Abiotic Physico-chemical factors characterizing a given ecosystem. Opposable to biotic factors, they constitute part of the ecological factors of this ecosystem. Climatic factors (temperature, light, air…), chemical factors (gases of the air, mineral elements…) are abiotic factors. An abiotic environment is unsuitable for the development of life.

ABO glycosyl transferase A particular type of glycosyl transferase involved in the ABO system (first blood group system discovered in 1900-1901). Glycosyl transferases are enzymes that allow the transfer of sugar-containing residues to proteins. Glycosyl transferase A and B differ by only 4 amino acids but they do not catalyze exactly the same reaction: transferase A transfers N-acetylgalactosamine and transferase B transfers galactose through a bond α1,3 to the galactose of the osidic chain H. They led respectively individuals to belong to group A or B. When both transferases are present, the individual is in group AB. In the case of a group O individual, the protein is inactive and the H chain is not glycosylated.

Activated carbon Solid in the form of granules or powder, resulting from the calcination of carbonaceous materials (wood, coal, coconut, etc.), with significant adsorption properties, particularly with regard to organic micropollutants (pesticides, for example).

Adaptive phenotypic response The ability of an organism to express different phenotypes from a given genotype under environmental conditions.

Adaptive radiation Rapid evolution, from a common ancestor, of a set of species characterized by great ecological and morphological diversity.

Adret A term mainly used in the Alps. Refers to the slope of the sunniest mountain in a valley (usually facing south), opposite the ubac. The adret is the most favourable slope for vegetation, crops and habitat.

Albedo The reflectivity of a surface, the fraction of solar energy that is reflected back to space. Its value is between 0 and 1, and the more reflective a surface is, the higher its albedo.

Alea An event (natural or man-made) that can cause damage (risk) to society or the environment.

Alkaline Bogs Natural habitat, with water-saturated soil, (i.e. no natural drainage possible), at basic or neutral pH.

Allele Any of two or more variants of a gene that have the same relative position on homologous chromosomes and are responsible for alternative characteristics. An allele can therefore correspond to a single sequence, or to a set of sequences that are different but not distinguishable at the phenotype level. (example of the color of the eyes blue/brown/green: at the nucleotide level we have several different alleles per color).

Allelic frequency Frequency at which an allele of a variant is found in a population. Expressed as a proportion or percentage. The sum of the allele frequencies of all alleles of a gene in a population is therefore by definition equal to 1. In population genetics, allele frequencies represent genetic diversity at the population or species level.

Alternative oxidase PTOX Enzyme of the chloroplast thylakoid membranes; its catalyzes the oxidation of the plastoquinone pool, hence its name alternative oxidase (PTOX).

Aminoacyl tRNA synthetases A family of enzymes that catalyse the esterification of amino acids on the 3′ end of transfer RNA (tRNA). Present in all living organisms, these enzymes help to translate the genetic message into proteins. The amino acids thus added to the end of the tRNAs are then incorporated by the ribosome into the polypeptide chain (protein) being synthesized. There is an aminoacyl tRNA synthetase for each of the 20 amino acids present in proteins. Each of these enzymes recognizes an amino acid and one or more iso-acceptor tRNAs. Their function is essential to the accuracy of the translation of the genetic code, as they ensure that the amino acid thus esterified at the end of the tRNA corresponds to the correct anticodon.

Amniotes A vertebrate taxon that includes species in which the embryo and then the fetus are protected by an amniotic sac, called amnion. The young, which develops in a shell or maternal uterus, grows in an aqueous medium, preserved through amnion. This characteristic has allowed these animals to colonize the terrestrial environment and to be permanently removed from the aquatic environment. Amniotes include reptiles, birds and mammals.

Amphipathic A molecule (usually organic) carrying both a hydrophilic group (able of binding to water) and a hydrophobic group (“which does not like water”).

Amplicons DNA fragment amplified by PCR (abbreviation for Polymerase Chain reaction).

Angular momentum The angular momentum of a point mass with respect to an axis is the product of its distance from the axis by its mass and its projected velocity perpendicular to the axis. The angular momentum of an extended object is obtained as the sum of the kinetic moments of its components. The angular momentum with respect to a point, generally the center of inertia of an object, is defined as a vector oriented along the axis of rotation.

Annual plant A plant that completes its life cycle over a year. Peas are annual plants.

Anomalocarididae A group of fossil Paleozoic predators. One of them, Anomalocaris “strange shrimp” measuring more than one meter in length was a giant hunter suitable for swimming and catching prey.

Anoxia Induced by a lack of dissolved oxygen supply in the body’s cells. In animals, refers to a decrease in the amount of oxygen distributed by blood to tissues. Anoxia can be caused by heart failure, lung disease, anemia, etc. At the level of the skin and mucous membranes, anoxia causes cyanosis, i.e. a blue-violet coloration. The brain is one of the most anoxia-sensitive organs. In ecology and hydrobiology, anoxia is a decrease in dissolved or present and bioavailable oxygen in the environment (soil, sediment, water, atmosphere…). For plants, anoxia is mainly exerted in the soil, during floods, at the root level.

Anthelion A rare optical phenomenon of the halo family. In relation to the observer, it is the point opposite to the Sun (helios). Also known as atmospheric halos visible at this point.

Anthropic factors Factors associated with human action that transforms spaces, landscapes and ecosystems.

Anthropized (anthropization) In geography and ecology, anthropization is the conversion of open spaces, landscapes, and natural environments by human action.

Anthropocene A neologism combining the Greek words “man” and “recent”, coined by meteorologist and atmospheric chemist Paul Crutzen, Nobel Prize winner in chemistry in 1995, to designate a new geological era. The anthropocene began with the industrial revolution and thus succeeded the Holocene, the geological period after the last ice age, which covered the last ten millennia.

Anthropocentrism A philosophical conception that considers man as the most significant central entity of the Universe and that apprehends reality through the sole human perspective. Aristotle was the first to develop its theory, along with that of geocentrism.

Antibiotic A natural substance or substance produced by chemical synthesis that prevents the growth of bacteria (bacteriostasis) or even destroys them (bactericide).

Antigenic determinant or epitope Part of the antigen recognized by an antibody or lymphocyte receptor. The same antigen can have several epitopes (identical or different) and thus induce a varied immune response.

Antiparallel In biochemistry, two biopolymers are said to be antiparallel if they are oriented parallel to each other, but in the opposite direction. The two main examples of this molecular configuration are the double helix of DNA and the β leaflet of proteins.

Apomixis (Astronomy) The point in the orbit of a planet furthest from the Sun.

Apomixis (Botany) Production of seeds identical to the mother plant without fertilization. Apomixis transmits somatic mutations (mutations occurring in a non-germinal cell), thus allowing the creation of diversity.

Apoplasm Extracellular continuum formed by the pectocellulosic walls of cells and the empty spaces between plant cells. Water and solutes can navigate through it by non-selective passive diffusion.

Archaea Unicellular microorganisms devoid of nucleus and living in extreme environments (anaerobic, high salinity, very hot…). Phylogenetic research by Carl Woese and George E. Fox (1977) differentiated between archaea and other organisms. Currently, living organisms are considered to consist of three groups: archaea, bacteria and eukaryotes.

Arthropods Branch of invertebrate animals whose organizational plane is characterized by a segmented body with articulated appendages and covered by a rigid cuticle or shell, which constitutes their exoskeleton, in most cases consisting of chitin. The arthropod branch appeared 543 million years ago and is by far the one with the most species and individuals in the entire animal kingdom (80% of known species).

Artificial sealing An ancient civil engineering technique that consisted in filling marshes or old river beds by decanting suspended matter during controlled flooding.

Associated crops Simultaneous cultivation of two or more species on the same surface for a significant period of their growth cycle. This association is based on the assumption that in a complex stand of several plant species, positive interactions (facilitation, complementarity) take precedence over negative interactions (competition) between plants.

Atheroma Or atheromatous plaque; Made up of various components (cholesterol, cellular debris and calcium) that will settle on the artery and contribute to its clogging. When the plaque clogs the vessel, it is called thrombosis. Atheroma is the leading cause of the majority of cardiovascular diseases.

Atomic nucleus (atom) Refers to the central part of an atom. The nucleus contains protons and neutrons tightened by strong nuclear interaction and almost its entire mass.

ATP Abbreviation for adenosine triphosphate. A triphosphate nucleoside composed of adenine (nitrogen base), ribose (sugar with 5 carbon atoms) and three phosphate groups forming a triphosphate group. A compound that both donates and stores energy present in all living organisms. Also used as building materials for nucleic acid synthesis.

Aurora Luminous draperies of polar nights, due to the luminescence of the upper atmosphere during falls of electrified particles from the Sun.

Autotrophy The ability of an organism to produce organic matter from the reduction of inorganic matter and an external energy source of light (photoautotrophy) or chemical reactions (chemoautotrophy).

Axenic Characterizes a culture (of prokaryotic or eukaryotic cells, organisms) free of any saprophytic or pathogenic germs.


Basalt Dark volcanic rock from rapidly cooled magma (i.e. magnesium-rich and iron-rich lava) exposed at or very near the surface of a terrestrial planet or a moon.

Binomial nomenclature A method of scientific designation of animal and plant species consisting of following the genus name with the qualifier of the species name. Linnaeus’s system of taxonomy is binomial.

Biocenosis All living beings that coexist in a given environment (the biotope). A biotope and its biocenosis are in constant interaction; they constitute an ecosystem.

Biofilms Also known as bacterial films or bacterial veils; a microbial community marked by the secretion of an adhesive and protective matrix. It is usually formed in water or in an aqueous medium. For instance, dental plaque is a biofilm that grows on surfaces within the mouth. Biofilms were probably the first colonies of living organisms more than 3.5 billion years ago. Together with stromatolites, they seem to be at the origin of the first biogenic rocks and reef structures.

Biogeochemical cycle The process of cyclic transformation of an element or chemical compound between the large reservoirs that are the geosphere, the atmosphere, the hydrosphere, in which the biosphere is found. Such a cycle often induces transitions from the organic to the mineral state within the biosphere. The various interacting cycles give the biosphere a regulatory capacity, called homeostasis.

Biomass Organic matter that composes living beings and their residues, whatever their origin (plants, bacteria, animals, fungi…), present at a given time in a particular biotope. It always contain carbon. From an energy point of view, biomass represents the energy that can be obtained by burning or fermenting living matter.

Biometrics In a very broad sense, refers to the quantitative study of living beings. Biometric identifiers are the distinctive, measurable characteristics used to label and describe individuals.

Biosphere Environments of the Earth adapted to and/or maintained by living organisms. They are an integral part of the ecosystems present in the lithosphere, the hydrosphere and part of the atmosphere. This dynamic living space is maintained by an energy supply (mainly due to the Sun) and the metabolism of living organisms in interaction with their environment.

Biotic Related to life. The biotic factors of an ecosystem are the flora and fauna and the relationships between them. The environment in which life can develop.

Biotope A place of life with relatively uniform defined physical and chemical characteristics. This environment is home to a set of life forms that make up the biocenosis of flora, fauna and micro-organisms. A biotope and the biocenosis it supports form an ecosystem.

Bioturbation Phenomenon of active mixing of soil or water layers by living species, mainly animals.

Black body Ideal body that has the property of totally absorbing the electromagnetic waves (including visible light) it receives.

Blood plasma The liquid part of the blood, which represents about 55% of its volume, in which red cells, white cells and platelets are suspended. Plasma is composed of water and contains lipids (fats), hormones, coagulation factors and more than a hundred proteins, the main one being albumin.

Boreal forest Forest dominated by conifers with discreet presence of hardwoods. In Europe, made up of deciduous (birch) and/or coniferous trees, it extends from the Baltic to the Urals. In Canada, it is the largest area of vegetation, accounting for 55% of the country’s land area.

Boundary layer A very thin region that surrounds any solid object in relative motion compared to a low-viscosity fluid such as air or water.

Bulbil A small bulb formed at the base of a main bulb. Intended to detach itself from the plant that produced it and give birth to a new plant.


Canopy Upper forest floor, directly influenced by solar radiation. Considered as a habitat or ecosystem as such, particularly in tropical forests where it is particularly rich in biodiversity and biological productivity.

Cantilever (in engineering) A Cantilever wall is a reinforced concrete retaining wall consisting of a footing and a veil. The advantage of this type of wall compared to a conventional wall is that the floor that is supported on the rear part of the footing contributes to its own stability.

Carbohydrates A biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula Cm(H2O)n (where m may be different from n). This formula holds true for monosaccharides.

Carbonaceous chondrites A type of meteorite considered to be the most primitive meteorite in the solar system (its elementary composition is very close to that of the sun). They are characterized by their high carbon, water and volatile gases (especially rare gases) content.

Carbonate Compensation Depth Abbreviated as CCD, the depth in the oceans to which all the calcium carbonate supplied from the surface is dissolved.

Carnitine Non-essential amino acid that is involved in the transport of fatty acids from the cytosol to the mitochondria within the cell during lipid catabolism in energy metabolism. Often used as a food supplement.

Catalyst An organic or mineral element that accelerates or slows down a chemical reaction. Used in very small quantities and specific to a given reaction, the catalyst does not appear in the reaction equation; it does not influence the direction of evolution of the transformation, nor the composition of the system in the final state. An enzyme is a biological catalyst.

Catalytic properties The ability of an enzyme (for example) to perform chemical reactions.

Cellular metabolism The set of biochemical reactions that take place within a cell to allow the body to keep itself alive, reproduce, develop and respond to its environment.

Centrifugal force Action taken by moving bodies on a curved trajectory, systematically directed towards the convex side of this trajectory.

Chaetognaths Phylum of arrow-shaped marine predators named after the mobile hooks that capture their prey. They play a major role in the planktonic ecosystem as the main direct predators of copepods and represent up to 10% of the zooplankton biomass.

Chelicerates A group of arthropods carrying chelicerae, a pair of appendages close to the mouth, corresponding to the second pair of antennas in mandibulates (crustaceans, insects…). This group includes merostomes (limules) and arachnids (spiders, scorpions, etc.). Only the horseshoe crabs are marine animals and live on the bottom of oceans.

Chemolithotrophs Metabolism of autotrophic organisms differing from each other by the nature of oxidation reactions energetically coupled to CO2 reduction. There are soil nitrification bacteria that oxidize ammonium salts to nitrites or nitrites to nitrates. Others oxidize either sulphides, colloidal sulphur suspended in water, thiosulphates, and many other mineral sulphur compounds, depending on the biological species. Other soil bacteria oxidize ferrous salts into ferric salts and use the energy released for their synthesis.

Chlorophyllous parenchyma A plant tissue (usually in leaves) composed of chlorophyll cells containing numerous chloroplasts. As the seat of photosynthesis, it participates in nutritional functions. It represents an important part of the inside of the leaves.

Chloroplast Organelle present in the cytoplasm of photosynthetic eukaryotic cells (plants, algae). As a site of photosynthesis, chloroplasts produce O2 oxygen and play an essential role in the carbon cycle. They use light energy to fix CO2 and synthesize organic matter. They are thus responsible for the autotrophy of plants. Chloroplasts are the result of the endosymbiosis of a photosynthetic prokaryote (cyanobacterium type) within a eukaryotic cell, about 1.5 billion years ago.

Choline Water-soluble nutrient. It is incorporated into different biological molecules present in our body. Among them, lecithin is a phospholipid that contains choline among other things.

Chromosome Located in the nucleus of cells, chromosomes are made up of DNA and proteins. As a carrier of genetic information, they carry genes and are transmitted from generation to generation.

Clade A group or group of organisms in which all the members, however different they may have become, descend from the same common ancestor group it is a monophyletic group. In a phylogenetic tree branch of the tree that contains an ancestor and all his descendants.

Climate forcing A parameter external to the climate system that requires a (temporary) change in energy exchange at the Earth’s surface, resulting in climate change.

Climate projection Simulation of changes in the average state of the atmosphere subjected to one (or more) forcing (typically: increase in the greenhouse effect), over several decades.

Cnidarians Phylum of aquatic animals (mainly marine) that are found in two forms: polyps, when fixed (as in the case of coral or sea anemones), and jellyfish when swimming.

Coagulation (Hydrology) Consists of quickly mixing the water to be treated with one (or more) chemical reagent(s) to destabilize the colloidal (very fine) particles of the water, and then agglomerating them under slow agitation (flocculation), in order to settle (or filter) them more easily.

Coalescence: Merger of two droplets to form a larger one.

Coding sequence Describes the part of the DNA or RNA of a gene translated into protein. Represents only a part of the gene from which it originates, as well as the mRNA in which it is written.

Coenzyme Molecules used as cofactors in certain reactions catalyzed by enzymes with which they are structurally linked within a stable complex.

Conjugation (Genetics) Exchange of DNA (especially plasmids) between two living bacteria.

Conservation Biology Discipline dealing with issues of biodiversity loss, maintenance or restoration. A synthetic discipline that applies the principles of ecology, biogeography, population genetics, anthropology, economics, sociology, etc., to the maintenance of biological diversity throughout the planet.

Consolidation Settling of a saturated fine soil undergoing loading and corresponding to the expulsion of the water it contains. This over-pressurized water due to the loading evacuates more or less quickly depending on the permeability of the soil.

Continuous numerical methods The most developed continuous methods in engineering are finite element or finite difference methods that allow the numerical solution of differential and partial differential equations. The environment to be studied is subdivided into different domains (mesh made up of elements) on which the equations of the problem are solved. The choice of mesh size, type of elements and behavioural models determine the relevance of the solution obtained.

Convection (Physics) The movement of a fluid such as air or water caused by gravity by the inhomogeneities of its density due to inhomogeneities of temperature or chemical composition (e.g. salinity).

Core (Earth) The earth’s inner core, made of iron and nickel, is located under the mantle of silicates, its radius is about 3500 km; its central solid state part, whose radius is about 1250 km, is called the seed.

Coriolis Force Action undergone by moving bodies in a rotating reference frame, such as a planet or a star.

Court jester (Genetics) Hypothesis proposed by Anthony Barnovsky as an antithesis of the “red queen”. It suggests that the transformation of species on a geological scale is not very much induced by competition between species but essentially due to the abiotic context. The case of the birch moth illustrates this hypothesis of the “court jester”.

Cryosphere All frozen parts of the Earth’s surface, especially snow, ice, and frozen ground (permafrost).

Cryptophytes Unicellular organisms, mostly photosynthetic. Their chloroplasts are limited by four membranes, indicating an endosymbiosis of a photosynthetic eukaryote. Cryptophytes occur in many environments, particularly aquatic ones (oceanic environments, fresh waters, wetland pore waters). Some species have become intestinal parasites of metazoans. Some of them are endosymbiotes of Dinophytes.

Ctenophores Small, hermaphroditic, predatory marine organisms. They have a vague similarity to jellyfish and are a very important part of the plankton.

Cuticle The outer layer that covers and protects the air organs of plants and the organs of certain animals. The various types of cuticles are not homologous and differ in origin, structure, function and chemical composition. In plants, it is composed of successive deposits of wax coated in a layer of hydrophobic fatty acids, cutin. In insects, it has no cells and is the exoskeleton (or external skeleton) of arthropods.

Cutine Amphiphilic lipid substance. It is a polymer formed of C16 or C18 hydroxy acids linked together by ester bonds. Together with intracuticular waxes, it forms the cuticle covering, for example, cells on the surface of leaves.

Cyclone A deep atmospheric depression large enough to be rotated by the Coriolis force in the direction of Earth’s rotation. This includes (but is not limited to) particularly intense tropical cyclones, also known as hurricanes (in America) or typhoons (in Asia).

Cytochrome oxidase 1 Subunit 1 of the enzyme complex of the respiratory chain (abbreviated to COX1). This subunit is encoded, unlike most genes encoding cytochrome oxidase subunits, by the mitochondrial genome. The use of COX1 sequences makes it possible to discriminate between the various animal species, with the exception of Cnidarians.

Cytoplasm Cellular component. It consists of a phase rich in water and proteins (cytosol) and contains cellular organelles (mitochondria, etc.).

Cytokines Set of polypeptide molecules involved in the regulation of immune functions, the best known of which are interleukins and interferons.

Cytosol A phase rich in water and protein from the inner environment of the cells contained in the cytoplasm and excluding cellular organelles (mitochondria, etc.).


Deccan Traps Stack of lava flows over 2000 meters thick located in India. They were formed 60 to 65 million years ago and could be involved in the Cretaceous-Tertiary crisis, which has seen the disappearance of non-avian dinosaurs in particular.

Decibel The decibel (dB), or tenth of the seldom use Bel, is the commonly used unit of sound power, named after Graham Bell (1847-1922), a Scottish scientist who invented the telephone. It is equal to 20 log10 (p/pref) where p denotes the acoustic pressure and pref a reference pressure arbitrarily set at 20 μPa (20×10-6 Pascal, or 0.2 billionth of atmospheric pressure), which represents the hearing threshold in most humans.

Degree of freedom This refers to each parameter, or coordinate, that characterizes the position of an object or its centre of gravity on its trajectory.

Dengue fever Viral infection transmitted by mosquitoes that occurs in tropical and subtropical regions of the world. Causes a flu-like syndrome that can progress to life-threatening complications. There is no specific treatment for dengue fever.

Diapause A phase, genetically determined in the development of an organism, during which it decreases the intensity of its metabolic activities.

Diatomite Light-coloured sedimentary rock formed by the accumulation in large quantities of siliceous frustules surrounding the diatom cell.

Dichotomy Splitting something into two elements that are clearly opposed. In plant biology, a two-part branching pattern at each growth level.

Diffusion Mechanism for the net movement of heat or of the components of a mixture of molecules from a region of higher concentration to a region of lower concentration, which tends to standardize the distribution of these quantities. This uniformity results from the random movement of molecules (molecular scattering) or plots of fluid (turbulent scattering).

Diploidy Property of a cell whose chromosomes it contains are present in pairs (2n chromosomes). The concept is generally to be contrasted with haploidy, a term referring to the ownership of cells with single copy chromosomes (n chromosomes). An organism or part of an organism is said to be diploid when its cells are themselves diploid.

Discreet character Character of a living organism that can only adopt very distinct states (examples: black or white; presence or absence of wisdom teeth).

Discrete numerical methods Discrete methods are more recent and come from contact dynamics or molecular dynamics. The environment to be studied is subdivided into a set of particles of various independent shapes that interact with each other at their points of contact and whose behaviour is governed by Newton’s second law. Interaction laws generally require few parameters and allow for a variety of fields of study. Unlike continuous models, these models are very well adapted to the very high deformations, cracking and fracturing of the studied environment.

Disinfection by-products Products of chemical reactions between a chemical disinfectant introduced into the water (chlorine gas, bleach, ozone, etc.) and substances naturally present in the water (natural organic matter, bromide, etc.).

Disjoint plant cover Characterizes an area of vegetation divided by rocks, screes, etc.

Distribution network Set of elements (pipes, tanks,…) used to distribute drinking water between the factory outlet (pumped water) and the consumer’s tap (distributed water).

Abbreviation for deoxyribonucleic acid. A macromolecule composed of nucleotide monomers formed of a nitrogenous base (adenine, cytosine, guanine or thymine) linked to deoxyribose, itself linked to a phosphate group. It is a nucleic acid, like ribonucleic acid (RNA). Present in all cells and in many viruses, DNA contains genetic information, called genome, that enables the development, functioning and reproduction of living beings. The DNA molecules of living cells are formed by two antiparallel strands wrapped around each other to form a double helix.

DNA polymerase Enzyme complex involved in DNA replication during the cell cycle, but also in DNA repair and recombination processes. DNA polymerases use deoxyribonucleoside triphosphates, using another strand of DNA as a matrix. This replication process uses the complementarity of the nucleic bases to guide the synthesis of the new strand from the matrix strand.

Dormant (Botany) Property of an organism with a slower life phase where growth and development are temporarily stopped.

Drageon (Botany) Formed by the development of an underground bud, the sucker allows a natural propagation of the plant which will thus be reproduced in the same way.

Drosophila Small fly also called vinegar fly or fruit fly. Because of its ease of breeding, the fruit fly is a model species in genetic research.

Drying Action of drying out. The removal of water, natural or otherwise, from a substance. Example: desiccation of the soil, of a plant.

Dynamic compaction Technique for densifying the soil to a depth of less than 10 m, under the impact of a mass of 15 to 150 tonnes falling from 20 to 40 m.


Ecologue Works in ecology. The job of an ecologue is to study the relationships between organisms and the surrounding world. Not to be confused with the ecologist, who campaigns to protect ecology.

Eco-space Three-dimensional representation of a theoretical ecosystem according to three axes: tiering, feeding mode and mobility of organisms.

Ecosystem A group formed by an association of living beings (or biocenosis) and its environment (the biotope): biological, geological, edaphic (the soil), hydrological, climatic, etc. An ecosystem is characterized by interactions between living species and their surrounding environment, material and energy flows between each of the ecosystem’s components that allow them to live, and a dynamic balance over time between sustainability and evolution.

Ecosystem services The benefits we derive from ecosystems without having to act to achieve them. The various types of services are the result of natural processes of ecosystem functioning and maintenance. Thus, supply services provide the goods themselves such as food, water, wood and fibre. Regulatory services regulate climate and precipitation, water (e.g. floods), waste, and the spread of disease. Cultural services are about beauty, inspiration and recreation ñ which contribute to our well-being. Assistance services include soil formation, photosynthesis and recycling of fertilizing substances, without which there would be no growth or production.

EDCH Abbreviation in french standing for “Water intended for human consumption” (i.e. drinking water).

Encephalitis A disease characterized by inflammation of the brain (brain, brain stem and/or cerebellum).

Endemic (Health) Characterizes a disease in humans whose incidence rate is generally quite regular and is located in a restricted area.

Endocellular Located inside the cell.

Endocytosis Or internalization, is a cellular mechanism of transport to the interior of the cell by invagination of the membrane and envelopment of fluids (molecules) or particles (viruses, bacteria, etc.).

Endogenous life A community of organisms living underground, as opposed to epigeous species that germinate or live on the surface of the soil.

Endogenous virus Virus whose genome has been integrated into the genome of their host (i.e. endogenized) and transmitted vertically in host populations.

Endoplasmic reticulum Membrane network of the cytoplasm of eukaryotic cells, essential for cellular metabolism (lipid and protein synthesis, calcium storage). Associated with ribosomes, it is the place of synthesis of proteins secreted outside the cell and, on the other hand, proteins and lipids constituting the membranes of cellular organelles (Golgi apparatus, lysosomes, mitochondria, nucleus, ribosomes, vesicles…).

Endosymbiosis Mutually beneficial cooperation between two living organisms -therefore a form of symbiosis- where one is located within the other. At the cellular level, represents the processes that led to the formation of organelles (mitochondria and chloroplasts) in eukaryotic cells. Thus, mitochondrion comes from the integration of a bacterium, probably an alpha-proteobacterium, into a primary eukaryotic cell. The chloroplast was formed by the incorporation of a cyanobacterium into the eukaryotic cell. These transformations were accompanied by gene transfers from endosymbiotes to host cells and by an integration of metabolism.

Endosymbiotic Characterizes a symbiotic association where one of the organisms, called endosymbionts, is present inside the cells of its host.

Enteropneuste Class of marine worms.

Enzootic Characterizes a disease in animals whose incidence rate is generally fairly stable.

Epibenthic An organism living on the surface of the substratum in the seabed area.

Epigenetic marks Biochemical modifications, applied by specialized enzymes to DNA or to proteins that structure it, histones. The best characterized brands are methyl groups (CH3) on DNA, as well as various chemical modifications of histones (methylation, acetylation…).

Epigenetics A discipline of biology that studies the molecular mechanisms that affect gene activity and expression, but can also be used to describe any heritable phenotypic change.

Epigenome Record of the chemical changes to the DNA and histone proteins of an organism. Changes to the epigenome can result in changes to the structure of chromatin and changes to the function of the genome.

Equator Large circle of the Earth, at equal distance from the poles. The Sun is at its zenith at the equinoxes.

Equinox The two positions of the Earth’s orbit (and the two corresponding days) for which the Sun is at its zenith in the tropics (longest or shortest day of the year). Day and night then have the same duration.

Ethology Study of the behaviour of various animal species, in their natural environment or not.

Eukaryotes Unicellular or multicellular organisms whose cells have a nucleus and organelles (endoplasmic reticulum, Golgi apparatus, various plasters, mitochondria, etc.) delimited by membranes. Eukaryotes are, along with bacteria and archaea, one of the three groups of living organisms.

Eumetazoans Upper metazoans (animals) comprising all major groups of animals except sponges and placozoa (see this term).

Eutrophication From the Greek εὖ, well, and τροφή, action of feeding. Enrichment of aquatic habitats with nutrients (nitrogen, phosphate, organic matter) through wastewater and drainage from cultivated fields, causing massive invasion by algae and angiosperms. The ultimate stage is characterized by the death of a large part of the fauna, due to the lack of oxygen.

Evaginated Which protrudes outwardly.

Evapotranspiration (Plant biology) A phenomenon characterizing the emission of water to the atmosphere, combining two phenomena: evaporation at ground level (which is a purely physical phenomenon) and plant transpiration (which is defined by water transfers in the plant and water vapour losses through the stomata of the leaves).

Evolutionist Person who accept the theory of evolution, especially Darwin’s theory that populations evolve over the course of generations through a process of natural selection.

Exponential Refers to the variation of a quantity when its rate of variation is proportional to the value of the quantity. When this rate is positive, the magnitude increases more and more rapidly compared to its initial value, and when it is negative it decreases towards zero.


Fixist Hypothesis (no longer accepted) according to which there is neither transformation nor drift of living species, nor is there any profound modification of the Universe.

Flagellate A single-celled cell or organism equipped with one or more flagellae, a structure ensuring their mobility.

Flavonoids Latin flavus, yellow. Secondary metabolites of plants all sharing the same basic structure; they are soluble in water and present in vacuoles. With several thousand compounds, flavonoids are the most important class of phenolic compounds in plants and an important family of natural dyes. They represent a gigantic family of antioxidants. Flavonoids are responsible for the brown, red and blue tones of flowers and fruits.

Food web or Food cycle. Natural interconnection of food chains of “what-eats-what” in an ecological community. Describe the relationships between species (predator-prey relationships in particular), energy and nutrient cycles and flows within ecosystems between producers, consumers and decomposers. The basic level of this network is that of autotrophic primary production, above this level, each link in a food chain corresponds to a trophic level.

Formose reaction A word formed by the contraction of the terms formaldehyde and aldose. This reaction, discovered by the Russian chemist Alexander Boutlerov in 1861, consists in polymerizing formaldehyde to form sugars including pentoses (sugars with five carbon atoms). This reaction is important in the abiotic formation processes of living molecules.

Fragmented (hydrology) A watercourse divided into small areas and isolated by ecological barriers related to development (such as dams), limiting its natural functioning and ecological continuity.

Frigate bird Sea bird, whose male has a bright red bag on its neck.

Frond (Biology) A structure of a flattened, relatively large, leaf-shaped living organ or organism.


Gaize A fine-grained, porous, siliceous sedimentary rock. Colloidal silica, of the opal type, impregnates the porous parts. Often fossiliferous, it can contain a carbonate and clay fraction.

Genome Genetic material of a living organism. It contains genetic information encoding proteins. In most organisms, the genome corresponds to DNA. However, in some viruses called retroviruses (e.g. HIV), the genetic material is RNA.

Genotype Information carried by the genome of an organism, contained in each cell in the form of deoxyribonucleic acid (DNA). In the DNA molecule, it is the sequence of nucleotides that constitutes the genetic information.

Genotypic frequency Genetic structure of the population. Determined from the allele frequencies.

Geochemical background Represents the average natural chemical composition, i.e. without anthropogenic impact, of a geological formation at a given location. It is used as a reference for defining a “normal” state of a site.

Geosynthetics Planar synthetic materials, permeable (geotextiles or related products) or waterproof (geomembranes) used in civil engineering. They can perform different functions: separation, protection, reinforcement, drainage, filtration, sealing, anti-erosion.

Germ line All cells from stem cells to gametes.

Germinal Qualifies a particular cell line: gametes. A germline mutation can be transmitted to the offspring.

Glaucophytes Unicellular plankton karyotes living in lakes, ponds or swamps in temperate regions. They have chloroplasts (called cyanelles) that are blue-green in colour, due to the presence of phycocyanins and allophycocyanins in phycobilisomes. It is a group of reduced diversity.

Glycemic index Criterion for classifying carbohydrate-containing foods based on their effects on blood sugar (blood glucose level) during the first two hours after ingestion. It allows comparing the glycemic power of each food, measured directly during digestion.

Glycoproteins Proteins on which sugars are added, which give them specific biological properties. Present, among other things, on cell membranes; they promote interactions between cells.

Gradient The gradient of a position-dependent quantity is a vector that indicates how much this quantity varies for a small displacement. If this quantity is, for example, the altitude of a terrain on a map, the gradient is a vector oriented upward along the line of greatest slope, of length proportional to the slope.

Grain (Botany) Indestructible dry fruit, single-seeded (other name: karyopsis, from the Greek κάρυον, walnuts and ὄψις, appearance); it is the characteristic fruit of grasses (family Poaceae).

Gram bacteria Bacteria highlighted by a staining technique called Gram staining, they appear pink under the microscope. The staining technique is based on the membrane and wall characteristics of the bacteria. However, it is not a phylogenetic classification factor as the groups “Gram +” and “Gram -” are both non-monophyletic.

Graminoids Herbaceous, monocotyledonous plants, mainly of the family Poaceae (grasses in the strict sense), Cyperaceae (sedges) and Juncaceae (rushes). They have a morphology similar to the “grass” type, i.e. they have stems close to the “thatch”, and leaves with a narrow and tapered blade.

Greenhouse effect The action of molecules in an envelope, such as the greenhouse in a garden or the atmosphere, which causes it to absorb and reflect back to the ground a fraction of the thermal radiation emitted by it. Egalitarianism Doctrine advocating the equality of citizens in political, economic and social matters and claiming the same rights, the same treatment for all and the equal redistribution of all wealth to all individuals. Within the framework of environmental inequalities, everyone should suffer the same environmental disadvantages (e.g. redistribution of infrastructure) and enjoy the same amenities (such as green spaces).

Guppy A tropical freshwater fish species that is highly valued in aquarium breeding.


Haplotypes A group of alleles of different loci located on the same chromosome and usually transmitted together. Haplotype is a formed by the contraction of the English phrase haploid genotype, or haploid genotype. All the genes located on the same chromosome and whose alleles segregate together during meiosis constitute a haplotype. These genes are called “genetically linked”.

Harmonic Any sound with a frequency multiple of that of the fundamental mode, or sub-multiple in the case of sub-harmonics. Even the purest sounds consist of the fundamental mode and a set of harmonics and subharmonics.

Helminthes A generic term used to describe various types of worms that are generally parasitic: round worms (nematodes), spiny trunk worms (acanthocephalus – “thorny-headed” worms) and flatworms (plathelminthes cestodes and trematodes).

Hercynian chain A mountain range that forms between the Devonian (-400 million years) and the end of the Permian (-240 million years). This chain is now eroded and most of the geological evidence of its formation is metamorphic rocks and granites, which were once the deep root of the massif. In France, the Hercynian chain corresponds essentially to the Armorican Massif, the Central Massif and part of Corsica. These massifs are generally called variscan massifs.

Heterosphere A region in the upper Earth’s atmosphere where the proportions of the various constituents are not uniform.

Heterotrophic Qualifies an organism (animals, fungi, prokaryotes) that is unable to synthesize its components itself and therefore uses sources of exogenous organic matter initially produced by autotrophic organisms.

Heterotrophy A mode of nutrition characteristic of organisms using exogenous organic matter sources for their growth and development. Animals, fungi, many protozoa, most prokaryotes and a few rare plants are heterotrophic.

Heterozygous Characterizes an organism that has two different alleles of the same gene at the same locus for each of its homologous chromosomes.

High throughput methods In recent years, new methods have emerged for the analysis of genomes, proteins, etc. Based on new physico-chemical and bioinformatics technologies, they allow parallel analyses on a very large number of short sequences, with flows infinitely higher than those used a few decades ago.

High-throughput sequencing Brings together new sequencing techniques allowing the production of a large number of sequences quickly and at low cost. They allow in particular the sequencing of a mixture of nucleic acid sequences present in a sample. This name is a French equivalent of English terminologies such as NGS (next-generation sequencing), HTS (high-throughput sequencing).

Histone Basic proteins that combine with DNA to form the basic structure of chromatin. Histones play an important role in DNA packaging and folding.

Holobionte Refers to the whole of an organism and the microorganisms it contains.

Homeostasis A set of biological regulations that will maintain a balance, for example, the regulation of our body temperature.

Homoeothermy Characteristic of animal species (birds, mammals) whose internal environment (blood and lymph) maintains a constant temperature, regardless of the temperature of the external environment, within very wide limits.

Homogeneous catalyst Catalyst having the same phase (solid, liquid or aqueous) as the reagents.

Homologous (Genetics) Two chromosomes or two genes are homologous if they match and mutually exclude each other from meiosis.

Homologous recombination A type of genetic recombination where nucleotide sequences are exchanged between identical or similar DNA molecules.

Homosphere A region of the Earth’s atmosphere where the proportions of the various constituents are uniform. This region includes the troposphere, stratosphere and mesosphere.

Homozygous Characterizes an organism that has two identical alleles of this gene at the same locus for each of its homologous chromosomes.

Hydrogenosome Organelle producing hydrogen, derived from a mitochondria. It is found in some anaerobic ciliates, Trichomonas, and fungi.

Hydrological year For glaciers, it extends from the beginning of the accumulation season to the end of the next ablation season.

Hydrophilic Property of a compound with an affinity for water and a tendency to dissolve in it. It is also ionic. It can be soluble in water (water soluble) or polar solvents.

Hydrophobic Property of a compound “that does not like water”; it repels water or is repelled by water. Hydrophobic products are often lipophilic (soluble in fats or organic solvents), but insoluble in water.

Hydrosphere Areas of the Earth occupied by water or ice (oceans, seas, rivers, lakes, glaciers, polar ice caps and groundwater). It should be noted that the atmosphere contains large quantities of water vapour.

Hydroxyacetaldehyde Chemical structure molecule C2H4O2. It is one of the simplest organic molecule: it has both a hydroxyl group (OH) and an aldehyde group (CHO).


Ice cap A mass of continental-sized ice (thousands of kilometres), which flows under its own weight. Currently there are Greenland and Antarctic ice caps.

Ice jam Natural accumulation of materials brought by water.

Immunoglobulins (Ig) Also called antibodies. Proteins produced by cells of our immunity, B lymphocytes, in response to a foreign molecule, which may be a bacterium. There are different forms (isoforms), A, G, M… depending on their role.

Inflorescence (Botany) Grouping of flowers on the same footing.

Inorganic material In contrast to organic matter, which contains organic compounds that are based on a carbon skeleton and usually have C-H bonds. In soils, inorganic matter consists of mineral compounds resulting from the decomposition of organic matter during mineralization processes. These compounds can also be produced by chemistry. However, some simple carbon compounds (carbonates, bicarbonates and ionic cyanides, carbides, except hydrocarbons) are classified as inorganic compounds.

Insulation The flow of solar energy received at the Earth’s surface (expressed in watts per square metre).

Integrative biology A discipline of biology that concerns the integrated description of the multiple phenomena occurring in the various levels of hierarchical structural and functional organizations of living organisms.

Integron Natural bacterial system for the capture, expression and dissemination of genes, particularly those encoding antibiotic resistance.

Interferons Proteins that are part of cytokines, they have an action against any pathogenic agent (virus, bacteria and parasite) and stimulate immune cells.

Interleukins Proteins that are part of the cytokines responsible for the communication between cells of immunity.

Intertidal zone Also known as the foreshore and seashore and sometimes referred to as the littoral zone, is the area that is above water at low tide and underwater at high tide (in other words, the area between tide marks). The word Estran, of Scandinavian origin, is sometimes used

Intraspecific A term that describes the relationships that are established between individuals belonging to the same species.

Ionosphere A region of the Earth’s upper atmosphere where the air is partially ionized and can therefore conduct electricity.

Ions An electrically charged chemical species, atom or groups of atoms, that has gained or lost one or more electrons.

Isotope A particular form of a chemical element. Isotopes of the same element different from each other by the number of neutrons but they have the same number of protons and electrons.

Isoxys An extinct genus of small primitive arthropods that lived in the Lower Cambrian. Its main characteristic is the existence of a pointed bivalve shell.


Jet stream Term used to describe the four air currents at the base of the stratosphere that circulate from west to east around the Earth approximately following the parallels located at ± 30° and ± 60° with large fluctuations. Polar jet streams are the most intense (up to 300 km/h) and the most unstable.


Karst Geomorphological structure resulting from water erosion of carbonate rocks, mainly limestone.

Keratinocytes Cells mainly present on our skin.

Kinase Enzymes catalyzing phosphorylation reactions by adding a phosphate group to a target molecule from ATP. The target molecule, called the substrate, can be a protein( like a kinase), a lipid or a sugar.

Kinetics (Chemistry) Describes the evolution of chemical systems over time, the time required to move from an initial state to a final state. The laws of chemical kinetics make it possible to determine the specific velocity of a chemical reaction.


Lagerstätten German word, plural, literally meaning “storage area”. Corresponds to geological sites with an extreme wealth of remarkably preserved fossils.

Lamarckism Movement relating to Lamarck’s ideas. Often reduced to the idea of the transmission of acquired characters, although Jean-Baptiste Lamarck’s transformist theory is much broader than that.

Laminar Refers to the regular flow where the trajectories of fluid particles have no random character, which reduces the resistance to their advancement. On the contrary, in turbulent flow the trajectories and velocities of the fluid particles are very random and the fluid particles are slowed down.

Landing Deposition of alluvial materials, particularly during flood phases by the river, forming banks that modify river dynamics.

Late Heavy Bombardment A period in the history of the solar system extending approximately 4.1 to 3.9 billion years ago, during which a significant increase in meteoric or cometary impacts on terrestrial planets would have occurred.

Leishmaniasis Parasitic diseases causing very debilitating or even fatal skin or visceral disorders if left untreated. They are caused by different parasites of the genus Leishmania, transmitted by the bite of insects commonly known as sandflies.

Lessivage / Leaching Latin lixivia, leaching, laundry. The downward movement of soil minerals caused by water percolation.

Liberalism Classical economic liberalism, whose authors were passionate about Newton’s theories of physics, considers that human beings are driven by their personal interests and advocates laissez-faire insofar as an invisible hand ensures general balance. However, this approach has evolved over the course of many debates. Environmental justice is partly reflected in Rawls’ liberalism. The latter admits that there may be inequalities in social justice as long as it favours the most disadvantaged, and at the same time, sets strict conditions for these inequalities. Therefore, it must be possible to correct the negative effects of certain measures or policies on the poorest.

Lichens Organisms resulting from a symbiosis between a fungus and an algae. Algae synthesize organic matter from carbon dioxide (CO2) in the air and solar radiation (photosynthesis). In return, the fungus takes water and mineral salts essential for lichen symbiosis from the environment.

Lift: Vertical air movement directed from the ground upwards.

Lignin Complex macromolecules formed by the polymerization of phenyl-propane monomers and associated with polysaccharides in the plant wall. Present mainly in vascular plants, lignin is the second most abundant renewable biopolymer on Earth, after cellulose. Together, they represent more than 70% of the total biomass. Lignin appeared 380 million years ago, in the Devonian, with the first vascular plants, the Ferns, and almost simultaneously the first trees.

Lipid Fatty substances are hydrophobic or amphipathic molecules (a hydrophobic part and a hydrophilic part). Lipids are characterized by their insolubility in water and their solubility in non-polar organic solvents.

Lipopolysaccharides Molecules having a lipid part and a carbohydrate part.

Lipoxygenase Enzyme that catalyzes the oxidation of fatty acids.

Lithology Corresponds to the geological nature of a rock.

Lithosphere The superficial part of the earth made up of two superposed terrestrial layers: the crust (oceanic or continental) and the rigid upper mantle. It is between 60 and 70 km thick under the oceans and 100 km under the continents.

Locus Plural loci. Position of the gene on the chromosome. In population genetics, all homologous genes (homology class). Two chromosomes or two genes are homologous if they match and mutually exclude each other from meiosis.

Lyssenkism Movement relating to Lyssenko’s ideas which led to the implementation in the USSR of a policy of genetic and agricultural control. Nowadays, Lyssenkism is regularly used metaphorically to denounce the manipulation or distortion of the scientific method to support a pre-determined conclusion, often linked to a social or political objective.


Macrophagy The mode of nutrition of a living organism that feeds on prey that is large in size in relation to itself.

Magnetosphere A region outside the Earth where the magnetic field generated by this planet is located.

Malate Salt of malic acid, a dicarboxylic acid widely used in the plant kingdom and naturally present in fruit, which contributes to its pleasant taste. Malate is an intermediate of the Krebs cycle, one of the major metabolic pathways of cellular respiration in almost all living beings, and is involved in the Benson & Calvin cycle, which is part of photosynthesis. Used as a food additive, under number E296.

Marcottage (Horticulture, Botany) Development of roots on a buried branch that allows the production of a new individual.

Mass extinction A relatively short event on a geological time scale (a few million years maximum) during which at least 75% of the animal and plant species on land and in the oceans disappear. Since life appeared on Earth, there have been five major episodes of extinction and a sixth is reported to be ongoing.

Meiosis A process of double cell division that takes place in the cells (diploids) of the germ line to form gametes (haploids), or sex cells in eukaryotic organisms.

Melanism Animal phenotype characterized by the entirely black colour of the body (skin, feathers, hair…).

Membranes (Water treatment) Sheets or tubes, mineral or organic, physically retaining particles and micro-organisms by direct filtration (microfiltration, ultrafiltration, nanofiltration) or separating dissolved species by osmotic phenomenon (reverse osmosis).

Mendel’s law Laws concerning the principles of biological heredity, laid down by the Czech monk and botanist Gregor Mendel (1822-1884). http://uel.unisciel.fr/biologie/analgen/analgen_ch01/co/apprendre_ch1_01_01_01.html

Mendelian heredity Heredity based on the transmission of a single gene under a dominant, recessive or sex chromosome X (or Y) linked mode. Refers to a genetic trait with simple determinism, by a couple or a small number of gene pairs.

Mendelian population Population of organisms whose heredity obeys Mendel’s laws.

Meristem From the Greek µεριστός, which can be shared, divisible. Undifferentiated plant tissue, perpetually young, from which the new cells originate.

Mesosphere Part of the upper atmosphere outside the stratosphere, which is the transition to the heterosphere and space.

Metabolism The set of biochemical reactions that take place within an organism, organ or cell to allow the organism to keep itself alive, reproduce, develop and respond to its environment.

Metagenomics Study of the genetic content of complex samples containing mixtures of organisms (e.g. soils for the environment, or the stools of humans and animals, etc.). The study of the gene encoding the 16S ribosomal RNA makes it possible to study the entire bacterial world, all bacterial species possessing this gene.

Metamorphic rock A rock that has undergone a mineralogical and structural transformation as a result of a rise in temperature and pressure.

Methylglucose Monosaccharide (glucose) with a methyl group (CH3).

Metric A unit or indicator of measurement used to judge the effectiveness of an activity.

Microaerophilia From the Greek μικρός, small, ἀήρ, air and φιλεῖν, love. Reduced oxygen concentration compared to atmospheric content (21%).

Microbiota All microorganisms (bacteria, yeasts, fungi, viruses) living in a specific environment (called microbiome) in a host (animal or plant). An important example is the set of microorganisms living in the intestine or gut microbiota, formerly called “intestinal flora”.

Microfiltration Process using membranes capable of retaining micrometer particles by direct filtration (see membranes).

Microphage Organism that consumes solid food (particles) of very small size and must be absorbed in large quantities. The particles ingested range from organic debris a few nanometres in size to shellfish and shrimp. This is an important part of the krill that whales feed on.

Microsymbiote From the Greek μικρός, kid. A microorganism living in symbiosis (see below) with a more evolved organism.

Organelle from the cytoplasm of eukaryotic cells (plants, algae, animals). As the site of cellular respiration, mitochondria convert the energy of organic molecules from digestion (glucose) into energy that can be directly used by the cell (ATP) during the “Krebs cycle”. This reaction requires the presence of oxygen and releases CO2, so it plays an essential role in the carbon cycle. Mitochondria originate from a prokaryotic organism (a-proteobacteria) integrated into eukaryotic protocells 2 billion years ago.

Mitosis Refers to the chromosomal events of cell division, the stage of the cell cycle of eukaryotic cells. This is the step of non-sexual/asexual duplication (unlike meiosis) of the chromosomes of the mother cell and their equal distribution in each of the two daughter cells.

Mitosomes Organelle present in some anaerobic or microaerophilic unicellular eukaryotic organisms that do not have mitochondria. They probably lack DNA but have some biosynthesis functions.

Molecular genetics Branch of biology and genetics, which consists of the analysis of gene function at the molecular level.

Molecular typing Laboratory techniques, such as whole genome sequencing, that allow sequences to be classified and compared.

Molluscs Branch of non-segmented animals, sometimes with altered bilateral symmetry. They have a soft body (hence the name mollusk) usually composed of a head, a visceral mass, and a foot. They may have a calcareous shell produced by a mantle covering the visceral mass.

Monomer Basic constituent of complex molecules. A molecule which, by successive sequences with identical or different molecules, gives rise to a polymer structure. Thus amino acids form proteins, oses form complex sugars, nucleotides form nucleic acids.

Moraine Accumulation of rocks of all sizes left by a glacier in its ablation zone.

Mucoprotein Protein containing carbohydrate macromolecules. Present in extracellular matrices.

Mycorrhizae Symbiotic association between the roots of plants and soil fungi. They affect more than 95% of terrestrial plants. They give plants better access to soil nutrients and help them better resist environmental stresses.

Mycorrhizal Relating to mycorrhizae, which are symbiotic associations between the roots of plants and soil fungi. Mycorrhizae affect more than 95% of terrestrial plants. They give plants better access to soil nutrients and help them better resist environmental stresses.


NADH & NADPH Acronyms for the reduced form of two coenzymes of similar structure: Nicotinamide Adenine Dinucleotide Phosphate (NADP) and Nicotinamide Adenine Dinucleotide (NAD). NADP is formed from NAD by binding a phosphate to the 2′ hydroxyl group of the ribose associated with adenine. They each exist in an oxidized form, called NAD(P)+, and a reduced form, called NAD(P)H. NADH and NADPH are said to carry reductive power: used in catalyses carried out by oxidoreductases, they are capable of supplying energy during the transfer of their hydrogen atom, allowing the reduction reactions necessary for cellular functioning.

Nanofiltration Process using membranes capable of retaining, by direct filtration, dissolved particles and species of the order of a few nanometers (see membranes).

Natural frequency Any oscillating system has a natural frequency, towards which the initial oscillations forced from the outside, whatever their frequency, eventually converge. In the case of the simple pendulum, this natural frequency depends only on its length and gravity.

Negative feedback Action in return of a system following the modification of a parameter. If the system response mitigates the phenomenon, this is called negative feedback. If it amplifies it, we will speak in reverse of positive feedback.

Nematodes Round worms, not segmented. Some lead a “free” life (in soil, water, etc.). Others have a parasitic life, within fungal, plant or animal organisms.

Nematomorphs Non-segmented worms, with cylindrical bodies, extremely long and thin (on average from 0.5 to 2.5 mm in diameter and 10 to 70 cm in length). Also called Gordian worms because of the impression they give of making complicated knots with their bodies

Neolithic Revolution An expression used to express the profound change in the habits, techniques and lifestyle of prehistoric mankind from the development of polished stone. In the Near East, this period began around 8000 BC, with the appearance of agriculture, and ended with the appearance of writing.

Nitrogenase Enzyme complex specific to certain prokaryotes that catalyzes the complete sequence of reactions during which the reduction of N2 dinitrogen leads to the formation of NH3 ammonia. This reaction is accompanied by a hydrogenation phenomenon.

Nitrophil (Botany) Refers to a plant that prefers or requires soils or waters rich in nitrates (nitrogen). A nitrophilic plant is also called a nitrophyte.

Normal mode Refers to an oscillating mode at the system’s natural frequency (see natural frequency).

Nucleobase Organic nitrogen compounds present in nucleic acids as nucleotides in which they are bound to a ose, ribose in the case of RNA and deoxyribose in the case of DNA. In genetics, they are often referred to simply as the bases of nucleic acids.

Nucleotide The basic element of a nucleic acid such as DNA or RNA. It is composed of a nucleic base (or nitrogenous base), a ose with five carbon atoms, known as pentose, whose association forms a nucleoside, and finally one to three phosphate groups.

Nucleus (living cell) Membrane-enclosed organelle found in eukaryotic cells. It contains the genome, which consists of DNA and is the main site of DNA synthesis (during replication for cell division) and RNA (for transcription).

Null hypothesis Refers to the basic point of view, the default position concerning a given phenomenon. In general, assumptions opposing the null hypothesis have the burden of proof.


Ockham’s Razor Principle of philosophical reasoning, also known as the principle of simplicity or parsimony.

Optimum climate Maximum temperature within a period

Ordovician radiation or the great Ordovician biodiversification event A period in the history of the Earth during which the biodiversity of ocean life has increased the most. It occurs about 40 to 80 million years after the Cambrian explosion. Its duration is of the order of 25 million years (a relatively short interval on the geological time scale), and is located during the lower and middle part of the Ordovician system, dated between 485 and 460 million years.

Organelles Specialised structure with a specific function within the cell. For example, the nucleus, mitochondria and chloroplasts are organelles.

Oropharyngeal pathways The oropharyngeal pathways include the upper air and digestive tracts, i.e. the oral and nasal cavities.

Osmolarity Number of moles of “osmotically active” particles in solution in 1 litre of solution. Concept related to the osmotic pressure exerted by the particles in solution, and responsible for osmosis. Sucrose is a small osmotically active molecule while starch is a huge osmotically inactive glucose polymer. The accumulation of sucrose in a compartment leads to an increase in osmotic pressure in that compartment, which is not the case for starch.

Osmoregulation All the homeostatic processes involved in regulating the concentration of dissolved salts in the internal fluids and cellular compartments of living beings. Osmoregulation also refers to all the mechanisms of adaptation to the osmotic pressure of the environment surrounding living organisms.

Osmotrophy A feeding method that consists of feeding from dissolved substances. The osmotrophic organisms are nourished by transmembrane exchange, i.e. by diffusion of ions or small molecules through the cytoplasmic membrane. This type of nutrition, which is very common among microorganisms, is also provided by a number of animals, both free and parasitic. It is only possible in liquid environments (aquatic environments, internal fluids of animals or plants) or by the synthesis of enzymes that “digest” their solid environment.

Oxidase Enzyme activating molecular oxygen and catalysing its binding to certain organic substances.

Oxidation-reduction reactions A chemical reaction based on the transfer of electrons between a molecule that oxidizes (loses an electron) and another that is reduced (gains an electron).

Oxidative stress Aggression of cells by free radicals, also called “reactive oxygen species” (see ROS). Also known as oxidative stress. Free radicals are produced permanently in the cell from oxygen, especially in the mitochondria, in the respiratory chain.

Oxidizing agent (In chemistry) Chemical element is oxidizing when it gives one or more electrons during an oxidation-reduction reaction (see also oxidation-reduction and reductant in the glossary).

Ozonation A process for disinfecting water and oxidizing pollutants by injecting a mixture of oxygen and ozone (manufactured in situ) into the water to be treated.


Paleo-environment Environmental reconstructions of ancient times, especially on a geological scale.

Palimpsest Manuscript consisting of a scroll already in use, the inscriptions of which have been removed so that they can be written on again.

Pangea A supercontinent formed in the Carboniferous from the collision of existing continents on the Earth’s surface, which then consolidated all the land masses. In the Triassic, it split into two continents: Laurasia in the north and Gondwana in the south.

Pangenesis Hypothesis inspired by very old ideas and proposed by Darwin to explain heredity, but also reproduction and development. Very small particles (gemmules) would be produced by the different parts of the body and transmitted to the reproductive organs. Darwin himself considered it to be very speculative and provisional.

Parasito-fauna All the parasitic fauna of an organism.

Parasitoid An organism that develops on or in a “host” organism in a two-phase process: it is first biotrophic and then predatory, leading to the final death of the host.

Parhelie A luminous phenomenon due to the reflection of rays from the sun (helios) on a cloud formed by ice crystals.

Partial pressure Refers to the partial pressure of a condensable gas, such as water vapour. In a perfect gas mixture, the pressures due to each component are added. The partial pressure of a gas relative to the total pressure is proportional to the concentration (proportion) of this gas in number of molecules. The saturated vapour pressure is the upper limit of this vapour pressure, increasing with temperature, obtained by a balance between vapour and condensed phase. This balance is achieved in a closed vessel or in clouds and fogs, thanks to the large contact surface of the steam with the droplets or ice crystals.

PCR Abbreviation for Polymerase Chain Reaction or polymerase chain reaction. The English abbreviation has become common parlance. An in vitro targeted replication technique that produces, from a complex and sparse sample, large quantities of a specific, double-stranded DNA fragment of defined length. Each PCR cycle consists of three steps: a denaturation of the DNA by heating to separate the two strands, a hybridization of the primers at the ends of the sequence, an elongation through the action of a DNA polymerase.

PCR Products Products obtained from the PCR reaction (see PCR). These are double-stranded DNA fragments.

Peat bog Wetland, colonized by vegetation, whose particular ecological conditions have allowed the formation of a soil characterized by its very high content of organic matter, little or no decomposition, of plant origin. It is a particular and fragile ecosystem whose characteristics make it, despite methane emissions, a carbon sink, because there is more synthesis of organic matter than degradation.

Peptide A polymer consisting of at least two amino acid residues linked together by peptide bonds. There is a huge variety of different peptides.

Peptidoglycan Composed of the wall of Gram-positive and Gram-negative bacteria. Consists of a carbohydrate part (= polysaccharide) and a peptide part. It maintains the shape of the cells and provides mechanical protection against osmotic pressure.

Peridotitis Magmatic rock, of an ultrabasic nature, which constitutes the major part of the Earth’s upper mantle.

Perihelion The point in the orbit of a planet closest to the Sun.

Permafrost or pergelisol  A geological term that refers to a soil whose temperature remains below 0°C for more than two consecutive years. Represents more than 20% of the Earth’s surface. The permafrost is covered by a layer of soil, called an “active zone”, which thaws in summer and thus allows the development of vegetation. The thawing of permafrost under the effect of global warming has major consequences for the environment: methane release, release of pathogenic microorganisms, etc.

Permanganate index (oxidability to potassium permanganate) Measures a large part of the carbonaceous organic matter present in water by chemical oxidation under heat.

pH Abbreviation for Hydrogen Potential, a measure of the activity of the hydrogen ion (or proton) in a solution. The pH is an indicator of the acidity (pH below 7) or alkalinity (pH above 7) of a solution. A solution of pH 7 is said to be neutral.

Phagocytosis A process by which a cell encompasses and then digests a foreign substance or organism (e. g. bacteria).

Phase During a sinusoidal oscillation as a function of time, of the sin form (2πt/T), where T denotes the period, each instant t corresponds to a phase. The phase difference, or phase shift, between two instants t1 and t2 is equal to 2π(t1-t2)/T. It is equal to π when t1-t2 is half a period, to π/2 when t1-t2 is a quarter period, etc. In a stationary variation as a function of an x-axis, of the sin form (2πx/λ), x/λ replaces t/T, λ being then the wavelength, or distance between two peaks. In a wave that propagates with a velocity c in the direction x, of the sin Form [2π(ct±x)/λ], the ratio λ/c characterizes the period T.

Phenotype All the observable characteristics or traits of an individual (anatomical, physiological, molecular, behavioural aspects, etc.).

Phenotypic A trait or character of a living organism (anatomical, physiological, molecular, behavioural, etc.) that can be analyzed. Example: eye colour is a phenotypic characteristic.

Phenotypic plasticity The ability of an organism to express different phenotypes from a given genotype under environmental conditions.

Phosphatase An enzyme whose function is to remove a phosphate group from a single molecule or biological macromolecule by hydrolysis.

Phosphorylation Addition of a phosphate group to a protein or small molecule, such as glucose or adenine.

Photoinhibition A process by which excess light reduces the rate of photosynthesis in organisms capable of photosynthesis. In case of excess light, the NADPH created by the electron transfer chain of thylacoids cannot be fully utilized by the CO2 binding reactions of the stroma, whose speed is limiting. The accumulation of NADPH creates saturation in the electron chain. The electrons then tend to react with the O2 present in the cell to form reactive oxygen species (ROS), which are very damaging to the cell, especially to the photosynthetic apparatus.

Photon A grain of light, or quantum of energy, necessary for the physical description of electromagnetic radiation.

Photosphere The outer layer of the Sun from which its light is emitted into space. This is the part of the Sun that can be seen from the Earth.

Photosynthesis Bioenergetic process that allows plants, algae and certain bacteria to synthesize organic matter from atmospheric CO2 using sunlight. Solar energy is used to oxidize water and reduce carbon dioxide in order to synthesize organic substances (carbohydrates). The oxidation of water leads to the formation of O2 oxygen found in the atmosphere. Photosynthesis is at the base of autotrophy, it is the result of the integrated functioning of the chloroplast within the cell and the organism.

Phyllosilicates or lamellar silicates: minerals from the group of silicates constructed by stacking tetrahedral layers of silicon and oxygen (SiO4) with added aluminium, magnesium, iron, calcium, potassium, sodium and other elements. Example: Clays are rocks composed mainly of aluminium sheet silicates (Phyllosilicates), more or less hydrated.

Phylogenetic analysis Analysis seeking to establish relationships between living beings. It is mainly based on cladistics, a phylogenetic reconstruction method formalized in 1950 by Willi Hennig.

Phylogenetic distance Represents an index of overall similarity between two taxa. This is the amount of evolution between the sequences and their ancestors. Allows to determine which species have branched first, which are the last species to appear.

Phylogenetic tree Schematic representation of kinship relationships between groups of living beings. Each of the nodes of the tree represents the common ancestor of its descendants; the name it bears is that of the clade formed by the brotherly groups that belong to it, not that of the ancestor, which remains impossible to determine. The tree may or may not be rooted, depending on whether the ancestor common to all leaves has been identified.

Phylogenetically Adverb describing the result of an analysis of the relationships between living beings.

Phylogeny Study of the links between related species. Allows to trace the main stages of the evolution of organisms from a common ancestor and to establish relationships between living beings.

Piedmont (piedmont area) Alluvial plain formed at the foot of a mountainous massif

Placozoa Metazoans (animals) with the simplest organizational plan. These tiny (between 1 and 3 mm) flattened animals have no symmetry, no mouth, no digestive tract, no nervous system, no basal blade. They have no organs and only four different types of somatic cells.

Planetoid A small celestial body with certain characteristics of a planet. The term refers to structures as varied as asteroids, dwarf planets, protoplanets, etc.

Plankton All microorganisms living in aquatic environments (fresh, brackish and salt water) and floating with the currents. Often invisible to the naked eye, their size varies from 0.2 micrometers (0.002 millimeters) to 0.2 millimeters. A distinction is made between vegetable plankton, or phytoplankton, and animal seedlings, or zooplankton (composed of gametes, larvae, animals unable to control the current such as small planktonic crustaceans, siphonophores and jellyfish). Planktonic organisms are defined based on their ecological niche and not on phylogenetic or taxonomic criteria.

Planktonic Bloom Also called planktonic bloom. Relatively rapid proliferation of the concentration of a few algal species, usually phytoplankton, in an aquatic system of fresh, brackish or salt water. It usually results in a coloration of the water (red, brown, yellow-brown or green). These colours are due to the dominant photosynthetic pigments of the algae involved. The phenomenon can be natural or favoured by pollution (nitrates, phosphates).

Plasma (Physics) Fluid medium in which particles bathe. Ionized gases, both from fluorescent tubes and from the ionosphere, carry ions.

Plasmid A DNA molecule usually circular distinct from chromosomal DNA, not essential for the survival of the bacterium, and capable of autonomous replication.

Point mutation Mutation of the genome where only one pair of nitrogenous bases is modified.

Polar (Chemistry) Characterizes a molecule within which the charges are not evenly distributed. Polar molecules attract each other. Water and most ionic compounds are polar.

Polygenic Dependent on many genes. We are talking about polygenic heredity. Diabetes is a polygenic disease.

Polymorphism Linked to variations induced by genetic mutations, polymorphism refers to variations in the nucleotide sequence of a gene’s DNA in a population. It refers to the coexistence of several alleles for a given gene or locus in an animal, plant, fungal or bacterial population.

Polysaccharides Polymers composed of several oses linked together by osidic bonds. Also known as glycans, polyosides, polyholosides or complex carbohydrates. The most common polyosides of the plant kingdom are cellulose and starch, both polymers of glucose.

Post-transcription changes The set of changes that an RNA undergoes after being transcribed. We also talk about the maturation of RNA.

Prebiotics Refers to an organic molecule formed without the intervention of living organisms. For example, Miller’s experiments made it possible to produce such molecules (amino acids, nitrogenous bases, etc.). We’re talking about prebiotic chemistry.

Prehensile Which has the ability to grasp.

Pressure Force acting per unit area. In a fluid, the pressure acting on a surface is independent of its orientation.

Priapulan Shaped like a small penis.

Priapulida or priapulid worms, having the shape of a small penis.

Primary consumer Living beings that need to consume other living beings to produce their own organic matter in order to grow and grow. They are heterotrophic organisms. Herbivores, who only consume terrestrial or aquatic plants, are primary consumers.

Primary Producer Be able to produce organic matter from mineral matter, for example through photosynthesis. It is an autotrophic organism, located at the base of the food chain. It is ingested by a primary consumer, who is himself the potential target of secondary consumers.

Primers Oligonucleotide sequences used in PCR reactions (abbreviated to Polymerase Chain reaction). They define, by limiting it, the sequence to be amplified.

Prokaryote Microorganisms (usually unicellular) with a simple cellular structure, no nucleus, and almost never internal compartmentalization (the only exception being thylakoids in cyanobacteria). Currently, living organisms are considered to consist of three groups: Archaea, Bacteria (Prokaryotes) andEukaryotes.

Proteobacteria An important group of bacteria called Gram-negative bacteria, because they have a cell wall rich in lipopolysaccharides and low in peptidoglycans. The mitochondria of current eukaryotic cells are thought to derive from one of these types of bacteria, alpha-proteobacteria.

Proteolysis Hydrolysis of proteins under the action of proteolytic enzymes.

Proto Prefix, from the Greek prôtos, first, expressing the first rank, the priority. For example, prefix used to characterize the structure that preceded the Sun (proto-solar), the Earth (proto-earth) or even a cell (proto-cell).

Proto-cell Cell prototype, rudimentary cell.

PRPDE Abreviation for the French expression corresponding to “Persons Responsible for Water Production and Distribution”.


Radiation Refers to the process of emission and propagation of energy by particles (radioactivity) or by waves, in particular electromagnetic waves. Synonymous with radiation.

Radiolarite Fine-grained sedimentary rock composed mainly of radiolar siliceous shells, actinopod planktonic protozoan living in warm seas. It is the source of some of the jasper.

Ramet Natural or artificial clone of a plant multiplied by cuttings.

Ranunculin Glucoside produced by plants such as ranunculus (Ranunculaceae). A very unstable molecule, it is hydrolyzed into an irritating lactone: proto-anemonin. The latter is easily destroyed by desiccation, hence the relative safety of dry plants (used for fodder). However, livestock avoid consuming plants containing ranunculin in pastures.

Reactive nitrogen All biologically, photochemically or radiatively active nitrogen compounds in the atmosphere and the terrestrial and aquatic biosphere. These compounds include reduced forms of nitrogen (such as ammonia, NH3) or oxidized (such as nitrogen oxides, NOx; nitric acid, HNO3; nitrous oxide, N2O or nitrate, NO3-), and organic forms (urea, amines, proteins, nucleic acids, etc.).

Receptive (plant biology) Characterizes the condition of a flower or inflorescence that can be fertilized by pollen from the outside.

Red Queen (Genetics) Hypothesis of the evolutionary biology proposed by Leigh Van Valen, which can be summarized as follows: “the permanent evolution of a species is necessary to maintain its ability following the evolution of the species with which it co-evolves”. It takes its name from an episode of Lewis Carroll’s book: Through the Looking-Glass (Alice in Wonderland‘s sequel) in which the main character and the Red Queen embark on a frantic race. Alice then asked: “‘I wonder if all the things move along with us?’ “And the queen replied, “My dear, here we must run as fast as we can, just to stay in place.”

Redox gradients Chemical concentration gradient between oxidized and reduced molecules.

Reducing agent  (Chemistry) A chemical element is said to be reductive when it loses one or more electrons during an oxidation-reduction reaction (see also oxidation-reduction and oxidant in the glossary).

Refining treatment Consists of adding at the end of the traditional water treatment process, one or more additional processes that will refine the quality of the treated water on certain chemical (natural organic matter, micropollutants, etc.) and microbiological (viruses, parasites, etc.) parameters.

Remineralization Consists in restoring sufficient mineralization to the water (to avoid corrosion in particular) by injecting calcium and carbonates.

Replication Process for obtaining two molecules identical to the initial molecule.

Reproductive isolation (Biology) A mechanism that prevents, or severely limits, the hybridization of two species living in the same region, even when they are closely related. There are mechanisms that act as barriers to mating or fertilization and those that, after fertilization, reduce the viability or fertility of fertilized eggs or the hybrid individuals that result from them.

Residence time (Hydrology) The average time that water remains in a given compartment. It depends on the speed of transfers and therefore on the dynamism of the sub-fund in question.

Resistome All antibiotic resistance genes present in microorganisms colonizing the planet Earth (humans, animals, plants and the environment).

Resonance This refers to the phenomenon that leads to a large increase in the amplitude of the oscillation of a system when it is subjected to an external load of frequency close to its natural frequency.

Respiration Refers both to the gaseous exchanges resulting from the inhalation and exhalation of air by living organisms (release of carbon dioxide CO2 and absorption of oxygen O2) and cellular respiration which allows, by degrading glucose through oxygen, to obtain energy.

Response time Delay between an action and its effect.

Retrovirus A family of RNA viruses with high genetic variability. Have an enzyme, reverse transcriptase, which allows the transcription of viral RNA into a particular DNA molecule capable of integrating with the DNA of the host cell.

Reverse osmosis Process using membranes capable of retaining, by osmotic (inverted) phenomenon under high (or low) pressure, all (or almost all) dissolved substances of a water (cf. membranes).

Rhizobium Aerobic soil bacteria that can create symbioses with legumes. They are located in nodules where they will fix and reduce atmospheric nitrogen, which will then be available to the plant. In exchange, plants provide carbonaceous substrates to bacteria.

Rhizome (Botany) Underground stem with leaf and root buds. A rhizome can be horizontal and more or less close to the surface, such as the iris, or much deeper, such as the bindweed.

Ribose An ose (sugar) composed of a chain of five carbon atoms and an aldehyde function. It is a component of RNA used in genetic transcription. It is related to deoxyribose, which is a component of DNA. It is also present in many molecules important in metabolic processes (in particular ATP or adenosine triphosphate).

Ribosome Huge complex composed of RNA and ribosomal proteins, associated with a membrane (at the granular endoplasmic reticulum) or free in the cytoplasm. The function of the ribosome is to translate messenger RNA (mRNA) into proteins. The enzymatic activity of the ribosome being carried by rRNAs, the ribosome is a ribozyme. Common to all cells (prokaryotes and eukaryotes), the structure and composition of the ribosome varies according to the organisms. In prokaryotes and cellular organelles (mitochondria, chloroplast), the ribosome is said to be 70S (S corresponding to the so-called Svedberg sedimentation unit) and consists of the 50S and 30S subunits. The ribosome of eukaryotes is called 80S and consists of two subunits 60S and 40S.

Riparian Refers to an environment corresponding to the banks of rivers; a transition zone where a particular wetland vegetation develops.

River corridor Ecological continuum consisting of a river, its tributaries and their appendices, from the source to the mouth.

River thresholds Fixed or movable structures that only block the minor bed of the river – partially or totally – in contrast to the dam that blocks the minor bed more than the minor bed.

RNA Ribonucleic acid, a macromolecule consisting of a sequence of ribonucleotides (adenine, cytosine, guanine, uracil) linked together by nucleotide bonds and performing many functions within the cell. It is a nucleic acid, just like DNA.

RNA-genome RNA becomes replicable, in the form of a double RNA helix. According to the law of complementarity, a copy of RNA acts as a matrix for the genesis of peptides.

RNA-metabolism RNA molecules have the ability to catalyze reactions between various metabolites, known as ribozymes.

Root cortex From Latin cortex, envelope, bark. The outer zone of the root, which surrounds the central cylinder where the conductive bundles of sap are located.

ROS Abbreviation for “Reactive oxygen species”. Free radicals derived from oxygen, very reactive and very toxic.

RubisCO Abbreviation for ribulose-1,5-bisphosphate carboxylase/oxygenase. It is the key enzyme for fixing CO2 carbon dioxide in plant biomass by initiating the Benson & Calvin cycle, thanks to the solar energy captured by chlorophyll during the photosynthesis process.


Saguaro Cactus (Carnegiea gigantea) of very large size (more than 20 m), originating from the Sonora desert, the largest desert area in North America, located straddling Arizona and northern Mexico.

Saline stress Stress due to soil salinity. This salinity can be natural or induced by agricultural activities such as irrigation (with poor water quality) or the use of certain types of fertilizers.

Sampling with replacement To make a successive draw with the delivery of tokens in an urn containing n tokens is to takea first token, take its value, put it back in the urn, take a second token, take its value, put it back in the urn, etc. until the p-th token. This means choosing p objects among n with repetition (you can choose the same object several times) and in order (the order in which you choose the objects is important). The number of successive draws with tokens among n is: n × n × n × … × n = np.

Scape (Botany) Stem without leaves and supporting a flower or inflorescence.

Scleritis Polycrystalline hard aggregate present in certain organisms, such as soft invertebrates (cnidarians, holothurians), arthropods (where they constitute the exoskeleton composed essentially of chitin).

Sea Ice Ice resulting from the freezing of sea water, and floating on its surface (typically a few decimetres thick).

Sebum Substance produced by small glands present in the skin. Sebum is made up of lipids. It acts as a protective layer on our skin.

Self-replication The act of copying or reproducing oneself.

Sessile fauna Organisms that are most often aquatic, living alone or in colonies and permanently attached directly to the substratum. This is the case, for example, for sponges, corals, hydrozoa, tunicates, bryozoans, etc.

Sexual dimorphism All the morphological differences more or less marked between male and female individuals of the same species.

Sexual selection Process involved in natural selection. Competition between individuals for mating is a factor in the evolution of certain hereditary traits. It is an intraspecific (between individuals of the same species) and gender-dependent competition (it is exercised differently on male and female individuals of the same population).

Shock wave It is a localized sound wave constituting a quasi-discontinuity of pressure. It is obtained in particular by the coherent superposition of waves emitted by an object, for example an aircraft, which occurs when the speed of the object is higher than the speed of the waves, so that the waves emitted at different times are locally reinforced.

Single-strand cuts Breaking a bond between two adjacent nucleotides on a strand of a nucleic acid fragment.

Solar irradiance The flow of energy radiated by the Sun, which decreases with distance from the Sun (expressed in W/m2 perpendicular to the rays).

Solar wind A flow of particles, including protons, electrons and some helium nuclei, from the Sun, whose part directed towards the Earth is diverted by the Earth’s magnetic field.

Solid charge The amount of particulate material that a watercourse can carry over a given section for a given time.

Somatic Qualifies non-reproductive cells, or soma. A somatic mutation, which affects a gene of a somatic cell, disappears with the carrier individual.

Sound pressure It is the maximum amplitude of the local fluctuation of atmospheric pressure in a fluid subjected to any noise. This sound pressure is proportional to the square of the maximum amplitude of the sound vibrations.

Speciation (Chemistry) Defines the degree of oxidation of a chemical species and the different forms of possible bonds.

Speciation (Biology) The evolutionary process that leads to the emergence of new living species that individualize from populations belonging to an original species.

Specific treatment A process that specifically removes a chemical substance present in water (iron, manganese, nitrates, etc.).

Spectrum (Physics) Refers to the distribution of the energy of radiation or a phenomenon that fluctuates according to the frequency of its oscillations or fluctuations…

Spicule (Zoology) Extracellular mineral secretion from various invertebrate groups (e.g. sponges, echinoderms). Spicules can be made of silica, calcite, chitin or protein.

Stationary wave In a medium of limited extent, such as a vibrating string, the waves emitted somewhere are reflected at the ends. The superposition of the emitted wave and the reflected waves leads to the formation of an oscillating shape with fixed points, called nodes, and others where the amplitude is maximum, called bellies. This oscillating form that does not propagate is called a standing wave.

Steam probe Device for drilling ice by steam injection through a pipe.

Stem cell Undifferentiated cell capable of generating specialized cells by cell differentiation. They can be maintained by proliferation in the body or indefinitely in culture. Stem cells are present in all multicellular living beings.

Stipe (Botany) False trunk corresponding to the robust stem of terrestrial plants such as palm trees, banana trees, tree ferns or banana trees. It also corresponds to the false stem of algae, which has no conductive vessels.

Stolons (Botany) A creeping stem starting from the base of the main stem of a plant with leaf and root buds that will become a new plant. This is the case for strawberries.

Stratosphere A region of the Earth’s atmosphere above the troposphere, between altitudes ranging from 12 to 50 km, marked by an increase in temperature with altitude due to the absorption of ultraviolet rays. This temperature profile gives it a layered structure that inhibits vertical movements.

Stress State, situation of an organism suffering from the shortage or excess of a resource (water, nutrients, light, etc.).

Stromatolites Structures often calcareous that develop in shallow water, marine or freshwater environments. They are of both biogenic (bioconstructed by cyanobacterial communities) and sedimentary origin. As a structure, the stromatolite is not alive, only the cyanobacteria that build it are. Stromatolites already existed 3.5 billion years ago as shown by fossils found in Western Australia; they exist on all continents.

Structural Health Monitoring Approach to the design and maintenance of a geotechnical structure based on its instrumentation. Based on non-destructive testing technologies, SHM (Structural Health Monitoring) systems make it possible to anticipate structural damage to prevent accidents. Backed by statistical processing systems, they also make it possible to optimize product life while reducing maintenance costs.

Structural proteins Proteins allow the cell to maintain its organization in space.

Sublimation Direct transformation of the solid phase of a body into the gas phase.

Subsidence A progressive, regular or jerky subsidence of the earth’s crust due to a load that is added either above the crust (water, sediments, volcano, ice cap, mountain range, lithospheric plate, etc.), inside the crust (phase change by metamorphism) or below it (heavy mantellian material).  Subsidence was first known at the surface by the geology of sedimentary basins.

Succulent (Botany) Plants, also known as succulents, that have some parts that are more than normally thickened and fleshy, usually to retain water in arid climates or soil conditions. The word “succulent” comes from the Latin word sucus, meaning juice, or sap. These plants are adapted to survive in arid environments.

Surface tension: Water molecules located at the interface between liquid water and air do not experience the same forces as those inside the volume of water. The interface therefore has a greater potential energy, and the surface tension is the force which tends to minimize the surface energy of the volume of water, and therefore its free surface (in the absence of external forces).

Symbiosis From the Greek σύν, with and βίος, life. An intimate, lasting association between two organisms belonging to different species that results in beneficial effects for both. The organisms involved are referred to as symbionts; the largest can be called host.

Sympatry Means “same homeland”, is said for species or populations of living beings who coexist in the same geographical area, thus promoting frequent exchanges between them.

Symplasm Intracellular continuum formed by plant cells through plasmodules that pass through cell walls. The cell cytoplasms are thus connected and form a single compartment shared by all cells.

Systematician Biologist who studies Systematics, the science of taxon (see this term) classification. It uses a system to count them and, above all, to classify them by organizing them in a certain order, on the basis of logical principles.


Taiga Forest-type plant formation traversed by a vast lake system resulting from fluvioglacial erosion. Strongly linked to the subarctic climate, it is one of the main terrestrial biomes. It is a transition zone between the boreal forest and the Arctic tundra.

Taxon Unit of hierarchical classifications of living beings. Generally the term is used in specific (species) and subspecific (subspecies) ranks.

Taxonomics Relating to taxonomy, or hierarchical classification of living beings.

Taxonomist A person skilled in taxonomy whose purpose is to describe living organisms and group them into entities called taxa in order to identify and name them and finally classify and recognize them via dichotomous determination keys.

Test (Zoology) A mineral envelope based on limestone or silica, which is used to protect certain animals, such as sea urchins.

Thallus (Biology) Refers to the relatively simple vegetative apparatus of primitive plants (algae, lichens, some bryophytes…) compared to that of evolved plants that have a cormus with stem, roots and leaves.

Thermal conductivity Physical quantity characterizing the ability of materials to transfer (or conduct) heat while remaining at rest. Electrical conductivity is its analog for electricity transfer.

Thermohaline circulation Share of ocean circulation due to variations in seawater density caused by both temperature (thermo-) and salinity (-haline) variations.

Thermosphere The lowest region of the heterosphere, where the chemical composition of the atmosphere loses its homogeneity. The temperature increases with altitude, while it decreases in the mesosphere below it. It begins at an altitude of 95 km and ends in the exosphere at an altitude dependent on solar activity.

TMA Trimethylamine

TMAO Trimethylamine oxide

Tornado Vortex structure with a quasi-vertical axis, carrying strong and devastating winds, often accompanied by storms. Its rotation is often caused by shear between horizontal winds of opposite directions.

Total Organic Carbon (TOC) Measures all the organic carbonaceous matter present in water by thermal or photochemical oxidation.

Trade winds Regular winds blowing mainly from the tropics towards the equator and deviated to the west. They converge from tropical high pressures to the equatorial low pressure zone, and are diviated westward by the Coriolis force.

Transcription factor Protein necessary for the initiation or regulation of transcription throughout the kingdom of life. Transcription factors are activators or repressors of the transcriptional complex formed around the RNA polymerase that act by binding to regulatory sequences upstream of the genes to be transcribed.

Transduction Transfer of DNA from one bacterium to another through a bacteriophage virus.

Transformation Incorporation and integration of a fragment of free foreign DNA by a bacterium.

Transit peptide Peptide sequence located at the NH2-terminal end of newly synthesized proteins in the cytoplasm and which allows them to be addressed to the specific organelle (mitochondria, etc…) where they function. We also talk about addressing peptide.

Transposable elements DNA sequence, sometimes called transposon, capable of moving autonomously in a genome, through a mechanism called transposition. These mobile DNA sequences are part of what are known as dispersed repeating sequences and are considered to be powerful drivers of evolution and biodiversity.

Transposition Autonomous movement in a genome of a DNA sequence called transposon, under the action of an enzyme, the transposase.

Transposon DNA sequence capable of moving autonomously in a genome by transposition.

Trichomes (Botany) Thin growths or appendages on the surface of leaves, stems or roots. Examples include hair, glandular hair and especially stinging hair. Trichomes are structures that adapt to environmental conditions and contain repellent substances that play an important role in the plant’s defence reactions against insects or other predators.

Trihalomethanes (THMs) Disinfection by-products of chlorine gas or bleach disinfection, resulting from chemical reactions between the oxidant “chlorine” and dissolved organic matter present (naturally or not) in the water.

Trilobite A class of fossil marine arthropods that existed during the Paleozoic (primary era) from Cambrian to Permian. The last trilobites disappeared during the mass extinction at the end of the Permian, 250 Ma ago.

Triphosphate group (Biochemistry) A compound that both donates and stores energy present in all living organisms. Also used as building materials for nucleic acid synthesis.

Trophic (Biology) Adjective relating to the nutrition of an individual, of a living tissue. Refers to the relationships between species (predator-prey relationships in particular), the cycles and flows of energy and nutrients within ecosystems between producers, consumers and decomposers. The basic level of this network is that of autotrophic primary production, above this level, each link in a food chain corresponds to a trophic level.

Tropics Large circles of the Earth, perpendicular to its axis of rotation, located at latitudes where the Sun’s rays are at their zenith only once a year (at the solstice). Currently located at latitudes of 23.4°N (Tropic of Cancer) and 23.4ºS (Tropic of Capricorn).

Troposphere The lowest region of the Earth’s atmosphere, between the ground and an altitude that varies from 7 to 8 km at the poles to 15 km at the equator, marked by a linear decrease in temperature as a function of altitude (on average 6.5 °C per km).

Trypanosomiasis Infections due to trypanosome parasites.

Tundra Discontinuous plant formation in cold climate regions, including some grasses, mosses and lichens, and even some dwarf trees (birches). The tundra is characterized by a ground perpetually frozen at depth (permafrost). It covers the far north of the Northern Hemisphere, before bare ground and ice, between 55° and 80° latitude.

Turgescence (Biology) A cellular state associated with the elongation of a plant or animal cell whose vacuoles or vesicles are expanding due to water entry into the same cell.

Type 2 diabetes Characterized by chronic hyperglycemia, i.e. the blood glucose level is too high. The insulin that regulates this level of glucose in the blood is still produced but it can no longer act on the organs, we call it insulin resistance.


Ubiquitination Post-translational modification of a substrate protein by covalently binding one or more ubiquitin proteins (8 kDa) to the substrate protein. This biochemical modification allows the degradation of the ubiquitinous protein by an enzymatic complex the proteasome.

Ultrafiltration Process using membranes capable of retaining, by direct filtration, particles of the order of several tens of nanometers (see membranes).

Unicellular organism Living organisms composed of a single cell, unlike multicellular organisms. This name includes various forms of life, including bacteria and archaea, but also many eukaryotes (such as some algae and fungi, etc…).

Utilitarianism A system of morality and ethics that considers the useful as the main principle of action. A morally just policy is one that produces the greatest happiness for members of society. As such, if a project is useful to the greatest number of people, it cannot be called into question by the effects suffered by a minority because they constitute a lesser evil.


Vagus nerve Also called pneumogastric nerve. There are two, each innervating one side of the body. These nerves start from the spinal bulb, the top of the spinal cord, and innervate the heart, lungs and intestine. The information transmitted is unconscious (autonomous).

Variance In a sample of individuals in whom a given trait was measured, the variance is the difference between the mean of the square of the values and the square of the mean of the values. This measure, which is always positive, indicates the dispersion of individuals.

Vegetative period (Botany) The period when a plant grows, develops and reproduces. This period is in contrast to the slower life phases in the form of seed, spore, underground organ, or defoliated tree.

Vegetative reproduction (Botany) Also known as vegetative propagation, vegetative multiplication or vegetative cloning. A method of multiplication that allows plant organisms to multiply without sexual reproduction. It generates new individuals with the same genome and which are therefore clones, we also speak of clonal reproduction.

Vibro-driving The act of introducing a tool into the ground by a simultaneous action of vibration and sinking.

Virome All the genomes of a viral population, found in a living organism or in an environment.

Vitalism Philosophical doctrine that establishes the existence of a vital principle distinct from both the thinking soul and the physico-chemical properties of the body, governing the phenomena of life (André Lalande’s definition).

Viviparity Reproductive mode where seed germination occurs while they are still in the fruit attached to the mother plant.

Vorticity Neologism from the Latin “vortex” (vortex), used to designate the intensity of a vortex structure, whether isolated as a tornado, or mixed with others as a turbulent structure. Vorticity represents the local angular rate of rotation of fluid particles.


Water column Volume of water above the bottom.

Wave Phenomenon of propagation of the oscillations of a physical quantity, characterized by a wavelength, a period and a celeriity. Depending on the physical mechanisms of oscillation, a distinction is made between gravity waves (waves), sound waves, elastic waves, or electromagnetic waves whose visible light represents wavelengths between 0.4 and 0.8 micrometers.

Waxes (Botany) Lipophilic compounds composed of straight-chain aliphatic hydrocarbons with a variety of substituted groups. A distinction is made between epicuticular waxes of various shapes, fixed on the surface of the cuticle and which can be mechanically removed, and intracuticular waxes which are an integral part of the cuticle. They contribute to the high hydrophobicity of leaf surfaces.

Whirl wind A fluid domain with a more or less intense rotation, often visible in water and air.

Woody (woody species) Intuitive plant categorization that evokes trees and shrubs. These are usually perennial plants whose stems and larger roots are reinforced with wood produced from secondary xylem (made up of cellulose and reinforced by lignin).


Xylophagus A living organism whose diet is composed mainly of wood. The so-called wood-eating insects, like termites, cannot digest cellulose and lignin alone. The presence (either in the substrate, or in their digestive tract or in wood) of fungi or symbiotic bacteria is essential for wood assimilation by woodworms. https://bugguide.net/node/view/53531/bgpage



Zooplankton Heterotrophic (sometimes detritivorous) plankton: it feeds on living matter, some species being herbivorous and others carnivorous.  Together with phytoplakton, zooplankton are drifting in oceans, seas, and bodies of fresh water.

Zooxanthellae Unicellular dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, and nudibranchs.