Biological systems use free energy based on empirical data that all organisms
require a constant energy input. The first law of thermodynamics states that
energy can be neither created nor destroyed. For living organisms, which of
the following statements is an important consequence of this first law?
• A) The energy content of an organism is constant except for when its
cells are dividing.
• B) The organism must ultimately obtain all the necessary energy for life
from its environment.
• C) The entropy of an organism decreases with time as the organism
grows in complexity.
• D) Organisms are unable to transform energy from the different states
in which it can exist.
In a biological reaction, succinate dehydrogenase catalyzes the conversion of
succinate to fumarate. The reaction is inhibited by malonic acid, a substance
that resembles succinate but cannot be acted upon by succinate
dehydrogenase. Increasing the amount of succinate molecules to those of
malonic acid reduces the inhibitory effect if malonic acid. Select the correct
identification of the molecules described in the reaction.
• A) Succinate dehydrogenase is the enzyme, and
fumarate is the substrate in the reaction.
• B) Succinate dehydrogenase is the enzyme, and
malonic acid is the substrate in the reaction.
• C) Succinate is the substrate, and fumarate is the
product in the reaction.
• D) Fumarate is the product, and malonic acid is a
noncompetitive inhibitor in the reaction.
New biosensors, applied like a temporary tattoo to the skin, can alert serious
athletes that they are about to "hit the wall" and find it difficult to continue
exercising. These biosensors monitor lactate, a form of lactic acid, released in
sweat during strenuous exercise.
Which of the statements below is the best explanation of why athletes would
need to monitor lactate levels?
• A) During aerobic respiration, muscle cells cannot produce
enough lactate to fuel muscle cell contractions and muscles begin
to cramp, thus athletic performance suffers.
• B) During anaerobic respiration, lactate levels increase when
muscles cells need more energy, however muscles cells eventually
fatigue, thus athletes should modify their activities to increase
aerobic respiration.
• C) During aerobic respiration, muscles cells produce too much
lactate which causes a rise in the pH of the muscle cells, thus
athletes must consume increased amounts of sports drinks, high in
electrolytes, to buffer the pH.
• D) During anaerobic respiration, muscle cells receive too little
oxygen and begin to convert lactate to pyruvate (pyruvic acid), thus
athletes experience cramping and fatigue.
ATP synthase is a key enzyme of mitochondrial energy conversion.
Mitochondrial ATP synthase deficiency is due to a mutation in a gene
important for the formation of a subunit in the ATP synthase complex.
Scientists could use cells with this gene mutation to investigate which
of the following questions?
• A) What effect does the mutation have on the movement of
electrons between the electron carriers of the electron transport
chain?
• B) What effect does the mutation have on the number of protons
pumped into the intermembrane space of the mitochondria?
• C) What effect does the mutation have on the amount of ATP
synthesized during cellular respiration?
• D) What effect does the mutation have on the number of water
molecules formed at the end of the electron transport chain?
The oxidation of glucose in the presence of oxygen involves glycolysis,
pyruvate oxidation, and the citric acid cycle (Krebs cycle). Some energy is
captured in glycolysis when glucose is converted to pyruvate (pyruvic acid). In
the citric acid cycle (Krebs cycle), more energy is captured in the form of
.
reduced electron carriers, NADH and FADH2
Select the best explanation for why the eventual reoxidation of NADH
and FADH2 is crucial for the continuation of the citric acid (Krebs)
cycle.
• A) In order for the cycle to continue, oxidized electron carriers
must be available.
• B) Without oxidized electron carriers, oxygen will not accept the
electrons at the end of the electron transport chain.
• C) Phosphate cannot attach to ADP to form ATP without oxidized
electron carriers.
• D) The presence of reduced forms of the electron carriers
prevents the formation of ATP.
Students conducted an experiment to determine the effect of light
intensity on the rate of photosynthesis. They punched 40 leaf disks
from spinach leaves and used a syringe partially filled with water to
pull the gases from the leaf disks so that all leaf disks sunk to the
bottom of the syringe. Ten (10) leaf disks from the syringe were
placed in each of four cups and covered with 50 ml of the solutions
as indicated below. All leaf disks were resting on the bottom of the
cups when the experiment began. The volume of liquid in each cup
and the temperature of the solutions were held constant. All cups
were placed 0.5 meters from the designated light source. A large
beaker of water was placed between the light and the cups to act as
a heat sink to prevent a change in temperature. At the end of 10
minutes, the number of disks floating in each cup was recorded.
Trial
Grams of
baking soda
(CO22 source)
Wattage of
light bulb
Disks floating
at 10 minutes
1
0.5
25
3
2
0.5
50
5
3
0.5
75
9
4
0
75
0
Use your knowledge of the mechanism of photosynthesis and the data
presented in the chart to determine which of the statements below
is a correct explanation for the student's data.
• a. Cup 1 had a low rate of photosynthesis because 0.5 grams of
baking soda did not provide a sufficient amount of CO2.
• b. Cup 2 had the highest rate of photosynthesis because 5 disks
were floating at the end of 10 minutes using a 50 watt light bulb.
• c. Cup 3 had the same rate of photosynthesis as Cup 1 because
they had the same ratio of disks floating to wattage of light.
• d. Cup 4 had the slowest rate of photosynthesis because it had
the least baking soda.
Anabolic pathways ____.
• A) are usually highly spontaneous chemical
reactions
• B) consume energy to build up polymers from
monomers
• C) release energy as they degrade polymers
to monomers
• D) consume energy to decrease the entropy
of the organism and its environment
The mathematical expression for the change in
free energy of a system is DG = DH - TDS.
Which of the following is (are) correct?
• A) DS is the change in enthalpy, a measure of
randomness.
• B) DH is the change in entropy, the energy
available to do work.
• C) DG is the change in free energy.
• D) T is the temperature in degrees Celsius.
Catabolic pathways ____.
• A) combine molecules into more energy-rich
molecules
• B) supply energy, primarily in the form of ATP,
for the cell's work
• C) are endergonic
• D) are spontaneous and do not need enzyme
catalysis
The active site of an enzyme is the region that ____.
• A) binds allosteric regulators of the enzyme
• B) is involved in the catalytic reaction of the
enzyme
• C) binds noncompetitive inhibitors of the
enzyme
• D) is inhibited by the presence of a coenzyme or
a cofactor
The following questions are based on the reaction A + B « C + D shown in the
accompanying figure.
Which of the following terms best describes the
forward reaction in the figure?
• A) endergonic, DG > 0
• B) exergonic, DG < 0
• C) endergonic, DG < 0
• D) exergonic, DG > 0
Allosteric enzyme regulation is usually
associated with ____.
• A) feedback inhibition
• B) activating activity
• C) an enzyme with more than one subunit
• D) the need for cofactors
Besides turning enzymes on or off, what other
means does a cell use to control enzymatic
activity?
• A) localization of enzymes into specific
organelles or membranes
• B) exporting enzymes out of the cell
• C) connecting enzymes into large aggregates
• D) hydrophobic interactions
Substrate-level phosphorylation occurs ____.
• A) in glycolysis
• B) in the citric acid cycle
• C) in both glycolysis and the citric acid cycle
• D) during oxidative phosphorylation
Which of the following statements about NAD+ is
true?
• A) NAD+ is reduced to NADH during glycolysis,
pyruvate oxidation, and the citric acid cycle.
• B) NAD+ has more chemical energy than NADH.
• C) NAD+ can donate electrons for use in
oxidative phosphorylation.
• D) In the absence of NAD+, glycolysis can still
function.
Starting with one molecule of glucose, the
energy-containing products of glycolysis are
____.
• A) 2 NAD+, 2 pyruvate, and 2 ATP
• B) 2 NADH, 2 pyruvate, and 2 ATP
• C) 2 FADH2, 2 pyruvate, and 4 ATP
• D) 6 CO2, 2 pyruvate, and 2 ATP
Which kind of metabolic poison would most directly
interfere with glycolysis?
• A) an agent that reacts with oxygen and depletes
its concentration in the cell
• B) an agent that binds to pyruvate and
inactivates it
• C) an agent that closely mimics the structure of
glucose but is not metabolized
• D) an agent that reacts with NADH and oxidizes
it to NAD+
Most of the CO2 from the catabolism of glucose
is released during ____.
• A) glycolysis
• B) electron transport
• C) chemiosmosis
• D) the citric acid cycle
Carbon dioxide (CO2) is released during which of
the following stages of cellular respiration?
• A) glycolysis and the oxidation of pyruvate to
acetyl CoA
• B) oxidation of pyruvate to acetyl CoA and
the citric acid cycle
• C) oxidative phosphorylation and
fermentation
• D) fermentation and glycolysis
In chemiosmosis, what is the most direct source of
energy that is used to convert ADP + i to ATP?
• A) energy released as electrons flow through the
electron transport system
• B) energy released from substrate-level
phosphorylation
• C) energy released from movement of protons
through ATP synthase, down their
electrochemical gradient
• D) No external source of energy is required
because the reaction is exergonic.
Energy released by the electron transport chain
is used to pump H+ into which location in
eukaryotic cells?
• A) mitochondrial outer membrane
• B) mitochondrial inner membrane
• C) mitochondrial intermembrane space
• D) mitochondrial matrix
Fatty acids usually have an even number of carbons in
their structures. They are catabolized by a process
called beta-oxidation. The end products of the
metabolic pathway are acetyl groups of acetyl CoA
molecules. These acetyl groups ____.
• A) directly enter the electron transport chain
• B) directly enter the energy-yielding stages of
glycolysis
• C) are directly decarboxylated by pyruvate
dehydrogenase
• D) directly enter the citric acid cycle
The process of photosynthesis probably
originated ____.
• A) in plants
• B) in prokaryotes
• C) in fungi
• D) three separate times during evolution
Refer to the figure. If the carbon atom of each of the incoming CO2 molecules is labeled
with a radioactive isotope of carbon, which organic molecules will be radioactively labeled
after one cycle?
A)
C only
B)
B, C, D, and E
C)
C, D, and E only
D)
B and C only
Why are C4 plants able to photosynthesize with
no apparent photorespiration?
• A) They do not participate in the Calvin cycle.
• B) They use PEP carboxylase to initially fix
CO2.
• C) They conserve water more efficiently.
• D) They exclude oxygen from their tissues.
Referring to the accompanying figure, oxygen would inhibit the CO2 fixation reactions in
____.
A)
cell I only
B)
cell II only
C)
neither cell I nor cell II
D)
both cell I and cell II