New Zealand Scholarship Biology key terms

The maintenance of a stable internal environment within narrow limits despite external change, achieved through receptors, control centres and effectors operating as negative feedback loops.

A control mechanism in which a detected deviation from a set point triggers a response that reduces the deviation, restoring the variable towards its optimal range.

A control mechanism in which a change is amplified rather than reversed, driving a rapid self-reinforcing process such as childbirth contractions or the action potential upstroke.

The target value around which a homeostatic variable is regulated; deviations above or below it are detected and corrected by feedback responses.

The control of water and solute balance in body fluids, achieved by adjusting water loss and salt uptake so that cell volume and osmotic concentration remain suitable.

A rapid, self-propagating reversal of membrane potential along a neuron or muscle fibre, produced by sequential changes in ion permeability and used for signalling over distance.

The steady voltage difference across a cell membrane at rest, typically negative inside, maintained by selective ion permeability and active ion pumping.

A brief interval after an action potential during which the membrane cannot be re-excited, ensuring signals travel in one direction and limiting firing frequency.

The junction across which a signal passes from one neuron to another cell, usually via release of a chemical neurotransmitter that binds receptors on the target membrane.

A chemical released from a presynaptic terminal that diffuses across a synaptic gap and alters the electrical state of the postsynaptic cell by binding specific receptors.

A signalling molecule secreted by endocrine cells into the bloodstream, which travels to distant target cells and alters their activity by binding specific receptors.

A protein (or RNA) catalyst that speeds a specific biochemical reaction by lowering its activation energy, without being consumed in the reaction.

The specific region of an enzyme where substrate binds and catalysis occurs, whose shape and chemical groups determine substrate specificity.

Loss of a protein's functional three-dimensional shape caused by heat, extreme pH or other agents, usually irreversible and destroying enzyme activity.

Control of enzyme activity by a molecule binding at a site away from the active site, changing the enzyme's shape and so its catalytic rate.

Adenosine triphosphate, the universal energy currency of cells; hydrolysis of its terminal phosphate bond releases energy to drive endergonic cellular processes.

The initial pathway of cellular respiration, occurring in the cytoplasm, in which one glucose molecule is partly oxidised to two pyruvate molecules with net production of ATP and reduced coenzyme.

Energy release from glucose without oxygen, yielding far less ATP than aerobic respiration and producing lactate or ethanol as reduced end products.

The net movement of particles from a region of higher concentration to one of lower concentration, driven by random thermal motion, without requiring energy input.

The net movement of water across a selectively permeable membrane from a region of higher water potential to one of lower water potential.

The relationship between an organism's or structure's exposed surface and its internal volume; as size increases the ratio falls, limiting exchange by diffusion alone.

An inherited feature of a population that increases fitness in a particular environment, arising through natural selection over generations rather than individual adjustment.

The differential survival and reproduction of individuals because of heritable variation, causing allele frequencies in a population to change across generations.

The relative contribution an individual makes to the next generation's gene pool, measured as reproductive success compared with other phenotypes in the population.

The proportion of all copies of a gene in a population that are a particular allele; changes in this value indicate that evolution is occurring.

Random change in allele frequencies between generations due to chance sampling of gametes, with strongest effects in small populations.

The total set of alleles present in a population at a given time, from which the next generation's genotypes are drawn.

The evolutionary formation of new species, typically when populations become reproductively isolated so that gene flow between them stops.

Any barrier preventing members of different populations from interbreeding and producing fertile offspring, whether by geography, timing, behaviour or genetic incompatibility.

The particular combination of alleles an individual carries at one or more loci, which interacts with the environment to produce observable traits.

The observable characteristics of an organism, resulting from the interaction between its genotype and the environment it experiences.

A heritable change in the base sequence of DNA, which is the ultimate source of new alleles and of genetic variation in populations.

The specialised cell division producing haploid gametes, involving one round of DNA replication and two divisions, with crossing over and independent assortment generating genetic variation.

The maximum population size an environment can sustain indefinitely given available resources, beyond which growth slows and the population may decline.

Competition between individuals of different species for a shared limiting resource, which can reduce the population size or distribution of one or both species.

The full set of environmental conditions and resources a species uses, together with its functional role in the community; no two species occupy identical niches indefinitely.

A feeding position in a food chain, such as producer, primary consumer or secondary consumer, defined by the number of energy-transfer steps from the sun.

The proportion of energy at one trophic level that is incorporated into biomass at the next, typically small because most energy is lost as heat and in waste.

In experimental design, the extent to which repeated measurements under the same conditions give consistent results, improved by replication, standardised technique and precise instruments.

The extent to which an investigation actually measures or tests what it claims to, requiring control of confounding variables and appropriate measurement of the dependent variable.

A factor other than the independent variable that is held constant or standardised across treatments so it cannot confound the observed effect on the dependent variable.