Category: Biology Dictionary

Monomer : A molecule that “can undergo polymerization thereby contributing constitutional units to the essential structure of a macromolecule”.

Molecular switch : A molecule that can be reversibly changed between two or more stable states.

Molecular biology : The branch of biology concerning biological activity at the molecular level. The field of molecular biology overlaps with biology and chemistry and in particular with genetics and biochemistry.

Molecule : The smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms.

Mitosis : In eukaryotic cells, the part of the cell cycle during which the division of the nucleus takes place and duplicated chromosomes are separated into two distinct nuclei. Mitosis is generally preceded by the “S” stage of interphase, when the cell’s DNA is replicated, and followed by cytokinesis, when the cytoplasm and cell membrane are divided into two new daughter cells. It is similar to but distinct from binary fission and meiosis.

Mitochondria : (sing.) mitochondrion

Microevolution : The alteration in allele frequencies that occurs over time within a population.

Microbiology : The study of microscopic organisms, such as bacteria, viruses, archaea, fungi and protozoa. This discipline includes fundamental research on the biochemistry, physiology, cell biology, ecology, evolution and clinical aspects of microorganisms, including the host response to these agents.

Metaphase : The third phase of mitosis, in which duplicated genetic material carried in the nucleus of a parent cell is separated into two identical daughter cells. During metaphase, the cell’s chromosomes align themselves in the middle of the cell through a type of cellular “tug of war”.

Messenger RNA : A large family of RNA molecules that convey genetic information from DNA to the ribosome.

Membrane potential : When a nerve or muscle cell is at “rest”, its membrane potential is called the resting membrane potential. In a typical neuron, this is about –70 millivolts (mV). The minus sign indicates that the inside of the cell is negative with respect to the surrounding extracellular fluid.

Meiosis : A specialized type of cell division in which a dividing parent cell proceeds through two consecutive divisions, ultimately producing four genetically unique daughter cells in each of which the chromosome number is half of that in the original parent cell. This process is exclusive to cells of the sex organs in sexually reproducing eukaryotes, where it serves the purpose of generating gametes such as eggs, sperm, or spores.

Medulla : The continuation of the spinal cord within the skull, forming the lowest part of the brainstem and containing control centres for the heart and lungs.

Mast cell : A cell filled with basophil granules, found in numbers in connective tissue and releasing histamine and other substances during inflammatory and allergic reactions.

Marine biology : The study of organisms in the ocean or other marine bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy.

Mammalogy : The branch of biology that studies mammals, a class of vertebrates with characteristics such as homeothermic metabolism, fur, four-chambered hearts, and complex nervous systems.

Macrophage : A kind of swallowing cell, which means it functions by literally swallowing up other particles or smaller cells. Macrophages engulf and digest debris (such as dead cells) and foreign particles through the process of phagocytosis, so macrophages act like scavengers.

Macronutrient : Nutrients needed in large amounts which provide calories or energy. Nutrients are substances needed for growth, metabolism, and for other body functions. There are three basic types of macronutrients: fats, proteins, and carbohydrates.

Macromolecule : A very large molecule, such as a protein, commonly created by polymerization of smaller subunits (monomers). They are typically composed of thousands or more atoms.

Macroevolution : Evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.

M phase : Mitosis and cytokinesis together define the mitotic (M) phase of an animal cell cycle – the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.

Lipoprotein : A biochemical assembly that contains both proteins and lipids, bound to the proteins, which allow fats to move through the water inside and outside cells. The proteins serve to emulsify the lipid molecules.

Lipid : A substance that is insoluble in water and soluble in alcohol, ether, and chloroform. Lipids are an important component of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells. Cholesterol and triglycerides are lipids.

Linked genes : Any set of one or more genes which are sufficiently close together on the same chromosome that they are very unlikely to assort independently and therefore are usually inherited together.

Light-independent reactions : See Calvin cycle.

Ligament : The fibrous connective tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.

Life : The characteristic or collection of characteristics that distinguishes physical entities that undergo biological processes (e.g. living organisms) from that those do not (e.g. non-living, inanimate matter), either because such processes have ceased or because they were not present in the first place. What constitutes “life” is notoriously difficult to define, and there is currently no consensus definition, though some popular criteria are that living things are composed of cells, have a life cycle, undergo metabolism, maintain homeostasis, adapt to environments, respond to stimuli, reproduce, and evolve. Biology is the scientific study of life and of living organisms.

Leukocyte : Also called a white blood cell.

A colourless cell of the immune system which circulates in the blood and body fluids and is involved in counteracting foreign substances and disease. There are several types of leukocytes, all amoeboid cells with a nucleus, including lymphocytes, granulocytes, and monocytes.

Law of Independent Assortment : The principle, originally formulated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together.

Larva : (pl.) larvaeA distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development, such as insects, amphibians, or cnidarians, typically have a larval phase of their life cycle.

Krebs cycle : See citric acid cycle.

Kinase : An enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates.

Tejunum : like gher vertebrates like mammals, birds, and reptiles. It is present between the duodenum and the ileum.

Isotonic solution : Refers to two solutions having the same osmotic pressure across a semipermeable membrane. This state allows for the free movement of water across the membrane without changing the concentration of solutes on either side.

Isomer : A molecule with the same chemical formula as another molecule, but with a different chemical structure. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms.

Ionic bond : A type of chemical bond involving the complete transfer of valence electron(s) between two atoms. Such bonds typically occur between elements characterized as metals and nonmetals, and generate two oppositely charged ions: the metal loses electrons to become a positively charged cation, and the nonmetal accepts those electrons to become a negatively charged anion.

Ion : An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Invertebrate : A group of animals that have no backbone, unlike animals such as reptiles, amphibians, fish, birds, and mammals, which all have a backbone. Among the many extant invertebrate phyla are the Cnidaria, Mollusca, Annelida, Nematoda, and Arthropoda.

Introduced species : Also called an exotic species, foreign species, alien species, non-native species, or non-indigenous species.
Any species living outside its native geographic range, and which has arrived there either by accidental or deliberate human activity. Such human-caused introduction of species to foreign environments is distinguished from biological colonization, by which species spread to new areas through “natural” means (i.e. without the involvement of humans).

Intracellular : Of or occurring inside or within the enclosed interior of a cell. Contrast extracellular.

International System of Units : (French: Système international d’unités; abbreviated SI) The modern standardized form of the metric system of units and measurements, and the system of measurement formally adopted for use in the physical and natural sciences.

Internal fertilization : A type of fertilization which takes place inside the egg-producing individual.

Interferon : A group of signaling proteins made and released by host cells in response to the presence of several pathogens, such as viruses, bacteria, parasites, or tumor cells. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their antiviral defenses.

Integrative biology : The various forms of cross-disciplinary and multitaxon research.

Insulin : An anabolic peptide hormone produced in the pancreas which helps to regulate the metabolism of carbohydrates, fats, and protein by promoting the absorption of glucose from the blood into liver, fat, and skeletal muscle cells. Abnormal insulin activity is the cause of diabetes mellitus.

Infection : The invasion of an organism’s cells or tissues by a disease-causing pathogen, its growth and/or multiplication, and the reaction of the host organism to the infectious agent and the toxins it produces. The variety of biological pathogens capable of causing infections includes certain bacteria, viruses, fungi, protists, parasitic worms, and arthropods.

Immunoglobulin : Any of a class of glycoprotein molecules produced by plasma cells (white blood cells) which act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. They are a major component of the group of immune defense molecules collectively called antibodies.

Immune response : The immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.

Ichthyology : The branch of biology devoted to the study of fish, including bony fishes (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha).

Hydrocarbon : An organic compound consisting entirely of hydrogen and carbon atoms. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls.

Host : Any living organism that harbors another living organism (known as a “guest” or symbiont), whether the guest is parasitic, mutualistic, or commensalist in its interactions with the host. The guest typically receives shelter and nourishment from the host.

Hormone : Any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.

Hodgkin–Huxley model  : A mathematical model that describes how action potentials in neurons are initiated and propagated.

Histology : The study of the microscopic anatomy of cells and tissues of plants and animals.

Heterosis : The improved or increased function of any biological quality in a hybrid offspring.

Herpetology : The branch of zoology that studies reptiles and amphibians.

Hermaphrodite : A sexually reproducing organism with both male and female reproductive organs.

Heredit : The passing on of phenotypic traits from parents to their offspring, either through sexual or asexual reproduction. Offspring cells and organisms are said to inherit the genetic information of their parents.

Habitat : A place for animals, people, and plants and non-living things.

Guanine : One of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA).

Gizzard : An organ found in the digestive tract of some animals, including archosaurs (pterosaurs, crocodiles, alligators, and dinosaurs, including birds), earthworms, some gastropods, some fish, and some crustaceans.

Genotype : Part of the genetic makeup of a cell, and therefore of an organism or individual, which determines one of its characteristics (phenotype).

Genome : The entire set of genetic material contained within the chromosomes of an organism, organelle, or virus.

Genetics : The study of heredity.

Genetic variation : Variations of genomes between members of species, or between groups of species thriving in different parts of the world as a result of genetic mutation. Genetic diversity in a population or species is a result of new gene combinations (e.g. crossing over of chromosomes), genetic mutations, genetic drift, etc.

Genetic drift : An alteration in the frequency of an existing gene variant in a population due to random sampling of organisms.

Genetic code : A set of rules used by living cells to translate information encoded within genetic material (DNA or mRNA sequences) into proteins.

Gene pool : A set of all genes, or genetic information, in any population, usually of a particular species.

Gene : Any segment of DNA that contains the information necessary to produce a functional RNA and/or protein product in a controlled manner. Genes are often considered the fundamental molecular units of heredity. The transmission of genes from a parent cell or organism to its offspring is the basis of the inheritance of phenotypic traits.

G protein : A family of proteins that act as molecular switches inside cells, and are implicated in transmitting signals from a diversity of stimuli outside a cell to its interior.

Founder effect : A loss of genetic variation that takes places when a new population is established by a very small number of individuals from a larger population.

Food chain : The chain of eating and getting nutrition which starts from a small herbivores animal and ends up at a big carnivorous organism.

Flavin adenine dinucleotide (FAD) : A redox cofactor, more specifically a prosthetic group of a protein, involved in different important enzymatic reactions in metabolism.

Flagellum : (pl.) flagella

A lash-like appendage that protrudes from the cell body of certain bacterial and eukaryotic cells.

Fetus : Also spelled foetus.

An animal embryo after eight weeks of development.

Fermentation : A metabolic process that consumes sugar in the absence of oxygen.fitness

Facultative anaerobe : An organism which is capable of producing energy through aerobic respiration and then switching to anaerobic respiration depending on the amounts of oxygen and fermentable material in the environment.

Extranuclear inheritance : A transmission of genes that takes place outside the nucleus.

Extracellular : Of or occurring in the space outside the plasma membrane of a cell. Contrast intracellular.

Extinction : The termination of the existence of a particular kind of organism or a particular taxon, often a species, as a result of the death of the last individual of the taxon (though the capacity to breed and recover may have been lost before this point, rendering the taxon functionally extinct).

External fertilization : A type of fertilization in which a sperm unites with an egg external to the body or bodies of the parent organisms. Contrast internal fertilization.

Exponential growth : It is exhibited when the rate of change of the value of a mathematical function is proportional to the function’s current value, resulting in its value at any time being an exponential function of time.

Exogenous : (of a substance or process) Originating outside of or external to a system (such as an organism, tissue, or cell), as with drugs and many pathogens. Contrast endogenous.

Exocytosis : A form of active transport and bulk transport in which a cell transports molecules out of the cell by expelling them through an energy-dependent process.

Evolutionary biology : The subfield of biology that studies evolution and the evolutionary processes that produced the diversity of life on Earth from a hypothesized single common ancestor. These processes include the descent of species and the origin of new species.

Evolution : The change in the heritable characteristics of populations of biological organisms over successive generations, which may occur by mutation, gene flow, natural selection, or random chance.

Eukaryote : A type of organism consisting of cells which have a nucleus enclosed within a distinct nuclear membrane, unlike prokaryotes. Eukaryotes include all organisms except the bacteria and archaea (i.e. all plants, animals, fungi, and protists are eukaryotes).

Ethology : The scientific study of non-human animal behaviour (i.e. excluding human behaviour) and usually with a focus on behaviour under natural conditions, and viewing behaviour as an evolutionarily adaptive trait.

Estrogen : The primary female sex hormone.

Essential nutrient : A nutrient required for normal physiological function which cannot be synthesized by a particular organism, either at all or in sufficient quantities, and which therefore must be obtained from external sources such as food. In humans, a set of nine amino acids, two fatty acids, thirteen vitamins, and fifteen minerals are considered essential nutrients.

Epiphyte : An organism that grows on the surface of a plant and derives moisture and nutrients from the air, rain, marine environments, or from debris accumulating around it.

Epigenetics : A sub-field of genetics that studies cellular and physiological phenotypic trait variations caused by external or environmental factors which affect how cells express genes, as opposed to those caused by changes in the DNA sequence.

Epidemiology : The study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.

Enzyme : A protein that acts as a biological catalyst by accelerating chemical reactions. Metabolic pathways depend upon enzymes to catalyze their individual steps, and almost all metabolic processes require enzyme catalysis in order to occur at rates fast enough to sustain life.

Environmental biology : The branch of biology concerned with the relations between organisms and their environments.

Entomology : The scientific study of insects.

Endotherm : An organism that is capable of maintaining a consistent, metabolically favorable body temperature, largely by the recycling of heat released by its internal physiological functions, instead of by relying on ambient sources of heat. Endotherms are generally able to maintain a stable body temperature despite changes in the temperature of their environment; colloquially, these organisms are often referred to as “warm-blooded”. Contrast ectotherm.

Endosymbiotic theory : Also called symbiogenesis.

An evolutionary theory regarding the origin of eukaryotic cells from a hypothetical internal symbiosis between prokaryotic organisms, first articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967.

Endosperm : The tissue produced inside the seeds of most of the flowering plants following fertilization.

Endoplasmic reticulum : A type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae.