Ready to master cellular respiration and boost your AP score? Our ap biology unit 2 practice test is engineered to challenge and refine your understanding of metabolic pathways, from glycolysis to the Krebs cycle and electron transport chain. Ideal for students seeking targeted ap bio chapter 9 practice test items and a comprehensive ap biology cellular respiration practice test, this quiz will test your recall of ATP yield, NADH and FADH2 production, and pathway regulation. You'll also get strategies for time management and question analysis to enhance your ap bio test practice sessions. Kick off your review with our ap biology practice quiz or drill down on cellular respiration chapter 9 essentials - dive in now to see where you excel and ace your exam!
What is the primary purpose of cellular respiration?
To synthesize proteins from amino acids
To convert light energy into chemical energy
To produce ATP for cellular activities
To break down DNA during cell division
Cellular respiration is the process by which cells convert nutrients into ATP, the main energy currency. Without ATP production, cells cannot perform vital activities such as metabolism and transport. This process is central to energy flow in all aerobic organisms. Learn more.
In which organelle does the citric acid cycle occur?
Nucleus
Mitochondrial intermembrane space
Mitochondrial matrix
Cytoplasm
The citric acid cycle takes place in the mitochondrial matrix where enzymes for the cycle are located. This localization allows NADH and FADH2 to shuttle electrons to the electron transport chain efficiently. The proximity of the matrix to the inner membrane is key for oxidative phosphorylation. Read more.
Which molecule serves as the final electron acceptor in the electron transport chain?
FAD
NAD+
ADP
Oxygen
Oxygen is the terminal electron acceptor in aerobic respiration, forming water when reduced. This step is essential to maintain the flow of electrons through the chain. Without oxygen, the electron transport chain would back up and ATP synthesis would cease. Details here.
During glycolysis, what is the net yield of ATP per glucose molecule?
2 ATP
4 ATP
6 ATP
0 ATP
Glycolysis invests 2 ATP molecules and produces 4 ATP by substrate-level phosphorylation, netting 2 ATP per glucose. It also yields 2 NADH and 2 pyruvate molecules. This process occurs in the cytosol and does not require oxygen. More info.
Which of the following is a product of glycolysis?
Pyruvate
Glucose-6-phosphate
Oxaloacetate
Acetyl-CoA
Pyruvate is the end product of glycolysis, formed after a series of ten enzyme-catalyzed reactions. It can be further oxidized to acetyl-CoA or fermented under anaerobic conditions. Pyruvate links glycolysis to the citric acid cycle. Learn more.
What type of phosphorylation generates ATP directly during glycolysis and citric acid cycle?
Chemiosmotic phosphorylation
Photophosphorylation
Oxidative phosphorylation
Substrate-level phosphorylation
Substrate-level phosphorylation transfers a phosphate group directly to ADP from an intermediate substrate. It occurs in glycolysis and the citric acid cycle. This mechanism is distinct from oxidative phosphorylation in the electron transport chain. Read more.
Which coenzyme carries electrons to the electron transport chain from glycolysis and the citric acid cycle?
ATP
NADH
Coenzyme A
FADH
NADH carries high-energy electrons from glycolysis and the citric acid cycle to the electron transport chain. It donates electrons to Complex I, driving proton pumping. This is essential for generating the proton gradient used in ATP synthesis. Details.
Where does oxidative phosphorylation take place in the mitochondrion?
Mitochondrial matrix
Inner mitochondrial membrane
Outer mitochondrial membrane
Intermembrane space
Oxidative phosphorylation occurs at the inner mitochondrial membrane where the electron transport chain complexes are located. Proton pumping across this membrane generates the gradient used by ATP synthase. This separation of compartments is key to chemiosmosis. See more.
Which process produces the most ATP overall during aerobic respiration?
Oxidative phosphorylation
Citric acid cycle
Pyruvate oxidation
Glycolysis
Oxidative phosphorylation via the electron transport chain generates the bulk of ATP (~26 - 28 ATP per glucose). It harnesses the proton gradient created by electron transfer. Glycolysis and the citric acid cycle contribute only a small fraction directly. More info.
Which compound links glycolysis to the citric acid cycle?
Citrate
Fructose-1,6-bisphosphate
Acetyl-CoA
Oxaloacetate
Pyruvate generated in glycolysis is converted to acetyl-CoA before entering the citric acid cycle. This reaction is catalyzed by the pyruvate dehydrogenase complex. Acetyl-CoA donates its acetyl group to oxaloacetate to form citrate. Learn more.
What is the net NADH yield from one glucose molecule after glycolysis and pyruvate oxidation?
8 NADH
4 NADH
2 NADH
6 NADH
Glycolysis produces 2 NADH per glucose. Each pyruvate oxidation yields 1 NADH, and since there are two pyruvates, that gives 2 more. The total NADH before the citric acid cycle is therefore 4. Reference.
Which enzyme directly synthesizes ATP using the proton gradient in mitochondria?
Succinate dehydrogenase
Cytochrome c oxidase
ATPase
ATP synthase
ATP synthase uses the proton-motive force across the inner membrane to phosphorylate ADP to ATP. It works like a rotary motor driven by protons flowing back into the matrix. This enzyme couples chemiosmosis to ATP production. More here.
Which byproduct is generated when oxygen accepts electrons at the end of the electron transport chain?
Ozone
Carbon dioxide
Water
Ammonia
When oxygen accepts electrons and protons at Complex IV, it is reduced to water. This reaction prevents backup of electrons in the chain. Formation of water is essential for efficient ATP production. Learn more.
What is substrate-level phosphorylation?
ATP generation by ATP synthase
Direct phosphate transfer to ADP
Phosphate pumping across membranes
Photon-driven ATP synthesis
Substrate-level phosphorylation is the enzymatic transfer of a phosphate group from a substrate to ADP, forming ATP. It occurs in glycolysis and the citric acid cycle. This process does not require a proton gradient. More info.
Which step of cellular respiration releases the most carbon dioxide?
Glycolysis
Electron transport chain
Citric acid cycle
Pyruvate oxidation
The citric acid cycle releases two CO? molecules per acetyl-CoA, totaling four per glucose. Pyruvate oxidation releases one CO? per pyruvate (two per glucose). Glycolysis releases no CO?. Learn more.
How many total ATP molecules can be produced from one molecule of glucose under ideal aerobic conditions?
30 ATP
32 ATP
24 ATP
36 ATP
Under ideal conditions, eukaryotic cells yield about 32 ATP per glucose (2 from glycolysis, 2 from the citric acid cycle, and ~28 from oxidative phosphorylation). The actual yield may vary. This tally accounts for shuttle losses and mitochondrial membrane transport. Reference.
Which complex of the electron transport chain pumps protons from the matrix to the intermembrane space?
Complex I, III, and IV
Complex I only
Complex II only
Complex IV only
Complexes I, III, and IV actively pump protons across the inner mitochondrial membrane. Complex II transfers electrons but does not pump protons. The proton gradient drives ATP synthase. Learn more.
Which shuttle system transfers electrons from cytosolic NADH into mitochondria in heart and liver cells?
Glycerol-3-phosphate shuttle
Pentose phosphate shuttle
Malate - aspartate shuttle
Urea cycle
The malate - aspartate shuttle carries electrons from NADH in the cytosol into the mitochondrial matrix. It regenerates NAD+ in the cytosol and produces NADH inside mitochondria. This shuttle is efficient in heart and liver cells. More.
What is the role of Coenzyme Q (ubiquinone) in the electron transport chain?
Catalyst for substrate-level phosphorylation
Proton carrier to ATP synthase
Final electron acceptor
Mobile electron carrier between complexes I/II and III
Coenzyme Q transfers electrons from Complexes I and II to Complex III. It is lipid-soluble and moves within the inner membrane. This step is critical for maintaining electron flow. Learn more.
Which enzyme in the citric acid cycle catalyzes a substrate-level phosphorylation?
Alpha-ketoglutarate dehydrogenase
Succinyl-CoA synthetase
Isocitrate dehydrogenase
Citrate synthase
Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, producing GTP (or ATP) directly. This is the only substrate-level phosphorylation in the citric acid cycle. The GTP can be converted to ATP. Details.
Which molecule inhibits the enzyme phosphofructokinase-1 in glycolysis?
Fructose-2,6-bisphosphate
Citrate
ADP
AMP
Citrate is an allosteric inhibitor of phosphofructokinase-1, linking the citric acid cycle to glycolysis. High citrate levels signal abundant energy, slowing glycolysis. This feedback prevents excess ATP production. Learn more.
How does uncoupling protein (UCP) affect oxidative phosphorylation?
Allows proton leak, producing heat
Enhances substrate-level phosphorylation
Blocks electron transport
Increases ATP yield
UCPs allow protons to re-enter the mitochondrial matrix without passing through ATP synthase. This uncoupling dissipates the proton gradient as heat. Brown adipose tissue uses UCP1 for thermogenesis. More info.
During intense exercise when oxygen is limited, which process regenerates NAD+ in muscle cells?
Alcohol fermentation
Electron transport chain
Lactic acid fermentation
Pentose phosphate pathway
Lactic acid fermentation reduces pyruvate to lactate, oxidizing NADH back to NAD+. This regeneration allows glycolysis to continue under anaerobic conditions. The buildup of lactate causes muscle fatigue. Reference.
Which factor would decrease the proton gradient across the inner mitochondrial membrane?
Presence of an uncoupler
Inhibition of ATP synthase
Enhanced electron flow
Increased ADP availability
Uncouplers dissipate the proton gradient by allowing protons to leak back into the matrix. This reduces the gradient without producing ATP. As a result, heat is generated instead of ATP. Learn more.
Why does FADH2 produce fewer ATP molecules than NADH in oxidative phosphorylation?
It bypasses Complex I, entering at Complex II
It is oxidized outside the mitochondria
It carries fewer electrons overall
It cannot donate protons
FADH2 donates electrons at Complex II, which does not pump protons. As a result, fewer protons are translocated, generating fewer ATP. NADH enters at Complex I, pumping more protons. More.
What is the P/O ratio for NADH oxidation in mitochondria?
2.5
1.5
3.0
4.0
The P/O ratio describes the number of ATP molecules formed per oxygen atom reduced. For NADH, the ratio is about 2.5. This reflects protons pumped by Complexes I, III, and IV. Learn more.
Which intermediate of the citric acid cycle is also a key amino acid precursor?
Citrate
Oxaloacetate
?-Ketoglutarate
Succinyl-CoA
?-Ketoglutarate is transaminated to form glutamate and other amino acids. It serves as a key link between carbon metabolism and nitrogen metabolism. This makes it important for biosynthesis. More info.
Which reaction in the citric acid cycle produces FADH2?
Succinate to fumarate
?-Ketoglutarate to succinyl-CoA
Isocitrate to ?-ketoglutarate
Malate to oxaloacetate
Succinate dehydrogenase oxidizes succinate to fumarate, reducing FAD to FADH2. This enzyme is part of both the citric acid cycle and Complex II of the ETC. It directly links the cycle to oxidative phosphorylation. Learn more.
How many NADH molecules are produced per turn of the citric acid cycle?
3 NADH
2 NADH
4 NADH
1 NADH
Each turn of the citric acid cycle yields 3 NADH from isocitrate dehydrogenase, ?-ketoglutarate dehydrogenase, and malate dehydrogenase. These NADH molecules carry electrons to the ETC. This yield is per acetyl-CoA oxidized. Details.
What drives the conformational changes in the beta subunits of ATP synthase?
Release of phosphate
Binding of ADP
Rotation of the ? subunit
Proton binding to alpha subunit
Proton flow through the Fo channel rotates the c-ring and attached ? subunit. The rotating ? subunit induces conformational changes in the beta subunits, driving ATP synthesis. This mechanical coupling is central to chemiosmotic theory. Learn more.
Which inhibitor binds to Complex IV and prevents electron transfer to oxygen?
Oligomycin
Cyanide
Antimycin A
Rotenone
Cyanide binds to the Fe³? center in cytochrome a3 of Complex IV. This prevents reduction of oxygen to water and halts the ETC. Cells cannot generate ATP through oxidative phosphorylation. More.
What is the effect of high NADH/NAD+ ratio on the citric acid cycle?
Converts cycle to anabolic mode
Inhibits cycle by feedback inhibition
Stimulates cycle by activating dehydrogenases
No effect on cycle rate
A high NADH/NAD+ ratio indicates abundant reducing power, leading to feedback inhibition of dehydrogenase enzymes. This slows the citric acid cycle when energy is sufficient. It prevents unnecessary oxidation of acetyl-CoA. Details.
Which statement about glycerol-3-phosphate shuttle is correct?
It yields fewer ATP per NADH than malate - aspartate shuttle
It regenerates FAD inside the matrix
It produces ATP directly in the cytosol
It transfers electrons to Complex I
The glycerol-3-phosphate shuttle transfers electrons from NADH to FAD in the inner membrane, forming FADH2. Because FADH2 enters at Complex II, it yields fewer ATP than NADH entering via the malate - aspartate shuttle. This shuttle is prominent in muscle. Learn more.
What is the ?G°? of ATP hydrolysis under standard conditions?
+7.3 kcal/mol
- 7.3 kcal/mol
- 3.0 kcal/mol
0 kcal/mol
The standard free energy change (?G°?) for ATP hydrolysis to ADP and Pi is approximately - 7.3 kcal/mol. This negative value makes ATP a high-energy molecule. Cellular conditions often make the in vivo ?G even more negative. More info.
Which reaction step produces GTP in the citric acid cycle?
Malate to oxaloacetate
Succinyl-CoA to succinate
?-Ketoglutarate to succinyl-CoA
Isocitrate to ?-ketoglutarate
Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, producing GTP via substrate-level phosphorylation. This GTP is readily converted to ATP by nucleoside diphosphate kinase. It is the sole GTP-generating step in the cycle. Details.
Which ion contributes directly to the proton-motive force besides protons?
Sodium
Electrical potential across the membrane
Calcium
Hydroxide
The proton-motive force has two components: the chemical gradient (?pH) and the electrical potential (??) across the inner membrane. The electrical component arises from charge separation by proton pumping. Both drive ATP synthesis. Learn more.
What is the stoichiometry of proton translocation per NADH oxidation?
4 H+ per NADH
14 H+ per NADH
10 H+ per NADH
6 H+ per NADH
Oxidation of NADH by the ETC pumps approximately 10 protons out: 4 by Complex I, 4 by Complex III (via Q cycle), and 2 by Complex IV. This establishes the proton gradient used by ATP synthase. Learn more.
Which metabolic intermediate exits the citric acid cycle for amino acid synthesis?
?-Ketoglutarate
Malate
Succinate
Fumarate
?-Ketoglutarate can be transaminated to form glutamate and other amino acids. Its removal from the cycle requires anaplerotic reactions to replenish oxaloacetate. This link integrates catabolism and biosynthesis. Reference.
How does arsenic poisoning affect cellular respiration?
Uncouples oxidative phosphorylation
Prevents ATP from binding synthase
Inhibits Complex IV
Blocks pyruvate dehydrogenase by binding lipoic acid
Arsenic compounds bind to lipoic acid cofactor of pyruvate dehydrogenase, halting pyruvate oxidation and citric acid cycle entry. This blocks ATP production by both substrate-level and oxidative phosphorylation. Poisoning leads to rapid ATP depletion. More.
Which cofactor is tightly bound to Complex II and directly participates in electron transfer?
FMN
NAD+
Coenzyme Q
FAD
Complex II (succinate dehydrogenase) contains FAD as a prosthetic group that accepts electrons from succinate. It then transfers electrons to Coenzyme Q. Unlike other complexes, Complex II does not pump protons. Learn more.
Which acid-base component contributes to the proton-motive force directly?
High matrix pH
Low intermembrane pH
Low ADP concentration
High ATP concentration
A low pH (high [H+]) in the intermembrane space compared to the matrix drives protons back through ATP synthase. This chemical gradient component is one half of the proton-motive force. The electrical component arises from charge separation. More.
How does substrate channeling in the pyruvate dehydrogenase complex increase efficiency?
By releasing intermediates into the matrix
By passing intermediates directly between active sites
By exporting products to the cytosol immediately
By sequestering substrates away from enzymes
Substrate channeling transfers intermediates directly between enzyme active sites without diffusion. This reduces side reactions and increases reaction rate. In PDH, lipoamide arms shuttle intermediates between E1, E2, and E3. Learn more.
Which alternative electron acceptor allows certain bacteria to perform anaerobic respiration?
ATP
Oxygen
Glucose
Nitrate (NO3 - )
Some bacteria use nitrate as a terminal electron acceptor when oxygen is absent. This anaerobic respiration yields less ATP than aerobic respiration. Nitrate reduction regenerates oxidized cofactors for ETC continuation. Details.
In mitochondria, which transporter exchanges ATP for ADP across the inner membrane?
Phosphate translocase
Malate - aspartate transporter
ATP - ADP translocase (ANT)
Pyruvate carrier
The ATP - ADP translocase exchanges matrix ATP for cytosolic ADP in a one-for-one exchange. This antiporter maintains ATP supply to the cytosol. It is driven by the membrane potential. More.
Which modification of the inner membrane increases its surface area for oxidative phosphorylation?
Cristae formation
Thylakoid stacking
Tectorial membrane development
Microvilli formation
Cristae are infoldings of the inner mitochondrial membrane that greatly increase surface area. This expansion allows more ETC complexes and ATP synthase molecules. Enhanced surface area boosts ATP production. Learn more.
How does mitochondrial NADH from the TCA cycle differ from cytosolic NADH in terms of ATP yield?
Cytosolic NADH cannot enter mitochondria
Cytosolic NADH yields more ATP
Mitochondrial NADH yields more ATP
They yield the same ATP amount
Mitochondrial NADH donates electrons at Complex I, yielding ~2.5 ATP. Cytosolic NADH must use shuttles (e.g., glycerol-3-phosphate) that deliver electrons to FADH2 at Complex II, yielding ~1.5 ATP. Thus, cytosolic NADH produces less ATP indirectly. Details.
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Study Outcomes
Understand Glycolysis Mechanisms -
Identify each step of glycolysis and explain how glucose is converted into pyruvate while generating ATP and NADH in the context of this AP Biology Unit 2 practice test.
Analyze Pyruvate Oxidation and the Citric Acid Cycle -
Break down the transformation of pyruvate into acetyl-CoA and evaluate the key reactions and energy yields in the citric acid cycle from AP Bio chapter 9.
Compare Aerobic and Anaerobic Pathways -
Distinguish between aerobic respiration and fermentation by examining their electron acceptors, ATP yields, and physiological roles in cellular metabolism.
Interpret Electron Transport Chain Function -
Explain how NADH and FADH₂ donate electrons, trace the proton gradient across the mitochondrial membrane, and link chemiosmosis to ATP synthesis in an ap biology cellular respiration practice test setting.
Assess how inhibitors, uncouplers, and substrate availability influence ATP production and respiratory control in this chapter 9 practice test on cellular respiration.
Apply AP Bio Test Strategies for Chapter 9 -
Use targeted question”solving techniques to approach multiple”choice items effectively and boost your confidence in ap bio test practice focused on cellular respiration.
Cheat Sheet
Glycolysis Overview -
Glycolysis occurs in the cytosol and converts one glucose into two pyruvate molecules, yielding a net gain of 2 ATP and 2 NADH per glucose (Campbell Biology, Chapter 9). Remember the investment phase (use 2 ATP) and payoff phase (produce 4 ATP); the overall reaction is: Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP. A handy mnemonic is "Goodness Gracious, Frankie's Fries Are Perfectly Yummy" to recall the key glycolytic enzymes in order.
Pyruvate Oxidation & Citric Acid Cycle -
In the mitochondrial matrix, each pyruvate is oxidized to acetyl-CoA, producing 1 NADH and 1 CO2, then enters the citric acid cycle to yield 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA (Lehninger Principles of Biochemistry). Use the acronym "OIL RIG" (Oxidation Is Loss, Reduction Is Gain) to track electron transfer and the phrase "Can I Keep Selling Sex For Money Officer?" to remember citrate synthase, isocitrate dehydrogenase, and other cycle enzymes.
Electron Transport Chain & Chemiosmosis -
The inner mitochondrial membrane hosts complexes I - IV that shuttle electrons from NADH and FADH2 to oxygen, pumping protons into the intermembrane space (NCBI Educational Resources). The resulting proton-motive force drives ATP synthase (Complex V) to generate about 26 - 28 ATP per glucose. A useful tip is "Please Excuse My Dear Aunt Sally" to remember the order: Protein complexes, Electron carriers, Membrane pump, Driving force, ATP synthase.
Total ATP Yield & Efficiency -
The theoretical maximum yield from one glucose is ~30 - 32 ATP, but actual yields hover around 26 - 28 ATP due to proton leak and shuttle costs (University of California, Berkeley Bio 1B Lecture Notes). Remember that the malate - aspartate and glycerol phosphate shuttles affect NADH's entry into mitochondria, altering net yield. When preparing for the AP Biology Unit 2 practice test, compare theoretical vs. real values to refine your calculations.
Regulation & Feedback Control -
Key regulatory enzymes include phosphofructokinase (PFK) in glycolysis, inhibited by high ATP and citrate and activated by AMP, and isocitrate dehydrogenase in the citric acid cycle (Harvard Biochemistry Lecture). This feedback ensures cells match ATP production to demand. A memory aid is "ATP tells PFK to Pause, AMP tells PFK to Proceed," helping you ace ap bio chapter 9 questions on allosteric regulation.
