PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
1.
The effect of light on the photosynthetic rate of chloroplasts is tested during a controlled
experiment. Two chloroplast suspensions are mixed with DPIP, an electron acceptor that
changes from blue to clear when it is reduced and takes the place of NADP+. One test tube is
exposed to light, while the other is covered with aluminum foil to provide a dark environment. The
two samples are placed in a machine that measures the percent of light transmittance, and the
percent transmittance is measured and recorded every five minutes for 20 minutes. The results
are shown in the table below.
Which statement best explains the results observed in the table?
(A) The suspension in the dark environment shows a decrease in free energy because no free
energy is available to excite the DPIP molecules and cause the solution to change color.
Distractor Rationale:
This answer suggests the student may understand that the free energy in light is required to
reduce the DPIP molecules, but does not understand that the data shows no change or a
very slight overall increase in free energy of the dark environment as evidenced by a
relatively constant percent transmittance, which indicates that DPIP molecules are not being
reduced and free energy capture via photosynthesis is not occurring.
(B) The suspension exposed to light shows a decrease in free energy because more DPIP
molecules are reduced, which causes the solution to change color from blue to clear, using
free energy in the process.
Page 1 of 7
PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
Distractor Rationale:
This answer suggests the student may understand that molecules of DPIP are reduced
during the light reaction and that the solution changes from blue to clear, but does not
understand that this indicates an increase in free energy, not a decrease, because the color
change indicates that energy is being captured from light during photosynthesis.
(C) The amount of free energy in both suspensions does not change because energy cannot
increase or decrease within a system and can only be converted from one form to another.
Distractor Rationale:
This answer suggests the student may understand that energy can be transferred within a
system, but does not understand that free energy must be continuously supplied to a
system because free energy is continually being used by organisms and that most of the
free energy captured is released as thermal energy and is no longer available as a source of
energy.
(D) The suspension exposed to light shows an increase in free energy because the color of the
solution changes from blue to clear, which indicates that DPIP molecules are reduced.
Rationale:
This answer suggests the student understands that the light transmittance of the
suspension exposed to light increases over time because the color of the solution changes
from blue to clear as the chloroplasts capture free energy from light and DPIP molecules are
reduced during photosynthesis, and this indicates that the free energy of the solution is
increasing.
Aligned to: LO 2.3 CA 2.3: Predict Free Energy
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PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
2.
The hydrolysis of ATP to ADP and phosphate is performed both inside and outside of living cells.
The table below shows the change in free energy in each environment.
Which statement best explains the data?
(A) Both samples are endergonic, but sample A shows a greater increase in entropy because
G is more negative than in sample B.
Distractor Rationale:
This answer suggests the student may understand that entropy is increasing in these
reactions, but does not understand that the reactions are exergonic because energy is
released, as indicated by the negative G.
(B) Both samples are energy-capturing reactions, but the total energy in sample A is greater
because
G is more negative than in sample B.
Distractor Rationale:
This answer suggests the student may understand that G is more negative in sample A,
but confuses enthalpy (total energy) with entropy (disorder) and does not understand that
a negative G indicates that free energy is being released, not gained.
(C) Both samples are exergonic, but sample A shows a greater decrease in entropy because
G is more negative than in sample B.
Distractor Rationale:
This answer suggests the student may understand that the reactions are exergonic, but
does not understand that there is an increase in entropy (disorder) when energy is
released, not a decrease.
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PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
(D) Both samples are energy-releasing reactions, but the entropy in sample A is greater
because
G is more negative than in sample B.
Rationale:
This answer suggests the student understands that the hydrolysis of ATP involves the
release of energy and that a more negative change in free energy ( G) results in an
increase in entropy (disorder).
Aligned to: LO 2.3 CA 2.3: Predict Free Energy
3.
Biochemical processes are influenced by changes in free energy. The graph below represents a
process that involves a change in free energy.
Which process does the graph most likely model?
(A) Cellular respiration, because energy from the reactants is transferred to the environment
and
G is negative
Rationale:
This answer suggests the student understands that cellular respiration involves the release
of free energy from energy-rich molecules and that G is negative because free energy is
released during cellular respiration.
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PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
(B) Dehydration synthesis, because energy is stored in the products and
G is positive
Distractor Rationale:
This answer suggests the student may understand that the reaction involves a transfer of
energy, but does not understand that free energy in this reaction is transferred to the
environment and not stored in the products, and that G for this reaction is negative.
(C) Photosynthesis, because energy is transferred to the products and
G is positive
Distractor Rationale:
This answer suggests the student may understand that energy is transferred through light
reactions and that light reactions have a positive G, but does not understand that light
reactions require free energy and that the reaction shown has a negative G since free
energy is released.
(D) Active transport, because energy is used to move products from a higher concentration to a
lower concentration and
G is negative
Distractor Rationale:
This answer suggests the student may understand that free energy is involved in active
transport and that the diagram shows a negative G, but does not understand that this
reaction shows a transfer of energy from the reactants to the environment and does not
show products moving from a higher concentration to a lower concentration.
Aligned to: LO 2.3 CA 2.3: Predict Free Energy
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PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
4.
Yeast cells are able to undergo both aerobic respiration and fermentation. The table below shows
the conditions in two flasks before yeast cells are added.
Once the yeast cells are added, the concentrations of sucrose and oxygen as well as the
temperature of each flask are monitored for 60 minutes. Which statement explains the changes
that will most likely be observed in the two flasks?
(A) The available free energy in both flasks will increase because both flasks will have more
sucrose, no oxygen, and an increase in temperature due to cellular respiration.
Distractor Rationale:
This answer suggests the student may understand that some free energy is transformed into
heat energy during cellular respiration and fermentation, but does not understand that
oxygen is not a source of free energy and will not increase in flask 2, that sucrose is
consumed during cellular respiration, that no oxygen will be consumed during fermentation
in flask 1, and that the available free energy in both flasks decreases during cellular
respiration and fermentation.
(B) The available free energy in flask 1 will not change because there is not enough oxygen for
cellular respiration, but the free energy in flask 2 will decrease because there will be less
sucrose and less oxygen due to cellular respiration.
Distractor Rationale:
This answer suggests the student may understand that oxygen and sucrose are consumed
during cellular respiration and that free energy will decrease, but does not understand that
sucrose will be used during fermentation in flask 2 due to the low oxygen concentration, and
that the available free energy in both flasks will decrease.
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PROCTOR VERSION
2.3 A: Free Energy of Molecules and Cells Quiz
(C) The available free energy in both flasks will decrease because both flasks will have less
sucrose and an increase in temperature, but the yeast cells in each flask will generate
different waste products.
Rationale:
This answer suggests the student understands that cellular respiration consumes oxygen
and generates low-energy waste products, that fermentation will occur in flask 1 due to low
oxygen, that sucrose is consumed as the free energy source in both cellular respiration and
fermentation, and that the available free energy in both flasks decreases as a result.
(D) The available free energy in neither flask will change because neither flask will have an
increase in temperature, since the yeast cells are heterotrophic and will consume all
available sucrose and oxygen.
Distractor Rationale:
This answer suggests the student may understand that yeast cells consume sucrose, but
does not understand that cellular respiration occurs in the presence of oxygen in flask 2
and that fermentation occurs in the absence of oxygen in flask 1, that the temperature will
increase in both flasks, and that the available free energy in both flasks decreases as a
result.
Aligned to: LO 2.3 CA 2.3: Predict Free Energy
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