclimatization (physiology) Adaptation to a new climate, as with a new temperature or altitude or environment.
acetyl-CoA (biochemistry) Acetyl coenzyme A is a molecule participating in many biochemical reactions in carbohydrate, protein and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.
acoelomate (zoology) A type of animal, such as a flatworm, with a body plan that lacks a fluid-filled cavity between the body wall and the digestive tract. Rather, semi-solid mesodermal tissues between the gut and body wall hold the animal's organs in place. Contrast coelomate and pseudocoelomate.
adaptation (evolutionary biology, population biology) Term can apply to an individual organism's adaptation to its environment, the adaptation of organisms to an environment through evolutionary processes, or the population dynamics intrisic to the evolutionary process.
adenine (biochemistry) A purine-derived organic compound which is one of the four canonical nucleobases used in the nucleic acids DNA and RNA. Its derivatives are involved in a wide variety of biochemical reactions, including cellular respiration.
aerobic Capable of surviving and growing in the presence of oxygen.
amino acid (biochemistry) A class of organic compounds containing an amine group and a carboxylic acid group which function as the fundamental building blocks of proteins and play important roles in many other biochemical processes.
anaerobic Any organism that does not require molecular oxygen for growth.
animal Any member of a clade of multicellular eukaryotic organisms belonging to the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a blastula during embryonic development. An estimated 7 million distinct animal species currently exist.
antibiotic Also called an antibacterial. A type of antimicrobial drug used in the treatment and prevention of bacterial infections.
Archaea One of the three recognized domains of organisms, the other two being Bacteria and Eukaryota.
artificial selection Also called selective breeding. The process by which humans use animal breeding and plant breeding to selectively control the development of particular phenotypic traits in organisms by choosing which individual organisms will reproduce and create offspring. While the deliberate exploitation of knowledge about genetics and reproductive biology in the hope of producing desirable characteristics is widely practiced in agriculture and experimental biology, artificial selection may also be unintentional and may produce unintended (desirable or undesirable) results.
asexual reproduction A type of reproduction involving a single parent that results in offspring that are genetically identical to the parent.
astrobiology The branch of biology concerned with the effects of outer space on living organisms and the search for extraterrestrial life.
autoimmunity The system of immune responses of an organism directed against its own healthy cells and tissues.
autotroph Sometimes used interchangeably with primary producer. An organism capable of producing complex organic compounds from simple substances present in its surroundings, generally by using energy from sunlight (as in photosynthesis) or from inorganic chemical reactions (as in chemosynthesis). Autotrophs do not need to consume another living organism in order to obtain energy or organic carbon, as opposed to heterotrophs.
B
B cell A type of lymphocyte in the humoral immunity of the adaptive immune system.
bacteria An enormous and diverse clade of microscopic, prokaryotic, single-celled organisms which lack a true nucleus. They represent one of the three fundamental biological domains.
bacteriophage A virus that infects and multiplies within bacteria.
Barr body The inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization, in those species in which sex is determined by the presence of the Y chromosome (including humans) or W chromosome rather than by the presence of two X chromosomes or two Z chromosomes.
basal body An organelle formed from a centriole, and a short cylindrical array of microtubules. Also called a basal granule, a kinetosome, and in older cytological literature, a blepharoplast.
behavioral ecology The study of the evolutionary basis for animal behavior due to ecological pressures.
bile A dark green to yellowish-brown fluid, produced by the liver of most vertebrates, which aids the digestion of lipids in the small intestine. Also called gall.
binary fission The process by which one prokaryotic cell divides into two identical daughter cells.
binomial nomenclature A formal system of classifying species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages.
biocatalysis The process of catalysis in biological systems. In biocatalytic processes, natural catalysts, such as protein enzymes, perform chemical transformations on organic compounds.
biochemistry The branch of biology that studies the chemical properties, compositions, reactions, and processes related to living organisms.
biodiversity A contraction of "biological diversity" generally referring to the variety and variability of life on Earth.
bioengineering The application of concepts and methods of biology to solve real-world problems related to the life sciences or the application thereof.
bioenergetics The study of the transformation of energy within and between living organisms.
biogeography The study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area.
bioinformatics The application of computer technology to the management of biological information.
biological organization The hierarchy of complex biological structures and systems, designed to define life through a reductionist approach.
biology The scientific study of life.
biomass Organic matter derived from living or recently living organisms. Biomass can be used as a source of energy and it most often refers to plants or plant-based materials which are not used for food or feed, and are specifically called lignocellulosic biomass.
biomathematics The theoretical use of mathematical models and abstractions of living systems to understand and predict biological problems.
biome Any very large ecological area on the Earth's surface containing fauna and flora (animals and plants) adapting to their environment. Biomes are often defined by abiotic factors such as climate, topographical relief, geology, soils, and water resources.
biomechanics The study of the structure and function of biological systems by means of the methods of "mechanics", which is the branch of physics involving analysis of the actions of forces.
biomedical engineering The application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g. diagnostic or therapeutic).
biomedical research The pursuit of answers to medical questions. These investigations lead to discoveries, which in turn lead to the development of new preventions, therapies, and cures for problems in human and veterinary health. Biomedical research generally takes two forms: basic science and applied research.
biomolecule Molecules and ions that are present in organisms, essential to some typically biological process such as cell division, morphogenesis, or development.
biophysics The application of approaches traditionally employed in physics to study biological systems.
biosynthesis
biotechnology Biotechnology is the use of living systems and organisms to develop or make products, or "any technological application that uses biological systems, living organisms or derivatives thereof, to make or modify products or processes for specific use" (UN Convention on Biological Diversity).
bipedal A form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs.
birth
blastocyst A mammalian blastula in which some differentiation of cells has occurred.
blood A body fluid that circulates in humans and other vertebrate animals and is generally responsible for delivering necessary substances such as oxygen and nutrients between the cells and tissues of the body and transporting metabolic waste products away from those same cells and tissues.
blood–brain barrier A semipermeable membrane separating the blood from the cerebrospinal fluid, and constituting a barrier to the passage of cells, particles, and large molecules.
botany The branch of biology that studies plants.
building biology A science that leads to natural healthy ecological homes, schools, and workplaces that exist in harmony with the environment.
C
Calvin cycle Also called the biosynthetic phase, light-independent reactions, dark reactions, or photosynthetic carbon reduction (PCR) cycle. A series of chemical reactions which occurs as one of two primary phases of photosynthesis, specifically the phase in which carbon dioxide and other compounds are converted into simple carbohydrates such as glucose. These reactions occur in the stroma, the fluid-filled area of the chloroplast outside the thylakoid membranes. In the Calvin cycle, the products of previous light-dependent reactions (ATP and NADPH) undergo further reactions which do not require the presence of light and which can be broadly divided into three stages: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
carbon fixation Also called carbon assimilation. The process by which inorganic carbon, particularly in the form of carbon dioxide, is converted to organic compounds by living organisms. Examples include photosynthesis and chemosynthesis.
carbonate Any member of two classes of chemical compounds derived from carbonic acid or carbon dioxide.
carotenoid One of a class of organic pigments produced by algae and plants, as well as certain bacteria and fungi.
catalase An enzyme found in nearly all living organisms exposed to oxygen, including bacteria, plants, and animals.
cell The basic structural and functional unit of all living organisms, and the smallest functional unit of life. A cell may exist as an independent, self-replicating unit (as in the case of unicellular organisms), or in cooperation with other cells, each of which may be specialized for carrying out particular functions within a larger multicellular organism. Cells consist of cytoplasm enclosed within a cell membrane and sometimes a cell wall, and serve the fundamental purpose of separating the controlled environment in which biochemical processes take place from the outside world. Most cells are visible only under a microscope.
cell biology Also called cytology. The branch of biology that studies the structure and function of living cells, including their physiological properties, metabolic processes, chemical composition, life cycle, the organelles they contain, and their interactions with their environment. This is done at both microscopic and molecular levels.
cell cycle The ordered series of events which take place in a cell leading to duplication of its genetic material and ultimately the division of the cytoplasm and organelles to produce two or more daughter cells. These events can be broadly divided into phases of growth and division, each of which can vary in duration and complexity depending on the tissue or organism to which the cell belongs. Cell cycles are essential processes in all unicellular and multicellular organisms.
cell division Any process by which a parent cell divides into two or more daughter cells. Examples include binary fission, mitosis, and meiosis.
cell membrane The semipermeable membrane surrounding the cytoplasm of a cell.
cell nucleus The "control room" for the cell. The nucleus gives out all the orders.
cell plate Grown in the cell's center, it fuses with the parental plasma membrane, creating a new cell wall that enables cell division.
cell theory The theory that all living things are made up of cells.
cell wall A tough, often rigid structural barrier surrounding certain types of cells (such as in fungi, plants, and most prokaryotes) that is immediately external to the cell membrane.
cellular Of or relating to a cell.
central dogma of molecular biology A framework for understanding the movement of genetic information between information-carrying biopolymers within biological systems. Popularly (though simplistically) stated as "DNA makes RNA and RNA makes protein", the principle attempts to capture the notion that the transfer of genetic information only naturally occurs between certain classes of molecules and in certain directions.
centriole A cylindrical cell structure found in most eukaryotic cells, composed mainly of a protein called tubulin.
centrosome An organelle that is the primary site at which microtubules are organized. They occur only in plant and animal cells and help to regulate cell division.
chemical compound A chemical substance consisting of two or more different chemically bonded elements, with a fixed ratio determining the composition. The ratio of each element is usually expressed by a chemical formula.
chemical equilibrium The state in which both reactants and products are present in concentrations which have no further tendency to change with time in a chemical reaction.
chemical reaction A process that leads to the transformation of one set of chemical substances to another.
chemistry A branch of the physical sciences that studies the composition, structure, properties, and change of matter. Chemical interactions underlie all biological processes.
chemosynthesis
chlorophyll Any of several photosynthetic pigments found in cyanobacteria, algae, or plants.
chloroplast A type of highly specialized organelle in the cells of plants and algae, the main role of which is to conduct photosynthesis, by which the photosynthetic pigment chlorophyll captures the energy from sunlight and converts and stores it in the molecules ATP and NADPH while freeing oxygen from water.
cholesterol A type of lipid molecule that is biosynthesized by all animal cells because it is an essential structural component of animal cell membranes, essential for maintaining both membrane structural integrity and fluidity.
chromosome A threadlike strand of DNA in the cell nucleus that carries the genes in a linear order.
cilia
circadian rhythm
citric acid cycle Also called the Krebs cycle and tricarboxylic acid cycle (TCA). A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide and chemical energy in the form of guanosine triphosphate (GTP). In addition, the cycle provides the chemical precursors for certain amino acids as well as the reducing agent NADH that is used in numerous other biochemical reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism and may have originated abiogenically.
clade
class
clonal selection A scientific theory in immunology that explains the functions of cells (lymphocytes) of the immune system in response to specific antigens invading the body. The theory has become the widely accepted model for how the immune system responds to infection and how certain types of B and T lymphocytes are selected for destruction of specific antigens.
cloning The process of producing individual organisms or molecules with identical or virtually identical DNA, either naturally or artificially. Many organisms, such as bacteria, insects, and plants, are capable of naturally producing clones through asexual reproduction. In biotechnology, cloning refers to the artificial creation of copies of cells, DNA fragments, or other biomolecules by various laboratory techniques.
coat, coating In the context of virus capsid, may refer colloquially to the defined geometric structure of a capsid, or the membrane of an endosome containing an intact virion. The coat of a virus is used in descriptions for the general public. Related slang: uncoating.
colony
comparative biology The use of comparative methods to study the similarities and differences between two or more biological organisms (e.g. two organisms from the same time period but different taxa, or two organisms from the same taxon but different times in evolutionary history). The side-by-side comparison of morphological or molecular characteristics of different organisms is the basis from which biologists infer the organisms' genetic relatedness and their natural histories. It is a fundamental tool in many biological disciplines, including anatomy, physiology, paleontology, and phylogenetics.
conservation biology The scientific study of nature and 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.
convergent evolution An evolutionary process by which species of different lineages independently develop similar characteristics, often to the point that the species appear to be more closely related than they actually are.
countercurrent exchange The crossover of some property, usually heat or some component, between two fluids flowing in opposite directions to each other. The phenomenon occurs naturally but is also frequently mimicked in industry and engineering.
crista A fold in the inner membrane of a mitochondrion.
cryobiology The branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in laboratory experiments.
cytology See cell biology.
cytoplasm All of the material within a cell and enclosed by the cell membrane, except for the nucleus. The cytoplasm consists mainly of water, the gel-like cytosol, various organelles, and free-floating granules of nutrients and other biomolecules.
cytosine One of the four main nitrogenous bases found in both DNA and RNA, along with adenine, guanine, thymine, and uracil (in RNA); it is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2).
cytoskeleton A complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane and which is present in the cytoplasm of all cells, including bacteria and archaea. The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell's requirements.
D
Darwinian fitness The genetic contribution of an individual to the next generation's gene pool relative to the average for the population, usually measured by the number of offspring or close kin that survive to reproductive age.
deciduous Deciduous means "falling off at maturity" or "tending to fall off", and it is typically used in botany in order to refer to trees or shrubs that lose their leaves seasonally (most commonly during autumn) and to the shedding of other plant structures such as petals after flowering or fruits when ripe.
decomposition The process by which the organic compounds of deceased organisms are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars, and mineral salts. These reactions occur naturally by both biotic means (biodegradation, such as that practiced by many bacteria and fungi) and abiotic means (basic physical and chemical processes, such as hydrolysis). Decomposition recycles matter present in the biosphere, making it an essential part of the nutrient cycle. Organisms that facilitate decomposition are known as decomposers; the scientific study of decomposition is known as taphonomy.
decomposer Any organism that facilitates the breakdown of dead or decaying organisms by carrying out the decomposition of complex biomolecules into simpler substances. Decomposers are heterotrophs which obtain energy and nutrition for their own growth and reproduction by recycling the chemical compounds contained in organic substrates. Microorganisms such as bacteria and fungi are the biosphere's chief decomposers, but invertebrates such as earthworms are also sometimes considered decomposers.
dehydration reaction A chemical reaction that involves the loss of a water molecule from the reacting molecule.
denaturation A process in which proteins or nucleic acids lose the quaternary, tertiary, and secondary structure which is present in their native state, when exposed to some external stress or chemical compound such as a strong acid or base, a concentrated inorganic salt, or an organic solvent.
dendrite A short branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.
denitrification The microbially facilitated process of nitrate reduction that ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. It is performed by a large group of heterotrophic facultative anaerobic bacteria and is a fundamental component of the nitrogen cycle.
deoxyribonucleic acid (DNA) A nucleic acid polymer that serves as the fundamental hereditary material in all living organisms. Each DNA molecule is composed of long sequences of nucleotides, each of which includes one of four nitrogenous bases – adenine (abbreviated A), cytosine (C), guanine (G), and thymine (T) – attached to a sugar-phosphate complex which acts as a "backbone" for the long-chain polymer. DNA most commonly occurs in "double-stranded" form, i.e. as a pair of nucleotide polymers bound together by complementary base pairing.
depolarization The process of reversing the charge across a cell membrane (such as that of a neuron), thereby causing an action potential. In depolarization, the inside of the membrane, which is normally negatively charged, becomes positive and the outside becomes negative. This is brought about by positively charged sodium ions rapidly passing into the axon.
desmosome Also called the macula adhaerens. A cell structure specialized for cell-to-cell adhesion.
developmental biology The branch of biology that studies the processes by which living organisms grow and develop over time. The field may also encompass the study of reproduction, regeneration, metamorphosis, and the growth and differentiation of stem cells in mature tissues.
disease Any particular abnormal condition that negatively affects the structure or function of all or part of a living organism and that is not the result of any immediate external injury. Diseases are medical conditions that are often identifiable by specific signs and symptoms. They may be caused by external factors such as infectious pathogens or by internal dysfunctions such as immune deficiency or senescence.
DNA See deoxyribonucleic acid.
DNA replication The chemical duplication or copying of a DNA molecule; the process of producing two identical copies from one original DNA molecule, in which the double helix is unwound and each strand acts as a template for the next strand. Complementary nucleotide bases are matched to synthesize the new partner strands.
DNA sequencing The process of determining the precise order of nucleotides within a DNA molecule.
drug Any substance that causes a change in an organism's physiology or psychology when consumed. Drugs may be naturally occurring or artificially produced, and consumption may occur in a number of different ways. Drugs are typically distinguished from substances that provide nutritional support such as food.
dimorphism The existence of a morphological distinction between organisms of the same species, such that individuals of that species occur in one of two distinct forms which differ in one or more characteristics, such as colour, size, shape, or any other phenotypic trait. Dimorphism based on sex – e.g. male vs. female – is common in sexually reproducing organisms such as plants and animals.
dynein A motor protein in cells which converts the chemical energy contained in ATP into the mechanical energy of movement.
E
ecological efficiency The efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.
ecological pyramid Also called a trophic pyramid, eltonian pyramid, energy pyramid, or sometimes food pyramid. A graphical representation of the biomass or bio-productivity generated at each trophic level in a given ecosystem.
ecological succession The more or less predictable and orderly set of changes that occurs in the composition or structure of an ecological community over time.
ecology The scientific analysis and study of interactions between organisms and their environment. It is an interdisciplinary field that combines concepts from biology, geography, and Earth science.
ecophysiology A biological discipline that studies the adaptation of an organism's physiology to environmental conditions.
ecosystem A community of living organisms in conjunction with the non-living components of their physical environment, interacting as a system.
ecotype Sometimes called an ecospecies. In evolutionary ecology, a genetically distinct geographic variety, population, or race within a species which is adapted to specific environmental conditions.
ectoderm The outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis, nerve tissue, and nephridia.
ectotherm An organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature compared to ambient sources of heat. Ectotherms generally experience changes in body temperature that closely match changes in the temperature of their environment; colloquially, these organisms are often referred to as "cold-blooded". Contrast endotherm.
effector A small molecule that selectively binds to a protein and regulates its biological activity. In this manner, effector molecules act as ligands that can increase or decrease enzyme activity, gene expression, or cell signaling.
efferent Conducted or conducting outwards or away from something (for nerves, the central nervous system; for blood vessels, the organ supplied). Contrast afferent.
egg The organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the developing organism emerges from the egg in a process known as hatching.
electrochemical gradient A gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts: the electrical potential and the difference in chemical concentration across the membrane.
electron acceptor Any chemical entity that accepts electrons transferred to it from another chemical entity. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Contrast electron donor.
electron carrier Any of various molecules that are capable of accepting one or two electrons from one molecule and donating them to another in the process of electron transport. As the electrons are transferred from one electron carrier to another, their energy level decreases, and energy is released.
electron donor A chemical entity that donates electrons to another chemical entity. It is a reducing agent that, by virtue of its giving up its electrons, is itself oxidized in the process. Contrast electron acceptor.
electron microscope A type of microscope that uses a beam of electrons to create an image of a sample or specimen. Electron microscopes are capable of much higher magnifications and have greater resolving power than conventional light microscopes, allowing them to see much smaller objects in finer detail.
electron transport chain The process of oxidative phosphorylation, by which the NADH and succinate generated by the citric acid cycle are oxidized and electrons are transferred sequentially down a long series of proteins, ultimately to the enzyme ATP synthase, which uses the electrical energy to catalyze the synthesis of ATP by the addition of a phosphate group to ADP. The process takes place in the cell's mitochondria and is the primary means of energy generation in most eukaryotic organisms.
embryo A developing stage of a multicellular organism.
embryology The branch of biology that studies the development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology involves the study of congenital disorders that occur before birth.
endangered species Any species which is very likely to become extinct in the near future, either worldwide or in a particular area. Such species may be threatened by factors such as habitat loss, hunting, disease, and climate change, and most have a declining population or a very limited range.
endemism The ecological state of an organism or species being unique to a defined geographic location, such as an island, nation, country, habitat type, or other defined zone. Organisms are said to be endemic to a place if they are indigenous to it and found nowhere else.
endergonic reaction Also called a nonspontaneous reaction or unfavorable reaction. A type of chemical reaction in which the standard change in free energy is positive, and energy is absorbed.
endocrine gland A gland of the animalian endocrine system that secretes hormones directly into the blood rather than through a duct. In humans, the major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, and adrenal glands.
endocrine system The collection of glands that produce hormones which regulate metabolism, growth and development, tissue function, and a wide variety of other biological processes.
endocytosis A form of active transport in which a cell transports molecules such as proteins into the cell's interior by engulfing them in an energy-consuming process.
endoderm One of the three primary germ layers in the very early human embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer), with the endoderm being the innermost layer.
endogenous (of a substance or process) Originating from within a system (such as an organism, tissue, or cell), as with endogenous cannabinoids and circadian rhythms. Contrast exogenous.
endoplasmic reticulum A type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae.
endosperm The tissue produced inside the seeds of most of the flowering plants following fertilization.
endosymbiotic theory Also called symbiogenesis. An evolutionary theory regarding the origin of eukaryotic cells from a hypothetical internal symbiosis between prokaryotic organisms, first articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967.
endotherm An organism that is capable of maintaining a consistent, metabolically favorable body temperature, largely by the recycling of heat released by its internal physiological functions, instead of by relying on ambient sources of heat. Endotherms are generally able to maintain a stable body temperature despite changes in the temperature of their environment; colloquially, these organisms are often referred to as "warm-blooded". Contrast ectotherm.
entomology The scientific study of insects.
environmental biology The branch of biology concerned with the relations between organisms and their environments.
enzyme A protein that acts as a biological catalyst by accelerating chemical reactions. Metabolic pathways depend upon enzymes to catalyze their individual steps, and almost all metabolic processes require enzyme catalysis in order to occur at rates fast enough to sustain life.
epidemiology The study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.
epigenetics A sub-field of genetics that studies cellular and physiological phenotypic trait variations caused by external or environmental factors which affect how cells express genes, as opposed to those caused by changes in the DNA sequence.
epiphyte An organism that grows on the surface of a plant and derives moisture and nutrients from the air, rain, marine environments, or from debris accumulating around it.
essential nutrient A nutrient required for normal physiological function which cannot be synthesized by a particular organism, either at all or in sufficient quantities, and which therefore must be obtained from external sources such as food. In humans, a set of nine amino acids, two fatty acids, thirteen vitamins, and fifteen minerals are considered essential nutrients.
estrogen The primary female sex hormone.
ethology The scientific study of non-human animal behaviour (i.e. excluding human behaviour) and usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait.
eukaryote A type of organism consisting of cells which have a nucleus enclosed within a distinct nuclear membrane, unlike prokaryotes. Eukaryotes include all organisms except the bacteria and archaea (i.e. all plants, animals, fungi, and protists are eukaryotes).
evolution The change in the heritable characteristics of populations of biological organisms over successive generations, which may occur by mutation, gene flow, natural selection, or random chance.
evolutionary biology The subfield of biology that studies evolution and the evolutionary processes that produced the diversity of life on Earth from a hypothesized single common ancestor. These processes include the descent of species and the origin of new species.
exocytosis A form of active transport and bulk transport in which a cell transports molecules out of the cell by expelling them through an energy-dependent process.
exogenous (of a substance or process) Originating outside of or external to a system (such as an organism, tissue, or cell), as with drugs and many pathogens. Contrast endogenous.
exponential growth It is exhibited when the rate of change of the value of a mathematical function is proportional to the function's current value, resulting in its value at any time being an exponential function of time.
external fertilization A type of fertilization in which a sperm unites with an egg external to the body or bodies of the parent organisms. Contrast internal fertilization.
extinction The termination of the existence of a particular kind of organism or a particular taxon, often a species, as a result of the death of the last individual of the taxon (though the capacity to breed and recover may have been lost before this point, rendering the taxon functionally extinct).
extracellular Of or occurring in the space outside the plasma membrane of a cell. Contrast intracellular.
extranuclear inheritance A transmission of genes that takes place outside the nucleus.
F
facultative anaerobe An organism which is capable of producing energy through aerobic respiration and then switching to anaerobic respiration depending on the amounts of oxygen and fermentable material in the environment.
family May mean a taxonomic rank, a protein family, a gene family or a domestic or social group.
fermentation A metabolic process that consumes sugar in the absence of oxygen.
fitness
fitness landscape
fertilization
fetus Also spelled foetus. An animal embryo after eight weeks of development.
flagellum (pl.) flagella A lash-like appendage that protrudes from the cell body of certain bacterial and eukaryotic cells.
flavin adenine dinucleotide (FAD) A redox cofactor, more specifically a prosthetic group of a protein, involved in different important enzymatic reactions in metabolism.
food chain The chain of eating and getting nutrition which starts from a small herbivores animal and ends up at a big carnivorous organism.
foramen (pl.) foramimina An open hole that is present in extant or extinct amniotes. Foramina inside the body of animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.
founder effect A loss of genetic variation that takes places when a new population is established by a very small number of individuals from a larger population.
fungi
G
G protein A family of proteins that act as molecular switches inside cells, and are implicated in transmitting signals from a diversity of stimuli outside a cell to its interior.
gamete
gene Any segment of DNA that contains the information necessary to produce a functional RNA and/or protein product in a controlled manner. Genes are often considered the fundamental molecular units of heredity. The transmission of genes from a parent cell or organism to its offspring is the basis of the inheritance of phenotypic traits.
gene pool A set of all genes, or genetic information, in any population, usually of a particular species.
generation
genetic code A set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.
genetic drift An alteration in the frequency of an existing gene variant in a population due to random sampling of organisms.
genetic variation Variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation. Genetic diversity in a population or species is a result of new gene combinations (e.g. crossing over of chromosomes), genetic mutations, genetic drift, etc.
genetics The study of heredity.
genome The entire set of genetic material contained within the chromosomes of an organism, organelle, or virus.
genotype Part of the genetic makeup of a cell, and therefore of an organism or individual, which determines one of its characteristics (phenotype).
genus
gizzard An organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, and dinosaurs, including birds), earthworms, some gastropods, some fish, and some crustaceans.
guanine One of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosin