A chiral molecule fails the whole-molecule mirror-superposition test defining chirality.

Online text: www.vernier.com/files/misc/nsta-2014/vernier_2014_nsta_rm_1_chem_lq.pdf

LabQuest Experiment 6 from Chemistry with Vernier, issued by Vernier Software & Technology as identified in its printed footer. No individual author or editor and no document date verified; the URL does not establish a publication year.

Cited passages: Experiment 6, printed p. 6–4, Extension steps 1–2: pressure versus reciprocal total volume and linear fitting; Experiment 6, printed pp. 6–1 to 6–3: Figure 1, preparation 1b–c, procedure 3–6, blank data table, and Processing the Data 7–9.

Online text: openstax.org/books/chemistry-2e/pages/3-3-molarity

Section of Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson. These are whole-book authors, with no separately credited chapter author. The book citation gives publication on 14 February 2019; no section revision date is inferred.

Cited passages: Chemistry 2e, §3.3: Solutions, definitions and solvent/solute conventions; Chemistry 2e, §3.3: Example 3.16, mass-to-moles conversion and total solution volume; Chemistry 2e, §3.3: Dilution of Solutions, conserved moles and dilution equation.

Online text: openstax.org/books/chemistry-2e/pages/1-2-phases-and-classification-of-matter

Section of Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson. These are whole-book authors, with no separately credited chapter author. The book citation gives publication on 14 February 2019; no section revision date is inferred.

Cited passages: Chemistry 2e, §1.2: Classification of Matter, pure substances, mixtures, variable proportions, homogeneous and heterogeneous examples.

Online text: openstax.org/books/chemistry-2e/pages/15-1-precipitation-and-dissolution

Section of Chemistry 2e by Paul Flowers and others. The 2019 date and author credits belong to the book; no separate section date or author is established.

Cited passages: §15.1, The Solubility Product: saturated solutions and silver chloride dissolution; Predicting Precipitation: comparison of the reaction quotient with the solubility product and mixing volumes.

Rubidium is the chemical element with atomic number 37 and symbol $\mathrm{Rb}$. It is a alkali metal. It commonly forms a singly charged positive ion. Its optical transitions are useful in atomic spectroscopy and laser-cooling experiments, while rubidium-87 adds an experimentally useful isotope-specific nuclear-spin structure.^[ref]

Nicotinamide adenine dinucleotide is a coenzyme with two nucleotide units, one containing nicotinamide and the other adenine. Its oxidized and reduced forms are NAD+ and NADH.

The nicotinamide ring accepts or donates a hydride equivalent in many enzyme-catalysed oxidation-reduction reactions. For example, oxidation of malate to oxaloacetate reduces NAD+ to NADH, transferring reducing power between metabolic processes.

An allene contains the unit $\mathrm{C}=\mathrm{C}=\mathrm{C}$ with two consecutive carbon–carbon covalent bonds of order two. Suitable terminal substituents give axial chirality.

Potassium hydroxide is $\mathrm{KOH}$, an ionic solid that provides potassium and hydroxide ions on dissolution. The hydroxide acts as a strong base in water.

Its stoichiometry is one hydroxide per potassium ion. Comparing it with potassium carbonate shows that sharing a cation does not give two salts the same acid-base behavior.

Silicon dioxide is $\mathrm{Si}{\mathrm{O}}_2$, a network-forming oxide occurring in crystalline forms such as quartz and in amorphous silica. Its solid is not a collection of isolated linear $\mathrm{Si}{\mathrm{O}}_2$ molecules.

The connectivity and arrangement of silicon-oxygen units affect density, optical behavior, and mechanical properties. This makes crystalline quartz and silica glass chemically similar but structurally distinct materials.

A polar linear molecule with composition OCS.

A respirometer measures gas changes associated with cellular respiration. In the absorber-based pea seed respirometry apparatus, the changing gas inventory is inferred from a liquid boundary's displacement. A respirometer is therefore a physical measurement coupled to a biological process, not a direct ATP counter.

Anaerobic respiration uses a respiratory electron transport chain with a final electron acceptor other than molecular oxygen. External acceptors can include sulfate, depending on the organism. “External” distinguishes a supplied terminal acceptor from the fuel-derived organic intermediates used in fermentation; it does not mean that the reduction must take place outside the biological cell. In fermentation, regeneration of carriers such as NADH to their oxidized form permits glycolysis to continue without a respiratory electron transport chain. Both routes can operate without molecular oxygen, but they are different mechanisms.^[ref]

Aerobic respiration uses molecular oxygen as the final electron acceptor. For complete oxidation of glucose, the net material balance isThis records the overall conversion of glucose, molecular oxygen, carbon dioxide and water; it is not one enzyme-catalyzed step, and it omits the separate ATP accounting. For an original stoichiometry check, each side contains six carbon, twelve hydrogen and eighteen oxygen chemical atoms. If exactly $1\mathrm{mmol}$ of glucose undergoes this complete conversion, the equation requires $6\mathrm{mmol}$ of molecular oxygen and yields $6\mathrm{mmol}$ each of carbon dioxide and net water. This is an equation-based calculation, not an observed seed measurement.

The molecular oxygen is reduced to water, rather than being the source of the carbon dioxide's carbon. A formal redox electron balance, using acidic half-reaction notation, makes the roles explicit:Adding and cancelling gives the net equation above. Both half-reactions conserve chemical atoms and electric charge. The $24$ electrons balance a net transfer; they are carried through cellular intermediates, rather than released as a pool of free electrons. The final respiratory reduction can be written ${\mathrm{O}}_2+4{\mathrm{H}}^{+}+4e^{-}⟶2{\mathrm{H}}_2\mathrm{O}$. These equations are bookkeeping, not a tracing experiment that assigns every product oxygen chemical atom to its original molecule.^[ref]

HeLa is a human continuous cell line originating in cervical cancer biological cells collected from Henrietta Lacks in 1951. Its name combines the beginning of her first and last names.^[ref]

ATCC's CCL-2 HeLa preparation grows attached to a surface. Its product sheet specifies a cell culture medium supplemented with fetal bovine serum, at $37{}^{\circ }\mathrm{C}$ with $5\%$ carbon dioxide in air.^[ref] These are specified conditions for that preparation, rather than defining conditions for every HeLa derivative.

Continuing access to related biological cells makes HeLa useful for comparisons of cell state and responses to interventions. But a continuous cell line is a laboratory model: its history and environment matter, and observations in it do not alone establish responses in an intact organism. Cell counting measures abundance; a trypan blue exclusion test measures a particular membrane-associated readout; neither proves cell line identity.

The cell-free extract experiment under yeast asks whether fermentation requires intact living biological cells. In his 1907 lecture, Eduard Buchner described grinding yeast with quartz sand and diatomite in a large mortar using a heavy pestle, wrapping the dough in canvas, then squeezing it in a hydraulic press. Adding concentrated sugar syrup to the expressed liquid produced carbon dioxide bubbles and foam; separate investigations identified ethanol.^[ref]

Activity persisted after filtration through cell-removing porcelain candles. Toluene inhibited live yeast fermentation while the cell-free extract retained activity, addressing a different objection from cell removal. These comparisons support extracted chemical machinery as the cause; bubbles alone would not identify alcoholic fermentation.^[ref]

The inference is activity outside intact living biological cells, not that biological cells are unnecessary for making or maintaining the machinery. Nor was this a purified single-enzyme mechanism: the lecture acknowledges unsuccessful purification and reports that two separated inactive fractions recovered fermentation when reunited. Such a reconstitution asks which components must work together, extending the initial separation of organism from chemical activity.^[ref]

Online text: openstax.org/books/calculus-volume-3/pages/4-6-directional-derivatives-and-the-gradient

Cited passages: Calculus Volume 3, Definition (4.36), the unit-direction convention, and Theorem 4.12 with the gradient formulation.

Online text: openstax.org/books/calculus-volume-3/pages/4-4-tangent-planes-and-linear-approximations

Cited passages: Calculus Volume 3, Tangent-plane equation (4.24), differentiability definition (4.26), and total differential (4.27).

Online text: openstax.org/books/calculus-volume-3/pages/4-3-partial-derivatives

Cited passages: Calculus Volume 3, Definitions (4.12)–(4.13), and the interpretation as ordinary derivatives of one-variable coordinate slices.