AP Biology Unit 3
The human oral microbiota contains over 700700700 species of bacteria. One species often found in the oral cavity is Streptococcus mutans, an anaerobic bacterium strongly associated with the formation of dental cavities. S. mutans metabolizes glucose and other dietary sugars remaining in the mouth after a meal, producing lactic acid as a byproduct. Over time, high levels of lactic acid can erode tooth enamel, eventually leading to the formation of dental cavities. Which of the following drugs would be most likely to prevent cavities caused by S. mutans? - A drug that inhibits the formation of a proton gradient across the cell membrane - A drug that prevents the movement of oxygen across the cell membrane - A drug that inhibits the production of NADH and FADH_22start subscript, 2, end subscript during the Krebs cycle - A drug that prevents the conversion of glucose into pyruvate
A drug that prevents the conversion of glucose into pyruvate
Which of the following best explains how the light reactions of photosynthesis generate ATP? - As photosystem II (PSII) absorbs energy from light, electrons are excited to a higher energy level and accepted by ADP to form ATP. - A proton gradient drives the formation of ATP from ADP and inorganic phosphate via ATP synthase. - Energy from light excites ATP synthase, causing it to bind ADP with inorganic phosphate to form ATP. - ADP accepts excited electrons at the end of the electron transport chain (ETC) to form ATP.
A proton gradient drives the formation of ATP from ADP and inorganic phosphate via ATP synthase.
Which of the following best describes the process of induced fit? - A substrate binds to the active site of an enzyme without either structure changing conformation. - A substrate binds to the active site of an enzyme, causing the conformation of the active site to change slightly. - A substrate binds to an allosteric site on an enzyme, causing the conformation of the allosteric site to change slightly. - A substrate changes conformation and then binds to the active site of an enzyme.
A substrate binds to the active site of an enzyme, causing the conformation of the active site to change slightly.
Bacteroides is the predominant genus of bacteria found in the human gut microbiota. As anaerobic bacteria, Bacteroides undergo fermentation in the gut, converting otherwise nondigestible carbohydrates into fermentation products that are used by the host for energy. Which of the following toxins would be most likely to disrupt carbohydrate metabolism in Bacteroides species? - A toxin that breaks down the membrane proteins of the electron transport chain - A toxin that inhibits the function of an enzyme during glycolysis - A toxin that prevents the formation of Krebs cycle products - A toxin that inhibits the function of ATP synthase
A toxin that inhibits the function of an enzyme during glycolysis
Acetylcholine (ACh) is an important signaling molecule in the nervous system. After it transmits a signal, ACh is broken down by the enzyme acetylcholinesterase (AChE) in a reaction known as ACh hydrolysis. Which of the following best describes the effect AChE has on the hydrolysis of ACh? - AChE increases the activation energy of ACh hydrolysis, increasing the rate of this reaction. - AChE increases the activation energy of ACh hydrolysis, increasing its rate. - AChE decreases the activation energy of ACh hydrolysis, increasing the rate of this reaction. - AChE decreases the activation energy of ACh hydrolysis, decreasing the rate of this reaction.
AChE decreases the activation energy of ACh hydrolysis, increasing the rate of this reaction.
Which of the following best indicates that the light reactions of photosynthesis have completed and that the Calvin cycle has begun? - An electrochemical gradient forms across the thylakoid membrane. - ATP and NADPH accumulate in the stroma. - Electrons are transferred across the electron transport chain (ETC) on the thylakoid membrane. - A high concentration of carbohydrates is found in the thylakoid lumen.
ATP and NADPH accumulate in the stroma.
The cytochrome complex is an integral thylakoid membrane protein that forms an electrochemical gradient by pumping protons. In an experiment, researchers apply a toxin to a plant cell that inhibits the cytochrome complex. Which of the following explains the most likely effect of this toxin on the light reactions of photosynthesis? - Hydrogen ions will move across the thylakoid membrane using simple diffusion. - NADP+ will not be reduced to NADPH. - ATP synthesis will not occur. - Carbohydrates will not be produced in the stroma.
ATP synthesis will not occur.
A group of students are conducting an experiment on Elodea canadensis, a species of aquatic plant. In order to test the effect of light intensity on the rate of photosynthesis, they place each Elodea canadensis plant into an aquarium tank and place each tank at a different distance from a light source. After a few minutes, oxygen bubbles begin to form in each of the tanks. The students count the number of oxygen bubbles released during a 555 minute period for each tank. The results of their experiment are shown below. - A decrease in light intensity increases the rate of photosynthesis. - An increase in light intensity decreases the rate of photosynthesis. - Light intensity does not affect the rate of photosynthesis. - An increase in light intensity increases the rate of photosynthesis.
An increase in light intensity increases the rate of photosynthesis.
A researcher claims that increased atmospheric carbon dioxide levels cause increased growth rates in plants. Which of the following statements best supports the researcher's claim? - Atmospheric carbon dioxide is produced by the burning of fossil fuels, which are formed from the remains of living organisms such as plants. - Atmospheric carbon dioxide is a byproduct of cellular respiration, which is a metabolic process that occurs in plants and other living organisms. - Atmospheric carbon dioxide typically enters plant leaves through stomata, which plants rely on for regulating gas exchange with the atmosphere. - Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.
Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.
RuBisCO catalyzes the joining of carbon dioxide with RuBP during carbon fixation. In an experiment, researchers apply a toxin to a plant cell that inhibits RuBisCO. Which of the following explains the most likely effect this toxin will have on the Calvin cycle? - Excited electrons will not be transferred across the electron transport chain. - Carbon and oxygen will not be released after the breakdown of carbon dioxide. - Carbon dioxide will not be converted into sugar. - ATP synthase will not catalyze the formation of ATP on the thylakoid membrane.
Carbon dioxide will not be converted into sugar.
Methotrexate is a drug that is commonly used to treat cancers and autoimmune diseases in humans. It functions by binding to the active site of the enzyme DHFR, preventing both DNA synthesis and excess cell proliferation. Which of the following terms best describes methotrexate? - Noncompetitive inhibitor - Cofactor - Competitive inhibitor - Allosteric activator
Competitive inhibitor
Cyanide poisoning is a type of poisoning caused by exposure to certain cyanide-containing compounds, such as hydrogen cyanide or cyanide salts. Inhalation or consumption of these compounds can cause histotoxic hypoxia, a condition in which cells are no longer able to take up or utilize oxygen during cellular respiration. As a result, ATP production during respiration is significantly reduced. Based on the information above, which of the following is the most likely explanation for how cyanide causes histotoxic hypoxia? - Cyanide inhibits the enzymatic breakdown of glucose during glycolysis. - Cyanide inhibits the transfer of electrons to the final acceptor in the electron transport chain. - Cyanide inhibits the reduction of NAD^++start superscript, plus, end superscript and FAD during the Krebs cycle. - Cyanide inhibits the transport of pyruvate across the mitochondrial membrane.
Cyanide inhibits the transfer of electrons to the final acceptor in the electron transport chain.
A group of biology students wants to study the effects of pH on enzyme activity. They measure the activity of enzymes A and B at various pHs and record their data in the graph below. A solution of enzyme A has pH of 8. Based on the graph, which pH change would result a higher enzyme activity? - Decreasing the pH of the solution to 444 - Increasing the pH of the solution to 1044 - Increasing the pH of the solution to 1244 - Decreasing the pH of the solution to 6
Decreasing the pH of the solution to 6
Pancreatic amylase is a digestive enzyme found in the small intestine. It helps break down large starch molecules later in the digestive process. Pancreatic amylase is unable to break down lipids. Which of the following best explains why pancreatic amylase is able to break down starches, but not lipids? - Lipids are too small to bind to enzymes. - Lipids are too hydrophobic to be broken down by enzymes. - Enzymes denature in the presence of lipids. - Enzymes bind only to their specific substrates.
Enzymes bind only to their specific substrates.
The enzyme glutamine synthetase facilitates the use of energy to combine glutamate and ammonia (NH4), forming glutamine. This process occurs in two steps, as represented in the following diagram. Which of the following statements best describes the process carried out by glutamine synthetase? - Glutamine synthetase uses energy to hydrolyze ATP, which then drives the formation of glutamine from glutamate and ammonia. - Glutamine synthetase forms glutamine by coupling two endothermic reactions, both of which occur in the enzyme's active site. - Glutamine synthetase uses an exothermic reaction to drive an endothermic one by catalyzing the formation of a phosphorylated intermediate. - Glutamine synthetase forms a phosphorylated intermediate by attaching a molecule of ATP to glutamate
Glutamine synthetase uses an exothermic reaction to drive an endothermic one by catalyzing the formation of a phosphorylated intermediate.
During step 3 of the Krebs cycle, the enzyme isocitrate dehydrogenase (IDH) catalyzes the conversion of isocitrate α-ketoglutarate. This step is represented in the model below. IDH is allosterically activated by ADP at high concentrations. Which of the following best describes how this interaction helps regulate the Krebs cycle? - High levels of ADP inhibit the Krebs cycle because ADP prevents IDH from catalyzing the conversion of isocitrate to α-ketoglutarate. - Low levels of ADP stimulate the Krebs cycle, leading to the production of excess ATP that is stored for later use. - High levels of ADP stimulate the Krebs cycle, leading to the increased conversion of ADP to ATP during oxidative phosphorylation. - Low levels of ADP inhibit the Krebs cycle because IDH requires ADP as a substrate for the reaction it catalyzes.
High levels of ADP stimulate the Krebs cycle, leading to the increased conversion of ADP to ATP during oxidative phosphorylation.
Which of the following statements about letter B is true? - Letter B represents the energy difference between the reactants and products for the uncatalyzed pathway. - Letter B represents the energy difference between the reactants and products for the catalyzed pathway. - Letter B represents the activation energy of the catalyzed reaction pathway. - Letter B represents the activation energy of the uncatalyzed reaction pathway.
Letter B represents the activation energy of the catalyzed reaction pathway.
Which of the following statements about letter C is true? - Letter C represents the activation energy of the catalyzed reaction pathway. - Letter C represents the activation energy of the uncatalyzed reaction pathway. - Letter C represents the energy difference between the reactants and products for the uncatalyzed pathway. - Letter C represents the energy difference between the reactants and products for the catalyzed pathway.
Letter C represents the activation energy of the uncatalyzed reaction pathway.
Maltase is an enzyme found in the small intestine. It helps break down maltose during the process of digestion. Which of the following best describes what happens when maltose binds with maltase? - Maltose binds to the active site of maltase, causing the conformation of the active site to change slightly. - The conformation of maltose is already complementary to the active site of maltase, so maltose binds to the active site without either structure changing conformation. - The conformation of maltose changes, and then maltose binds to the active site of maltase. - Maltose binds to an allosteric site on maltase, causing the conformation of the allosteric site to change slightly.
Maltose binds to the active site of maltase, causing the conformation of the active site to change slightly.
In mitochondria, the rate of ATP synthesis during oxidative phosphorylation is tightly coupled to the movement of electrons through the electron transport chain (ETC). When ADP levels rise and the demand for ATP synthesis increases, electron flow through the ETC also increases. Based on the information above, which of the following best describes an effect of rising ADP levels in mitochondria? - Fewer protons will be pumped across the inner mitochondrial membrane. - The flow of protons through ATP synthase will decrease. - NADH and FADH2 will be oxidized to NAD+ and FAD less rapidly. - Oxygen consumption will increase.
Oxygen consumption will increase.
Pepsin, a proteolytic enzyme found in the stomach, is essential for digestion. Pepsin functions optimally at approximately 37oC 37∘C37∘C37, degrees, start text, C, end text. Which of the following would most likely result if pepsin's environmental temperature was lowered from 37oC 37∘C37∘C37, degrees, start text, C, end text to 25oC 25∘C25∘C25, degrees, start text, C, end text25oC? - Pepsin would catalyze reactions at a faster rate. - Pepsin would be less efficient at catalyzing reactions. - Pepsin would lose its three-dimensional shape. - Pepsin would more easily lower the activation energy of reactions.
Pepsin would be less efficient at catalyzing reactions.
Unlike most other cells in the human body, mature red blood cells (RBCs) do not contain a nucleus or mitochondria. This allows RBCs to carry more hemoglobin, and therefore oxygen, through the bloodstream. Based on the information above, which of the following is most likely true about RBCs? - Due to a lack of mitochondria, RBCs do not produce ATP. - CO2 and ethanol are byproducts of ATP production in RBCs. - Oxygen is used as the terminal electron acceptor in RBCs. - RBCs generate lactate as a waste product.
RBCs generate lactate as a waste product.
Which of the following best describes how the Calvin cycle and the light reactions of photosynthesis function together? - The Calvin cycle uses ATP and NADPH generated by the light reactions to synthesize carbohydrates. - The Calvin cycle uses ATP and NADPH generated by the light reactions to break down carbohydrates. - The Calvin cycle generates ATP and NADPH to excite electrons during the light reactions. - The Calvin cycle produces ATP and NADPH to drive the formation of an electrochemical gradient during the light reactions.
The Calvin cycle uses ATP and NADPH generated by the light reactions to synthesize carbohydrates.
A single-step reaction is represented below. A + B -> AB + heat Which of the following best explains how the addition of an enzyme would affect the above reaction? - The enzyme would increase the activation energy of the reaction, increasing its rate. - The enzyme would decrease the activation energy of the reaction, increasing its rate. - The enzyme would increase the activation energy of the reaction, decreasing its rate. - The enzyme would decrease the activation energy of the reaction, decreasing its rate.
The enzyme would decrease the activation energy of the reaction, increasing its rate.
Which of the following statements accurately describes an energy-releasing process that is coupled to an energy-requiring process in the cell? - The movement of motor proteins is powered by the formation of ADP and inorganic phosphate from ATP. - An exothermic chemical reaction is powered by ATP hydrolysis in the chloroplast - The transport of ions across a membrane is powered by the formation of ATP from ADP and inorganic phosphate. - An endothermic chemical reaction provides the energy for ATP hydrolysis in the mitochondria.
The movement of motor proteins is powered by the formation of ADP and inorganic phosphate from ATP.
Several scientists are studying the effect of initial substrate concentration on the activity of an enzyme. They perform a series of enzyme-controlled reactions, keeping the concentration of enzyme constant but increasing the initial concentration of substrate in each trial. The graph below shows their results. Based on the data above, which of the following best describes what happens to the rate of product formation at higher initial substrate concentrations? - The rate of product formation levels off because no substrate is available to bind with the enzyme. - The rate of product formation levels off because nearly all of the enzyme is bound to substrate. - The rate of product formation decreases because nearly all of the enzyme is bound to substrate. - The rate of product formation decreases because no substrate is available to bind with the enzyme.
The rate of product formation levels off because nearly all of the enzyme is bound to substrate.
Which of the following best describes what will result when a glucose-fed yeast cell is placed in an anaerobic environment? - The yeast cell will produce ATP through fermentation, generating CO2 and ethanol as byproducts. - The yeast cell will produce ATP through fermentation, generating lactic acid as byproducts. - Due to a lack of oxygen, the yeast cell will no longer produce ATP, and its ATP stores will be depleted. - Due to the presence of oxygen, the yeast cell will produce ATP through oxidative phosphorylation.
The yeast cell will produce ATP through fermentation, generating CO2 and ethanol as byproducts.
When light is absorbed by pigments in photosystem II (PSII), energy is passed inward from pigment to pigment until it reaches the reaction center. Electrons are then boosted to a high energy level and captured by the primary electron acceptor. Which of the following occurs immediately after the electrons from PSII are captured by the primary electron acceptor? - Water is broken down. - The electrons return to PSII. - ADP is converted to ATP. - NADP+ accepts the electrons.
Water is broken down.
