Mastering Biology Exam 2
Which statement is true of enzymes? (a) Enzymes can be either proteins or RNA molecules. (b) When a cell makes an enzyme, it makes many copies. (c) Their substrate specificity involves matching of shapes. Both (a) and (b). (a), (b), and (c).
(a), (b), and (c)
A(n) _____ reaction occurs spontaneously. A. exergonic B. kinetic C. endergonic D. anabolic E. chemical
A
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions? A. pyruvate, ATP, and NADH B. NADH only C. CO2 only D. pyruvate and ATP only E. O2 only F. ATP and NADH only G. ATP only
A
Carbon fixation involves the addition of carbon dioxide to _____. A. RuBP B. Rubisco C. G3P D. 3-PGA E. NADPH
A
Complete the following sentences about enzyme function: Enzymes speed reaction rates by ______ and lowering activation energy. Activation energies drop because enzymes stabilize _______. Enzyme specificity is a function of the active site's shape and the chemical properties of _______ at the active site. A. 1. orienting substrates; 2. the transition state; 3. R-groups B. 1. orienting substrates; 2. the transition state; 3. reaction products C. 1. orienting products; 2. the transition state; 3. R-groups D. 1. orienting substrates; 2. reaction products; 3. R-groups
A
Enzymes speed reactions mainly by ... A. lowering EA. B. protecting the catalysts. C. providing activation energy. D. raising the kinetic energy of the reactants. E. None of the above.
A
How many carbon dioxide molecules must be added to RuBP to make a single molecule of glucose? A. 6 B. 2 C. 4 D. 10 E. 8
A
Which type of control agent never speeds an enzyme's action? A. Substrate analog B. Regulatory protein C. Protein kinase D. Allosteric effector E. None of the above.
A
What phosphorylates ADP to make ATP?
ATP synthase
Inputs of the Calvin cycle
ATP, NADPH, CO2
Outputs of the light reactions
ATP, NADPH, O2
Based on the data from the pulse-chase experiment shown in the graph in Figure 7.20b, which is the best estimate for the time it takes for proteins to pass through the Golgi apparatus? A. It is impossible to estimate based on these data. B. 10-37 min C. Approximately 117 min D. Less than 1 min
B
During the Calvin cycle, carbon dioxide is _____, in order to drive the formation of sugars. A. oxidized B. reduced C. destroyed D. produced
B
Early investigators thought the oxygen produced by photosynthetic plants came from carbon dioxide. In fact, it comes from ________. A. H2S. B. water. C. glucose. D. electrons from NADPH.
B
In the energy-yielding phase of glycolysis, energy is extracted in the form of _____. A. NADH B. ATP and NADH C. pyruvate D. ATP
B
What is the difference between NAD+ and NADP? A. NAD+ functions as a free-energy source for cells, whereas NADP does not. B. Both function as electron carriers, but NADP has a phosphate group and NAD+ does not. C. Both transport electrons to the electron transport chain (ETC) found on the inner mitochondrial membrane, but NADP transfers its electrons to the ETC at a higher energy level. D. NAD+ functions as an electron transporter, whereas NADP does not.
B
How do cells replace the energy-rich ATP that is destroyed in energy-coupled reactions? (a) Chloroplasts use light energy to synthesize ATP. (b) Mitochondria synthesize ATP using energy that's released by oxidizing sugars and fats. (c) Ribosomes use catalytic RNA to couple ADP with Pi. Both (a) and (b). (a), (b), and (c).
Both (a) and (b).
After 3-PGA is phosphorylated, it is reduced by _____. A. ATP B. NADP+ C. NADPH D. CO2 E. ADP
C
As electrons are passed through the system of electron carriers associated with photosystem II, they lose energy. What happens to this energy? A. It excites electrons of the reaction center of photosystem I. B. It is lost as heat. C. It is used to establish and maintain a proton gradient. D. It is used to phosphorylate NAD+ to NADPH, the molecule that accepts electrons from photosystem I.
C
Following glycolysis and the Krebs cycle and before the electron transport chain and oxidative phosphorylation, the carbon skeleton of glucose has been broken down to CO2. Most of the energy from the original glucose at that point is still in the form of ________. A. H2O. B. CO2. C. NADH. D. ATP.
C
How are the light-dependent and light-independent reactions of photosynthesis related? A. They cannot occur in the absence of light. B. The products of light-independent reactions must be present for light-dependent reactions to take place. C. The products of light-dependent reactions are used in light-independent reactions. D. They are not related.
C
How do cells use ATP to raise the energy level of reaction substrates? A. ATP is hydrolyzed to release its energy. B. The ADP part of ATP is bound to the substrate. C. The terminal phosphate of ATP is bound to the substrate. D. All of the above
C
In autumn, the leaves of deciduous trees change colors. This is because the chlorophyll is degraded, and ________. A. degraded chlorophyll becomes a pigment with different colors. B. water supply to the leaves has been reduced. C. the carotenoids and other pigments are still present in the leaves. D. the cells of the leaves begin to die.
C
In cooperativity, ... A. two or more enzymes are needed to bind one control agent. B. two enzymes cooperate to produce a control agent. C. if one substrate is bound, the next binds more easily. D. two control agents must bind to affect enzyme action. E. two enzymes share a binding site for a control agent.
C
In muscle cells, fermentation produces _____. A. pyruvate B. carbon dioxide, ethanol, and NAD+ C. lactate and NAD+ D. lactate, NADH, and ATP E. carbon dioxide, ethanol, NADH, and ATP
C
In the carbon fixation step of the Calvin cycle, ribulose-1,5-bisphosphate (a five-carbon compound) is carboxylated to produce ________. A. citric acid. B. acetyl CoA (two carbons) and oxaloacetate (four carbons). C. 2 three-carbon compounds. D. glucose.
C
Melvin Calvin introduced radiolabeled carbon dioxide into plants. Which of the following molecules should he have expected to see radiolabeled first? A. oxaloacetate B. glutamate C. 3-phosphoglycerate D. succinate
C
Select the INCORRECT association. A. enzyme ... protein B. kinetic energy ... motion C. exergonic ... uphill D. potential energy ... positional energy E. exergonic ... spontaneous
C
The reactions of pyruvate processing, the citric acid cycle, and the electron transport chain occur within the _____ in the cell. A. cytoplasm B. chloroplast C. mitochondria D. nucleus
C
The reactions of pyruvate processing, the citric acid cycle, and the electron transport chain occur within the _____ in the cell. A. nucleus B. chloroplast C. mitochondria D. cytoplasm
C
What is the function of coenzyme A in the Krebs cycle? A. It is the coenzyme of redox reactions. B. It is the coenzyme of carboxylation reactions. C. It is the coenzyme of acetylation reactions. D. It is a coenzyme of decarboxylation reactions.
C
Which of these equations best summarizes photosynthesis? A. C6H12O6 + 6 O2 → 6 CO2 + 12 H2O B. H2O → 2 H+ + 1/2 O2 + 2e- C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy E. 6 CO2 + 6 O2 → C6H12O6 + 6 H2O
C
Which statement is characteristic of allosteric effectors? (a) They bind to the active site. (b) Covalent bonds attach them to the enzyme. (c) They may not resemble the enzyme's substrates. Both (b) and (c). (a), (b), and (c).
C
Why are there several structurally different pigments in the reaction centers of photosystems? A. Excited electrons must pass through several pigments before they can be transferred to electron acceptors of the electron transport chain. B. They enable the reaction center to excite electrons to a higher energy level. C. This setup enables the plant to absorb energy from sunlight from a variety of wavelengths. D. They enable the plant to absorb more photons from light energy, all of which are at the same wavelength.
C
Why is ATP a good source of energy for biological reactions? A. Peroxide links are highly reactive. B. Links between sugar and phosphate are unstable. C. Triphosphate chains are unstable. D. The answer is still unknown. E. Links between adenine and sugar are unstable.
C
The elections derived from this oxidation reaction in the Calvin cycle are used to reduce _____ to _____.
CO2... G3P
Canine phosphofructokinase (PFK) deficiency afflicts springer spaniels, affecting an estimated 10% of the breed. PFK is the glycolytic enzyme that phosphorylates fructose-1-phosphate and catalyzes the committed step in glycolysis. Given its critical role in glycolysis, one implication of the genetic defect resulting in PFK deficiency in dogs is _____. A. elevated blood-glucose levels in the dog's blood B. early embryonic mortality C. a reduced life span D. an intolerance for exercise
D
Gaseous hydrogen burns in the presence of oxygen to form water: 2H2 + O2 → 2H2 O + energy Which molecule is oxidized and what kind of bond is formed? A. Hydrogen, nonpolar. B. Oxygen, nonpolar. C. Oxygen, polar. D. Hydrogen, polar.
D
If pigments from a particular species of plant are extracted and subjected to paper chromatography, which of the following is the most believable result? A. Paper chromatography for the plant would isolate a single band of pigment that is characteristic of that particular plant. B. The isolated pigments would always be some shade of green. C. Paper chromatography would isolate only the pigments that reflect green light. D. Paper chromatography would separate the pigments from a particular plant into several bands.
D
In the Calvin cycle, how many ATP molecules are required to regenerate RuBP from five G3P molecules? A. 2 B. 4 C. 5 D. 3 E. 1
D
Two ATP molecules are expended in the energy investment phase of glycolysis. Why is this energy needed to begin the process of glucose catabolism? A. It is needed because glycolysis is considered an exergonic process which always requires input of energy from ATP. B. It is needed to induce the enzymes of glycolysis. C. It is needed to generate the electron carrier NAD+. D. Some energy must be invested to make the glucose molecule unstable and begin the process of catabolism.
D
Which electron carrier(s) function in the Krebs cycle? A. the electron transport chain B. NADH and FADH2 C. NAD+ only D. both NAD+ and FAD
D
In the citric acid cycle, ATP molecules are produced by _____. A. photophosphorylation B. photosynthesis C. oxidative phosphorylation D. cellular respiration E. substrate-level phosphorylation
E
The reaction ADP + P --> ATP is a(n) _____ reaction. A. spontaneous B. chemical C. exergonic D. hydrolysis E. endergonic
E
Outputs of the Calvin cycle
G3P, ADP, NADP+
In the light reactions, light energy is used to oxidize ______ to _____.
H2O.... O2
______ is the compound that functions as the electron acceptor in glycolysis.
NAD+
The reduced form of the electron acceptor NAD+ is _____.
NADH
Inputs of the light reactions
NADP+, ADP, water, light
The elections derived from this oxidation reaction in the light reactions are used to reduce ______ to ______.
NADP+... NADPH
The Calvin cycle oxidizes the light-reactions product _______ to _______.
NADPH... NADP+
_____ splits water into 1/2 O2, H+, and e- .
Photosystem II
True or false? The potential energy in an ATP molecule is derived mainly from its three phosphate groups.
True
True or false? The reactions that generate the largest amounts of ATP during cellular respiration take place in the mitochondria.
True
For each intermediate compound in the Calvin cycle, identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. As an example, the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms.
a. 3 molecules, 3 carbons b. 6 molecules, 18 carbons c. 6 molecules, 18 carbons d. 5 molecules, 15 carbons e. 3 molecules, 15 carbons f. 3 molecules, 15 carbons
Identify the membranes or compartments of the chloroplast by dragging the blue labels to the blue targets. Then, identify where the light reactions and Calvin cycle occur by dragging the pink labels to the pink targets.
a. stroma b. thylakoid membrane c. cytosol d. location of Calvin cycle e. thylakoid space f. location of light reactions g. envelope membranes
A substrate binds to an enzyme at the ______, where the reaction occurs.
active site
The competitive inhibitor competes with the substrate for the ______ on the enzyme.
active site
An enzyme is considered a ______ because it speeds up chemical reactions without being used up.
catalyst
A ______ binds to an enzyme and plays a role in catalysis.
cofactor
A(n) ______ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.
competitive
When properly aligned, the enzyme and substrate form an enzyme-substrate _______.
complex
An enzyme is ______ when it loses its native conformation and its biological activity.
denatured
When the noncompetitive inhibitor is bonded to the enzyme, the shape of the _______ is distorted.
enzyme
In glycolysis, the carbon-containing compound that functions as the electron donor is _______.
glucose
Usually, a(n) ______ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.
irreversible
A(n) _______ inhibitor binds to a site on the enzyme that is not the active site.
noncompetitive
When a compound donates (loses) electrons, that compound becomes ______. Such a compound is often referred to as an electron donor.
oxidized
Energized electrons from ____ enter an electron transport chain and are then used to reduce NADP+.
photosystem I
An enzyme is considered ____ because of its ability to recognize the shape of a particular molecule.
specific
Enzyme inhibitors disrupt normal interactions between an enzyme and its ______.
substrate
In a catalyzed reaction a reactant is often called a ______.
substrate
The first CO2 that is released during aerobic cellular respiration is _____. A. just after the Krebs cycle B. during the Krebs cycle C. between glycolysis and the Krebs cycle D. during glycolysis
C
The light reactions of photosynthesis use _____ and produce _____. A. NADPH ... NADP+ B. carbon dioxide ... sugar C. NADPH ... oxygen D. carbon dioxide ... oxygen E. water ... NADPH
E
Chlorophyll can be found in _____.
photosystems I & II
Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called _______.
pyruvate
When a compound accepts (gains) electrons, that compound becomes reduced. Such a compound is often referred to as an electron acceptor.
reduced
The Calvin cycle occurs in the _____.
stroma
How are the light-dependent and light-independent reactions of photosynthesis related? A. The products of light-dependent reactions are used in light-independent reactions. B. The products of the light-independent reactions are used in the light-dependent reactions. C. The products of light-independent reactions must be present for light-dependent reactions to take place. D. They are not related.
A
How does carbon fixation differ between C3 and C4 plants? A. Rubisco is the primary enzyme that catalyzes carbon fixation in C3 plants, and phosphoenolpyruvate carboxylase can catalyze carbon fixation in C4 plants. B. Both C3 and C4 plants involve carboxylation of ribulose-1,5-bisphosphate by rubisco; but in C3, the first stable intermediate is 3-phosphoglycerate, and in C4, it is oxaloacetate. C. C3 plants don't undergo photorespiration, but C4 plants do. D. C4 plants undergo carbon fixation by carboxylation of a four-carbon substrate (oxaloacetate), while in C3 plants, a three-carbon compound (phosphoglycerate) is carboxylated.
A
The proteins of the electron transport chain active in the light-dependent reactions _____. A. are membrane proteins present in the thylakoid B. are free proteins present in the thylakoid lumen C. absorb the same wavelengths of light as their associated chlorophylls D. are considered to be part of the reaction center of photosystem I
A
If you were to add one of the eight Krebs cycle intermediates to the culture medium of yeast growing in the laboratory, what do you think would happen to their rates of ATP and carbon dioxide production? A. The rates of ATP production and carbon dioxide production would both increase. B. Rates of ATP and carbon dioxide production would probably both decrease. C. There would be no change in ATP production, but we would observe an increased rate of carbon dioxide production. D. The rate of ATP production would decrease, but the rate of carbon dioxide production would increase.
A
In addition to proteins, thylakoid membranes must contain a large number of _____ molecules in the reaction centers in order to harvest light energy. A. pigment B. electron carrier C. water D. phospholipid
A
In an experiment with an enzyme, the 58th amino acid seems to form a covalent bond with a substrate molecule as part of the catalytic process. What would you say? A. At some point the bond between the amino acid and the substrate must break. B. This is probably a case where the enzyme changes the position of equilibrium. C. There must be an error. Enzymes don't make covalent bonds with substrates. D. It couldn't happen. Catalysis doesn't alter the enzyme. E. This is possible in theory, but it's never been observed.
A
In cells, what is usually the immediate source of energy for an endergonic reaction? A. ATP B. sugar C. ADP D. as spontaneous reactions, endergonic reactions do not need an addition of energy E. glucose
A
In fermentation _____ is reduced and _____ is oxidized. A. pyruvate ... NADH B. lactate ... ethanol C. NADH ... lactate D. NAD+ ... pyruvate E. lactate ... NADH
A
Most of the enzymes of the Calvin cycle also function in other metabolic pathways. This should not be a surprising finding, because _____. A. there is a close relationship between carbohydrate synthesis and carbohydrate metabolism B. the Calvin cycle probably evolved at the same time as did glycolysis C. metabolic reactions are catalyzed by enzymes that have multiple functions D. the Calvin cycle is nearly ubiquitous in cells, as are metabolic pathways
A
Refer to the figure in the text. What characteristic of this molecule (ATP) is responsible for its high energy level? A. the closely spaced negative charges associated with the phosphate groups B. the phosphorus atoms in the phosphate groups C. the CH bonds of the ribose sugar D. the three phosphate groups
A
The electrons of photosystem II are excited and transferred to electron carriers. From which molecule or structure do the photosystem II replacement electrons come? A. water B. the electron carrier, plastocyanin D. oxygen E. photosystem I
A
The following reaction A --> B + C + heat is a(n) _____ reaction. A. exergonic B. anabolic C. endergonic D. dehydration synthesis E. exchange
A
The process of photosynthesis probably originated ________. A. in prokaryotes. B. in fungi. C. three separate times. D. in plants.
A
The proteins of the electron transport chain active in the light-dependent reactions ________. A. are membrane proteins present in the thylakoid. B. have hydrophilic exterior surfaces. C. are part of the reaction center of photosystem I. D. are free proteins present in the thylakoid lumen.
A
Using concepts from Chapter 3, which statement best explains why proteins—and not RNA, DNA, carbohydrates, or lipids—are the molecules responsible for "reading" the array of molecular zip codes in cells? A. Because proteins can have diverse structures and chemical properties, different proteins can "read" different zip codes by interacting specifically with them. B. Because proteins store and process information, they can "read" different zip codes via base pairing. C. Because proteins can store energy, they provide the energy to transport other proteins with zip codes to their correct destinations. D. Because protein enzymes can have a diversity of active site structures, they can "read" different zip codes by specifically degrading them.
A
What about anabolic reactions? Anabolic reactions will often have A. a positive ΔG based on an increase in enthalpy and decrease in entropy B. a positive ΔG based on a decrease in enthalpy and increase in entropy C. a negative ΔG based on a decrease in enthalpy and increase in entropy D. a negative ΔG based on an increase in enthalpy and decrease in entropy
A
What is the correct sequence for secreted protein movement through the endomembrane system? A. ER, cis-Golgi, trans-Golgi, vesicles B. cis-Golgi, trans-Golgi, ER, vesicles C. vesicles, ER, trans-Golgi, cis-Golgi D. ER, trans-Golgi, cis-Golgi, vesicles
A
Which of the following statements about the electron transport chain is true? A. NADH and FADH2 donate their electrons to the chain. B. The electron transport chain is the first step in cellular respiration. C. Electrons gain energy as they move down the chain. D. Water is the last electron acceptor.
A
Which of the following statements represents a major difference between prokaryotic cells and eukaryotic cells? A. Eukaryotic cells tend to have much more extensive inner membrane systems and larger numbers of intracellular organelles than do prokaryotes. B. Prokaryotes are generally larger in size than eukaryotes. C. Prokaryotes have cells while eukaryotes do not. Prokaryotes are not able to carry out aerobic respiration, a process that requires a complex inner-membrane system.
A
Which of these reactions requires a net input of energy from its surroundings? A. endergonic B. ATP --> ADP + P C. exergonic D. hydrolysis E. catabolic
A
Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell? A. Fermentation B. Krebs cycle C. Glycolysis D. Electron transport chain
A
Which stage of glucose metabolism produces the most ATP? A. Electron transport and chemiosmosis B. Krebs cycle C. Fermentation of pyruvate to lactate D. Glycolysis
A
Which statement best explains how pulse-chase experiments allowed researchers to study cells as dynamic enterprises—specifically looking at how molecules move inside cells? A. By marking a specific population of molecules with a pulse of label, researchers were able to follow their fate over time. B. By pulsing cells with light at regular intervals, researchers were able to take "snapshot" images of molecules moving inside cells. C. By marking a specific population of molecules by providing label continuously, researchers were able to follow their fate over time. D. By marking a specific population of molecules with a chase of label, researchers were able to follow their fate over time
A
Which statement is most accurate concerning how photosystem II (PS II) compares to the electron transport chain (ETC) of mitochondria? A. In both systems, ATP is produced by chemiosmosis. B. The ETC associated with PS II shares no similar components with the ETC of mitochondria. C. PS II produces ATP by chemiosmosis; the ETC of mitochondria produces ATP by substrate-level phosphorylation. D. In both systems, high-energy electrons come from NADH.
A
Which term describes the degree to which an element attracts electrons? A. Electronegativity. B. Reduction. C. Oxidation. D. Polarity.
A
Data suggest that rubisco (ribulose-1,5-bisphosphate carboxylase) makes up 10% of the total protein found in spinach leaves. Research elucidating the structure of rubisco shows that it has four active sites. Why, with four active sites, might there be such a large concentration of rubisco in plant matter? A. All heterotrophic organisms depend on plants, either directly or indirectly, for their food supply. B. Rubisco is a very slow enzyme; what it lacks in speed, it makes up in numbers. C. Three of the four active sites bind carbon dioxide; only one binds ribulose-1,5-bisphosphate. D. Rubisco catalyzes four of the six reactions found in the Calvin cycle.
B
Eukaryotic cells manufacture cytoskeletal proteins that help to maintain the cells' shapes and functions. What would you predict about these proteins? A. They might travel to the nucleus in a transport vesicle with a specific zip code. B. They would be manufactured on free ribosomes in the cytoplasm. C. They would be glycosylated in the Golgi apparatus. D. They would initially contain signal sequences that would allow their entrance into the endoplasmic reticulum.
B
Flagella and cilia bend or move, imparting mobility to cells. How do these structures move? A. Two microtubules at the core of the structure serve as motor proteins. B. Dynein is a motor protein that hydrolyzes ATP and is responsible for movement of the cilium or flagellum. C. The basal body at the base of the structure hydrolyzes ATP, causing a conformational change that results in movement of the cilium or flagellum. D. Axonemes are structured such that movement is constant.
B
For the oxidation of pyruvate shown in the figure below, which answer correctly identifies molecules involved in the positive (+) and negative (-) control of this reaction? A. +: NAD+, acetyl CoA, AMP; -:CoA, NADH, ATP B. +: NAD+, CoA, AMP;-: acetyl CoA, NADH, ATP C. +: NADH, CoA, ATP; -: acetyl CoA, NAD+, AMP D. +: NAD+, CoA, ATP; -: acetyl CoA, NADH, AMP
B
Some photosynthetic organisms have versions of chlorophyll pigments that absorb most strongly at 390 nm and 880 nm. For the experiment shown in the figure below, which answer best explains how the wavelength graph would change if these organisms were used instead of the alga? A. Bacteria would congregate at all wavelengths across the spectrum. B. Bacteria might still congregate near the violet, but not the red, end of the spectrum because 880 nm is outside of the visible light range used in the experiment. C. Bacteria might still congregate near the red, but not the violet, end of the spectrum. D. The results would not change from those shown.
B
The energy for an endergonic reaction comes from a(n) _____ reaction. A. synthesis B. exergonic C. anabolic D. ADP + P --> ATP E. glucose + glucose --> maltose
B
The final electron acceptor(s) associated with photosystem I is/are _____. A. oxygen B. NADP+ C. water D. NADPH
B
The high-energy electron carrier that is reduced during glycolysis, pyruvate processing, and the citric acid cycle, and which carries electrons to the electron transport system, is _____. A. CSAP B. NADH C. G protein D. RAS
B
The most abundant enzyme on Earth, which catalyzes the fixation of carbon dioxide in photosynthesis, is _____. A. carbon dioxidase B. rubisco C. carotenoids D. chlorophyll
B
Why is photosynthesis so important to life on Earth? A. Photosynthesis is used to drive the formation of carbon dioxide, which releases the energy that allows the planet Earth to remain warm. B. Photosynthesis captures light energy from the Sun and stores it in the bonds of glucose, which is then used during cellular respiration to drive the formation of ATP in all plants and animals. C. Photosynthesis releases carbon dioxide into the air, which is then used during cellular respiration, which in turn drives the release of oxygen, completing the respiration cycle. D. Photosynthesis breaks down glucose, which provides ATP for all plants and animals.
B
The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions. But is the inverse true as well? Do the light reactions depend on the Calvin cycle? Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.) A. The rate of O2 production would remain the same because the light intensity did not change. B. The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease. C. The rate of O2 production would remain the same because the light reactions are independent of the Calvin cycle. D. The rate of O2 production would decrease because the rate of G3P production by the Calvin cycle would decrease.
B
Which molecule is metabolized in a cell to produce energy for performing work? A. ATP B. Glucose C. Phosphate D. ADP
B
Which of the following statements is not true of most cellular redox reactions? A. Changes in potential energy can be released as heat. B. A hydrogen atom is transferred to the atom that loses an electron. C. The electron acceptor is reduced. D. The reactant that is oxidized loses electrons.
B
Which statement most accurately explains why ATP hydrolysis is highly exergonic? A. ATP contains the carbohydrate ribose, which stores a large amount of chemical energy. B. There is a large drop in potential energy because charge repulsion is reduced, accompanied by a large increase in entropy. C. Energy is released when a phosphate group is added. D. There is a large increase in potential energy because charge repulsion is reduced, accompanied by a large increase in entropy.
B
Which step of the cellular respiration pathway can take place in the absence of oxygen? A. Electron transport chain B. Glycolysis C. Fermentation D. Krebs cycle
B
Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other? A. Ionic and covalent. B. Anion and cation. C. Polar and nonpolar. D. Proton and electron.
B
Why are there several structurally different pigments in the reaction centers of photosystems? A. They enable the reaction center to excite electrons to a higher energy level. B. This setup enables the plant to absorb light energy of a variety of wavelengths. C. Excited electrons must pass through several pigments before they can be transferred to electron acceptors of the electron transport chain. D. They enable the plant to absorb more photons from light energy, all of which are at the same wavelength.
B
You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? A. Removing the irreversible inhibitor should get the reaction working again. B. The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. C. Adding more substrate will increase the rate of reaction. D. Adding more inhibitor should get the reaction up to speed again.
B
You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again? A. Add more inhibitor to speed up the reaction. B. Add more substrate; it will outcompete the inhibitor and increase the reaction rate. C. Increase the temperature. D. Increase the pH.
B
Which features are common to all cells? Check all that apply. A. vacuoles B. genetic information (DNA) in chromosomes C. photosynthetic membranes D. chloroplasts E. the cytoplasm F. the endoplasmic reticulum G. cytoskeleton H. lysosomes I. ribosomes J. the cell wall K. flagella and fimbriae L. the plasma membrane M. mitochondria N. the nucleus
B, E, G, I, L
A reaction is said to be unfavorable if ... (a) it will be very slow without a catalyst. (b) the free energy change for the reaction is positive. (c) equilibrium favors the reactants, not the products. Both (a) and (b). Both (b) and (c).
Both (b) and (c).
How can "induced fit" influence the specificity of an enzyme? (a) It can not influence the specificity of an enzyme. (b) It moves the reactive portion of the enzyme closer to the substrate. (c) The enzyme's active site changes shape to fit the correct substrate but not other molecules. Both (b) and (c). None of the above.
Both (b) and (c).
Which type of control agent exerts noncompetitive inhibition? (a) Substrate analog (b) Protein kinase (c) Allosteric effector Both (b) and (c). (a), (b), and (c).
Both (b) and (c).
The reaction A → B is unfavorable by itself, but through energy-coupling, cells can use ATP to convert A into B. How is this done? (a) Hydrolysis of ATP releases heat that is used by the unfavorable reaction. (b) ATP acts as a catalyst to speed the unfavorable reaction. (c) The unfavorable reaction is replaced by two favorable reactions. Both (a) and (b). Both (b) and (c).
C
What is the main purpose of the light-dependent reactions of photosynthesis? A. to produce NADPH for use in respiration B. to generate oxygen by "splitting" H2O C. to produce NADPH and ATP D. to use ATP to make glucose
C
When a photon of light is absorbed by a pigment molecule, electrons in the molecule _____. A. fall back down to ground level B. are blown away from the entire complex C. enter an excited state D. remain unchanged
C
Which of the following statements is true of the bonds in a water molecule? A. Oxygen acts as the electron acceptor and is oxidized. B. The electron in each hydrogen atom is completely transferred to the oxygen atom, and each hydrogen atom has a net charge of +1. C. Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero. D. There is equal sharing of the electrons between the oxygen atom and the two hydrogen atoms, and the net charge is zero.
C
Which statement most accurately describes what happens to proteins that lack an ER signal sequence? A. They are inserted into the plasma membrane. B. They bypass the ER but enter the Golgi apparatus. C. They are released into the cytosol. D. They are inserted into the ER membrane but do not enter the ER lumen.
C
Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration? A. NADH B. Water C. ATP D. Carbon dioxide
D
Mitochondria are separated into two compartments (the matrix and the intermembrane space) by their inner and outer membranes. How does the presence of two compartments contribute to mitochondrial function? A. It allows the cell to conserve energy by reducing the frequency of endergonic reactions. B. It segregates the mitochondrial DNA and the ribosomes from the functional compartment of the mitochondria. C. It enables the mitochondrion to glycosylate proteins more rapidly. D. It permits different but complementary functions to be accomplished in the same organelle.
D
Photorespiration is _____. A. a process that rarely occurs in photosynthetic organisms B. a process involving addition of oxygen to ribulose-1,5-bisphosphate and the formation of ribose-1,5-diphosphate C. a process involving the carboxylation of ribulose-1,5-bisphosphate D. a process involving the addition of oxygen to ribulose-1,5-bisphosphate and the formation of the products 3-phosphoglycerate and 2-phosphoglycolate
D
Scientists found that polypeptides that are normally synthesized in the endoplasmic reticulum are about 20 amino acids longer when they are synthesized by ribosomes not attached to the endoplasmic reticulum. What is/are possible explanations for the greater length of these polypeptides? A. The protein has a different function in the cytosol than in the endoplasmic reticulum. B. The ribosomes that function as free ribosomes function differently than the ribosomes that are attached to the endoplasmic reticulum. C. The 20-amino-acid sequence helps the endoplasmic reticulum package these proteins for shipping to the Golgi. D. The 20 amino acids serve as a signal sequence that directs the forming polypeptide to the endoplasmic reticulum, where they are cleaved off during processing.
D
Stomata, openings in the leaf, are important to photosynthesis for ________. A. entry of oxygen that is used in the Calvin cycle. B. removal of water and carbon dioxide, the end-products of photo-oxidation. C. removal of nitrogen-containing waste products. D. entry of carbon dioxide that is used in the Calvin cycle.
D
Using what you have learned about changes in free energy, would you predict the ΔG value of catabolic reactions to be positive or negative? Catabolic reactions will often have A. a positive ΔG based on a decrease in enthalpy and increase in entropy B. a negative ΔG based on an increase in enthalpy and decrease in entropy C. a positive ΔG based on an increase in enthalpy and decrease in entropy D. a negative ΔG based on a decrease in enthalpy and increase in entropy
D
What is a nuclear localization signal? A. a molecule that is attached to nuclear proteins so that they are retained inside the nucleus B. a stretch of amino acids that directs proteins from the nucleus to the ER C. a component of the multiprotein nuclear pore complex D. a signal built into a protein that directs it to the nucleus
D
What is energy coupling? A. a description of the energetic relationship between the reactants and products in an exergonic reaction B. the use of an enzyme to reduce EA C. a barrier to the initiation of a reaction D. the use of energy released from an exergonic reaction to drive an endergonic reaction E. the hydrolysis of ATP to ADP + P
D
What is the fate of the phosphate group that is removed when ATP is converted to ADP? A. It is acquired by a reactant in an exergonic reaction. B. It is used to convert an ATP into an AQP. C. It is acquired by a reactant in a spontaneous reaction. D. It is acquired by a reactant in an endergonic reaction. E. It is broken down into one phosphorus and four oxygen atoms.
D
What purpose does fermentation serve? A. Under aerobic conditions, it drives the formation of acetyl CoA, which then feeds into the citric acid cycle. B. It allows for the production of NADH, which keeps the electron transport chain going. C. It produces an abundance of ATP when oxygen is present. D. It regenerates NAD+ from NADH to keep glycolysis going in the absence of oxygen.
D
When a pathway is subject to allosteric feedback inhibition, ... A. the last enzyme in the pathway is allosteric. B. an increase in effector concentration speeds the pathway. C. the concentration of effectors does not change with time. D. an accumulation of effectors slows the pathway. E. the effector is made by another pathway.
D
When allosteric effector X binds to enzyme #1, the enzyme stops working. Nevertheless, the speed of the reaction can be altered by adjusting the concentration of X. How? A. When X detaches from an enzyme, the enzyme regains full activity. B. X easily escapes from the allosteric site. C. There are many copies of the enzyme. D. All of the above. E. None of the above.
D
Which fact is most important in explaining how enzymes speed reactions? A. It takes less energy to break a hydrogen bond than a covalent bond. B. Every reaction step adds to the time required for the overall reaction. C. Very low potential energy tends to make molecules unstable. D. High-energy collisions are less common than low-energy collisions. E. Large molecules collide more energetically than small molecules.
D
Why is it not entirely accurate to adopt the common phrase "light-independent reactions" when referring to the Calvin cycle? A. Calvin cycle enzymes are found in the same cellular location as photosystems I and II. B. The Calvin cycle occurs only when stomata are open, which is triggered by light. C. Biologists have discovered that its reactions are triggered directly by light. D. Although its reactions are not triggered directly by light, they depend on the products of light-capturing reactions.
D
Why is measuring the rate of oxygen production in chloroplasts appropriate for estimating the rate of photosynthesis? A. Oxygen is produced by splitting CO2 in the photosystem II complex. B. The Calvin cycle produces oxygen. C. Oxygen is produced by "splitting" water in the photosystem I complex. D. Oxygen is produced by "splitting" water in the photosystem II complex.
D
Which of these enters the citric acid cycle? A. glucose B. pyruvate C. NADH + H+ D. G3P E. acetyl CoA
E
Which of these is NOT a product of the citric acid cycle? A. FADH2 B. CO2 C. ATP D. NADH + H+ E. acetyl CoA
E
_____ releases energy that is used to pump hydrogen ions from the stroma into the thylakoid compartment.
Electron transport chain
Drag the labels to the appropriate targets to indicate the numbers of molecules of ATP/ADP, NADPH/NADP+, and Pi (inorganic phosphate groups) that are input to or output from the Calvin cycle.
a. 6 ATP --> 6 ADP b. 6 NADPH --> 6 NADP+ c. 6 Pi d. 2 Pi e. 3 ATP --> 3 ADP