AP Biology Chapter 9 Practice Test

In a redox or oxidation-reduction reaction, the molecule that functions as the reducing agent donates electrons to another molecule. When a molecule loses electrons, it is oxidized and loses energy. Therefore, the correct answer is "loses electrons and loses energy."

An agent that closely mimics the structure of glucose but is not metabolized would directly interfere with glycolysis. Glycolysis is the metabolic pathway that breaks down glucose into pyruvate, producing energy in the form of ATP and NADH. If an agent closely resembles glucose but cannot be metabolized, it would bind to the enzymes involved in glycolysis, preventing the normal breakdown of glucose and disrupting the energy production process. This would inhibit the cell's ability to generate ATP through glycolysis.

Approximately 40% of the energy of glucose is transferred to storage in ATP as a result of the complete oxidation of glucose to CO2 and water in cellular respiration. This means that during cellular respiration, 40% of the energy released from the breakdown of glucose is used to produce ATP, which is the main energy currency of cells. The remaining energy is released as heat.

Carbon dioxide (CO2) is released during the oxidation of pyruvate to acetyl CoA and during the citric acid cycle in cellular respiration. These stages involve the decarboxylation of carbon compounds, releasing CO2 as a byproduct. Glycolysis does not release CO2, and oxidative phosphorylation is involved in ATP production, not CO2 release. Fermentation processes can produce CO2, but it is not part of the cellular respiration pathway being asked about.

Chemiosmotic phosphorylation is the process by which ATP is synthesized in the mitochondria during cellular respiration. It involves the movement of protons across the inner mitochondrial membrane, creating an electrochemical gradient. This gradient is then used by ATP synthase to generate ATP. This process is highly efficient and produces the most chemical energy compared to the other options listed. Substrate-level phosphorylation refers to the direct transfer of a phosphate group to ADP to form ATP, but it is not as efficient as chemiosmotic phosphorylation. Converting oxygen to ATP, transferring electrons from organic molecules to pyruvate, and generating carbon dioxide and oxygen in the electron transport chain are all steps involved in cellular respiration, but they do not specifically harvest the most chemical energy.

Oxidative phosphorylation is the metabolic process that is most closely associated with intracellular membranes. This process occurs in the inner mitochondrial membrane and involves the transfer of electrons from electron carriers to oxygen, generating a proton gradient across the membrane. This gradient is then used by ATP synthase to produce ATP. Therefore, oxidative phosphorylation relies on the integrity and functionality of intracellular membranes for its proper functioning.

ATP synthase is located in the inner membrane of the mitochondrion. This is where the electron transport chain takes place, and ATP synthase is an enzyme that is responsible for producing ATP during oxidative phosphorylation. The inner membrane is highly folded, forming structures called cristae, which increase the surface area available for ATP synthesis. Therefore, ATP synthase is embedded within the inner membrane to facilitate the production of ATP from the energy generated during the electron transport chain.

NADH is the reducing agent in the given reaction. A reducing agent is a substance that donates electrons to another substance, causing it to be reduced. In this reaction, NADH donates electrons to pyruvate, causing it to be reduced to lactate. NADH itself is oxidized in the process and is converted to NAD+. Therefore, NADH acts as the reducing agent in this reaction.

During aerobic respiration, glucose is completely oxidized, meaning it reacts with oxygen to produce carbon dioxide and water. The balanced equation for the oxidation of glucose is C6H12O6 + 6O2 → 6CO2 + 6H2O. From this equation, we can see that for every molecule of glucose, 6 molecules of oxygen are required. Therefore, the correct answer is 6.

During cellular respiration, glucose is broken down in a series of reactions. The majority of the energy released from glucose is transferred to ATP (adenosine triphosphate), which is the primary energy currency of cells. ATP is produced through glycolysis and the citric acid cycle, where glucose is broken down into smaller molecules and energy is released. Therefore, ATP is the correct answer as it receives approximately 40% of the energy content of glucose during cellular respiration.

NADH is produced both in the cytosol and the mitochondria. In the cytosol, NADH is produced during the glycolysis step of both respiration and fermentation. In the mitochondria, NADH is produced during the citric acid cycle and the electron transport chain steps of respiration. Therefore, NADH is not produced only in the mitochondria, making this statement false.

During glycolysis, glucose is oxidized to pyruvate. However, only a small amount of the free energy available from the oxidation of glucose is used to produce ATP. Most of the free energy remains in pyruvate, which is one of the products of glycolysis. This is why only two molecules of NADH are formed during glycolysis, even though it seems that more could be formed.

During oxidative phosphorylation, H2O is formed through the process of electron transport chain in the mitochondria. The oxygen used for the synthesis of water comes from molecular oxygen (O2). Oxygen molecules from the inhaled air are transported to the mitochondria where they accept electrons and protons to form water. This process is essential for the production of ATP, the energy currency of the cell.

The electron transport chain is a series of protein complexes located in the inner mitochondrial membrane. As electrons are passed along the chain, energy is released and used to pump H+ ions across the inner membrane and into the intermembrane space. This creates a concentration gradient of H+ ions, which can then flow back into the mitochondrial matrix through ATP synthase, driving the production of ATP. Therefore, the correct answer is the mitochondrial intermembrane space.

When a molecule is phosphorylated, it means that a phosphate group has been added to it. This addition of a phosphate group increases the chemical reactivity of the molecule, making it more likely to participate in cellular work. The phosphate group can be transferred to other molecules, providing energy for various cellular processes such as metabolism and signal transduction. Therefore, a phosphorylated molecule is considered to be primed and ready to carry out cellular work.

The primary function of the mitochondrion is the production of ATP through a process called oxidative phosphorylation. This process involves the membrane-bound electron transport chain carrier molecules, proton pumps embedded in the inner mitochondrial membrane, mitochondrial ATP synthase, and enzymes for the citric acid cycle. Glycolysis, on the other hand, occurs in the cytoplasm and does not require the mitochondrion. Therefore, enzymes for glycolysis are not needed by the mitochondrion to carry out its primary function of ATP production.

The statement that a gram of glucose oxidized by cellular respiration produces more than twice as much ATP as a gram of fat oxidized by cellular respiration is not true. In reality, a gram of fat oxidized by cellular respiration produces more than twice as much ATP as a gram of glucose oxidized. This is because fats have a higher energy content per gram compared to glucose.

The correct answer is that electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O). This movement of electrons results in the formation of more stable compounds, such as CO2 and water, which have lower energy bonds compared to the organic compounds being oxidized. This release of energy is what makes the oxidation of organic compounds exergonic.

During glycolysis, glucose is broken down into pyruvate. This process involves the transfer of energy from glucose to various molecules, including ADP and ATP. However, the majority of the energy from glucose is actually retained in the pyruvate molecules that are produced. This energy can be further utilized in subsequent stages of cellular respiration to generate more ATP. Therefore, the correct answer is that most of the energy of glucose is retained in the pyruvate.

In the presence of oxygen, pyruvate undergoes several steps to be catabolized in the citric acid cycle. First, pyruvate loses a carbon atom as CO2. Then, it is oxidized to form a two-carbon compound called acetate. Finally, it is bonded to coenzyme A, resulting in the formation of acetyl CoA. In this process, NAD+ is reduced to NADH, meaning it gains a hydrogen ion (H+). Additionally, another carbon atom is lost as CO2. Therefore, the correct answer is acetyl CoA, NADH, H+, and CO2.

The breakdown of glucose to carbon dioxide and water is exergonic, meaning it releases energy. This is supported by the statement that the breakdown has a free energy change of -686 kcal/mol, indicating a negative value and therefore an exergonic process. Additionally, the breakdown involves oxidation-reduction or redox reactions, which is the transfer of electrons between molecules. Therefore, all the given statements are true and the correct answer is that the breakdown of glucose to carbon dioxide and water is exergonic, has a free energy change of -686 kcal/mol, and involves oxidation-reduction or redox reactions.

The organism's ability to consume sugar and thrive in the absence of air suggests that it can generate energy through alternative pathways that do not require oxygen. This is a characteristic of facultative anaerobes, which can switch between aerobic and anaerobic metabolism depending on the availability of oxygen. The fact that the organism does fine when returned to normal air further supports this explanation.

When electrons move closer to a more electronegative atom, energy is released because the electrons are moving to a lower energy state. Additionally, the more electronegative atom is reduced because it gains electrons and becomes more negatively charged.

In cellular respiration, NADH is oxidized by the electron transport chain, which generates ATP. This process occurs in the presence of oxygen and is the final step in aerobic respiration. On the other hand, fermentation does not involve the electron transport chain and does not require oxygen. Instead, it uses an organic molecule as the final electron acceptor. Therefore, NADH is only oxidized by the electron transport chain in respiration, making this statement a true distinction between fermentation and cellular respiration.

In the presence of oxygen, an increase in the amount of ATP would indicate that the cell has sufficient energy and does not require further glycolysis or citric acid cycle activity. Phosphofructokinase is an allosteric enzyme that is inhibited by ATP. Therefore, an increase in ATP would inhibit the enzyme, slowing down the rates of glycolysis and the citric acid cycle. This is because the cell does not need to produce more ATP when it already has an excess amount.

NAD+ is actually an oxidized form of the molecule, while NADH is the reduced form. The reduction of NAD+ to NADH occurs during both glycolysis and the citric acid cycle. NAD+ is reduced by the action of dehydrogenases, and it can receive electrons for use in oxidative phosphorylation. In the absence of NAD+, glycolysis cannot function. Therefore, the statement that NAD+ has more chemical energy than NADH is false.

During cellular respiration, acetyl CoA accumulates in the mitochondrial matrix. This is the innermost compartment of the mitochondria where the citric acid cycle (also known as the Krebs cycle) takes place. Acetyl CoA is produced from the breakdown of glucose during glycolysis and further enters the mitochondria to be oxidized in the citric acid cycle. The mitochondrial matrix contains the enzymes necessary for the citric acid cycle, and it is here that acetyl CoA is utilized to produce energy through the oxidation of carbon compounds.

When the body breaks down fat, it is converted into carbon dioxide (CO2) and water (H2O). The carbon dioxide is then exhaled through the lungs, while the water is excreted through sweat, urine, and other bodily fluids. This process is how the body eliminates fat when someone loses weight.

During oxygen deprivation, muscle cells undergo anaerobic respiration. In this process, pyruvate is converted to lactate. This conversion allows the regeneration of NAD+ from NADH, which is necessary for glycolysis to continue producing ATP. Therefore, the correct answer is lactate; NAD+.

ATP synthase activity could be compared to how rushing steam turns a water wheel because ATP synthase is an enzyme that harnesses the energy from a proton gradient to produce ATP. Similarly, rushing steam turns a water wheel by utilizing the energy from the steam to generate mechanical work. Both processes involve the conversion of energy from one form to another to perform useful work.

During cellular respiration, each molecule of glucose undergoes glycolysis, the Krebs cycle, and oxidative phosphorylation to produce a total of 36 molecules of ATP. Since two molecules of glucose are being oxidized, the total number of ATP molecules produced would be 36 multiplied by 2, which equals 72. However, during glycolysis, two molecules of ATP are used, so we need to add those back to the total. Therefore, the correct answer is 72 + 2 = 74 molecules of ATP.

The carbon skeleton for synthesis of a five-carbon amino acid would be supplied by α-ketoglutarate. α-ketoglutarate is an intermediate of the citric acid cycle and can be converted into a five-carbon amino acid through various enzymatic reactions.

During aerobic respiration, electrons travel downhill in the sequence of food being broken down into NADH, which then enters the electron transport chain, and finally, oxygen acts as the final electron acceptor. This sequence allows for the production of ATP through oxidative phosphorylation.

CO2 is already completely oxidized because oxidation refers to the loss of electrons or an increase in the oxidation state of an atom. In CO2, carbon is in its highest oxidation state (+4) and is already bonded to two oxygen atoms, which are highly electronegative. This means that carbon is already fully oxidized and cannot undergo further oxidation.

In fermentation, NADH is oxidized. This means that NADH loses electrons and is converted back into NAD+. This process is essential for the continuation of fermentation as it allows for the regeneration of NAD+, which is needed for glycolysis to continue producing ATP.

Exergonic redox reactions in mitochondria provide the energy to establish the proton gradient. The electron transport chain in mitochondria transfers electrons from electron donors to electron acceptors, releasing energy in the process. This energy is used to pump protons across the inner mitochondrial membrane, creating a concentration gradient. The proton gradient is then used by ATP synthase to produce ATP through chemiosmosis. Therefore, the energy from exergonic redox reactions is essential for establishing the proton gradient, which is crucial for ATP synthesis in mitochondria.

In the presence of a metabolic poison that inhibits mitochondrial ATP synthase, the production of ATP would be inhibited. ATP synthase is responsible for the synthesis of ATP by utilizing the proton gradient across the inner mitochondrial membrane. Without ATP synthesis, the proton gradient would not be utilized, resulting in an increase in the pH difference across the inner mitochondrial membrane. This is because ATP synthase normally helps to balance the pH by allowing protons to flow back into the matrix, but without its function, the protons would continue to accumulate in the intermembrane space, leading to an increase in the pH difference.

Substrate-level phosphorylation refers to the direct transfer of a phosphate group from a substrate molecule to ADP, resulting in the formation of ATP. In glycolysis, substrate-level phosphorylation is the only mechanism by which ATP is produced. Therefore, all the ATP formed during glycolysis is through substrate-level phosphorylation, making the correct answer 100%.

Isocitrate can undergo one round of substrate-level phosphorylation to produce alpha-ketoglutarate, which can then enter the citric acid cycle and eventually produce one ATP molecule through oxidative phosphorylation. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation starting with one molecule of isocitrate is 1.

During the complete aerobic respiration of a molecule of sucrose (C12H22O11), it is broken down into glucose and fructose. Each glucose molecule produces 6 molecules of carbon dioxide (CO2), and each fructose molecule produces 6 molecules of carbon dioxide (CO2). Since there are 12 carbon atoms in a molecule of sucrose, it will produce a total of 12 molecules of carbon dioxide (CO2) during the complete aerobic respiration.

Inside an active mitochondrion, most electrons follow the pathway of the citric acid cycle, where NADH is produced. NADH then carries the electrons to the electron transport chain, where they are passed along a series of protein complexes, ultimately leading to the reduction of oxygen to form water. This flow of electrons generates a proton gradient, which drives the synthesis of ATP through oxidative phosphorylation. Therefore, the correct pathway is citric acid cycle → NADH → electron transport chain → oxygen.

Fatty acids cannot be converted to an intermediate of glycolysis because glycolysis is the metabolic pathway that breaks down glucose into pyruvate. Fatty acids, on the other hand, are metabolized through beta-oxidation to produce acetyl-CoA, which enters the citric acid cycle. Therefore, fatty acids follow a different metabolic pathway than glycolysis and cannot be converted to an intermediate of glycolysis.

As electrons flow along the electron transport chains of mitochondria, protons are pumped across the inner mitochondrial membrane from the matrix to the intermembrane space. This creates an electrochemical gradient, with a higher concentration of protons in the intermembrane space and a lower concentration in the matrix. The movement of protons back into the matrix through ATP synthase drives the synthesis of ATP. The pumping of protons also leads to a decrease in pH in the intermembrane space and an increase in pH in the matrix. Therefore, the correct answer is that the pH of the matrix increases.

The efficiency of cellular respiration can be calculated by dividing the number of moles of ATP produced by the number of moles of glucose oxidized and then multiplying by 100 to get a percentage. In this case, the mutant organism produces 29 moles of ATP for every mole of glucose oxidized. Therefore, the efficiency is (29/1) x 100 = 2900%. However, since the question asks for the approximate efficiency, we round this value to the nearest tens place, which is 29.0%. Therefore, the correct answer is 30%, as it is the closest option to 29.0%.

The best explanation for the young relative's condition is that his mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane. This means that pyruvate, which is the end product of glycolysis, cannot enter the mitochondria to undergo further respiration. As a result, the mitochondria are unable to fully utilize glucose for energy production, leading to an increased production of lactate as an alternative energy source. This condition is known as pyruvate transport deficiency and can result in a lack of energy and fatigue.

FADH2 directly donates electrons to the electron transport chain at the lowest energy level during aerobic respiration. NAD+ and NADH also donate electrons, but at a higher energy level. ATP and ADP + Pi are not directly involved in donating electrons to the electron transport chain.

The electron transport chain is a series of electron carriers that transfer electrons from one molecule to another. The sequence of electron carriers in the chain starts with the least electronegative and ends with the most electronegative. In this case, FMN is the least electronegative, followed by Fe•S, ubiquinone, and cytochromes (Cyt). Therefore, the correct answer is FMN, Fe•S, ubiquinone, cytochromes (Cyt).

Prokaryotic cells are simple cells that lack a true nucleus and membrane-bound organelles like mitochondria or chloroplasts. Their genetic material is organized into a single circular chromosome located in the cytoplasm. Prokaryotes are typically much smaller than eukaryotic cells, which have a more complex internal structure.

The process of oxidative phosphorylation occurs in the inner membrane of mitochondria. It involves the transfer of electrons from electron carriers to oxygen, resulting in the production of ATP. Therefore, if vesicles can be prepared from portions of the inner membrane, it means that the proteins and enzymes necessary for oxidative phosphorylation are still present and functional in these vesicles. Hence, oxidative phosphorylation could still be carried out by the isolated inner membrane.

Both alcohol fermentation and lactic acid fermentation regenerate NAD+ from NADH. This is essential for glycolysis to continue in the absence of oxygen. During glycolysis, NAD+ is reduced to NADH. If NAD+ is not regenerated, glycolysis will stop, and the cell will not be able to produce ATP. Fermentation pathways ensure the continuation of glycolysis by oxidizing NADH back to NAD+.

For NAD+ to remove electrons from glucose or other organic molecules, the free energy released during the process must be greater than the energy required to transfer the electrons to NAD+. This is because the transfer of electrons is an energetically unfavorable process and requires energy input. If the free energy released is not sufficient to overcome the energy barrier, the transfer of electrons will not occur. Therefore, it is necessary for the free energy liberated during the removal of electrons from the organic molecules to be greater than the energy required for the transfer to NAD+.

The fact that glycolysis can occur without oxygen (anaerobically) suggests it evolved early in life's history when Earth's atmosphere lacked free oxygen. Ancient prokaryotes would have relied on glycolysis for energy production before the evolution of more complex, oxygen-dependent metabolic pathways. While the other options are true statements about glycolysis, they don't directly support the idea of its ancient origin in the same way.

The most direct source of energy used to convert ADP + Pi to ATP in chemiosmotic phosphorylation is the energy released from the movement of protons through ATP synthase. This process, known as proton motive force, occurs when protons flow down their concentration gradient through ATP synthase, causing the enzyme to rotate and catalyze the synthesis of ATP. This movement of protons provides the energy necessary for the phosphorylation of ADP to ATP.

The process of substrate-level phosphorylation produces 1 ATP molecule per succinyl CoA molecule. Since we started with 3 molecules of succinyl CoA, we would have 3 ATP molecules from substrate-level phosphorylation. Oxidative phosphorylation (chemiosmosis) produces 2.5 ATP molecules per molecule of succinyl CoA. Therefore, we would have an additional 7.5 ATP molecules from oxidative phosphorylation. Adding the ATP molecules from substrate-level phosphorylation and oxidative phosphorylation, we get a total of 10.5 ATP molecules. However, ATP cannot exist in fractional amounts, so we round down to the nearest whole number, which is 10. Therefore, the correct answer is 18 ATP molecules.

Cellular respiration is the process by which cells break down glucose to generate ATP, the energy currency of cells. It involves three main stages: glycolysis, the Krebs cycle, and the electron transport chain. The Calvin cycle, on the other hand, is part of photosynthesis, the process by which plants convert light energy into chemical energy in the form of glucose.

Fermentation, specifically the glycolytic pathway that precedes it, takes place in the cytosol (the fluid portion of the cytoplasm) of both prokaryotic and eukaryotic cells. This location is significant because it allows for quick and efficient energy production when oxygen is limited or absent. The other options are incorrect as they refer to locations within the mitochondria, which are involved in aerobic respiration, not fermentation.

Cell membranes are primarily composed of lipids (phospholipids and cholesterol), proteins, and carbohydrates. Lipids form the structural basis of the membrane, proteins carry out various functions like transport and signaling, and carbohydrates are involved in cell recognition. Nucleic acids, such as DNA and RNA, are primarily found within the cell's nucleus or cytoplasm and are not major components of the cell membrane.