Cell Biology Exam #2-2014
Name____Key________________
Lab Section_______________
Multiple choice. Choose the best answer (2 points each)
1. __D___A reaction with a positive △G: a) Is exergonic b)can occur if an enzyme is present that
changes its △G to a negative value; c)Is spontaneous; d)Proceeds from a state of lower free
energy to higher free energy.
2.
___E__ Why is ATP an important molecule in metabolism? a) Its synthesis is exergonic; b) It is
extremely stable; c) Its hydrolysis is endergonic; d) It is readily obtained from an organism's
environment. e) Its phosphate bonds are easily formed and broken.
3. __B___Which of the following terms is not associated with an anabolic pathway? a) overall the
process is not spontaneous; b) overall the process is exergonic ; c) substrates become reduced;
d) smaller simple molecules are joined together to form larger more complex molecules; e) none
of the above-all of the choices are correct.
4. ___C__ Which of the following reactions below could occur by coupling the reaction to ATP
hydrolysis (ATP + H2O ADP + Pi (-7.3 kcal))? Numbers in ( ) indicate the delta G of each
reaction.
a)
b)
c)
d)
e)
CP C + Pi (-4 kcal)
A + Pi  AP (+9 kcal)
E + Pi EP (+5 kcal)
B + Pi BP (+8 kcal)
DP D + Pi (-10 kcal)
5. __B___If an enzymatic reaction is slowed down by an inhibitor and speeds up as more substrate
is added; the inhibition is most likely: a) Irreversible; b) Competitive; c) Noncompetitive;
d) a and c.
6. ___C__ Which of the following statements about enzymes is false? a) enzymes are not
permanently changed during the reaction they catalyze; b) enzymes only combine with specific
substrates; c) enzymes increase the rate of a reaction by providing the necessary energy to make the
reaction occur; d) the part of the enzyme where the substrate binds is called the active site;
e) enzymes are proteins.
7.___C_or D_When an inhibitor binds to the allosteric site of an enzyme, this type of inhibition
occurs:
a) Irreversible; b)Competitive; c)Noncompetitive; d) feedback; e)denaturation.
8. __D___When the end product of a metabolic pathway (tryptophan for example) regulates the
amount of that product (tryptophan) produced by the pathway, it is referred to as: a) denaturation;
b)catalysis; c) conformational change; d) feedback inhibition; e) activation energy.
9.__C___ Which of the following statements about enzymes is true? a) the energy of activation barrier is
higher for an enzyme catalyzed reaction than for the same reaction not catalyzed by an enzyme;
b) enzymes are rigid molecules whose shape never changes; c) some enzymes require a partner
co-enzyme in order to work; d) all enzymes have an allosteric site as well as a catalytic site.
10.___A__ Researchers measured the reaction rate of an enzyme in a series of experiments where
substrate concentration was sequentially increased by 10 percent. Initially they observed a linear
increase in rate, but eventually the rate leveled; after which time additional substrate had no effect on
reaction rate. How can this be explained?
a) The enzyme was saturated.
b) At high concentrations the substrate becomes an allosteric inhibitor.
c) At high concentrations the substrate becomes a competitive inhibitor.
d) At high concentrations the substrate becomes a noncompetitive inhibitor.
e) At high concentrations the substrate feedback inhibition begins.
11.__B___ During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a △G
of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the △G for the new
reaction? a) -40 kcal/mol; b) -20 kcal/mol; c) 0 kcal/mol; d) +20 kcal/mol; e) +40 kcal/mol
12. __D___Which of these methods is (are) used to store energy that is released during the exergonic
breakdown of glucose during aerobic respiration: a) phosphorylation of ADP; b) reduction of NAD+;
c) hydrolysis of ATP; d) a and b; e) all of the above
13. __A___Why is the citric acid cycle important? a) It produces a lot of NADH and FADH2 which are
potential energy sources; b) It produces a lot of ATP by chemiosmosis ; c) It recycles oxidized NAD+ back
into reduced NADH; d) It generates O2 that is needed by the ETS
14.__D___ In which metabolic pathway(s) is (are)ATP produced by substrate-level phosphorylation?
a) glycolysis; b) citric acid cycle; c) electron transport system; d) a and b; e) all of the above.
15.___D__ If a cell is deprived of oxygen: a) ATP production by oxidative phosphorylation will cease;
b) FADH2 will not be recycled; c) The citric acid cycle will stop; d) All of the above.
16. __C___ During respiration in a eukaryotic cell, the electron transport system is located in or on: a)
the cytoplasm b) the matrix of the mitochondrion c) the inner membrane of the mitochondrion d) the
intermembrane space of the mitochondrion e) None of the above
17. __C___ In addition to ATP, which of the following are end products of glycolysis? a) CO2 and H2O
b) CO2 and ethyl alcohol c) NADH and pyruvate d) CO2 and NADH e) H2O and ethyl alcohol
18.__C___Which of the following statements is false? a) glycolysis requires the input of ATP; b) for
every glucose molecule, the transition reaction plus the citric acid cycle produce a combined 8 NADH
and 2 FADH2; c) gycolysis produces 2 NADH and 1 FADH2 per glucose; d) the citric acid cycle produces 2
ATP/glucose; e) the electron transport system produces 34 of the 38 ATP produced from one glucose
molecule under ideal conditions.
19.___B__ The most CO2 released during cell respiration is from: a) glycolysis. b) the citric acid cycle.
c) lactate fermentation. d) electron transport. e) oxidative phosphorylation.
20.___A__Which of the following about substrate-level phosphorylation is true? a) it involves the
enzymatic transfer of an organic phosphate to ADP; b) it occurs in the electron transport system;
c) it produces the majority of ATP produced by aerobic cellular respiration; d) it requires mitochondrial
membranes to occur; e) it utilizes the energy of an H+ gradient.
21. __A___Fermentation: a) Recycles reduced NADH back into oxidized NAD+; b)Is the same as
glycolysis; c )Only occurs in yeast; d) Produces more ATP than glycolysis; e) All of the above
22. __C___ Which metabolic pathway is common to both fermentation and aerobic cellular respiration?
a) Citric acid cycle; b) electron transport chain; c) glycolysis; d) synthesis of acetyl-COA from pyruvate;
e) reduction of pyruvate to lactate
23. __A___In photosynthesis, which of the following substances becomes reduced? a) Carbon dioxide;
b)Water; c) ADP; d) ATP.
24.___B__ Which of the following is not part of the light dependent reactions of photosynthesis?
a) Splitting of water; b)Reduction (fixation) of C02; c) Reduction of NADP; d) Formation of ATP;
e) Photophosphorylation
25.__B or C or D or E___ Which of the following occurs in the stroma? a) Splitting of water; b)Reduction
(fixation) of C02; c)Formation of ATP; d) Photophosphorylation
26.__D___ In photosynthesis, what is the source of the electrons that reduce CO2 into glucose?
a) Oxygen; b)NADP; c) ATP; d)water
27. _D____ Which of the following statements is a correct distinction between autotrophs and
heterotrophs? a) Only heterotrophs require chemical compounds from the environment; b) Cellular
respiration is unique to heterotrophs; c) Only heterotrophs have mitochondria; d) Autotrophs, but not
heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are entirely
inorganic; e) Only heterotrophs require oxygen.
28.__D___ During photosynthesis, water is split and oxygen is produced: a) in the Calvin cycle; b) in the
Citric Acid Cycle; c) in Photosystem I; d) in Photosystem II; e) in the electron transport system.
29.__B___ While on a field trip to the tropical rain forest, you discover a plant with orange leaves. It
contains a photosynthetic pigment called orangophyll. Tests show that orangophyll absorbs purple,
blue, and green light most strongly, and it reflects orange, red, and yellow light. You plan to grow these
plants and sell them. What wavelengths of light should your grow-tubes supply for best growth?
a) Orange, red, and yellow light because the color of the leaves indicates the best wavelengths;
b) Purple, blue, and green light because orangophyll absorbs those wavelengths;
c) Red and blue light because those are the best wavelengths for photosynthesis;
d) Orange, red, and yellow light because orangophyll reflects those wavelengths;
e) Purple, blue, and green light because orangophyll reflects those wavelengths.
30.___B__Which of the following is not required for the Calvin cycle to function? a) carbon dioxide;
b) oxygen; c) ATP; d) RUBP; e) NADPH2
31.___B__This leaf structure can open and close depending on environmental conditions and allow gas
exchanges (CO2 andO2) to occur between the leaf and the atmosphere: a) cuticle; b) stomate;
c) vascular bundle; d) mesophyll
32.___B_ Which of the following sequences correctly represents the flow of electrons during
photosynthesis?
a) NADPH —› O2 —› CO2;
b) H2O —› NADPH —› Calvin cycle;
c) NADPH —› chlorophyll —› Calvin cycle;
d) H2O —› photosystem I —› photosystem II;
e) NADPH —› electron transport chain —› O2.
34. (4 points each) Agree or disagree. Fully defend your position.
A. The Second Law of Thermodynamics and the related concept of entropy helps to explain
this statement “cells live at the expense of their environment.”
Agree-The second law states that the systems become spontaneously more disordered (increase in
entropy). The only way a cell can maintain its low state of entropy is to break down molecules from
the environment to use as energy sources, and convert these molecules into waste products that are
returned to the environment. This maintains a state of low entropy in the cell by increasing the
entropy of the surrounding environment.
B. One of the most important things that enzymes do in cells is to convert an endergonic reaction into
an exergonic reaction.
Disagree-Enzymes cannot alter the delta G of a reaction. Enzymes can increase the rate of a reaction
that is already spontaneous but can’t convert a nonspontaneous reaction into a spontaneous one.
C. The final steps of alcoholic fermentation (reduction of pyruvate into ethanol) and the electron
transport system occur in the cell for the same basic underlying purpose
Agree-Both process are designed to recycle coenzyme back into their oxidized state so enzymes that
require oxidized co-enzymes can continue to function. The ETS does the and also produces ATP but no
additional ATP is made during the final steps of alcoholic fermentation.
D. The structure of a chloroplast is directly related to its function.
Agree-chloroplast thylakoids are stacked into grana o increase surface area so more chlorophyll
molecules can be packed into the chloroplast. Additionally, the thylakoid membrane separates two
compartments (the stroma and the thylakoid space). This arrangement is needed to make ATP by
chemiosmosis.
35. (10 points) Other than producing ATP, what is the primary function of the electron transport system
(ETS)? Using a labeled diagram and accompanying explanations, explain how the ETS produces ATP
while carrying out its primary function. Be sure to include a discussion about the types and distribution
of the electron transport system carriers in the mitochondrial inner membrane and explain how this
relates to the ability of the ETS to produce ATP.
The main purpose of the ETS is to recycle NADH and FADH2 back into their oxidized states.
Important points related to the diagram2 types of ETS carriers (electron donors/acceptors and hydrogen donors/acceptors). Both types are
asymmetrically distributed in the mitochondrial inner membrane.
For each NADH that donates its hydrogens to the ETS, 6 H+ are pumped into the inner membrane
space.
For each FADH2 that donates its hydrogens to the ETS, 4 H+ are pumped into the inner membrane
space.
For every two H+ that move through the ATPase channel protein from the inner membrane space into
the matrix, 1 ATP is made.
The inner membrane is normally impermeable to H+.
36. (10 points) What is a photosystem? Where is it located? Describe how photosystem I and
photosystem II interact to produce the three primary products of the light dependent reactions of
photosynthesis. Be sure to describe the products that are produced by each of the two photosystems
and explain how the two photosystems are dependent on one another.
A photosystem is a cluster of several hundred chlorophyll molecules that surround a special molecule
at the center of the photosystem called the reactive center. Photosystems (I and II) are imbedded in
the chloroplast thylakoid membrane.
In photosystem II, a water molecule is split into O and H using light energy. Two released oxygen
molecules bond (because they are unstable) and form a molecule of molecular oxygen (one of the
three products of the light reaction). The electron from the hydrogen (released from the splitting of
water) is transferred to the reactive center of PS II (to replace electrons that have been previously
lost). The H+ left over (after the electron has been removed from the Hydrogen atom (that came from
water) accumulates in the thylakoid space. This will contribute to the H+ gradient that will be used to
make ATP (the second product of the light reaction). The electron from water is now part of the
reactive center chlorophyll molecule of PS II. That electron will be boosted to a higher energy level by
a photon of light absorbed by PS II, passed off to an electron transport system that connects PS II and
PS I, and eventually go to the reactive center chlorophyll of PS I to replace electrons it has lost. As the
electrons move through the ETS between PS II and I, H+ ions are pumped into the thylakoid space.
This will contribute to the H+ gradient that will be used to make ATP (the second product of the light
reaction). The electrons from water (now in the reactive center of PS I) are boosted to a higher energy
level by a photon of light. These electrons are then passed to NADP. These electrons (along with
protons released by the dissociation of water in the stroma) reduce NADP into NADPH2 (the third
product of the light reaction)