Curious how cells convert nutrients into energy? Our free respiration quiz is designed to test your knowledge of the respiration process questions - from glycolysis and the Krebs cycle to gas exchange in human lungs and ATP production. In this respiration quiz, you'll tackle electron transport chain steps, anaerobic pathways, and real-life scenarios that reinforce key concepts while earning instant feedback. Dive into energy pathways with our in-depth cellular respiration quiz and see how photosynthesis ties in through a fun photosynthesis and respiration challenge . Whether you're exploring types of respiration quiz topics or brushing up for a human respiration quiz final, this adventure is perfect for students, educators, and bio buffs alike. Ready to power up? Take the quiz now and challenge a friend!
Where in the cell does glycolysis take place?
Nucleus
Cytosol
Mitochondrial matrix
Intermembrane space
Glycolysis is the metabolic pathway that breaks down glucose into pyruvate and occurs in the cytosol of the cell, independent of mitochondria. This allows quick ATP production under both aerobic and anaerobic conditions. For more details on each step of glycolysis, see Glycolysis.
What is the net ATP yield per molecule of glucose in glycolysis?
4 ATP
38 ATP
2 ATP
36 ATP
Glycolysis uses 2 ATP in its preparatory phase and generates 4 ATP in the payoff phase, giving a net yield of 2 ATP per molecule of glucose broken down. It also yields NADH which feeds into oxidative phosphorylation. Review steps and energy accounting at Glycolysis energy yield.
Which molecule is the final electron acceptor in aerobic cellular respiration?
FAD
NAD+
Water
Oxygen
In aerobic respiration, oxygen accepts electrons at the end of the electron transport chain, combining with protons to form water. Without oxygen, the chain cannot operate and ATP production halts. For more, see Electron transport chain.
What is the main reduced molecule produced by the Krebs cycle that feeds electrons into the electron transport chain?
NADH
ATP
Acetyl-CoA
Pyruvate
The Krebs cycle generates NADH (and FADH2) by oxidizing acetyl-CoA. NADH carries high-energy electrons to the electron transport chain for ATP production. Detailed reactions are available at Citric acid cycle.
Which molecule is considered the primary energy currency of the cell?
ADP
ATP
FADH2
NADH
Adenosine triphosphate (ATP) stores and transfers energy in cells. Hydrolysis of its high-energy phosphate bonds releases energy to drive cellular processes. Learn more at ATP.
Fermentation occurs in cells when which of the following is absent?
Glucose
Mitochondria
Oxygen
ATP
Fermentation pathways regenerate NAD+ from NADH when oxygen is not available to accept electrons in the electron transport chain. This enables glycolysis to continue producing ATP anaerobically. See Fermentation.
Pyruvate is transported into which organelle for conversion to acetyl-CoA?
Mitochondria
Cytosol
Golgi apparatus
Chloroplast
Pyruvate crosses the mitochondrial membranes into the matrix, where the pyruvate dehydrogenase complex converts it to acetyl-CoA. This links glycolysis to the Krebs cycle. More at Pyruvate dehydrogenase complex.
Which enzyme uses the proton gradient to synthesize ATP during oxidative phosphorylation?
Hexokinase
ATP synthase
DNA polymerase
Dehydrogenase
ATP synthase harnesses the energy of protons flowing down their gradient through its Fo component to drive ATP formation in the F1 portion. This process is called chemiosmosis. See ATP synthase.
How many CO2 molecules are released during the Krebs cycle per molecule of glucose?
2 CO2
8 CO2
6 CO2
4 CO2
Each glucose yields two acetyl-CoA molecules. Each acetyl-CoA entering the Krebs cycle produces two CO2, for a total of four CO2 per glucose. Further CO2 is released in the PDH reaction before the cycle. Read more at Citric acid cycle.
Which complex of the electron transport chain does NOT pump protons across the inner mitochondrial membrane?
Complex IV
Complex III
Complex I
Complex II
Complex II (succinate dehydrogenase) transfers electrons from FADH2 to the chain but does not translocate protons. Complexes I, III, and IV all contribute to the proton gradient. Details at Electron transport chain.
What is the approximate P/O ratio for oxidation of one NADH molecule?
About 2.5
About 1.5
About 2
About 3
The P/O ratio represents ATP produced per oxygen atom reduced. For NADH, it's about 2.5 ATP. This accounts for protons pumped and the stoichiometry of ATP synthase. See P/O ratio.
Which shuttle transfers electrons from cytosolic NADH into the mitochondria in muscle cells?
Hexose phosphate shuttle
Citrate shuttle
Glycerol 3-phosphate shuttle
Malate - aspartate shuttle
In muscle and brain, the glycerol 3-phosphate shuttle transfers electrons from NADH to FADH2 at complex II, bypassing complex I. This yields fewer ATP but operates rapidly. Details at Glycerol phosphate shuttle.
Which enzyme catalyzes the condensation of acetyl-CoA with oxaloacetate in the first step of the Krebs cycle?
Isocitrate dehydrogenase
Succinate dehydrogenase
Citrate synthase
?-Ketoglutarate dehydrogenase
Citrate synthase catalyzes the irreversible condensation of acetyl-CoA and oxaloacetate to form citrate in the mitochondrial matrix. It's a key regulatory step in the cycle. More information at Citrate synthase.
What role does oxygen play in oxidative phosphorylation?
Electron donor
Final electron acceptor
Substrate for ATP synthase
Proton carrier
Oxygen accepts electrons from cytochrome c oxidase (Complex IV) and combines with protons to form water. This maintains the flow of electrons and the proton gradient necessary for ATP synthesis. See Cytochrome c oxidase.
Chemiosmosis refers to the movement of which ions across a membrane during respiration?
Water molecules
Protons
Electrons
ATP molecules
Chemiosmosis describes the flow of protons down their electrochemical gradient through ATP synthase, driving ATP production. It couples electron transport to phosphorylation. Learn more at Chemiosmosis.
What happens to the NADH produced in glycolysis in eukaryotic cells?
Used in cytosolic electron transport
Shuttled into mitochondria for oxidation
Oxidized directly in the cytosol
Converted to NADPH
Cytosolic NADH cannot cross the mitochondrial membrane directly, so its electrons are shuttled into the matrix via specific shuttles (e.g., glycerol 3-phosphate or malate - aspartate). This regenerates cytosolic NAD+ and feeds electrons into the ETC. See Malate - aspartate shuttle.
What is the primary function of cytochrome c in the electron transport chain?
Synthesize ATP
Oxidize FADH2
Transfer electrons between complexes III and IV
Pump protons across the membrane
Cytochrome c is a mobile electron carrier that shuttles single electrons from Complex III (cytochrome bc1) to Complex IV (cytochrome c oxidase). It is essential for maintaining electron flow and proton gradient. More at Cytochrome c.
Which inhibitor specifically blocks ATP synthase activity?
Cyanide
Rotenone
Oligomycin
Antimycin A
Oligomycin binds to the Fo subunit of ATP synthase, preventing proton flow and thus blocking ATP synthesis. It is often used experimentally to study mitochondrial respiration. Reference: Oligomycin.
Uncoupling proteins increase heat production by which mechanism?
Dissipating the proton gradient
Increasing ATP synthesis
Inhibiting the electron transport chain
Blocking Complex IV
Uncoupling proteins such as UCP1 allow protons to re-enter the mitochondrial matrix without passing through ATP synthase, dissipating the gradient as heat. This thermogenic mechanism is vital in brown adipose tissue. Learn more at Uncoupling protein.
The glycerol 3-phosphate shuttle transfers electrons from cytosolic NADH into the ETC at which complex?
Complex II
Complex III
Complex I
Complex IV
In the glycerol 3-phosphate shuttle, cytosolic electrons from NADH reduce dihydroxyacetone phosphate to glycerol 3-phosphate, which transfers electrons to FAD in mitochondrial glycerol-3-phosphate dehydrogenase and enters at Complex II. Details at Glycerol phosphate shuttle.
What does the respiratory control ratio measure?
Rate of oxygen consumption with ADP versus without ADP
Proton gradient magnitude
Ratio of ADP to ATP
Ratio of NADH to NAD+
The respiratory control ratio (RCR) is the ratio of mitochondrial oxygen consumption rates in the presence of ADP (state 3) to rates in the absence of ADP (state 4). It indicates coupling efficiency between respiration and phosphorylation. Reference: Oxygen consumption.
Approximately how many ATP molecules are produced per FADH2 oxidized in the electron transport chain?
1.5 ATP
3 ATP
2 ATP
2.5 ATP
The oxidation of FADH2 via Complex II into the electron transport chain results in pumping fewer protons compared to NADH, yielding about 1.5 ATP per FADH2. See P/O ratio for details.
The Q-cycle mechanism is associated with which electron transport chain complex?
Complex I
Complex III
Complex IV
Complex II
The Q-cycle is the mechanism by which Complex III (cytochrome bc1) transfers electrons from ubiquinol to cytochrome c, pumping protons in two steps and enhancing the proton gradient. More at Q cycle.
Phosphorylation of the pyruvate dehydrogenase complex by PDH kinase results in which effect?
Increased acetyl-CoA production
Inhibition of the complex
Increased NADH production
Activation of the complex
PDH kinase phosphorylates and inactivates the pyruvate dehydrogenase complex, reducing the conversion of pyruvate to acetyl-CoA when energy supplies are sufficient. Dephosphorylation by PDH phosphatase reactivates it. See Pyruvate dehydrogenase.
In the Q-cycle of Complex III, the ubisemiquinone intermediate facilitates which process?
Substrate-level phosphorylation
Electron bifurcation
Proton translocation directly through the membrane
ATP synthesis
During the Q-cycle, ubisemiquinone donates one electron to cytochrome c and one back to the pool of ubiquinone, a process called electron bifurcation. This mechanism enhances proton pumping efficiency. Details at Q cycle.
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Study Outcomes
Understand Cellular Respiration Stages -
After completing the respiration quiz, you will be able to outline the key steps of glycolysis, the Krebs cycle, and the electron transport chain and their roles in energy production.
Differentiate Aerobic and Anaerobic Respiration -
By tackling the cellular respiration quiz, you can distinguish how aerobic pathways in mitochondria compare to anaerobic processes like fermentation in both plants and animals.
Explain Energy Yields and ATP Production -
The respiration process questions will help you calculate ATP yields from each stage and understand the efficiency of energy conversion in human respiration quiz scenarios.
Analyze Gas Exchange Mechanisms -
Through the types of respiration quiz, you will explore how oxygen and carbon dioxide are exchanged at cellular membranes and their impact on metabolic rates.
Apply Knowledge to Human Respiration Scenarios -
The human respiration quiz sections will let you apply your understanding to real-world examples, interpreting breathing dynamics and energy needs in different conditions.
Evaluate Common Misconceptions -
The quiz questions provide feedback that helps you identify and correct misunderstandings about cellular respiration and the respiration process questions.
Cheat Sheet
Glycolysis Basics -
Glycolysis is the first step in cellular respiration, converting one glucose molecule into two pyruvate molecules while generating a net gain of 2 ATP and 2 NADH (Campbell Biology). The overall reaction is: Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP. Remember the mnemonic "Goodness Gracious, I Prefer Picking Pumpkins (to) Prepare Pies" - it outlines the ten glycolytic enzymes in order.
Krebs Cycle (Citric Acid Cycle) -
Occurring in the mitochondrial matrix, the Krebs cycle oxidizes acetyl-CoA to CO2, producing 6 NADH, 2 FADH2, and 2 GTP (or ATP) per glucose (NCBI). A classic memory aid: "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate." Each turn of the cycle releases two CO2 molecules and regenerates oxaloacetate for continuous operation.
Electron Transport Chain & Chemiosmosis -
Embedded in the inner mitochondrial membrane, the ETC uses NADH and FADH2 to drive proton pumping through complexes I - IV, creating an electrochemical gradient (Harvard Medical School). ATP synthase then harnesses this proton motive force to produce ~28 ATP per glucose via chemiosmosis. Think of it like a waterwheel - protons flow back down to spin ATP synthase and power ATP production.
Types of Respiration: Aerobic vs. Anaerobic -
Aerobic respiration requires oxygen and yields up to 32 ATP per glucose, while anaerobic pathways (e.g., lactic acid fermentation in muscles or ethanol fermentation in yeast) only yield 2 ATP (MIT OpenCourseWare). In a types of respiration quiz you may be asked to compare these: muscles produce lactate, yeast produce CO2 plus ethanol. Remember: "Anaerobic = Absent Oxygen, Always Acidic Byproducts."
Gas Exchange & Human Respiration -
In human lungs, oxygen diffuses from alveoli (PO2 ~100 mmHg) into blood (PO2 ~40 mmHg), while CO2 moves in the opposite direction following Fick's law (respiratory system overview, WHO). Surface area (~70 m²) and thin respiratory membranes optimize gas exchange efficiency. A handy tip: "High Surface Area + Low Diffusion Distance = Rapid Respiration."
