55 of the Biology glossary’s terms, each with the part of the syllabus where you first meet it.
An electronic device that records measurements from one or more sensors at set intervals over a period of time.
An early model of membrane structure, proposed in 1935, in which a phospholipid bilayer is sandwiched between two continuous layers of protein; falsified by later evidence.
The removal of a carboxyl group from a molecule, releasing carbon dioxide, as in the link reaction and the Krebs cycle.
An organism that breaks down dead organic matter and releases carbon dioxide and mineral ions that can be reused; mainly saprotrophic fungi and bacteria.
Reasoning from a general statement or theory to a specific prediction, such as predicting that a newly discovered organism will be made of cells.
The permanent removal of forest and its conversion to another land use, such as agriculture, plantations or urban development.
The feature of the genetic code that most amino acids are coded by more than one codon.
The number of values in a statistical calculation that are free to vary; for a contingency table it equals (rows − 1) × (columns − 1).
A gene mutation in which one or more nucleotides are removed from the base sequence of DNA.
A change in the three-dimensional conformation of a protein, caused by heat or pH breaking the bonds that hold its shape, so that it loses its function; usually permanent.
One of the multiple short, branched nerve fibres of a neuron that receive signals and carry impulses towards the cell body.
A factor whose effect on a population becomes greater as the population density increases, such as competition, predation and disease; it controls population size by negative feedback.
A factor that affects the same proportion of a population whatever its density, such as a frost, flood, drought or fire.
The number, type, shape and arrangement of the teeth of an animal, which reflect its diet.
The pentose sugar in DNA nucleotides, which has a hydrogen atom instead of an –OH group on carbon 2′.
The variable that is measured in an investigation, because it is expected to change when the independent variable changes.
A reduction in the potential difference across a membrane, making the inside less negative, as when Na⁺ ions diffuse into a neuron.
An animal that ingests dead organic matter (detritus) and digests it internally in its gut, such as an earthworm or woodlouse.
Dead organic matter, including faeces, dead parts of organisms such as leaves and shed skin, and the remains of whole dead organisms.
The ratio of deuterium (heavy hydrogen) to ordinary hydrogen atoms in a sample of water, used to identify where water came from; abbreviated D/H.
A dome-shaped sheet of muscle below the lungs; it contracts and flattens during inspiration, increasing the volume of the thorax.
The phase of the cardiac cycle in which the heart muscle relaxes and the chambers fill with blood.
An identification tool made of a series of steps, each offering a choice between two contrasting descriptions of an observable feature, leading to the name of an organism.
A flowering plant whose seeds have two seed leaves (cotyledons), typically with net-veined leaves and vascular bundles arranged in a ring in the stem.
Natural selection acting in different directions on two populations because they experience different selection pressures, so that they diverge.
The process by which an unspecialised cell becomes specialised for a particular function, by expressing some of its genes and not others.
The breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed, by mechanical action and by enzyme-catalysed hydrolysis.
A genetic cross that follows the inheritance of two different genes at the same time.
A molecule made of two amino acids joined by a peptide bond in a condensation reaction.
Describes a nucleus or cell that has two sets of chromosomes, so that each chromosome has a homologous partner (2n).
Natural selection in which individuals at one extreme of the range of a trait have the highest fitness, so the mean value of the trait in the population shifts in that direction over generations.
The difference between the two ends of a nucleic acid strand, the 5′ end with a phosphate and the 3′ end with a free –OH; strands are built 5′ to 3′.
A sugar made of two monosaccharides joined by a glycosidic bond in a condensation reaction, such as maltose, sucrose or lactose.
Variation in which individuals fall into a small number of distinct categories with no intermediates, such as the four ABO blood groups; also called discontinuous variation.
Natural selection in which individuals at both extremes of the range of a trait have higher fitness than intermediates, so the distribution may split into two groups.
A wrong option in a multiple-choice question, written to be attractive to a candidate who holds a common misconception or makes a common error.
A covalent bond between the sulfur atoms of two cysteine R-groups, which stabilises the tertiary or quaternary structure of a protein.
The process by which species descended from a common ancestor become increasingly different as they adapt to different environments, producing homologous structures with different functions.
Deoxyribonucleic acid: a double-stranded nucleic acid with deoxyribose and the bases A, C, G and T, which is the genetic material of all living organisms.
The identification of species using the base sequence of a short, standardised region of DNA, such as part of the COI gene in animals, compared with a reference database.
A mixture of DNA fragments of known lengths run in one lane of a gel, used as a scale to estimate the sizes of unknown fragments.
An enzyme that joins DNA fragments, such as Okazaki fragments, by forming a phosphodiester bond between the 3′ end of one and the 5′ end of the next.
The addition of methyl groups to cytosine bases in DNA; methylation of a promoter represses transcription of the gene that follows it.
An enzyme that links free nucleotides into a new DNA strand complementary to a template strand, forming covalent phosphodiester bonds between them.
A prokaryotic enzyme that removes RNA primers from new DNA strands and replaces them with DNA nucleotides.
The main replicating enzyme in prokaryotes: it extends primers by adding nucleotides to the 3′ end of the new strand (5′ to 3′) and proofreads it.
An enzyme that builds short RNA primers complementary to the template, giving DNA polymerase III a 3′ end to extend.
Analysis of an individual’s DNA, usually the lengths of several short tandem repeat loci, to give a pattern of fragments that is almost unique to that individual.
The production of exact copies of a DNA molecule, with base sequences identical to the original, using each existing strand as a template.
The highest rank in the classification of organisms; all life is divided into three domains, Bacteria, Archaea and Eukarya.
An allele that has the same effect on the phenotype whether it is present in the homozygous or the heterozygous state.
A circulatory system in which blood passes through the heart twice in each complete circuit, through separate pulmonary (lungs) and systemic (body) circulations, as in mammals.
The shape of a DNA molecule: two antiparallel strands of nucleotides coiled around each other, with the backbones outside and paired bases inside.
A condition caused by trisomy 21, three copies of chromosome 21, usually resulting from non-disjunction during meiosis.
A state in which movement or change continues in opposite directions at equal rates, so that there is no net change; for example water entering and leaving a cell in an isotonic solution.