USABO EXAMS SCRIPT 2026 QUESTIONS AND
ANSWERS SET A+
✔✔first law of thermodynamics - ✔✔The energy of the universe is constant. Energy can
be transferred and transformed, but not created or destroyed. (AKA principle of
conservation of energy, 143)
✔✔entropy - ✔✔The quantification of a measure of disorder or randomness. (144)
✔✔second law of thermodynamics - ✔✔Every energy transfer or transformation
increases the entropy of the universe. For a process to occur spontaneously, it must
increase the entropy of the universe (for example, disorder is added to a cheetah's
surroundings in the form of heat and by-products of metabolism, 144)
✔✔spontaneous process - ✔✔A process that can occur without an input of energy.
(144)
✔✔free energy - ✔✔the portion of a system's energy that can perform work when
temperature and pressure are uniform throughout the system, (as in a living cell,145)
✔✔Change in free energy - ✔✔ΔG = ΔH - TΔS
✔✔ΔG - ✔✔Change in (Gibbs') free energy
✔✔ΔH - ✔✔change in enthalpy (equivalent to total energy)
✔✔ΔS - ✔✔change in entropy
✔✔Spontaneous processes - ✔✔Processes characterized with having a negative ΔG.
✔✔T - ✔✔Absolute temperature in K.
,✔✔free energy - ✔✔(conceptual way of thinking) "A measure of a system's instability"
Unstable = higher G, stable = lower G.
✔✔exergonic reaction - ✔✔A spontaneous chemical reaction, in which there is a net
release of free energy.
✔✔endergonic reaction - ✔✔A nonspontaneous chemical reaction, in which free energy
is absorbed from the surroundings.
✔✔energy coupling - ✔✔The use of an exergonic process to drive an endergonic one.
✔✔three types of cellular work - ✔✔chemical, transport, mechanical
✔✔phosphorylation - ✔✔The 'giving' of Pi, a phosphate group.
✔✔activation energy - ✔✔The amount of energy that reactants must absorb before a
chemical reaction will start; also called free energy of activation.
✔✔active site - ✔✔The specific portion of an enzyme that binds the substrate by means
of multiple weak interactions and that forms the pocket in which catalysis occurs.
✔✔allosteric regulation - ✔✔The binding of a regulatory molecule to a protein at one
site that affects the function of the protein at a different site.
✔✔anabolic pathway - ✔✔A metabolic pathway that consumes energy to synthesize a
complex molecule from simpler compounds.
✔✔bioenergetics - ✔✔(1) The overall flow and transformation of energy in an organism.
(2) The study of how energy flows through organisms.
✔✔catabolic pathway - ✔✔A metabolic pathway that releases energy by breaking down
complex molecules to simpler compounds.
✔✔catalyst - ✔✔A chemical agent that increases the rate of a reaction without being
consumed by the reaction.
✔✔chemical energy - ✔✔Energy available in molecules for release in a chemical
reaction; a form of potential energy.
✔✔coenzyme - ✔✔An organic molecule serving as a cofactor. Most vitamins function as
coenzymes in metabolic reactions.
, ✔✔cofactor - ✔✔Any nonprotein molecule or ion that is required for the proper
functioning of an enzyme. Cofactors can be permanently bound to the active site or may
bind loosely with the substrate during catalysis.
✔✔competitive inhibitor - ✔✔A substance that reduces the activity of an enzyme by
entering the active site in place of the substrate whose structure it mimics.
✔✔cooperativity - ✔✔A kind of allosteric regulation whereby a shape change in one
subunit of a protein caused by substrate binding is transmitted to all the others,
facilitating binding of subsequent substrate molecules.
✔✔energy coupling - ✔✔In cellular metabolism, the use of energy released from an
exergonic reaction to drive an endergonic reaction.
✔✔enzyme - ✔✔A macromolecule serving as a catalyst, a chemical agent that changes
the rate of a reaction without being consumed by the reaction.
✔✔enzyme-substrate complex - ✔✔A temporary complex formed when an enzyme
binds to its substrate molecule(s).
✔✔feedback inhibition - ✔✔A method of metabolic control in which the end product of a
metabolic pathway acts as an inhibitor of an enzyme within that pathway.
✔✔free energy - ✔✔The portion of a biological system's energy that can perform work
when temperature and pressure are uniform throughout the system. (The change in free
energy of a system is calculated by the equation ΔG = ΔH - TΔS, where H is enthalpy
[in biological systems, equivalent to total energy], T is absolute temperature, and S is
entropy.)
✔✔hemoglobin - ✔✔An iron-containing protein in red blood cells that reversibly binds
oxygen.
✔✔induced fit - ✔✔Induced by entry of the substrate, the change in shape of the active
site of an enzyme so that it binds more snugly to the substrate.
✔✔kinetic energy - ✔✔The energy associated with the relative motion of objects.
Moving matter can perform work by imparting motion to other matter.
✔✔metabolic pathway - ✔✔A series of chemical reactions that either builds a complex
molecule (anabolic pathway) or breaks down a complex molecule into simpler
compounds (catabolic pathway).
ANSWERS SET A+
✔✔first law of thermodynamics - ✔✔The energy of the universe is constant. Energy can
be transferred and transformed, but not created or destroyed. (AKA principle of
conservation of energy, 143)
✔✔entropy - ✔✔The quantification of a measure of disorder or randomness. (144)
✔✔second law of thermodynamics - ✔✔Every energy transfer or transformation
increases the entropy of the universe. For a process to occur spontaneously, it must
increase the entropy of the universe (for example, disorder is added to a cheetah's
surroundings in the form of heat and by-products of metabolism, 144)
✔✔spontaneous process - ✔✔A process that can occur without an input of energy.
(144)
✔✔free energy - ✔✔the portion of a system's energy that can perform work when
temperature and pressure are uniform throughout the system, (as in a living cell,145)
✔✔Change in free energy - ✔✔ΔG = ΔH - TΔS
✔✔ΔG - ✔✔Change in (Gibbs') free energy
✔✔ΔH - ✔✔change in enthalpy (equivalent to total energy)
✔✔ΔS - ✔✔change in entropy
✔✔Spontaneous processes - ✔✔Processes characterized with having a negative ΔG.
✔✔T - ✔✔Absolute temperature in K.
,✔✔free energy - ✔✔(conceptual way of thinking) "A measure of a system's instability"
Unstable = higher G, stable = lower G.
✔✔exergonic reaction - ✔✔A spontaneous chemical reaction, in which there is a net
release of free energy.
✔✔endergonic reaction - ✔✔A nonspontaneous chemical reaction, in which free energy
is absorbed from the surroundings.
✔✔energy coupling - ✔✔The use of an exergonic process to drive an endergonic one.
✔✔three types of cellular work - ✔✔chemical, transport, mechanical
✔✔phosphorylation - ✔✔The 'giving' of Pi, a phosphate group.
✔✔activation energy - ✔✔The amount of energy that reactants must absorb before a
chemical reaction will start; also called free energy of activation.
✔✔active site - ✔✔The specific portion of an enzyme that binds the substrate by means
of multiple weak interactions and that forms the pocket in which catalysis occurs.
✔✔allosteric regulation - ✔✔The binding of a regulatory molecule to a protein at one
site that affects the function of the protein at a different site.
✔✔anabolic pathway - ✔✔A metabolic pathway that consumes energy to synthesize a
complex molecule from simpler compounds.
✔✔bioenergetics - ✔✔(1) The overall flow and transformation of energy in an organism.
(2) The study of how energy flows through organisms.
✔✔catabolic pathway - ✔✔A metabolic pathway that releases energy by breaking down
complex molecules to simpler compounds.
✔✔catalyst - ✔✔A chemical agent that increases the rate of a reaction without being
consumed by the reaction.
✔✔chemical energy - ✔✔Energy available in molecules for release in a chemical
reaction; a form of potential energy.
✔✔coenzyme - ✔✔An organic molecule serving as a cofactor. Most vitamins function as
coenzymes in metabolic reactions.
, ✔✔cofactor - ✔✔Any nonprotein molecule or ion that is required for the proper
functioning of an enzyme. Cofactors can be permanently bound to the active site or may
bind loosely with the substrate during catalysis.
✔✔competitive inhibitor - ✔✔A substance that reduces the activity of an enzyme by
entering the active site in place of the substrate whose structure it mimics.
✔✔cooperativity - ✔✔A kind of allosteric regulation whereby a shape change in one
subunit of a protein caused by substrate binding is transmitted to all the others,
facilitating binding of subsequent substrate molecules.
✔✔energy coupling - ✔✔In cellular metabolism, the use of energy released from an
exergonic reaction to drive an endergonic reaction.
✔✔enzyme - ✔✔A macromolecule serving as a catalyst, a chemical agent that changes
the rate of a reaction without being consumed by the reaction.
✔✔enzyme-substrate complex - ✔✔A temporary complex formed when an enzyme
binds to its substrate molecule(s).
✔✔feedback inhibition - ✔✔A method of metabolic control in which the end product of a
metabolic pathway acts as an inhibitor of an enzyme within that pathway.
✔✔free energy - ✔✔The portion of a biological system's energy that can perform work
when temperature and pressure are uniform throughout the system. (The change in free
energy of a system is calculated by the equation ΔG = ΔH - TΔS, where H is enthalpy
[in biological systems, equivalent to total energy], T is absolute temperature, and S is
entropy.)
✔✔hemoglobin - ✔✔An iron-containing protein in red blood cells that reversibly binds
oxygen.
✔✔induced fit - ✔✔Induced by entry of the substrate, the change in shape of the active
site of an enzyme so that it binds more snugly to the substrate.
✔✔kinetic energy - ✔✔The energy associated with the relative motion of objects.
Moving matter can perform work by imparting motion to other matter.
✔✔metabolic pathway - ✔✔A series of chemical reactions that either builds a complex
molecule (anabolic pathway) or breaks down a complex molecule into simpler
compounds (catabolic pathway).
