AP Bio final part 2

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. Based on the graph, what is the approximate optimal pH for enzyme B?

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Which of the following best explains how the light reactions of photosynthesis generate ATP?

A proton gradient drives the formation of ATP from ADP and inorganic phosphate via ATP synthase.

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 decreases the activation energy of ACh hydrolysis, increasing the rate of this reaction. AChE increases the rate of ACh hydrolysis by lowering the activation energy of the reaction.

The cytochrome b6f 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 b6f complex. Which of the following explains the most likely effect of this toxin on the light reactions of photosynthesis?

ATP synthesis will not occur.

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 a pH of 8. Based on the graph, which pH change would result in higher enzyme activity?

Decreasing the pH of the solution to 6

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 an exothermic reaction to drive an endothermic one by catalyzing the formation of a phosphorylated intermediate.

The image above depicts the signal transduction pathway of epinephrine. During one step in the pathway, the enzyme glycogen synthase is phosphorylated, which inactivates the enzyme. If a toxin prevents the phosphorylation of glycogen synthase during this pathway, which of the following will most likely occur when epinephrine comes into contact with its receptor?

Glycogen breakdown will still occur, but glycogen synthesis will not be affected.

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?

Oxygen consumption will increase.

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.

During the cell-mediated immune response, killer T-cells target and kill infected cells. This process is shown in the image below. During the cell-mediated immune response, killer T-cells target and kill infected cells. This process is shown in the image below.

The killer T-cell will no longer bind to the infected cell, and as a result, the infected cell will not be killed.

Which of the following best describes the cell communication occurring in the figure above?

A signal-emitting cell communicates with a nearby cell by releasing local regulators.

Which of the following best describes the process of induced fit?

A substrate binds to the active site of an enzyme, causing the conformation of the active site to change slightly.

Gifblaar, a small shrub native to Southern Africa, is a common cause of lethal poisoning in cattle and other livestock living in the region. The plant's extreme toxicity is due to fluoroacetate, a potent metabolic poison that is present in all parts of the plant. In the body, fluoroacetate is converted into fluorocitrate, which irreversibly binds the enzyme that converts citrate to isocitrate in step 2 of the Krebs cycle. As a result, the cycle is unable to proceed past step 111. Based on the model of the Krebs cycle shown above, which of the following best describes an effect of gifblaar poisoning?

ATP would be depleted, inhibiting many biological processes.

Acetylcholine is a neurotransmitter that helps control muscle contraction. This neurotransmitter functions differently depending on which type of muscle it interacts with. For example, acetylcholine promotes muscle contraction in skeletal muscle but inhibits contraction in heart muscle. Which of the following best explains why acetylcholine leads to different cellular responses in skeletal and heart muscle?

Acetylcholine binds to different types of receptors in skeletal and heart muscle.

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 5 minute period for each tank. The results of their experiment are shown below. Which of the following conclusions is best supported by the results of the experiment?

An increase in light intensity increases the rate of photosynthesis.

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?

Enzymes bind only to their specific substrates.

During step 3 of the Krebs cycle, the enzyme isocitrate dehydrogenase (IDH) catalyzes the conversion of isocitrate to \alphaαalpha-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 stimulate the Krebs cycle, leading to the increased conversion of ADP to ATP during oxidative phosphorylation.

Enzymes often play a major role in signal transduction pathways. For example, enzymes can help convert an extracellular signal into an intracellular response. Specifically, adenylyl cyclase is an enzyme that catalyzes the conversion of ATP to cyclic AMP (cAMP). One competitive inhibitor of adenylyl cyclase is called MANT-ITP. Which of the following questions would best direct an investigation on how MANT-ITP impacts a signal transduction pathway?

How does MANT-ITP affect the response to intracellular signals?

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 following is an excerpt from a scientific paper written by Levy et al. The plant cell wall is a barrier to virus exit from and entry into cells. Thus, successful infection requires that plant viruses encode movement proteins to transport the viral genome locally cell-to-cell within a leaf and on into the vascular system, through which the virus will systematically invade the plant. Which of the following best predicts how movement proteins help plant viruses travel from one plant cell to another?

Movement proteins increase the permeability of the plasmodesmata between plant cells.

During cell communication in the nervous system, chemical messengers called neurotransmitters travel between neurons. As they travel, neurotransmitters send messages from one neuron to another. Which of the following best describes the role of neurotransmitters in neuron-to-neuron communication?

Neurotransmitters are local regulators that allow neurons to communicate over short distances.

Although organisms are highly ordered systems that may appear to contradict the second law of thermodynamics, they don't actually violate this law. Which of the following statements provides the best explanation for why living organisms do not violate the second law of thermodynamics?

Organisms require a constant input of energy to maintain order, and some of this energy is released into the environment as heat.

Many species of bacteria regulate gene expression using a cell signaling system known as quorum sensing (QS). In this system, bacteria synthesize QS signaling molecules and release them into the surrounding environment. The effects of these molecules on gene expression depend on the density of the bacterial population. Which of the following best describes what occurs as the density of a QS bacterial population increases?

The concentration of QS signaling molecules increases, eventually triggering a change in gene expression throughout the bacterial population.

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 decrease the activation energy of the reaction, increasing its rate.

The formation of the amino acid tryptophan is catalyzed by the enzyme tryptophan synthase. This enzyme is made up of alpha and beta subunits. Each type of subunit catalyzes a different step in the tryptophan biosynthesis pathway. The alpha subunit forms an indole molecule from indole-3-glycerol phosphate (IGP), and the beta subunit forms tryptophan from this indole. This process is summarized in the following diagram. Within the tryptophan synthase protein, the active sites of the alpha and beta subunits are connected by a hydrophobic channel. This channel allows the small, hydrophobic indole molecule to diffuse directly from the active site of an alpha subunit to the active site of a beta subunit. Which of the following statements describes a likely effect of the channel on the process carried out by tryptophan synthase?

The indole molecule does not diffuse across the cell membrane before it can be used by the beta subunit.

The tobacco mosaic virus (TMV) is a plant virus that infects a wide range of plants, including tobacco. In order to enter and travel through the cells of a plant, TMV produces a movement protein. This protein helps the virus travel directly between the cytoplasms of interconnected plant cells. Which of the following best predicts how the movement protein modifies plant cells in order to help TMV travel from cell-to-cell?

The movement protein modifies the plasmodesmata between plant cells.

The plant Sorghum bicolor produces an anti-herbivory chemical called dhurrin. Dhurrin is synthesized from the amino acid tyrosine in a three-step metabolic pathway. Each step in the dhurrin biosynthesis pathway is catalyzed by a different enzyme. Dhurrin, the final product, can be stored safely in the cell. However, a molecule produced from the reaction catalyzed by Enzyme 2 can be immediately metabolized to form hydrogen cyanide, which is a toxic substance. These pathways are summarized in the following diagram.

The product of the reaction catalyzed by Enzyme 2 is efficiently transferred to Enzyme 3.

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 nearly all of the enzyme is bound to substrate.

The human oral microbiota contains over 700 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 prevents the conversion of glucose into pyruvate

Thyroid-stimulating hormone (TSH) is a long-distance signaling molecule released by the anterior pituitary gland. Once released, TSH travels through the bloodstream to the thyroid gland, where it binds to G protein-coupled receptors called TSH receptors. This binding initiates signal transduction pathways that produce two thyroid hormones, T3 and T4. In individuals with hypothyroidism, TSH is released by the pituitary gland normally, but these individuals have consistently low levels of T3 and T4. Which of the following best explains why individuals with hypothyroidism have low levels of T3 and T4?

A mutation in their TSH receptors decreases TSH recognition, resulting in decreased signal transduction.

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 inhibits the function of an enzyme during glycolysis

Which of the following statements is true? A Cell processes that decrease entropy within a living organism can occur without an input of energy. (Choice B) B Living cells can violate the second law of thermodynamics when they build large, ordered molecules from smaller, less-ordered starting materials. (Choice C) C The organization seen in living cells, tissues, and organs is maintained by a constant input of energy. (Choice D) D The net effect of endothermic reactions in an organism and the release of heat into the surroundings is an overall decrease in the entropy of the universe.

C. The organization seen in living cells, tissues, and organs is maintained by a constant input of energy.

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?

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 transfer of electrons to the final acceptor in the electron transport chain.

Cyanide is a toxin that can affect cellular respiration. It functions by binding to an allosteric site on the enzyme cytochrome c oxidase, disrupting the electron transport chain. Cyanide is able to bind to cytochrome c oxidase whether or not the enzyme is bound to a substrate. Which of the following terms best describes cyanide?

Noncompetitive inhibitor

To complete external fertilization in fish, sperm cells must swim through open water in order to fertilize egg cells. During this process, females release a substance called ovarian fluid. Researchers hypothesized that ovarian fluid may play a role in attracting sperm cells towards egg cells. To test this hypothesis, researchers performed an experiment in which they observed the swimming paths of sperm cells as they moved towards egg cells. The researchers recorded swimming paths in water (A) and ovarian fluid (B), as shown in the image below. Sperm cell swimming paths in water (A) and ovarian fluid (B). Scale bars represent}25μm. Which of the following conclusions about ovarian fluid is best supported by the information above?

Ovarian fluid contains long-distance signaling molecules that help sperm cells swim straighter, making them more likely to fertilize eggs.

To complete external fertilization in fish, sperm cells must swim through open water in order to fertilize egg cells. During this process, females release a substance called ovarian fluid, which helps guide the sperm cells toward the egg cells. Researchers hypothesized that sperm cells are mainly attracted by ovarian fluid released from the same species. To test this hypothesis, researchers performed an experiment in which they studied the effects of salmon ovarian fluid and trout ovarian fluid on salmon sperm. In each trial within the experiment, the researchers placed salmon sperm on one side of a porous membrane and either salmon ovarian fluid, trout ovarian fluid, or water on the other side. After two minutes, the researchers counted how many salmon sperm had passed through the membrane and into the fluid. The results are presented in the graph below. Which of the following conclusions is best supported by the data above?

Salmon sperm respond more strongly to long-distance signaling molecules in salmon ovarian fluid than to those in trout ovarian fluid.

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 predicts how the rate of product formation will change if the initial substrate concentration is increased from 0.7M to 1.0M?

The rate of product formation will not change significantly

The major source of energy in a cell is adenosine triphosphate, or ATP. Most of the ATP in a eukaryotic organism is synthesized in mitochondria using ATP synthase. ATP synthase is an enzyme made up of multiple protein subunits. Some of these subunits are essential for the function of ATP synthase, while others are not. A group of scientists generated a population of fruit flies with a mutation in a gene encoding a protein subunit of ATP synthase. Analysis showed that this was a null mutation, meaning that no protein product was made from the gene. Which of the following pieces of evidence best supports the claim that the wild type version of the gene described above is not essential for ATP synthase function?

There is no lethal phenotype associated with a null mutation in the gene.

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 major source of energy in a cell is adenosine triphosphate, or ATP. ATP can be synthesized in mitochondria using a protein complex called ATP synthase. A group of scientists studied a collection of fruit flies that had fewer ATP synthase complexes than normal due to various gene mutations. Many of these mutant flies died early in development. Some of the mutant flies lived into adulthood, but had severe defects in their ability to move. The scientists collected data about the likelihood of surviving into adulthood and the average number of ATP synthase complexes for each mutant population. They then used this data to generate Figure 1. Figure 1. A model of the relationship between ATP synthase levels and fruit fly survivorship. ATP synthase complex number is measured as a percentage of the level normally found in fruit flies. Survivorship is measured as the percentage of individuals in a population of flies that live to adulthood. A newly discovered gene mutation causes fruit flies to have ATP synthase levels that are about one-third of normal. Based on the information presented in Figure 1, which of the following describes a likely outcome for a population made up of these flies?

~70% of flies in the mutant population will die before reaching adulthood because the supply of ATP will not meet energy demands.

Which of the following best indicates that the light reactions of photosynthesis have completed and that the Calvin cycle has begun?

ATP and NADPH accumulate in the stroma.

Trypsin, a proteolytic enzyme found in the small intestine, is essential for digestion. Trypsin functions optimally at approximately 37∘C At very high temperatures, the enzyme's activity stops almost completely. Which of the following best explains why trypsin is not active at high temperatures?

At high temperatures, trypsin loses its tertiary and secondary structures.

The image above depicts the signal transduction pathway of epinephrine. During one step in the pathway, the enzyme glycogen phosphorylase is phosphorylated, which activates the enzyme. If an inhibitor prevents glycogen phosphorylase from being activated during this pathway, which of the following will most likely occur?

Blood glucose levels will not increase in response to epinephrine.

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?

Carbon dioxide will not be converted into carbohydrates.

The following is an excerpt from a scientific paper written by Pan & Ren. Since the discovery in 1960s, a cell-cell signaling system known as quorum sensing (QS) has been identified in numerous microbial species. During cell growth, small signaling molecules are synthesized and secreted into the surrounding environment. As a result, the local QS signal concentration increases with cell density. When the cell density is above a certain threshold, a significant amount of signaling molecules bind to intracellular or membrane receptors and trigger the expression of a series of genes to control a wide spectrum of phenotypes .Some microbes use QS signaling pathways to trigger the expression of virulence genes. The expression of these genes enhances the virulence, or harmfulness, of the microbial infection. Which of the following represents the best method to decrease the virulence of a microbe capable of QS?

Develop a drug that decreases the cell density of the microbial infection.

Several essential mechanisms in the cell, including protein synthesis, require the amino acid glutamine. The formation of glutamine from glutamate and ammonia is an energy-requiring process. This process is carried out by an enzyme called glutamine synthetase. The action of glutamine synthetase is summarized in the diagram below. Based on the information provided, which of the following statements is true?

During glutamine synthesis, an exothermic reaction provides energy to drive an endothermic reaction.

Ptyalin is a digestive enzyme found in saliva. It helps break down large starch molecules early in the digestive process. Ptyalin is unable to break down proteins. Which of the following best explains why ptyalin is able to break down starches, but not proteins?

Enzymes are specific to their substrates.

Consider a reaction in which reactants X and Y combine to form the product Z. The diagram below compares the reaction coordinates for the catalyzed and uncatalyzed pathways of this reaction. Which of the following statements about letter B is true?

Letter B represents the activation energy of the catalyzed reaction pathway.

Consider a reaction in which reactants X and Y combine to form the product Z. The diagram below compares the reaction coordinates for the catalyzed and uncatalyzed pathways of this reaction. Which of the following statements about letter C is true?

Letter C represents the activation energy of the uncatalyzed reaction pathway.

Pepsin, a proteolytic enzyme found in the stomach, is essential for digestion. Pepsin functions optimally at approximately 37∘C Which of the following would most likely result if pepsin's environmental temperature was lowered from 37∘C to 25∘C?

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?

RBCs generate lactate as a waste product.

During the humoral immune response, helper T-cells activate B-cells through cell communication. This process is shown in the image below. During an experiment, researchers introduced a substance that caused the T-cell receptor to break down. Which of the following best describes how the humoral immune response will be affected?

The helper T-cell will no longer bind to the B-cell, and as a result, the B-cell will not be activated.

A mutation causes the extracellular domain of a G protein-coupled receptor (GPCR) to be misfolded. The misfolded GPCR is packaged into a vesicle that travels to the cell membrane. Upon reaching the cell membrane, the vesicle deposits the misfolded GPCR, which fuses with the cell membrane and functions as a membrane receptor. Which of the following best predicts what will occur whenever the misfolded GPCR is in the presence of its specific ligand?

The ligand-binding domain of the misfolded GPCR will not bind with its specific ligand.

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.