BCS Written Zoology key terms

A membrane-bound or membrane-less structure inside a eukaryotic cell that performs a specialised job, such as energy release, protein sorting, or waste breakdown, keeping incompatible reactions separated in space and time.

Folds of the inner mitochondrial membrane that greatly increase surface area, holding the electron transport chain and ATP synthase so that oxidative phosphorylation can proceed efficiently within a small cell volume.

The final stage of aerobic respiration in which electrons passed along membrane carriers drive proton pumping, and the returning protons power ATP synthase to phosphorylate ADP into ATP.

A rotary membrane enzyme that lets protons flow down their electrochemical gradient and couples that flow to the joining of ADP and inorganic phosphate, producing most cellular ATP.

One of the alternative versions of a gene occupying the same locus on homologous chromosomes; different alleles may produce distinct phenotypes and are segregated during meiosis.

The fixed physical position of a gene or DNA sequence on a chromosome; alleles of a gene occupy the same locus on each homologue.

The tendency of genes located close together on the same chromosome to be inherited together, because the chance of a crossover separating them during meiosis is low.

The proportion of offspring in which two loci are separated by crossing over, expressed as a percentage; it estimates genetic distance and approaches fifty percent for unlinked loci.

A diagram ordering loci along a chromosome according to recombination frequencies between them, with distances measured in centimorgans rather than physical base pairs.

The condition in which allele and genotype frequencies in a large, randomly mating population remain constant across generations when mutation, migration, selection, and drift are absent.

Random change in allele frequencies between generations due to sampling of finite gametes, strongest in small populations, and capable of fixing alleles regardless of their fitness effects.

The altered allele frequencies that arise when a small group splits from a larger population and establishes a new one, carrying only a sample of the original genetic variation.

A body cavity fully lined by mesoderm-derived epithelium that separates the gut from the body wall and provides space for organ packing, mesenteries, and hydrostatic support.

The division of a bilaterian body into a series of similar repeating segments along the anterior-posterior axis, each with its own muscles, nerves, and often excretory and circulatory structures.

Similarity between structures or genes inherited from a shared ancestor, reflecting common descent rather than analogous function, and forming the primary evidence for phylogenetic grouping.

Similarity of function or appearance between structures that evolved independently in unrelated lineages, such as wings of insects and birds, and therefore misleading for classification.

A derived character shared by two or more taxa and their common ancestor, used in cladistics to define monophyletic groups and to reconstruct branching relationships.

A taxon comprising an ancestor and all of its descendants, forming a complete branch of the tree of life and the only kind of group recognised in strict cladistic classification.

The maintenance of internal conditions such as temperature, pH, and solute concentration within narrow limits despite external fluctuation, achieved through negative feedback control loops.

A control mechanism in which the output of a system reduces the original stimulus, damping deviation and stabilising physiological variables around a set point.

A chemical messenger secreted by endocrine cells into the blood or haemolymph that acts on distant target tissues bearing specific receptors, often at very low concentrations.

The release of hormones by specialised neurons, such as hypothalamic cells, into the circulation or portal system, linking nervous detection with endocrine response.

The active control of water and dissolved solute balance across body surfaces and excretory organs, keeping body fluids within tolerable osmotic limits in fresh, marine, or terrestrial habitats.

The embryonic stage in which the blastula is reorganised into three germ layers, ectoderm, mesoderm, and endoderm, establishing the body axes and the gut opening.

One of the three primary cell layers of an embryo, each giving rise to a defined set of adult tissues such as skin and nerves, muscle and bone, or gut lining.

The process by which one group of embryonic cells signals neighbouring cells to change their developmental fate, a key mechanism in patterning the embryo.

The maximum population size of a species that a habitat can sustain indefinitely with the resources available, at which births and deaths balance and growth ceases.

The full set of environmental conditions and resources a species uses, together with its functional role in a community, including its tolerances, diet, and interactions.

A species whose influence on community structure is disproportionately large relative to its abundance, so that its removal triggers major changes in many other species.

A region with exceptionally high endemism and species richness that has already lost a large proportion of its original habitat, and is therefore prioritised for conservation action.

The condition in which a species occurs naturally in one restricted area and nowhere else, making it especially vulnerable to local habitat loss and extinction.

The independent evolution of similar traits in lineages exposed to comparable selection pressures, producing analogous rather than homologous structures and complicating phylogenetic inference.

The number of offspring produced by an individual or population, usually measured as eggs or young per female per breeding season, and a key input to life-table analysis.

The host in which a parasite reaches sexual maturity and reproduces, as distinct from intermediate hosts that harbour larval or asexual stages.

An organism in which a parasite passes one or more larval or asexual stages before reaching its definitive host, often essential for completing the life cycle.

A living organism, usually an arthropod, that transmits a pathogen from one host to another, either mechanically on its body or biologically after internal multiplication.

Any substance that a specific immune receptor recognises and that can provoke an adaptive immune response, typically a protein or polysaccharide on a pathogen surface.

A Y-shaped immunoglobulin produced by plasma cells that binds a specific antigen and helps neutralise or eliminate the pathogen carrying it.

Indirect protection of susceptible individuals that arises when a sufficiently large fraction of a population is immune, reducing pathogen transmission and interrupting outbreaks.