Investigating the Chemistry of Life — Chapter Practice, Grade 10

6 units/min

18 ÷ 3 = 6.

Enzyme amount

Changing enzyme amount would introduce another potential cause.

Repeated readings emphasize measurement variability; independent samples also reflect preparation and biological variation.

No; use independent plants, appropriate comparisons and controlled conditions to test a broader claim.

The ten readings describe repeatability for one plant.

They do not capture variation among plants or provide an untreated comparison.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Replication helps assess variation but does not by itself remove confounding.

Use several comparable plants per treatment, assigned fairly, with other conditions held constant.

State what the supplied observations or conditions establish, and separate that from any assumption.

An operational measure such as height change or dry mass allows repeatable comparisons; appearance alone is subjective.

No. Twenty-five is the mean, while the individual plants range from 10 to 40 mm. Retain variation and the sampling conditions.

A mean is the sum of measured values divided by their number. The range describes the spread from minimum to maximum; it is not an uncertainty interval for a population mean. These four plants have mean 25 mm and range 10–40 mm. A bar showing only the mean would hide the variation. Report sample size, units and individual results or a useful distribution plot. Do not discard a low result solely because it weakens the preferred hypothesis; exclusions require a stated reason such as a documented measurement failure.

No. Twenty-five is the mean, while the individual plants range from 10 to 40 mm. Retain variation and the sampling conditions.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

There is only one treated biological/treatment unit per condition; six readings are repeated observations. Use several independently assigned plants or trays per condition, keep light/water/species comparable and preserve all time records.

There is only one treated biological/treatment unit per condition; six readings are repeated observations. Use several independently assigned plants or trays per condition, keep light/water/species comparable and preserve all time records.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

Covalent bond

In a covalent bond, two atoms share a pair of electrons — as oxygen does with two hydrogens in water.

it shares its electrons unequally, giving it a slightly positive end and a slightly negative end

Oxygen pulls the shared electrons closer, leaving the oxygen end slightly negative and the hydrogen ends slightly positive — that charge separation makes water polar.

1000 times

Each pH unit is a factor of 10. The difference is 5 − 2 = 3 units, so 10³ = 1000 times more acidic.

Hydrogen bonds attract water molecules to one another, so they stick together — this is cohesion. It creates surface tension that lets a water strider walk on a pond and helps tall trees pull an unbroken column of water up from their roots to their leaves.

Salt is held together by ionic bonds, not covalent bonds; water surrounds and separates its ions without breaking any covalent bonds

Salt (NaCl) is held together by ionic bonds. Polar water molecules surround the Na⁺ and Cl⁻ ions and pull them apart — it separates ions rather than breaking covalent bonds.

Different molecular interactions explain the contrasting behavior; water does not dissolve everything.

Water interacts strongly with ions and many polar groups.

Nonpolar oil does not make similarly favorable interactions with water and separates in bulk.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Do not treat hydrogen bonds between molecules as the covalent bonds inside water.

Oxygen attracts shared electrons more strongly, creating an uneven charge distribution rather than full ionic charges.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. It mainly alters intermolecular organization; water molecules remain intact.

Use matched masses, equal energy inputs, stated phases and comparable heat losses. The supplied water-model sample rises 6 °C, the comparison 18 °C.

Temperature describes a thermal state, while thermal energy also depends on amount and material. Specific heat capacity is energy per unit mass per degree of temperature change under stated conditions. Matched masses receiving equal energy can warm at different rates. Water’s interactions and degrees of freedom contribute to its relatively high heat capacity, moderating temperature changes in organisms and environments. This is different from evaporation, which transfers energy through a phase change. Heat-loss conditions, mass and phase must be comparable before assigning the observed slope only to a material property.

Use matched masses, equal energy inputs, stated phases and comparable heat losses. The supplied water-model sample rises 6 °C, the comparison 18 °C.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

The pH 5 sample has 10³ = 1,000 times the hydrogen-ion concentration of the pH 8 sample in the dilute-solution comparison. A buffer has a finite working range and capacity; sufficiently large additions can exceed it.

The pH 5 sample has 10³ = 1,000 times the hydrogen-ion concentration of the pH 8 sample in the dilute-solution comparison. A buffer has a finite working range and capacity; sufficiently large additions can exceed it.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

It can form four covalent bonds, letting it build long chains, branches, and rings

Each carbon atom can form four covalent bonds, so carbon can link into the large, varied skeletons that macromolecules need.

amino acid

Proteins are polymers of amino acids; there are 20 kinds that cells string together in different orders.

Nucleic acid

Nucleic acids — DNA and RNA — store and carry the genetic instructions for building proteins.

11 bonds

In a single chain, the number of bonds is one less than the number of monomers: 12 − 1 = 11 bonds.

A protein's chain of amino acids folds into a specific 3-D shape, and that shape decides which molecules it can fit and interact with. Enzymes depend on this because their folded shape forms an active site that fits one specific substrate — change the shape and the enzyme can no longer do its job.

Atmospheric carbon dioxide is a major carbon source; water and mineral nutrients are also required.

Photosynthesis incorporates carbon from atmospheric CO₂.

That carbon can be rearranged into carbohydrates and other organic molecules.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Do not infer that every carbon-containing molecule has the same biological role.

DNA contains nucleotides; base sequence carries information affecting RNA and proteins.

State what the supplied observations or conditions establish, and separate that from any assumption.

Composition, digestibility and molecule types differ; mass alone does not identify chemical stores or biological roles.

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

A protein consists of one or more folded polypeptides, chains of amino acids joined by peptide bonds. Each amino acid has a side group whose interactions influence folding. A different sequence can change a binding site, stability or location, but some sequence changes have little detectable effect. Denaturation disrupts an important folded arrangement; it is not the same as cutting every peptide bond. Enzymes, structural components, receptors and transporters are protein roles. A correct explanation connects a particular structural change to a tested function rather than saying all proteins behave alike.

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

Folding and active-site arrangement may change while amino-acid sequence remains largely intact. Compare catalytic rates under matched conditions and examine whether the fold/function can recover; unfolding is not automatically complete peptide hydrolysis.

Folding and active-site arrangement may change while amino-acid sequence remains largely intact. Compare catalytic rates under matched conditions and examine whether the fold/function can recover; unfolding is not automatically complete peptide hydrolysis.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

protein that speeds up a chemical reaction without being used up

Enzymes are protein catalysts — they speed up specific reactions and are not consumed, so they can be reused.

substrate

The substrate is the molecule that binds the active site and gets changed into product.

The heat denatures the enzyme, changing the shape of its active site so the substrate no longer fits

Too much heat unravels the protein's folding (denaturing), distorting the active site so the substrate can't bind.

1000 molecules per second

5 products/second × 200 = 1000 products per second.

An enzyme's function depends on its precise folded shape, which is held by chemical attractions sensitive to the surrounding H⁺ concentration (pH). At its optimum pH the active site keeps the right shape to fit the substrate; at the wrong pH those attractions are disrupted, the active site distorts, and the enzyme works poorly or denatures. Pepsin evolved to fold correctly in stomach acid, so its optimum is pH 2.

Enzyme saturation can explain the plateau; the design must rule out other limiting conditions.

At low substrate, more substrate increases encounters with active sites.

At high substrate, available sites can become occupied much of the time.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

A falling rate does not establish the exact molecular mechanism without additional tests.

Competitive inhibition is consistent with competing for the substrate-binding site.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. It lowers activation barriers; it does not change the overall free-energy requirement or create an energy source.

No. It describes an initial-rate example under selected conditions; long-term stability and other enzyme identities require different evidence.

A reaction rate measures change per time; an initial rate uses a defined early interval before large substrate depletion or product buildup. Warming can increase productive collisions, but higher temperature can disrupt an enzyme’s fold and stability. The balance creates a condition-dependent optimum. pH, enzyme identity, exposure duration and substrate conditions matter too. Low rate in the cold is not automatically denaturation; activity may return on warming. A steep loss after heating needs suitable recovery and structural evidence before its cause is assigned.

No. It describes an initial-rate example under selected conditions; long-term stability and other enzyme identities require different evidence.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

The lower barrier can increase the approach rate in both directions. It does not by itself change the equilibrium or net free-energy change, and an unfavorable isolated process still needs suitable coupling or conditions.

The lower barrier can increase the approach rate in both directions. It does not by itself change the equilibrium or net free-energy change, and an unfavorable isolated process still needs suitable coupling or conditions.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.

synthesis reaction

Synthesis joins smaller molecules; its energy balance depends on the full reaction and may require coupling.

ATP

ATP is the cell's energy currency. Glucose is an energy source, but its energy is banked into ATP before the cell spends it.

ADP + a phosphate group

ATP hydrolysis forms ADP and phosphate; the overall reaction can release free energy under cellular conditions.

1200 ATP

3,600 ions ÷ 3 ions per ATP = 1,200 ATP.

Energy-releasing metabolism supports ATP production. ATP hydrolysis coupled to synthesis or transport can make the combined process favorable. No energy is created, and the full reactions, not bond breaking alone, determine the balance.

Energy availability comes from the whole reaction and coupling mechanism, not bond breaking by itself.

Bond breaking requires an input of energy.

The full reaction forms new interactions and products; its overall free-energy change can be favorable and coupled to work.

Response criteria

• Use the stated conditions.
• Show the evidence or calculation.
• Explain the conclusion and any stated limitation.

Energy is transferred through a mechanism, not created by the enzyme.

Energy disperses to surroundings; cells need usable energy to maintain organization and drive processes.

State what the supplied observations or conditions establish, and separate that from any assumption.

No. Catalysis speeds approach to equilibrium without changing the equilibrium determined by the reaction and conditions.

The total is +5 model units, so this stated pair alone is not favorable; additional coupling or changed conditions would be needed.

An endergonic process requires a positive free-energy change under the stated conditions; an exergonic process has a negative change. Coupling links processes through a mechanism so their combined outcome can proceed. Here a +12 synthesis step and −20 hydrolysis contribution sum to −8 model units. This accounting does not say that two unconnected reactions in neighboring beakers drive each other. Enzymes or molecular machines must link the relevant changes, and actual concentrations and pathways determine feasibility and rate.

The total is +5 model units, so this stated pair alone is not favorable; additional coupling or changed conditions would be needed.

Response criteria

• Read the structures, axes, directions and units correctly.
• Connect the evidence with the biological mechanism.
• Respect stated model assumptions and distinguish an observation from a further inference.

The net is −8 units under the supplied conditions. A catalyst can lower the activation barrier but does not make the isolated +18 process favorable by changing its endpoint free-energy balance.

The net is −8 units under the supplied conditions. A catalyst can lower the activation barrier but does not make the isolated +18 process favorable by changing its endpoint free-energy balance.

Response criteria

• Use the stated measurements or conditions, with correct units.
• Connect the result to the biological mechanism or evidence relationship.
• Identify the assumption, model limit or further evidence requested.