New Zealand Scholarship Biology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Emergent property

A characteristic of a higher level of biological organisation that cannot be predicted from the properties of its component parts alone, such as consciousness emerging from neurones or community stability from species interactions.

Cell theory

The principle that all living organisms are made of one or more cells, that the cell is the basic unit of structure and function, and that all cells arise from existing cells by division.

Surface area to volume ratio

The ratio of an object's surface area to its volume, which decreases as size increases; it limits diffusion-only exchange and explains flattened, folded, or branched exchange surfaces such as alveoli and villi.

Negative feedback

A control mechanism in which a detected deviation from a set point triggers an effector response that reverses the deviation, restoring the variable toward its normal range, as in thermoregulation and blood glucose control.

Water potential

The potential energy of water per unit volume relative to pure water at atmospheric pressure, expressed as solute potential plus pressure potential; water moves from higher to lower water potential.

Facilitated diffusion

Passive movement of polar or charged solutes across a membrane down their concentration gradient through specific channel or carrier proteins, requiring no ATP input.

Active transport

Movement of solutes across a membrane against their concentration gradient using energy from ATP hydrolysis, typically via pump proteins such as the sodium-potassium ATPase.

Km

The substrate concentration at which an enzyme works at half its maximum rate; a low Km indicates high affinity between enzyme and substrate, while competitive inhibition raises the apparent Km.

Semiconservative replication

DNA replication in which each parental strand acts as a template for a new complementary strand, so each daughter double helix contains one original and one newly synthesised strand.

Codon

A sequence of three mRNA bases that specifies one amino acid or a stop signal during translation; the code is degenerate, meaning several codons can encode the same amino acid.

Frameshift mutation

An insertion or deletion of a number of bases not divisible by three, which shifts the reading frame and usually alters every subsequent amino acid in the encoded protein.

Test cross

A cross between an individual of unknown genotype and a homozygous recessive individual; a 1:1 ratio of phenotypes among offspring indicates the unknown parent was heterozygous.

Hardy–Weinberg equilibrium

A model in which allele and genotype frequencies (p² + 2pq + q² = 1) remain constant across generations provided there is no selection, mutation, migration, non-random mating, or genetic drift.

Genetic drift

Random change in allele frequencies between generations due to chance sampling of gametes, with strongest effects in small populations; it can fix or eliminate alleles regardless of fitness.

Allopatric speciation

Formation of new species when a geographic barrier separates populations, preventing gene flow so that mutation, drift, and different selection pressures accumulate until reproductive isolation evolves.

Homologous structures

Body parts in different species that share a common evolutionary origin and similar underlying anatomy, even if they now perform different functions, such as the forelimbs of mammals.

Carrying capacity

The maximum population size of a species that an environment can sustain indefinitely given available resources; in the logistic model it is denoted K and growth slows as N approaches K.

Trophic level

A feeding position in a food chain, such as producer, primary consumer, or secondary consumer; energy transfer between levels is inefficient, typically only about ten percent.

Keystone species

A species whose influence on community structure is disproportionately large relative to its abundance, so its removal causes substantial changes in the populations of other species.

Primary succession

Colonisation of a newly formed or sterilised substrate lacking soil, beginning with pioneer species that weather rock and accumulate organic matter, gradually building a soil and a more complex community.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by bacteria such as Rhizobium in legume root nodules or by free-living cyanobacteria, making nitrogen available for assimilation into amino acids.

Bohr effect

The reduction in haemoglobin's affinity for oxygen when carbon dioxide concentration and acidity rise, which promotes oxygen release in actively respiring tissues.

Transpiration pull

Upward movement of water through xylem driven by evaporation from leaves; cohesion between water molecules and adhesion to xylem walls allow the column to be pulled under tension.

Photophosphorylation

Production of ATP from ADP and inorganic phosphate using light energy in the thylakoid membranes during the light-dependent reactions of photosynthesis, coupled to electron transport.

Random error

Unpredictable variation in measurements around the true value caused by uncontrolled factors; it reduces precision but not accuracy on average and is reduced by replication and averaging.

Standard error of the mean

A measure of the precision of a sample mean, calculated as the standard deviation divided by the square root of sample size; larger samples give smaller standard errors.

Restriction enzyme

A bacterial enzyme that cuts DNA at a specific palindromic recognition sequence, producing fragments with sticky or blunt ends used in recombinant DNA technology.

Polymerase chain reaction

An in vitro technique that amplifies a target DNA sequence through repeated cycles of denaturation, primer annealing, and extension by a thermostable DNA polymerase, doubling the target each cycle.

Hybridoma

A cell formed by fusing a B lymphocyte with a myeloma cell, combining antibody production with unlimited division to yield a continuous supply of a single monoclonal antibody.

Meiosis

A reduction division producing four haploid cells from one diploid cell through two successive divisions, with crossing over and independent assortment generating genetic variation in gametes.

Apoptosis

Programmed cell death controlled by the cell's own signalling, producing orderly dismantling without inflammation; it is essential in development and in removing damaged cells.

Three-domain system

A classification dividing cellular life into Bacteria, Archaea, and Eukarya, based primarily on ribosomal RNA sequence comparisons rather than on cell shape or metabolism alone.