# Electron Transport Chain Practice Exam Questions With Answers

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Take this Electron Transport Chain (ETC) practice exam questions with answers quiz and evaluate for yourself. An ETC is a series of four protein complexes (and/or other molecules) that couple redox reactions and transfer electrons from electron donors to electron acceptors. Here, in this quiz, you'll be asked questions related to the citric acid cycle, enzymes involved in this, and the products formed during the cycle. If you know about these processes, why don't you play the quiz? Good luck!

• 1.

### A reaction has a positive delta G. This means...

• A.

It is endergonic

• B.

It is exergonic

• C.

It is endothermic

• D.

It is exothermic

A. It is endergonic
Explanation
A positive delta G indicates that the reaction is endergonic, meaning it requires an input of energy in order to proceed. This energy input can come from various sources such as heat, light, or other chemical reactions. In an endergonic reaction, the products have higher energy than the reactants, and the reaction does not occur spontaneously.

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• 2.

### Which is the correct Gibbs free energy equation?

• A.

ΔG = ΔT - S*ΔH

• B.

ΔG = ΔH + T*ΔS

• C.

ΔG = ΔH - T*ΔS

• D.

None of the above

C. ΔG = ΔH - T*ΔS
Explanation
The correct Gibbs free energy equation is Î”G = Î”H - T*Î”S. This equation represents the change in Gibbs free energy (Î”G) as the difference between the change in enthalpy (Î”H) and the product of temperature (T) and the change in entropy (Î”S). This equation is derived from the fundamental equation of thermodynamics and is used to determine the spontaneity and direction of a chemical reaction.

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• 3.

### A reaction needs some energy put into it in order to start. The reaction is...

• A.

Endergonic

• B.

Exergonic

• C.

Endothermic

• D.

Not enough information

D. Not enough information
Explanation
Endergonic reactions need a net input of energy; however, even exergonic reactions can have an activation energy required to start it.

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• 4.

### Enzymes...

• A.

Supply activation energy, making the reaction more likely to occur

• B.

Are reactants in endergonic reactions

• C.

Stabilize the transition state

• D.

Are a type of catalytic substrate

C. Stabilize the transition state
Explanation
Enzymes stabilize the transition state during a chemical reaction. The transition state is the state that the reactants must pass through in order to form the products. By stabilizing the transition state, enzymes lower the activation energy required for the reaction to occur. This means that the reaction is more likely to happen and proceed at a faster rate. Enzymes do not act as reactants in endergonic reactions, nor are they a type of catalytic substrate.

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• 5.

### What is allosteric inhibition?

• A.

The enzyme is withdrawn into the cytoplasm

• B.

A protein binds to another active site, affecting the first active site

• C.

A molecule binds to and blocks the active site

• D.

None of the above

D. None of the above
Explanation
Allosteric inhibition is when an inhibitor binds to a site OTHER than the active site.

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• 6.

### An enzyme can have multiple ____________.

• A.

Active sites

• B.

Reacting sites

• C.

Losing sites

• D.

None of the above

A. Active sites
Explanation
Enzymes are proteins that catalyze chemical reactions in living organisms. The active site of an enzyme is the region where the substrate binds and the reaction takes place. Since enzymes can catalyze multiple reactions, they can have multiple active sites. This allows them to interact with different substrates and perform various functions in the cell. Therefore, the correct answer is "active sites".

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• 7.

• A.

1

• B.

2

• C.

3

• D.

4

B. 2
Explanation
In glycolysis, two molecules of NADH are produced. NADH is formed through the oxidation of NAD+ during the conversion of glucose to pyruvate. This occurs in two steps: the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, and the oxidation of 3-phosphoglycerate to 2-phosphoglycerate. In both of these reactions, NAD+ is reduced to NADH, resulting in the production of two molecules of NADH in total.

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• 8.

### The acetyl group is extracted from pyruvate, releasing:

• A.

ATP and H2O

• B.

ATP and CO2

• C.

• D.

Explanation
During the process of cellular respiration, pyruvate undergoes a series of reactions called the citric acid cycle or Krebs cycle. In this cycle, the acetyl group from pyruvate is extracted and combined with coenzyme A to form acetyl-CoA. This reaction releases carbon dioxide (CO2) as a waste product. Additionally, NAD+ is reduced to NADH, which carries high-energy electrons to the electron transport chain for ATP production. Therefore, the correct answer is NADH and CO2.

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• 9.

### Which citric acid cycle stages converts NAD+ to NADH+H+? Select all that apply.

• A.

Citrate→isocitrate

• B.

Isocitrate→α-ketoglutarate

• C.

α-ketoglutarate→succinyl CoA

• D.

Succinyl CoA→succinate

• E.

Succinate→fumarate

• F.

Fumarate→malate

• G.

Malate→oxaloacetate

B. Isocitrate→α-ketoglutarate
C. α-ketoglutarate→succinyl CoA
G. Malate→oxaloacetate
Explanation
The stages in the citric acid cycle that convert NAD+ to NADH+H+ are isocitrate to Î±-ketoglutarate, Î±-ketoglutarate to succinyl CoA, and malate to oxaloacetate. In these reactions, NAD+ accepts electrons and a hydrogen ion (H+) to form NADH+H+. This process is known as oxidative decarboxylation, as a carbon atom is removed from the molecule being converted. The NADH+H+ produced in these reactions will go on to donate electrons to the electron transport chain, where they will be used to generate ATP through oxidative phosphorylation.

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• 10.

### Succinyl CoA is converted to succinate, directly doing which of the following?

• A.

• B.

Releases H2O

• C.

• D.

GDP to GTP

D. GDP to GTP
Explanation
Succinyl CoA is converted to succinate through the process of substrate-level phosphorylation, which involves the transfer of a phosphate group from succinyl CoA to GDP, forming GTP. This conversion does not involve the conversion of ADP to ATP, the release of H2O, or the conversion of FAD to FADH2.

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• 11.

### How many net molecules of ATP are made in glycolysis?

• A.

1

• B.

2

• C.

3

• D.

4

B. 2
Explanation
In glycolysis, a total of 4 ATP molecules are produced, but 2 ATP molecules are used in the initial steps of the process. Therefore, the net production of ATP in glycolysis is 2 molecules.

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• 12.

### Where does glycolysis occur?

• A.

Cytoplasm

• B.

Mitochondria

• C.

Golgi apparatus

• D.

GLUT receptors

A. Cytoplasm
Explanation
Glycolysis is the process by which glucose is broken down into pyruvate in the cytoplasm of cells. This process occurs in the cytoplasm because it does not require oxygen and can occur in the absence of mitochondria. The mitochondria, on the other hand, are responsible for the later stages of cellular respiration, where pyruvate is further broken down to produce ATP in the presence of oxygen. The Golgi apparatus is involved in protein modification and transport, while GLUT receptors are responsible for glucose transport across cell membranes. Therefore, the correct answer is cytoplasm.

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• 13.

### What is the last carrier in the electron transport chain?

• A.

GTP

• B.

H+

• C.

• D.

O2

D. O2
Explanation
The last carrier in the electron transport chain is O2. During cellular respiration, electrons are passed along a series of carriers in the inner mitochondrial membrane, ultimately leading to the production of ATP. O2 is the final electron acceptor in this chain, accepting the electrons and combining with H+ ions to form water. This process is crucial for the generation of energy in the form of ATP.

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• 14.

### Which way does the electron transport chain pump H ions?

• A.

Against the concentration gradient: from the inner membrane space to the matrix

• B.

Down the concentration gradient: from the inner membrane space to the matrix

• C.

Against the concentration gradient: from the matrix to the inner membrane space

• D.

Down the concentration gradient: from the matrix to the inner membrane space

C. Against the concentration gradient: from the matrix to the inner membrane space
Explanation
The electron transport chain pumps H ions against the concentration gradient, from the matrix to the inner membrane space.

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• 15.

### Which complex is also involved in the citric acid cycle (succinate dehydrogenase)?

• A.

Complex I

• B.

Complex II

• C.

Complex III

• D.

Complex IV

B. Complex II
Explanation
Complex II, also known as succinate dehydrogenase, is involved in the citric acid cycle. This complex plays a crucial role in the conversion of succinate to fumarate, a step in the citric acid cycle. It is located in the inner mitochondrial membrane and acts as both an enzyme and an electron carrier. Complex II is unique compared to other complexes in the electron transport chain as it does not pump protons across the membrane. Instead, it transfers electrons directly to coenzyme Q, contributing to the generation of ATP in the oxidative phosphorylation process.

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• 16.

### How many alpha subunits are in the F1 portion of ATP synthase?

• A.

1

• B.

2

• C.

3

• D.

4

C. 3
Explanation
The F1 portion of ATP synthase consists of three alpha subunits. These subunits are responsible for catalyzing the synthesis of ATP from ADP and inorganic phosphate. The alpha subunits play a crucial role in the enzymatic activity of ATP synthase by providing the necessary binding sites for the substrates and coordinating the chemical reactions involved in ATP synthesis. Therefore, the correct answer is 3.

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• 17.

### H+ ions cause the gamma rod in ATP synthase to rotate, triggering a conformational change in alpha subunits that catalyze a reaction between ADP and inorganic phosphate

• A.

True

• B.

False

B. False
Explanation
The reaction occurs with beta subunits, not alpha.

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• 18.

### About how many H+ are needed to make 1 ATP?

• A.

1

• B.

2

• C.

3

• D.

4

D. 4
Explanation
The H+/ATP ratio, defined as the number of protons necessary to synthesize one ATP at equilibrium, is four, according to the data of the present work. For synthesis of 1 ATP, 4 H+ are required. ATP synthase synthesizes 1 ATP for every 4 H+ that passes through it.

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• 19.

### Per glucose molecule, how many NADH are produced? Account for glycolysis, pyruvate oxidation, and the citric acid cycle.

• A.

8

• B.

10

• C.

11

• D.

12

B. 10
Explanation
During glycolysis, one glucose molecule is converted into two molecules of pyruvate. In this process, two NADH molecules are produced. During pyruvate oxidation, each pyruvate molecule is converted into one molecule of acetyl-CoA. In this step, two NADH molecules are produced per glucose molecule. Lastly, during the citric acid cycle, each acetyl-CoA molecule goes through a series of reactions, producing three NADH molecules. Therefore, in total, there are 2 NADH molecules produced during glycolysis, 2 NADH molecules produced during pyruvate oxidation, and 6 NADH molecules produced during the citric acid cycle, resulting in a total of 10 NADH molecules produced per glucose molecule.

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• 20.

### Which electron carrier moves from complex III to complex IV?

• A.

Flavin

• B.

Ubiquinone

• C.

Iron sulfur cluster

• D.

Cytochrome C

D. Cytochrome C
Explanation
Cytochrome C is the electron carrier that moves from complex III to complex IV. Cytochrome C is a small heme protein that is located in the inner mitochondrial membrane. It plays a crucial role in the electron transport chain by shuttling electrons between complex III and complex IV. It accepts electrons from complex III and transfers them to complex IV, which is responsible for the final step in the electron transport chain, the reduction of oxygen to water.

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• 21.

### Which route does an electron from NADH take in the ETC?

• A.

Complex II, ubiquinone, complex III, complex IV

• B.

Complex I, ubiquinone, complex III, complex IV

• C.

Complex I, complex II, cytochrome C, complex IV

• D.

Complex II, ubiquinone, cytochrome C, complex IV

B. Complex I, ubiquinone, complex III, complex IV
• 22.

### What is the actual yield of ATP per NADH?

• A.

3

• B.

2.5

• C.

2

• D.

1.5

B. 2.5
Explanation
The actual yield of ATP per NADH is 2.5. During cellular respiration, NADH is produced in the citric acid cycle and then goes through the electron transport chain, where it donates electrons. This process leads to the pumping of protons across the inner mitochondrial membrane, creating an electrochemical gradient. As these protons flow back through ATP synthase, ATP is produced. Each NADH molecule produces enough energy to generate 2.5 ATP molecules.

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• 23.

### Which of the following are true of fermentation? Select all that apply.

• A.

It occurs in the presence of oxygen.

• B.

One of the products can be lactic acid

• C.

CO2 can be released

• D.

B. One of the products can be lactic acid
C. CO2 can be released
Explanation
Fermentation is a metabolic process that occurs in the absence of oxygen. It is a way for cells to produce energy when oxygen is not available. One of the products of fermentation can be lactic acid, which is commonly produced in muscle cells during intense exercise. CO2 can also be released during fermentation, leading to the formation of bubbles or fizziness in certain food and beverage products. Additionally, fermentation converts NADH, which is a high-energy molecule, to NAD+, which is a lower-energy molecule that can be used in other metabolic processes.

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• 24.

### How are amino acids integrated into the catabolic pathways?

• A.

Their nitrogen is removed, converting them into components of the CAC.

• B.

Their carbon is removed, releasing energy.

• C.

They are oxidized by pyruvate and join the CAC.

• D.

Amino acids are products of anabolic reactions, never part of the catabolic pathway.

A. Their nitrogen is removed, converting them into components of the CAC.
Explanation
Amino acids are integrated into the catabolic pathways by having their nitrogen removed, which then converts them into components of the CAC (Citric Acid Cycle). This process allows the amino acids to be further broken down and utilized for energy production.

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• 25.

### Where does photosynthesis get its electrons from initially?

• A.

• B.

CO2

• C.

• D.

H2O

D. H2O
Explanation
Photosynthesis is the process by which plants convert sunlight into energy. During photosynthesis, water molecules are split, and their electrons are used to generate energy. This process is known as photolysis, and it occurs in the thylakoid membranes of the chloroplasts. The electrons from water are transferred through a series of reactions, ultimately leading to the production of ATP and NADPH, which are used in the synthesis of glucose. Therefore, the correct answer is H2O, as photosynthesis initially gets its electrons from water molecules.

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• 26.

### Which of the following presents the movement of electrons in the light-dependent reactions in the correct order (steps may be omitted)?

• A.

Photosystem I, plastoquinone, photosystem II, NADPH

• B.

Photosystem II, photosystem I, plastocyanin, NADPH

• C.

Photosystem II, plastoquinone, ferredoxin, photosystem I

• D.

Photosystem II, cytochrome b6f, ferredoxin, NADPH

D. Photosystem II, cytochrome b6f, ferredoxin, NADPH
Explanation
The correct answer is "Photosystem II, cytochrome b6f, ferredoxin, NADPH." In the light-dependent reactions of photosynthesis, Photosystem II is the first step where light energy is absorbed and electrons are excited. The excited electrons then move to the cytochrome b6f complex, which pumps protons across the thylakoid membrane. Ferredoxin then receives the electrons from cytochrome b6f and transfers them to NADPH, which is the final product of the light-dependent reactions.

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• 27.

### What is the role of antenna molecules in a photosystem?

• A.

Provide structure to the photosystem

• B.

Transfer energy to the reaction center

• C.

Produce high-energy electrons

• D.

Perform photolysis (splitting H2O)

B. Transfer energy to the reaction center
Explanation
Antenna molecules in a photosystem play a crucial role in transferring energy to the reaction center. These molecules capture light energy and efficiently transfer it through a process called resonance energy transfer. This energy transfer allows the reaction center to convert the absorbed light energy into chemical energy, which is essential for the photosynthetic process. The antenna molecules act as a bridge between the captured light energy and the reaction center, ensuring that the energy is effectively utilized for the production of high-energy electrons.

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• 28.

### In photosynthesis, what is cyclic electron flow?

• A.

Electrons are put back into H+ pumps instead of going to NADPH.

• B.

After electrons have lost energy from photosystem II, they are recharged by photosystem I.

• C.

When NADPH has lost its electron, it goes back to the beginning of photosynthesis to pick up a new electron.

• D.

Electrons gain and loose their energy in a cyclic z-shape.

A. Electrons are put back into H+ pumps instead of going to NADPH.
Explanation
Cyclic electron flow in photosynthesis refers to the process where electrons are returned to the electron transport chain and are pumped back into the H+ pumps instead of being used to produce NADPH. This process occurs when there is a surplus of ATP and a need to generate additional ATP molecules. By bypassing the production of NADPH, cyclic electron flow allows for the generation of more ATP, which is used as an energy source for various cellular processes.

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• 29.

### CO2 fixation is performed by which enzyme?

• A.

RuBisCo

• B.

RuBP

• C.

CO2 dehydrogenase

• D.

Carbon-evolving complex

A. RuBisCo
Explanation
RuBisCo is the correct answer because it is the enzyme responsible for carbon dioxide fixation in the process of photosynthesis. It catalyzes the reaction between carbon dioxide and a five-carbon sugar called RuBP (ribulose-1,5-bisphosphate), leading to the formation of two molecules of a three-carbon compound called 3-phosphoglycerate. This is the first step in the Calvin cycle, where carbon dioxide is converted into organic molecules that can be used by plants for growth and energy production.

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• 30.

### 6 glyceraldehyde 3-phosphate molecules are produced in the Calvin cycle. How many of these go towards glucose production?

• A.

All 6

• B.

3

• C.

2

• D.

1

D. 1
Explanation
In the Calvin cycle, 6 molecules of glyceraldehyde 3-phosphate are produced. However, only one of these molecules is used towards glucose production. This is because glucose is a six-carbon molecule, and each molecule of glyceraldehyde 3-phosphate contains only three carbons. Therefore, it takes two molecules of glyceraldehyde 3-phosphate to produce one molecule of glucose.

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