Exam 3 File Pt.1

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1/50 Questions

ATP is
- A. a short-term energy-storage compound.
- B. the cell's principal compound for energy transfers
- C. synthesized within mitochondria.
- D. the molecule all living cells rely on to do work.
- E. All of the above

About This Quiz

The 'Exam 3 File pt. 1' assesses key concepts in cellular metabolism, focusing on ATP roles, oxidation processes, fermentation, glycolysis, and electron transfer in respiration. This quiz is essential for students studying advanced biology or preparing for exams like AP, IB, or MCAT.

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2.

When a molecule loses hydrogen atoms (as opposed to hydrogen ions), it becomes
- A. reduced.
- B. oxidized.
- C. redoxed.
- D. hydrogenated.
- E. hydrolyzed.
Correct Answer

A. B. oxidized.

Explanation

When a molecule loses hydrogen atoms, it means that it is losing electrons along with the hydrogen atoms. This process is known as oxidation. In an oxidation reaction, a molecule loses electrons and becomes more positive or less negative in charge. Therefore, the correct answer is b. oxidized.

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3.

Which of the following processes occurs when oxygen is unavailable?
- A. Pyruvate oxidation
- B. The citric acid cycle
- C. Fermentation
- D. An electron transport chain
- E. All of the above
Correct Answer

A. C. Fermentation

Explanation

Fermentation is the process that occurs when oxygen is unavailable. During fermentation, cells convert pyruvate, the end product of glycolysis, into either alcohol and carbon dioxide or lactic acid. This allows glycolysis to continue producing ATP in the absence of oxygen. Both pyruvate oxidation and the citric acid cycle require oxygen to proceed, while an electron transport chain is dependent on the presence of oxygen to generate ATP. Therefore, the correct answer is c. Fermentation.

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4.

In all cells, glucose metabolism begins with
- A. glycolysis.
- B. fermentation.
- C. pyruvate oxidation.
- D. the citric acid cycle.
- E. chemiosmosis.
Correct Answer

A. A. glycolysis.

Explanation

Glucose metabolism begins with glycolysis, which is the process of breaking down glucose into pyruvate. This occurs in the cytoplasm of the cell and does not require oxygen. Glycolysis is the first step in both aerobic and anaerobic respiration, and it produces a small amount of ATP and NADH. The other options, fermentation, pyruvate oxidation, the citric acid cycle, and chemiosmosis, are all subsequent steps in glucose metabolism that occur after glycolysis.

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5.

When NADH donates two electrons to ubiquinone during respiration, ubiquinone is
- A. reduced.
- B. oxidized.
- C. phosphorylated.
- D. aerobic.
- E. hydrolyzed.
Correct Answer

A. A. reduced.

Explanation

When NADH donates two electrons to ubiquinone during respiration, it transfers those electrons to ubiquinone, causing a reduction in ubiquinone's overall charge. Therefore, the correct answer is a. reduced.

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6.

The end product of glycolysis is
- A. pyruvate.
- B. the starting point for pyruvate oxidation.
- C. the starting point for the fermentation pathway.
- D. Both a and b
- E. All of the above
Correct Answer

A. E. All of the above

Explanation

Glycolysis is the process that breaks down glucose to produce energy in the form of ATP. The end product of glycolysis is pyruvate, which is then converted into acetyl-CoA to enter the citric acid cycle (pyruvate oxidation). Additionally, pyruvate can also be converted into other molecules through the fermentation pathway, depending on the absence of oxygen. Therefore, all of the given options are correct as they describe different outcomes of glycolysis.

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7.

The function of NAD+ is to
- A. cause the release of energy to adjacent cells when energy is needed in aerobic conditions.
- B. hasten the release of energy when the cell has been deprived of oxygen.
- C. carry hydrogen atoms and free energy from compounds being oxidized and to give hydrogen atoms and free energy to compounds being reduced.
- D. block the release of energy to adjacent cells.
- E. None of the above
Correct Answer

A. C. carry hydrogen atoms and free energy from compounds being oxidized and to give hydrogen atoms and free energy to compounds being reduced.

Explanation

The function of NAD+ is to carry hydrogen atoms and free energy from compounds being oxidized and to give hydrogen atoms and free energy to compounds being reduced. This is important in cellular respiration, as NAD+ acts as a coenzyme that accepts and donates electrons during redox reactions. This allows for the transfer of energy from molecules being broken down to molecules being built up, ultimately facilitating the production of ATP, the cell's main source of energy.

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8.

In the cell, the site of oxygen utilization is the
- A. nucleus.
- B. chloroplast.
- C. endoplasmic reticulum.
- D. mitochondrion.
- E. cytosol.
Correct Answer

A. D. mitochondrion.

Explanation

The mitochondrion is the site of oxygen utilization in the cell. It is responsible for producing energy in the form of ATP through a process called cellular respiration. Oxygen is used in the electron transport chain within the mitochondrion to generate ATP. The other options, such as the nucleus, chloroplast, endoplasmic reticulum, and cytosol, do not play a direct role in oxygen utilization for energy production.

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9.

The end result of glycolysis is the
- A. creation of 38 molecules of ATP.
- B. reduction of 8 molecules of NAD.
- C. formation of 2 molecules of pyruvate.
- D. conversion of 1 molecule of glucose to lactic acid.
- E. None of the above
Correct Answer

A. C. formation of 2 molecules of pyruvate.

Explanation

The end result of glycolysis is the formation of 2 molecules of pyruvate. Glycolysis is the first step in cellular respiration and occurs in the cytoplasm of cells. During glycolysis, glucose is broken down into two molecules of pyruvate. This process also produces a small amount of ATP and NADH. The pyruvate molecules can then be further broken down in the presence of oxygen to produce more ATP through the process of aerobic respiration, or they can be converted to lactic acid in the absence of oxygen through the process of anaerobic respiration.

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10.

Substrate-level phosphorylation is the transfer of a(n)
- A. phosphate to a protein.
- B. phosphate to a substrate.
- C. phosphate to an ADP.
- D. ATP to a protein.
- E. phosphate from ATP to a substrate.
Correct Answer

A. C. phosphate to an ADP.

Explanation

Substrate-level phosphorylation is the process in which a phosphate group is directly transferred from a substrate molecule to an ADP molecule, resulting in the formation of ATP. This occurs during glycolysis and the Krebs cycle in cellular respiration, where high-energy phosphate bonds are formed. Therefore, option c is the correct answer as it accurately describes the process of substrate-level phosphorylation.

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11.

The citric acid cycle begins with
- A. glucose.
- B. pyruvate.
- C. acetyl CoA.
- D. NADH + H+.
- E. ATP synthase.
Correct Answer

A. C. acetyl CoA.

Explanation

The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is the second stage of cellular respiration and is responsible for generating energy in the form of ATP. The cycle begins with the entry of acetyl CoA, which is derived from the breakdown of glucose and fatty acids. Acetyl CoA combines with oxaloacetate to form citrate, initiating the cycle. Therefore, the correct answer is c. acetyl CoA.

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12.

The formation of ethanol from pyruvate is an example of
- A. an exergonic reaction.
- B. an extra source of energy as the result of glycolysis.
- C. a fermentation process that takes place in the absence of oxygen.
- D. cellular respiration.
- E. None of the above
Correct Answer

A. C. a fermentation process that takes place in the absence of oxygen.

Explanation

The formation of ethanol from pyruvate is an example of a fermentation process that takes place in the absence of oxygen. Fermentation is an anaerobic process that occurs in the absence of oxygen and involves the partial breakdown of glucose or other organic molecules to produce energy. In this case, pyruvate, which is a product of glycolysis, is converted into ethanol through fermentation. This process is commonly observed in yeast and some bacteria.

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13.

Animals breathe in air containing oxygen and breathe out air with less oxygen and more carbon dioxide. The carbon dioxide comes from
- A. hydrocarbons and the air.
- B. the citric acid cycle.
- C. glycolysis.
- D. waste products.
- E. All of the above
Correct Answer

A. B. the citric acid cycle.

Explanation

Animals produce carbon dioxide as a waste product during cellular respiration. The citric acid cycle, also known as the Krebs cycle, is a part of cellular respiration where carbon dioxide is produced. During this cycle, glucose is broken down and converted into energy, releasing carbon dioxide as a byproduct. Therefore, the correct answer is b. the citric acid cycle.

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14.

For glycolysis to continue, all cells require
- A. a respiratory chain.
- B. oxygen.
- C. mitochondria.
- D. chloroplasts.
- E. NAD+.
Correct Answer

A. E. NAD+.

Explanation

Glycolysis is the process by which glucose is broken down into pyruvate to produce energy in the form of ATP. One of the key steps in glycolysis involves the conversion of NAD+ to NADH. NAD+ is an important coenzyme that acts as an electron carrier, accepting electrons from glucose during glycolysis. Without NAD+, this step cannot occur, and glycolysis cannot continue. Therefore, all cells require NAD+ for glycolysis to continue. The other options (a. a respiratory chain, b. oxygen, c. mitochondria, d. chloroplasts) are not necessary for glycolysis to occur.

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15.

More free energy is released during the citric acid cycle than during glycolysis, but only 1 mole of ATP is produced for each mole of acetyl CoA that enters the cycle. Most of the remaining free energy that is produced during the citric acid cycle is
- A. used to synthesize GTP.
- B. used to reduce electron carriers.
- C. lost as heat.
- D. used to reduce pyruvate.
- E. converted to kinetic energy.
Correct Answer

A. B. used to reduce electron carriers.

Explanation

During the citric acid cycle, more free energy is released compared to glycolysis. However, only 1 mole of ATP is produced per mole of acetyl CoA that enters the cycle. This means that most of the remaining free energy is not used to produce ATP. Instead, it is used to reduce electron carriers such as NAD+ and FAD, which are important for the electron transport chain and oxidative phosphorylation. These reduced electron carriers play a crucial role in generating ATP through the process of chemiosmosis. Therefore, option b, used to reduce electron carriers, is the correct answer.

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16.

In human muscle cells, the fermentation process produces
- A. lactic acid.
- B. 12 moles of ATP.
- C. pyruvic acid.
- D. an excessive amount of energy.
- E. None of the above
Correct Answer

A. A. lactic acid.

Explanation

In human muscle cells, the fermentation process produces lactic acid. During intense exercise, when oxygen supply is limited, the cells switch to anaerobic respiration. This process involves the breakdown of glucose into pyruvate, which is then converted into lactic acid. This allows the cells to continue producing ATP, the energy currency of the cell, even in the absence of oxygen. The accumulation of lactic acid in the muscles can cause fatigue and muscle soreness. Therefore, option a. lactic acid is the correct answer.

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17.

During the fermentation of one molecule of glucose, the net production of ATP is _______ molecule(s).
- A. one
- B. two
- C. three
- D. six
- E. eight
Correct Answer

A. B. two

Explanation

During the process of fermentation, one molecule of glucose is broken down into two molecules of pyruvate. This process occurs in the cytoplasm of cells and does not require oxygen. Each molecule of pyruvate then undergoes further reactions to produce two molecules of ATP through substrate-level phosphorylation. Therefore, the net production of ATP during the fermentation of one molecule of glucose is two molecules.

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18.

The electron transport chain contains four large protein complexes (I, II, III, and IV), cytochrome c, and ubiquinone. The function of these molecules is to
- A. transport electrons.
- B. ensure the production of water and oxygen.
- C. regulate the passage of water through the chain.
- D. oxidize NADH.
- E. None of the above
Correct Answer

A. A. transport electrons.

Explanation

The electron transport chain is responsible for the transfer of electrons from electron donors to electron acceptors, ultimately generating ATP. The four protein complexes, cytochrome c, and ubiquinone work together to shuttle electrons along the chain, allowing for the production of ATP through oxidative phosphorylation. Therefore, the correct answer is a. transport electrons.

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19.

Which of the following statements about the electron transport chain is true?
- A. Electrons are received from NADH and FADH2.
- B. Electrons are passed from donor to recipient carrier molecules in a series of oxidation-reduction reactions.
- C. Usually the terminal electron acceptor is oxygen.
- D. Most of the enzymes are part of the inner mitochondrial membrane.
- E. All of the above
Correct Answer

A. E. All of the above

Explanation

All of the statements mentioned in options a, b, and c are true. In the electron transport chain, electrons are received from NADH and FADH2 (option a), and they are passed from donor to recipient carrier molecules in a series of oxidation-reduction reactions (option b). Usually, the terminal electron acceptor in the electron transport chain is oxygen (option c). Therefore, option e, "All of the above," is the correct answer as it includes all the true statements.

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20.

Water is a by-product of cellular respiration. The water is produced as a result of the
- A. combining of carbon dioxide with protons.
- B. conversion of pyruvate to acetyl CoA.
- C. degradation of glucose to pyruvate.
- D. reduction of oxygen at the end of the electron transport chain.
- E. None of the above
Correct Answer

A. D. reduction of oxygen at the end of the electron transport chain.

Explanation

Water is produced as a result of the reduction of oxygen at the end of the electron transport chain. During cellular respiration, electrons are transferred along the electron transport chain and ultimately combine with oxygen to form water. This process, known as oxidative phosphorylation, generates ATP and produces water as a by-product. Therefore, the correct answer is d. reduction of oxygen at the end of the electron transport chain.

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21.

The proton-motive force is
- A. ATP synthase.
- B. the proton concentration gradient and electric charge difference.
- C. a metabolic pathway.
- D. a redox reaction.
- E. None of the above
Correct Answer

A. B. the proton concentration gradient and electric charge difference.

Explanation

The proton-motive force refers to the energy stored in the form of a proton concentration gradient and an electric charge difference across a membrane. This force is generated during cellular respiration and photosynthesis, where protons are pumped across the membrane, creating a gradient. This gradient can then be used by ATP synthase to produce ATP, making option b the correct answer.

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22.

The chemiosmotic generation of ATP is driven by
- A. osmotic movement of water into an area of high solute concentration.
- B. the addition of protons to ADP and phosphate via enzymes.
- C. oxidative phosphorylation.
- D. a difference in H+ concentration on both sides of a membrane.
- E. None of the above
Correct Answer

A. D. a difference in H+ concentration on both sides of a membrane.

Explanation

The chemiosmotic generation of ATP is driven by a difference in H+ concentration on both sides of a membrane. This is because during oxidative phosphorylation, electrons are transferred through the electron transport chain, pumping protons (H+) across the membrane. This creates a difference in H+ concentration, with a higher concentration on one side of the membrane. The H+ ions then flow back across the membrane through ATP synthase, which uses the energy from this movement to generate ATP. Therefore, the correct answer is d. a difference in H+ concentration on both sides of a membrane.

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23.

The component of aerobic respiration that produces the most ATP per mole of glucose is
- A. the electron transport chain.
- B. the citric acid cycle.
- C. glycolysis.
- D. lactic acid fermentation.
- E. alcoholic fermentation.
Correct Answer

A. A. the electron transport chain.

Explanation

The electron transport chain is the component of aerobic respiration that produces the most ATP per mole of glucose. During this process, electrons from NADH and FADH2 are passed along a series of protein complexes, generating a proton gradient across the inner mitochondrial membrane. This gradient is then used by ATP synthase to produce ATP. The electron transport chain is highly efficient in generating ATP, producing a total of 32-34 ATP molecules per mole of glucose. In comparison, the citric acid cycle produces only 2 ATP molecules, while glycolysis produces 2 ATP molecules and lactic acid fermentation and alcoholic fermentation produce no ATP.

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24.

In some mammals, such as new born humans and hibernating animals, body temperature is raised by means of
- A. the uncoupling of respiration by the protein thermogenin.
- B. an increase in the rate of glycolysis.
- C. shivering.
- D. leakage of hydrogen ions across the cell’s plasma membrane.
- E. cytochrome reductase.
Correct Answer

A. A. the uncoupling of respiration by the protein thermogenin.

Explanation

The correct answer is a. the uncoupling of respiration by the protein thermogenin. This is because thermogenin, also known as uncoupling protein 1 (UCP1), is responsible for uncoupling oxidative phosphorylation in the mitochondria. This means that instead of producing ATP, the energy generated from the electron transport chain is released as heat. This process is important for thermoregulation in newborn humans and hibernating animals, as it helps to raise their body temperature.

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25.

Before starch can be used for respiratory ATP production, it must be hydrolyzed to
- A. pyruvate.
- B. fatty acids.
- C. amino acids.
- D. glucose.
- E. oxaloacetate.
Correct Answer

A. D. glucose.

Explanation

Starch is a polysaccharide made up of glucose molecules. Before it can be used for ATP production, it needs to be broken down into its monomer, glucose. This process is called hydrolysis, where water molecules are used to break the bonds between the glucose molecules in starch. Once hydrolyzed, the glucose molecules can enter the process of cellular respiration to produce ATP. Therefore, the correct answer is d. glucose.

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26.

When acetyl CoA builds up in the cell, it increases the activity of the enzyme that synthesizes oxaloacetate from pyruvate and carbon dioxide. Acetyl CoA is acting as a(n)
- A. electron carrier.
- B. substrate.
- C. allosteric activator.
- D. acetate donor.
- E. proton pump.
Correct Answer

A. C. allosteric activator.

Explanation

When acetyl CoA builds up in the cell, it increases the activity of the enzyme that synthesizes oxaloacetate from pyruvate and carbon dioxide. This indicates that acetyl CoA is acting as an allosteric activator. Allosteric activators are molecules that bind to enzymes at a site other than the active site and enhance their activity. In this case, the build-up of acetyl CoA causes a conformational change in the enzyme, leading to an increase in its catalytic activity for the synthesis of oxaloacetate.

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27.

When the supply of acetyl CoA being produced exceeds the demands of the citric acid cycle, some of the acetyl CoA is diverted to the synthesis of
- A. pyruvate.
- B. NAD.
- C. proteins.
- D. fatty acids.
- E. lactic acid.
Correct Answer

A. D. fatty acids.

Explanation

When the supply of acetyl CoA being produced exceeds the demands of the citric acid cycle, some of the acetyl CoA is diverted to the synthesis of fatty acids. This is because acetyl CoA is a precursor molecule for fatty acid synthesis. Excess acetyl CoA can be converted into fatty acids through a series of enzymatic reactions, leading to the production of lipids for energy storage or other cellular processes. This process is important for maintaining lipid homeostasis and ensuring that excess acetyl CoA is not wasted.

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28.

Which of the following biological groups is dependent on photosynthesis for its survival?
- A. Vertebrates
- B. Mammalia
- C. Fishes
- D. Plants
- E. All of the above
Correct Answer

A. E. All of the above

Explanation

All of the above options, vertebrates, mammals, fishes, and plants, are dependent on photosynthesis for their survival. Photosynthesis is the process by which plants convert sunlight into energy, and this energy is then transferred to other organisms through the food chain. Vertebrates, including mammals and fishes, rely on plants either directly or indirectly for their food and energy. Therefore, all of the mentioned biological groups are dependent on photosynthesis for their survival.

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29.

The first phase of photosynthesis, a series of reactions that requires the absorption of photons, is referred to as the _______ phase.
- A. reduction
- B. dark reactions
- C. carbon fixation
- D. light reactions (or photophosphorylation)
- E. None of the above
Correct Answer

A. D. light reactions (or photophosphorylation)

Explanation

The correct answer is d. light reactions (or photophosphorylation). The first phase of photosynthesis is referred to as the light reactions because it requires the absorption of photons. During this phase, light energy is converted into chemical energy in the form of ATP and NADPH, which are used in the second phase of photosynthesis, known as the dark reactions or carbon fixation. Photophosphorylation is the process by which ATP is synthesized using the energy from light.

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30.

Which of the following occurs during the light-independent reactions of photosynthesis?
- A. Water is converted into hydrogen and water.
- B. CO2 is converted into sugars.
- C. Chlorophyll acts as an enzyme.
- D. Nothing occurs; the plant rests in the dark.
- E. None of the above
Correct Answer

A. B. CO2 is converted into sugars.

Explanation

During the light-independent reactions of photosynthesis, also known as the Calvin cycle, carbon dioxide (CO2) is converted into sugars. This process occurs in the stroma of the chloroplasts and is fueled by the ATP and NADPH produced during the light-dependent reactions. The CO2 molecules are fixed and combined with a five-carbon sugar molecule called ribulose bisphosphate (RuBP) to form a six-carbon molecule, which is then converted into glucose and other sugars through a series of enzymatic reactions. This is how plants produce the organic compounds necessary for their growth and survival.

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31.

Which of the following is the revised, balanced equation for the generation of sugar from sunlight, water, and CO2?
- A. 6 CO2 + 6 H2O  C6H12O6 + O2
- B. 6 CO2 + 12 H2O  C6H12O6 + 6 O2 + 6 H2O
- C. 6 CO2 + 6 H2O  C6H12O6 + 6 O2
- D. 12 CO2 + 12 H2O  2 C6H12O6 + 2 O2
- E. None of the above
Correct Answer

A. B. 6 CO2 + 12 H2O  C6H12O6 + 6 O2 + 6 H2O

Explanation

The correct answer is b. 6 CO2 + 12 H2O  C6H12O6 + 6 O2 + 6 H2O. This equation is the revised, balanced equation for the generation of sugar from sunlight, water, and CO2. It shows that for every 6 molecules of CO2 and 12 molecules of H2O, 1 molecule of C6H12O6 (sugar) and 6 molecules of O2 are produced, along with an additional 6 molecules of H2O. This equation follows the law of conservation of mass, with the same number of atoms on both sides of the equation.

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32.

When a suspension of algae is incubated in a flask in the presence of light and CO2 and then transferred to the dark, the reduction of 3-phosphoglycerate to glyceraldehyde 3-phosphate is blocked. This reaction stops when the algae are placed in the dark because
- A. the reaction requires CO2.
- B. the reaction is exergonic.
- C. the reaction requires ATP and NADPH + H+.
- D. the reaction requires O2.
- E. chlorophyll is not synthesized in the dark.
Correct Answer

A. C. the reaction requires ATP and NADPH + H+.

Explanation

The reduction of 3-phosphoglycerate to glyceraldehyde 3-phosphate is an energy-requiring process that occurs during photosynthesis. This reaction requires ATP and NADPH + H+ as sources of energy to drive the conversion. When the algae are placed in the dark, there is no light available to generate ATP and NADPH + H+ through the light-dependent reactions of photosynthesis. As a result, the reaction is blocked and cannot proceed without the necessary energy sources.

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33.

A molecule that has an absorption spectrum showing maximum absorption within the wavelengths of visible light is
- A. a reducing agent.
- B. a quantum.
- C. a photon.
- D. electromagnetic radiation.
- E. a pigment.
Correct Answer

A. E. a pigment.

Explanation

A molecule that has an absorption spectrum showing maximum absorption within the wavelengths of visible light is a pigment. Pigments are molecules that are able to absorb certain wavelengths of light and reflect or transmit others. They are responsible for the colors we see in plants, animals, and other natural substances. The fact that this molecule has an absorption spectrum showing maximum absorption within the wavelengths of visible light indicates that it is a pigment, as it is specifically absorbing the light in the visible range.

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34.

When white light strikes a blue pigment, blue light is
- A. reduced.
- B. absorbed.
- C. converted to chemical energy.
- D. scattered or transmitted.
- E. used to synthesize ATP.
Correct Answer

A. D. scattered or transmitted.

Explanation

When white light strikes a blue pigment, the blue pigment absorbs all the colors of the spectrum except for blue. The blue light is either scattered or transmitted through the pigment, resulting in the perception of the color blue.

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35.

When a photon interacts with molecules such as those within chloroplasts, the photons may
- A. bounce off the molecules, having no effect.
- B. pass through the molecules, having no effect.
- C. be absorbed by the molecules.
- D. Both a and c
- E. All of the above
Correct Answer

A. D. Both a and c

Explanation

When a photon interacts with molecules such as those within chloroplasts, it can either bounce off the molecules, having no effect, or be absorbed by the molecules. Therefore, both options a and c are correct.

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36.

Plants are green because
- A. chlorophylls absorb blue and orange-red wavelengths of light and reflect green light.
- B. chloroplasts transmit green light.
- C. energized chlorophyll a emits green light.
- D. plants possess green pigment.
- E. chlorophylls absorb green light.
Correct Answer

A. A. chlorophylls absorb blue and orange-red wavelengths of light and reflect green light.

Explanation

Plants are green because chlorophylls, the pigments responsible for photosynthesis, absorb blue and orange-red wavelengths of light and reflect green light. This absorption and reflection process allows plants to capture the energy from sunlight and convert it into chemical energy through photosynthesis.

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37.

When a photon is absorbed by a molecule, the photon
- A. loses its ability to generate any energy.
- B. raises the molecule from a ground state of low energy to an excited state.
- C. affects the molecule in ways that are not clearly understood.
- D. causes a change in the velocity of the wavelengths.
- E. None of the above
Correct Answer

A. B. raises the molecule from a ground state of low energy to an excited state.

Explanation

When a photon is absorbed by a molecule, it transfers its energy to the molecule, causing the molecule to move from its ground state (lowest energy state) to an excited state (higher energy state). This process is known as electronic excitation and is a fundamental step in various chemical and biological processes, such as photosynthesis and vision. Therefore, option b is the correct answer.

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38.

The main photosynthetic pigments in plants are _______ and _______.
- A. chlorophyll s; chlorophyll a
- B. chlorophyll x; chlorophyll y
- C. retinal pigment; accessory pigment
- D. chlorophyll a; chlorophyll b
- E. None of the above
Correct Answer

A. D. chlorophyll a; chlorophyll b

Explanation

The main photosynthetic pigments in plants are chlorophyll a and chlorophyll b. These pigments are responsible for capturing light energy and converting it into chemical energy through the process of photosynthesis. Chlorophyll a is the primary pigment and absorbs light most efficiently in the red and blue regions of the electromagnetic spectrum. Chlorophyll b is an accessory pigment that absorbs light in the blue and red-orange regions, expanding the range of light that can be utilized for photosynthesis. Together, these pigments work in harmony to maximize the absorption of light energy for photosynthesis.

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39.

A graph that plots the rate at which CO2 is converted to glucose versus the wavelength of light illuminating a leaf is called
- A. a Planck equation.
- B. an absorption spectrum.
- C. enzyme kinetics.
- D. an electromagnetic spectrum.
- E. an action spectrum.
Correct Answer

A. E. an action spectrum.

Explanation

An action spectrum is a graph that shows the rate at which a specific biological process occurs at different wavelengths of light. In this case, the action spectrum would show the rate at which CO2 is converted to glucose in a leaf, depending on the wavelength of light illuminating it. The other options are not relevant to this specific graph.

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40.

Accessory pigments
- A. play no role in photosynthesis.
- B. transfer energy from chlorophyll to the electron transport chain.
- C. absorb only the red wavelengths.
- D. allow plants to absorb visible light of intermediate wavelengths.
- E. transfer electrons to NADP.
Correct Answer

A. D. allow plants to absorb visible light of intermediate wavelengths.

Explanation

Accessory pigments are additional pigments found in chloroplasts that are involved in photosynthesis. While chlorophyll is the primary pigment responsible for capturing light energy, accessory pigments such as carotenoids and phycobilins broaden the range of wavelengths that can be absorbed. These pigments allow plants to absorb visible light of intermediate wavelengths that chlorophyll alone cannot capture. Therefore, option d is the correct answer.

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41.

The O2 gas produced during photosynthesis is derived from
- A. CO2.
- B. glucose.
- C. water.
- D. CO.
- E. bicarbonate ions.
Correct Answer

A. C. water.

Explanation

During photosynthesis, plants use sunlight to convert carbon dioxide and water into glucose and oxygen. The oxygen gas produced is derived from the water molecule, as it is split during the light-dependent reactions of photosynthesis. This process, known as photolysis, releases oxygen gas as a byproduct. Therefore, the correct answer is c. water.

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42.

In both photosynthesis and respiration, protons are pumped across a membrane during
- A. electron transport.
- B. photolysis.
- C. CO2 fixation.
- D. reduction of O2.
- E. glycolysis.
Correct Answer

A. A. electron transport.

Explanation

In both photosynthesis and respiration, protons are pumped across a membrane during electron transport. This process occurs in the thylakoid membrane during photosynthesis and in the inner mitochondrial membrane during respiration. During electron transport, electrons from electron carriers are passed along a series of proteins, creating a proton gradient across the membrane. This proton gradient is then used to generate ATP through ATP synthase. Therefore, option a, electron transport, is the correct answer.

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43.

Cyclic electron transport
- A. occurs when the ratio of NADPH + H+ to NADP+ in the chloroplasts of some organisms is high.
- B. is a series of redox reactions.
- C. stores its released energy as a proton gradient.
- D. is completed when the electron returns to P700+.
- E. All of the above
Correct Answer

A. E. All of the above

Explanation

The correct answer is e. All of the above. This is because all the statements mentioned in options a, b, c, and d are true for cyclic electron transport. Cyclic electron transport occurs when the ratio of NADPH + H+ to NADP+ in the chloroplasts of some organisms is high, it involves a series of redox reactions, it stores its released energy as a proton gradient, and it is completed when the electron returns to P700+. Therefore, all the statements mentioned in the options are correct explanations for cyclic electron transport.

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44.

Photophosphorylation provides the Calvin–Benson cycle with
- A. protons and electrons.
- B. CO2 and glucose.
- C. water and photons.
- D. light and chlorophyll.
- E. ATP and NADPH.
Correct Answer

A. E. ATP and NADPH.

Explanation

Photophosphorylation is the process by which light energy is used to generate ATP and NADPH in photosynthesis. These two molecules are essential for the Calvin-Benson cycle, which is the process that converts carbon dioxide into glucose. Therefore, option e, ATP and NADPH, is the correct answer as they directly provide the Calvin-Benson cycle with the necessary energy and reducing power.

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45.

How many moles of CO2 must enter the Calvin–Benson cycle for the synthesis of one mole of glucose?
- A. 1
- B. 2
- C. 3
- D. 6
- E. 12
Correct Answer

A. D. 6

Explanation

In the Calvin-Benson cycle, 6 molecules of carbon dioxide (CO2) are required to synthesize one molecule of glucose. This cycle is a series of chemical reactions that occur in plants during photosynthesis, where carbon dioxide is converted into glucose. Therefore, the correct answer is d. 6.

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46.

The Calvin cycle uses _______ to produce glucose.
- A. CO2
- B. ATP
- C. NADPH + H+
- D. rubisco
- E. All of the above
Correct Answer

A. E. All of the above

Explanation

The Calvin cycle uses all of the options mentioned (CO2, ATP, NADPH + H+, and rubisco) to produce glucose. CO2 is the source of carbon for glucose synthesis, ATP provides the energy required for the reactions, NADPH + H+ supplies the reducing power needed for the synthesis, and rubisco is the enzyme responsible for fixing CO2. Therefore, all of these components are essential for the Calvin cycle to produce glucose.

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47.

During photorespiration, rubisco uses _______ as a substrate.
- A. CO2
- B. O2
- C. glyceraldehyde 3-phosphate
- D. 3-phosphoglycerate
- E. NADPH
Correct Answer

A. B. O2

Explanation

During photorespiration, rubisco uses oxygen (O2) as a substrate. Photorespiration is a process that occurs in plants when the concentration of carbon dioxide (CO2) is low and the concentration of oxygen is high. Rubisco, the enzyme responsible for carbon fixation in photosynthesis, can also react with oxygen instead of carbon dioxide. This results in the production of phosphoglycolate, which is then metabolized and recycled by a series of reactions. This process is energetically costly and reduces the efficiency of photosynthesis.

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48.

How does rubisco “decide” whether to act as an oxygenase or a carboxylase?
- A. Rubisco has 10 times more affinity for O2 than CO2; therefore, it favors O2 fixation.
- B. If O2 is relatively abundant, rubisco acts as a carboxylase.
- C. If O2 predominates, rubisco fixes it and the Calvin–Benson cycle occurs.
- D. Photorespiration is more likely at low temperatures.
- E. As the ratio of CO2 to O2 falls in the leaf, the reaction of rubisco with O2 is favored and photorespiration proceeds.
Correct Answer

A. E. As the ratio of CO2 to O2 falls in the leaf, the reaction of rubisco with O2 is favored and photorespiration proceeds.

Explanation

Rubisco "decides" whether to act as an oxygenase or a carboxylase based on the ratio of CO2 to O2 in the leaf. When the ratio of CO2 to O2 falls, the reaction of rubisco with O2 is favored, leading to photorespiration. This means that when there is a relatively higher concentration of O2 compared to CO2, rubisco is more likely to fix O2 instead of CO2, resulting in photorespiration. Therefore, option e correctly explains how rubisco "decides" its action based on the CO2 to O2 ratio.

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49.

Photosynthesis takes place in plants only in the light. Respiration takes place
- A. in the dark only.
- B. in the light only.
- C. in all organisms except plants.
- D. both with and without light.
- E. None of the above
Correct Answer

A. D. both with and without light.

Explanation

Photosynthesis is the process by which plants convert light energy into chemical energy to produce glucose. This process occurs in the presence of light, specifically in the chloroplasts of plant cells. On the other hand, respiration is the process by which cells break down glucose to release energy. While respiration can occur in the absence of light, it can also occur in the presence of light. Therefore, the correct answer is d. both with and without light.

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Exam 3 File Pt.1

ATP is

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