GLOBAL KNOWLEDGE ARK

Reference library

Foundations

Explore concepts, laws, equations and methods, with clear explanations of their use and sources. Choose an area of study or find a specific entry.

More filters

Reference entries

Showing 751–780 of 1709 reference entries

Earth & cosmosGravitational cloud collapse and protostars

Cold dense regions of molecular clouds can contract gravitationally when support is insufficient.

ModelEarth & cosmosPlanetary material classes and interior inference

Terrestrial planets are dominated by rock and metal; giant planets contain larger proportions of light gases and volatile-rich material.

ModelEarth & cosmosComparative planetary atmospheres and energy balance

Atmospheric mass, composition and opacity affect a planet's surface conditions.

ModelEarth & cosmosAsteroid and comet material evidence

Asteroids include bodies with differing rocky, carbon-rich and metallic material signatures; meteorites and spacecraft observations test interpretations of their histories.

ModelEarth & cosmosGas phases of the interstellar medium

The interstellar medium contains ionized, atomic and molecular gas alongside dust.

DefinitionEarth & cosmosGalactic components and stellar populations

The Milky Way contains disk, bulge and halo components with differing distributions, motions and stellar populations.

ModelEarth & cosmosGalaxy morphology and physical populations

Spiral galaxies commonly contain a disk, bulge and spiral patterns with gas and ongoing star formation.

DefinitionEarth & cosmosGravitational lens geometry and image multiplicity

A thin gravitational lens relates a source's unlensed angular position to observed image positions through a mass-dependent deflection.

ModelEarth & cosmosCosmological redshift and expansion

In an FLRW expansion model, light emitted and observed by comoving observers is stretched by the ratio of their scale factors.

ModelEarth & cosmosEarly-universe nuclei and photon decoupling

The hot expanding universe passed through changing particle and radiation conditions.

ModelEarth & cosmosCosmic structure growth and dark-matter modelling

In the standard cosmological model, small density variations grow gravitationally and dark-matter structures help concentrate baryonic matter after photon coupling becomes less effective.

ModelBiology · Physics · ChemistryIon equilibrium potentials and membrane current balance

An ion's equilibrium potential balances its chemical and electrical driving terms.

ModelBiologyUbiquitin, proteasomes and lysosomal turnover

Eukaryotic protein abundance depends on synthesis and degradation.

ModelBiologyCaspases and mitochondrial/death-receptor apoptosis

In representative animal apoptosis pathways, activated initiator caspases promote an execution cascade that cleaves cellular targets.

ModelBiologyBase excision versus nucleotide excision repair

Base-excision repair begins when a glycosylase removes a recognized damaged base, leaving a site that is processed and restored by DNA synthesis and ligation.

ModelBiologyNonhomologous DNA end joining

End joining can restore continuity of a double-strand-broken DNA molecule without using a long homologous donor template.

ModelBiologySensory transduction and graded receptor potentials

Sensory receptors convert appropriate physical or chemical stimuli into changes in cellular electrical signalling.

ModelBiologyExperimental units and biological inference

The experimental unit is the entity independently assigned to a treatment in a specified design.

MethodBiologyNephron transport and the concentrating gradient

In the mammalian nephron model, selective tubular transport modifies filtered fluid.

ModelBiologyVasopressin and renal sodium-water control

Vasopressin released from the posterior pituitary can increase collecting-duct water permeability through aquaporin insertion.

ModelBiologyEndocrine axes and negative feedback

In the vertebrate thyroid-axis example, hypothalamic signals stimulate pituitary hormone release, which stimulates the thyroid.

ModelBiologyHormonal coordination of glucose storage and release

In the mammalian model, pancreatic insulin and glucagon coordinate nutrient use and storage with blood-glucose availability.

ModelBiologyRespiratory partial pressures and oxygen transport

Gases diffuse across respiratory surfaces down their own partial-pressure gradients.

ModelBiologyVentilation, pressure and alveolar surface tension

Mammalian ventilation moves air when respiratory-muscle action changes thoracic volume and pressure.

ModelBiologyMammalian cardiac conduction and blood flow

Coordinated electrical activation drives atrial and ventricular contractions.

ModelBiologyActin–myosin cycling and contraction control

Myosin interaction with actin converts ATP-dependent molecular cycling into force.

ModelBiologyNeural and hormonal coordination of digestion

In the vertebrate digestive example, signals coordinate secretion, motility and delivery of material between compartments.

ModelBiologyAntigen presentation and lymphocyte specificity

In jawed-vertebrate adaptive immunity, B-cell receptors recognize suitable antigen structures, while T-cell receptors recognize antigen presented with appropriate MHC molecules.

ModelBiologyOperons and integrated bacterial transcription control

In the E. coli lac example, a repressor and a cAMP-linked activator integrate lactose-related and glucose-related conditions to regulate transcription.

ModelBiologyPost-transcriptional RNA stability and silencing

RNA-binding proteins, RNA processing and degradation influence how long a transcript remains available for translation.

Model
MethodSource checked

Experimental units and biological inference

Biology

The experimental unit is the entity independently assigned to a treatment in a specified design.

Key knowledge

The experimental unit is the entity independently assigned to a treatment in a specified design. Multiple observations from one treated unit need an appropriate within-unit analysis and do not automatically increase the number of independent treatment replicates. Defining units, randomization and masking helps relate biological variability and measurement variability to the intended inference.

Conditions and scope

  • The unit can differ with the intervention: an animal, culture, cage or independently treated cell may be relevant.
  • Use the actual dependence/design structure; a label such as biological replicate alone does not prove independence.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. UK National Centre for the Replacement, Refinement and Reduction of Animals in Research2 sources
    1. Experimental Design Assistant, Experimental UnitUK National Centre for the Replacement, Refinement and Reduction of Animals in ResearchTextbook chaptereda.nc3rs.org.ukRead source
    2. Key Elements of a Well-Designed Experiment, randomization and blindingUK National Centre for the Replacement, Refinement and Reduction of Animals in ResearchTextbook chapternc3rs.org.ukRead source

Evidence and review

Read entity-assignment examples and randomization/masking guidance; source examples are in vivo and the more general unit definition must be applied to the actual design, not copied as an animal-only requirement.

2026-10-10 · Independent AI editorial review: All 115 actual compact claims, hypotheses, equation/variable/unit tables and 251 origin semantic links independently read. All exact author source-binding rows and disclosed extents assessed; targeted original bodies or specifically identified indexed primary passages rechecked below. All retained biology compact records read for combined breadth. Independent AI editorial content and practical common-core inventory review; no human specialist, degree/laboratory proficiency, whole-textbook certification or experimental replication. Receipt: biology-independent-content-inventory-review.1.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–9 of 9 relationships

Scientific relationships · 9 / 9

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 2

    Linked statements

    • The experimental unit is the entity independently assigned to a treatment in a specified design. Multiple observations from one treated unit need an appropriate within-unit analysis and do not automatically increase the number of independent treatment replicates. Defining units, randomization and masking helps relate biological variability and measurement variability to the intended inference.

    Controls and independent treatment units serve different purposes.

  2. Related to
    Relationship sources · 2

    Linked statements

    • The experimental unit is the entity independently assigned to a treatment in a specified design. Multiple observations from one treated unit need an appropriate within-unit analysis and do not automatically increase the number of independent treatment replicates. Defining units, randomization and masking helps relate biological variability and measurement variability to the intended inference.

    Dependence affects variance of an estimated response.

  3. Related to
    Relationship sources · 2

    Linked statements

    • The experimental unit is the entity independently assigned to a treatment in a specified design. Multiple observations from one treated unit need an appropriate within-unit analysis and do not automatically increase the number of independent treatment replicates. Defining units, randomization and masking helps relate biological variability and measurement variability to the intended inference.

    Analysis must check design/model assumptions.

  4. Related to
    Relationship sources · 3

    Linked statements

    • Epistasis means that the phenotypic effect associated with a locus depends on another locus, including masking effects in a biochemical pathway. Pleiotropy means that one gene can affect multiple traits. Penetrance describes the proportion or probability of the specified phenotype among carriers of a specified genotype in a defined context; expressivity describes the nature or degree of that phenotype. Genetic background, environment and age can influence genotype–phenotype relationships.

    Context and observation design affect phenotype inference.

  5. Related to
    Relationship sources · 2

    Linked statements

    • A cohort life table follows individuals born together. Its survival fraction l_x is the fraction reaching age x; conditional interval survival is p_x=l_{x+1}/l_x where l_x>0. With daughters per surviving female m_x at specified birth-pulse ages, R₀=Σ_{x≥1}l_xm_x is expected lifetime daughters per newborn female. A cross-sectional age count is not automatically a cohort survival curve.

    Individuals and birth cohorts must be identified as the actual units.

  6. Related to
    Relationship sources · 2

    Linked statements

    • A genetic perturbation tests a causal prediction when the intended change and relevant phenotype are measured against appropriate controls. Agreement across independent perturbations or clones and restoration by a suitable resistant allele can strengthen gene-function attribution. DNA alteration, transcript level, protein detection and phenotype are different readouts; none automatically certifies all the others.

    Independent clones and repeated readouts are different experimental units.

  7. Related to
    Relationship sources · 1

    Linked statements

    • Guide-linked single-cell perturbation screens measure transcriptomic responses in surviving sampled cells. Those responses can identify candidate regulatory dependencies, but transcript abundance is not direct protein occupancy, enzyme activity or the whole-organism phenotype.

    Cells sharing a treatment/sample are nested observations, not automatically independent treatment replicates.

  8. Related to
    Relationship sources · 1

    Linked statements

    • Cells sampled from one animal or culture share experimental history. Squair and colleagues show that treating such cells as independent biological replicates can inflate differential-expression discoveries; sample-level aggregation or appropriate hierarchical models preserve the treatment unit.

    The biological treatment unit remains distinct from the measured single cell.

  9. Related to
    Relationship sources · 2

    Linked statements

    • Spatial transcriptomics retains coordinates but its observable depends on platform: capture-based spots can mix cells, while imaging-based panels sample selected transcripts. Nearby observations share tissue context and cannot automatically be counted as independent perturbation replicates.

    Spatially adjacent cells may be correlated within the same biological specimen.

Entry detailsPermanent link to this entry ↗
Record identity
uni-bio-experimental-unit
Revision
core.1
Structured reference record
University core expansion