Foundations

Absorbance can be proportional to path length and absorbing-species concentration.

Characteristic structural groups organize organic compounds and recurring reactivity.

The same molecular formula can describe different connectivity or spatial arrangements.

Addition, elimination, substitution and rearrangement classify net structural changes.

Curved arrows record proposed changes in electron-pair bonding.

Carbohydrates, lipids, proteins and nucleic acids organize much of cell chemistry.

Sequence, folding and assembly provide different levels of protein description.

A simple enzyme–substrate mechanism predicts saturating initial rates.

Coupled reaction pathways connect favourable chemistry with cellular work.

Mutation changes DNA sequence and can introduce inherited variation.

Movement contributes to gene flow when genetic material enters a population's reproduction.

Allele segregation and phenotype dominance are different questions.

DNA-binding regulators and cellular signals affect transcription.

DNA-associated marks can affect expression without changing DNA sequence.

Species boundaries depend on the organisms and the question being investigated.

Reduced reproductive exchange can permit populations to diverge into lineages.

Evolutionary trees are hypotheses inferred from comparative evidence.

Shared ancestry and independent similarity are different explanations.

Bacteria, archaea and eukaryotes differ in important cellular organization.

Vascular plants move water and organic solutes through different transport tissues.

Diffusion across exchange surfaces and bulk transport serve different roles.

Membrane electrical changes and synapses connect neural cells.

Animal hormones influence cells that possess appropriate response machinery.

Kidney tubules modify filtered fluid through selective transport.

Simple growth equations expose assumptions about density dependence.

Interaction categories describe effects on participating populations.

Production is a flow over time, whereas biomass is a standing amount.

Repeated samples can estimate a population under explicit sampling assumptions.

Barrier and recognition mechanisms cooperate with antigen-specific responses.

The placement of meiosis and fertilization differs among life cycles.