Foundations

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

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

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

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

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

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

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

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

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

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

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

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

Eukaryotic protein abundance depends on synthesis and degradation.

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

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.

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

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

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

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

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

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

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

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

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

Coordinated electrical activation drives atrial and ventricular contractions.

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

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

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

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

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