STPM Biology 964 flashcards

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

Water potential

The tendency of water to move from one region to another, measured in kPa. Pure water at atmospheric pressure is 0 kPa; dissolved solutes lower it, making values more negative.

Glycosidic bond

A covalent bond formed between two monosaccharides by a condensation reaction with the loss of one water molecule, as in maltose, sucrose and the chains of starch and cellulose.

Competitive inhibition

An inhibitor with a shape similar to the substrate binds the enzyme active site, so increased substrate concentration can overcome it. Vmax is unchanged but apparent Km rises.

Resolution

The smallest distance at which two points can be distinguished as separate. Electron microscopes resolve better than light microscopes because electrons have a shorter wavelength than visible light.

Semi-conservative replication

Each parental DNA strand acts as a template for a new strand, so every daughter molecule has one original and one new strand. DNA polymerase adds nucleotides in the 5′ to 3′ direction.

Frameshift mutation

The insertion or deletion of a number of bases not divisible by three, which shifts the reading frame and alters every subsequent codon, usually producing a non-functional protein.

Test cross

A cross between an individual of unknown genotype showing the dominant phenotype and a homozygous recessive individual; offspring ratios reveal whether the unknown was homozygous or heterozygous.

Lac operon

A gene cluster in E. coli controlled by a repressor. Lactose inactivates the repressor, allowing RNA polymerase to transcribe the genes for lactose metabolism.

Bohr shift

The movement of the oxygen dissociation curve to the right when carbon dioxide concentration rises or pH falls, reducing haemoglobin's affinity for oxygen and aiding oxygen release to respiring tissues.

Ultrafiltration

Filtration of blood in the glomerulus under high hydrostatic pressure, forcing water, glucose, amino acids, salts and urea into the Bowman's capsule while proteins and cells are retained.

Refractory period

The brief interval after an action potential during which the neurone cannot be stimulated again, ensuring impulses travel in one direction and limiting impulse frequency.

Cardiac output

The volume of blood pumped by one ventricle per minute, equal to heart rate multiplied by stroke volume; typical resting value in an adult is about 5 litres per minute.

Corpus luteum

The glandular body formed from the ruptured follicle after ovulation. It secretes progesterone and oestrogen, maintaining the endometrium; it degenerates if fertilisation does not occur.

Acrosome reaction

Release of hydrolytic enzymes from the acrosome of the sperm head when it contacts the zona pellucida, digesting a path that allows the sperm to reach and fuse with the egg membrane.

Apical dominance

Inhibition of lateral bud growth by auxin produced at the shoot apex; removing the apex reduces auxin concentration and allows lateral branches to grow.

Carrying capacity

The maximum population size of a species that an environment can sustain indefinitely, denoted K in the logistic growth model, where growth rate becomes zero.

Mark-recapture estimate

Population size estimated as (marked in first sample × total in second sample) divided by marked recaptures. It assumes random mixing, no migration, no mortality and no mark loss.

Eutrophication

Nutrient enrichment of water, often by nitrates and phosphates, causing algal blooms; decomposition of dead algae depletes oxygen, killing fish and other aerobic organisms.

Ecological succession

The gradual, directional change in species composition of a community over time, from pioneer species on bare substrate to a stable climax community.

Hardy-Weinberg principle

Allele and genotype frequencies in a population remain constant across generations if there is no mutation, migration, selection or genetic drift and mating is random.

Homologous structures

Structures with the same basic anatomy and embryonic origin but different functions, such as the forelimbs of vertebrates, providing evidence of common ancestry.

Allopatric speciation

Formation of new species when populations are separated by a geographic barrier, accumulate genetic differences and later become reproductively isolated.

Binomial nomenclature

The two-part scientific naming system in which each species has a capitalised genus name and a lower-case species epithet, both italicised or underlined.

Serial dilution

A stepwise dilution in which each step reduces concentration by a constant factor, used to prepare a range of concentrations for a standard curve or enzyme assay.

Negative control

A treatment that lacks the key factor being tested, used to show that any observed effect is caused by the independent variable and not by other components of the procedure.

Benedict's test

A test for reducing sugars: the blue solution is heated with the sample and turns green, yellow or brick-red as copper(II) ions are reduced to copper(I) oxide.

Precision

The closeness of repeated measurements to one another, reflecting random error; it is improved by careful technique and averaging replicates, but does not guarantee accuracy.

Null hypothesis

A statement that there is no significant difference or relationship between variables; statistical tests determine whether the data justify rejecting it at a chosen significance level.

Dependent variable

The variable that is measured in an experiment and expected to change in response to the independent variable; it must be defined operationally with a stated method and unit.

Chi-squared test

A statistical test comparing observed frequencies with expected frequencies, calculated as the sum of (O − E)²/E, used for categorical data with degrees of freedom equal to classes minus one.

Validity

The extent to which an experiment measures what it claims to measure, achieved by appropriate controls and by ensuring only the independent variable affects the dependent variable.

Reliability

The consistency of results when an investigation is repeated; it is increased by taking multiple readings, using sufficient sample size and calculating means.