A perturbation restricted to a chosen tissue or lineage. Driver specificity and indirect effects through neighbouring tissues must be validated.

A genetic test asking whether two mutant genomes together restore a function. Failure of recessive alleles to complement can support a shared affected genetic locus, subject to exceptions such as interacting loci and deletions.

A fossil deposit preserving early land-plant anatomy, including reproductive structures interpreted as gametophytes and sporophytes.^[ref]

Preserved evidence of biological activity, such as a track or burrow. It can reveal movement or feeding even without body remains, but usually does not uniquely identify the producer.

A fossil with a combination of ancestral and derived characters informative about an evolutionary transition. It need not be the direct ancestor of a named living group.

single-molecule Förster resonance energy transfer records energy-transfer signals from individual donor–acceptor pairs. State occupancies and dwell times can constrain structural dynamics, provided dye photophysics, labeling geometry and time resolution are controlled.

A parallel string-rewriting system: at each generation, every symbol is replaced simultaneously by its assigned word. Symbols can also encode drawing commands such as moving forward or turning. Large recursively defined drawings can be queried without expanding the whole word by precomputing the length, displacement, and rotation of each expanded block.

Stripe-like thickness variations caused by nonuniform milling through regions with different sputtering response.

A fluorescent readout engineered to report a molecular state or lineage history. Signal onset can lag the biological event because of expression and fluorophore maturation.

A fluorescent protein whose emission can be changed by controlled illumination. Conversion of one imaged progenitor enables independent spatial lineage tracing, limited by dilution, turnover and inadvertent conversion of neighbouring cells.

Microfluidics controls and studies small fluid volumes in confined channels. In cellular assays it can impose reproducible flow and chemical fields, but channel geometry, wall interactions and flow-induced stresses can themselves alter behaviour.

Computational fluid dynamics uses numerical methods to solve models of fluid flow. A calculation specifies governing balance laws, constitutive equations, initial data and boundary conditions, then represents the fields on a finite set of degrees of freedom. The computed velocity, pressure and other fields approximate the selected model rather than directly reproducing every molecular interaction.

A useful pipe-flow calculation checks the incoming and outgoing mass flow rates, compares the pressure drop with an appropriate analytic regime and refines the spatial and time resolution. Small changes under refinement test numerical resolution; agreement with an independent experiment tests physical modeling. These checks answer different questions. Approximations for turbulence, geometry and wall behavior can dominate the uncertainty even when the discretized equations are solved accurately. In reconstructing flow around a fossil, uncertain anatomy and imposed flow conditions remain part of the scientific interpretation.

Four times a flow passage's cross-sectional area divided by its wetted perimeter. It provides a characteristic length for many internal-flow correlations, with applicability depending on geometry and flow regime.

A pump supplies mechanical energy to a fluid so that it can flow against resistance or gain elevation. For a steady incompressible stream, a rise in pressure $\Delta p$ at similar inlet and outlet heights and speeds represents useful fluid power $P=Q\Delta p$, where $Q$ is the volumetric flow rate. Differences in kinetic energy and gravitational potential energy must be included when those conditions do not hold.

A real installation chooses its flow through the interaction between the pump's pressure-flow response and the connected passages. More resistance generally shifts the pump operating point, so the nameplate or rotational speed alone does not determine mass flow rate. Measuring inlet/outlet pressures, flow and supplied mechanical power separates useful fluid output from dissipative losses. A centrifugal pump uses a rotating impeller; a displacement device instead moves a defined volume during a cycle, with leakage and compressibility affecting the actual delivery.

A liquid in steady rigid rotation has a free surface $z-z_0={\Omega }^2{r}^2/(2g)$. Comparing with a paraboloid $z-z_0=r^2/(4f)$ gives $f=g/(2{\Omega }^2)$. The result follows from hydrostatic equilibrium in the rotating frame and is independent of density.

Relative tangential motion between material and its solid boundary. In rheometry it can produce an apparent shear rate greater than the actual bulk rate and distort inferred viscosity or modulus.

For a planar polymer with $N$ segments of length $\ell$, approximate its coil free energy by $F/(k_{B}T)\sim R^2/(N{\ell }^2)+v_2{N}^2/R^2$. The first term is the entropic stretching cost of an ideal chain, while $v_2$ is an excluded-area coefficient. Minimizing gives $R^4\sim v_2{\ell }^2{N}^3$ and size exponent $\nu =3/4$. For $v_2\sim {\ell }^2$, this becomes $R\sim \ell N^{3/4}$. A parameter multiplying $N^2/R^2$ must carry area units; using an unsquared segment length there would be dimensionally inconsistent.