Unit 3 Biology Review Questions

A researcher designs an experiment to investigate the effect of environmental temperature on the function of an enzyme. For each trial included in the experiment, the researcher will add the enzyme and its substrate to an aqueous buffer solution and then measure the amount of product formed over 20 minutes. Which of the following must remain the same for all trials of this experiment? A) The initial concentration of the substrate B) The final concentration of the product C) The three-dimensional structure of the enzyme D) The temperature of the aqueous buffer solution

A

A researcher designs an experiment to investigate whether soil bacteria trigger the synthesis of defense enzymes in plant roots. The design of the experiment is presented in Table 1. For each group in the experiment, the researcher will determine the average rate of change in the amount of defense enzymes in the roots of the seedlings. Which of the following statements best helps justify the inclusion of group 2 as one of the controls in the experiment? A) It will show whether the changes observed in group 1 depend on the metabolic activity of soil bacteria. B) It will show whether the changes observed in group 1 depend on the type of plants used in the experiment. C) It will show the average growth rate of seedlings that are maintained in a nonsterile environment. D) It will show the changes that occur in the roots of seedlings following an infection by soil bacteria.

A

Acetylcholinesterase (AChE) is a protein that catalyzes the conversion of acetylcholine to acetate and choline. When the concentration of AChE in an aqueous solution is held constant, the rate of the reaction catalyzed by AChE increases with increasing concentrations of substrate. At low concentrations of acetylcholine, a small increase in the substrate concentration results in a large increase in the reaction rate. At high concentrations of acetylcholine, however, a large increase in the substrate concentration results in only a small increase in the reaction rate. Which of the following statements correctly explains the observed effect of the acetylcholine concentration on the rate of the enzyme-catalyzed reaction? A) The active site of AChE is specific for acetylcholine, and only one substrate molecule can occupy the active site at a time. B) AChE begins converting product into substrate as the acetylcholine concentration changes from low to high. C) The AChE protein becomes denatured as the acetylcholine concentration changes from low to high. D) The substrate specificity of AChE changes as the acetylcholine concentration changes from low to high.

A

Based on Figure 1, which of the following statements best predicts the effect that a change from a moderately acidic environment (pHpH near 6) to a basic environment will have on peroxidase activity? A) Peroxidase activity will decrease. B) Peroxidase activity will increase. C) Peroxidase activity will stay the same. D) Peroxidase activity will increase at first and then decrease.

A

Based on the data, scientists claim that the reproductive behavior of European flycatchers is influenced by the availability of energy sources. Which of the following statements best justifies this claim? A) Young European flycatchers hatch from eggs when caterpillar biomass is available for the young birds to consume and convert into energy for growth. B) European flycatcher hatchlings begin to need energy to leave the nest only after the caterpillars have turned into pupae. C) Female European flycatchers require energy to lay eggs, so they lay their eggs when the caterpillar biomass is maximal. D) The energy requirements for hatching European flycatchers and caterpillars are proportional to each other.

A

Muscle contraction depends on ATP hydrolysis. During periods of intense exercise, muscle cells rely on the ATP supplied by three metabolic pathways: glycolysis, mitochondrial respiration, and the phosphagen system. Figure 1 shows the rates at which the three metabolic pathways produce ATP following the start of an intense period of exercise. Which of the following correctly uses the data to justify the claim that the phosphagen system is an immediate, short-term source of ATP for muscle cells? A) ATP production by the phosphagen system increases and decreases rapidly following the start of the exercise period. B) ATP production by the phosphagen system increases gradually and continuously throughout the entire exercise period. C) The ATP produced by the phosphagen system contains more energy per molecule than does the ATP produced by the other pathways. D) ATP hydrolysis in muscle cells occurs immediately after the start of the exercise period but stops before the end of the exercise period.

A

Researchers investigated the effect of urea on the three-dimensional structure of a certain enzyme. The researchers dissolved the enzyme in an aqueous buffer solution and added urea to the solution. The enzyme did not appear to have a secondary or tertiary structure. The researchers carefully removed the urea from the solution and determined that the enzyme had the original secondary and tertiary structure again.Based on the results of the experiment, which of the following statements best predicts the effect of urea on the enzyme's function? A) Function will be disrupted by adding the urea and regained by removing the urea. B) Function will be disrupted by adding the urea, but it will not be regained by removing the urea. C) Function will be gained by adding the urea and disrupted by removing the urea. D) Function will be unaffected by the addition and removal of the urea.

A

Which of the following statements best justifies the inclusion of test tubes 3 and 7 in the experiment? A) They will show whether the isolated cellular contents have enzymatic activity. B) They will show whether environmental pHpH affects the function of the enzyme. C) They will show the rate of product formation in the absence of bacterial factors. D)They will show the rate of product formation in the absence of the substrate.

A

A researcher claims that a certain herbicide suppresses plant growth by inhibiting chloroplast function. To test the claim, the researcher treats isolated chloroplasts with increasing concentrations of the herbicide. Which of the following statements best clarifies how the data support the researcher's claim? A) The thylakoid membrane is more permeable to carbon dioxide than to polar molecules. B) ATP synthase activity depends on a proton gradient across the thylakoid membrane. C) Some enzymes embedded in the thylakoid membrane catalyze the hydrolysis of ATP D) Carbon fixation in the Calvin-Benson cycle takes place in the stroma of chloroplasts.

B

A researcher claims that different metabolic pathways allow bacteria to use different molecules as sources of matter and energy. Which of the following statements best helps justify the researcher's claim by providing a relevant example? A) Rhizobia bacteria form close associations with the roots of bean plants. B) E. coli bacteria reproduce in liquid media containing either glucose or galactose. C) The antibiotic rifampicin inhibits the growth of some bacterial strains but not of others. D) Some viruses that infect bacteria reproduce by either the lysogenic cycle or the lytic cycle.

B

A researcher claims that spinach leaves capture the most energy from light waves in the range of 500 nm to 600 nm. To test the claim, the researcher will place spinach leaves in separate chambers and expose the leaves to different wavelengths of light. For each chamber, the researcher will measure the amount of oxygen gas (O2) that is produced in one hour. Which of the following graphs best represents data from the experiment that will support the researcher's claim? A) Cereal Bowl B) Upside Down Cereal Bowl C) Weird Curve Down D) Weird Curve Up

B

A researcher claims that the synthesis of ATP from ADP and inorganic phosphate (Pi) is essential to cellular function. Which of the following statements best helps justify the researcher's claim? A) ADP is a small molecule that some cells release into their environment as a way of communicating with other cells. B) ATP hydrolysis is an energy-releasing reaction that is often coupled with reactions that require an input of energy. C) Inorganic phosphate (Pi) is a substance that cells typically acquire from their environment. D) ATP synthase is a mitochondrial enzyme that catalyzes the conversion of ADP and Pi to ATP.

B

A scientist claims that Elysia chlorotica, a species of sea slug, is capable of photosynthesis. Which of the following observations provides the best evidence to support the claim? A) Elysia chlorotica will die if not exposed to light. B) Elysia chlorotica grows when exposed to light in the absence of other food sources. C) Elysia chlorotica grows faster when exposed to light than when placed in the dark. D) Elysia chlorotica grows in the dark when food sources are available.

B

Cyanobacteria contain a variety of pigment molecules, as shown in Table 1. As a result, the color of cyanobacteria cultures can vary significantly based on the relative amount of each pigment produced. A researcher placed a culture of cyanobacteria under green lights. Within a few weeks, the appearance of the cyanobacteria changed from green to red. The researcher claimed the color change in the culture was the result of an adaptation allowing greater photosynthesis. Which of the following provides the best reasoning to justify the researcher's claim? A) In green light, more chlorophyll a molecules are produced, reflecting more light to other cyanobacteria to be used for photosynthesis. B) In green light, more phycoerythrin molecules are produced, allowing more green light to be absorbed, thus increasing photosynthesis. C) In green light, cyanobacteria that have more phycocyanin molecules are less likely to survive and reproduce. D) In green light, cyanobacteria that have more allophycocyanin molecules are more likely to survive and reproduce.

B

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be A) the same as the level at pH 7 B) lower than the level at pH 9 C) greater than the level at pH 9 D) between the levels observed at pH 5 and pH 7.

B

Which of the following statements best helps justify the inclusion of test tube 5 as a control in the experiment? A) It will provide a measurement of product formation in the absence of the substrate. B) It will provide a measurement of product formation in the presence of a denatured enzyme. C) It will show the effect of doubling the amount of substrate on the rate of product formation. D) It will show the effect of increased enzyme activity on the rate of product formation.

B

Which of the following statements provides reasoning that supports the claim that brown fatty tissue keeps an animal warm? A) The uncoupling protein in this tissue increases the production of ATP and causes more body heat to be produced to warm the animal. B) The uncoupling protein in this tissue reduces the proton gradient across the membrane and thus produces heat to warm the animal without ATP production. C) The uncoupling protein in this tissue causes an increase in the proton gradient, which causes more ATP to be produced that helps to warm the animal. D) The uncoupling protein in this tissue reduces the production of ATP and creates an increase in the proton gradient that allows more heat energy to be produced to warm the animal.

B

A researcher claims that budding yeast are able to survive in different environments because they produce enzymes that allow them to use different molecules as sources of matter and energy. Which of the following statements best helps justify the researcher's claim by providing a relevant example? A) Yeast cells produce protein kinases, which are enzymes that catalyze the transfer of phosphate groups from ATP to protein substrates. B) Yeast cells produce DNA polymerases, which are enzymes that catalyze the conversion of free nucleotides into strands of DNA. C) Yeast cells produce invertase, which is an enzyme that catalyzes the conversion of the disaccharide sucrose into glucose and fructose. D) Yeast cells produce catalase, which is an enzyme that catalyzes the conversion of hydrogen peroxide into water and oxygen gas.

C

A researcher claims that only a portion of the light energy captured by green plants is available for growth and repair. Which of the following observations best helps justify the researcher's claim? A) Light-capturing pigment molecules in green plants absorb red, blue, and violet light but reflect green light. B) The energy of a photon of light is proportional to its frequency and inversely proportional to its wavelength. C) As light energy is converted to chemical energy by metabolic processes, some of the energy is lost as heat. D) Captured energy is stored in the molecular bonds of organic molecules, including simple sugars and starch.

C

A student designs an experiment to investigate the influence of temperature on enzyme function. The student's plan is presented in Table 1. Which test tubes are controls in the experiment? A) Test tubes 1 and 2 only B) Test tubes 5 and 6 only C) Test tubes 1, 3, 5, and 7 D) Test tubes 2, 4, 6, and 8

C

A test tube containing a piece of exposed camera film and all three enzyme solutions A) Repeating the experiment with a fourth enzyme B) Repeating the experiment at several different temperatures C) Repeating the experiment with denatured enzymes D) Repeating the experiment using several different methods for measuring pH

C

Aminolevulinate dehydratase (ALAD) is an enzyme that relies on zinc as a cofactor. A zinc ion binds to the ALAD active site, where it forms favorable interactions with the side chains of three amino acids. Researchers have found that substituting a lead ion for a zinc ion in the ALAD active site causes inhibition of ALAD. Which of the following statements best helps explain how the lead ion causes inhibition of ALAD? A) It changes the shape and charge of the substrate so that it becomes more compatible with ALAD's active site. B) It changes the amino acid sequence of the ALAD protein so that the enzyme catalyzes a different reaction. C) It changes the three-dimensional structure of the active site so that ALAD is no longer compatible with its substrate. D) It changes the enzyme-substrate complex so that the transition state is more stable and the reaction proceeds at a faster rate.

C

Amylase is a protein that catalyzes the conversion of starch to simple sugars. Amylase activity in an aqueous solution can be measured by using iodine as a starch indicator. A solution containing iodine and starch will have a dark-blue color, whereas a solution containing iodine but no starch will have a light-brown color. The color change of an iodine solution from dark blue to light brown can be used to measure the rate at which starch is converted to simple sugars. A student designs an experiment to investigate the effect of environmental pHpH on amylase function. Which of the following statements best justifies the inclusion of test tube V as a control in the experiment? A) It will provide a measurement of amylase activity at an acidic pH B) It will provide a measurement of amylase activity at a basic pH C) It will show the color change that occurs in the absence of enzyme activity. D) It will show the color change that occurs in the absence of the amylase protein.

C

Gelatin is a protein that is derived from collagen which is found in the bones, skin, and connective tissue of animals. To investigate the ability of various enzymes to digest gelatin, a group of students set up an assay involving camera film. Camera film contains gelatin and appears black when exposed to light but turns clear as the gelatin gets broken down. The students incubated pieces of exposed camera film in test tubes, each containing one of three different enzyme solutions (trypsin, lipase, or amylase) as indicated in Figure 1. The students recorded the time it took for the enzymes to digest the gelatin in each test tube, turning the film from black to clear. Which of the following would be the most appropriate control for this experiment? A) A test tube containing no camera film B) A test tube containing only a piece of exposed camera film C) A test tube containing a piece of exposed camera film submerged in water D) A test tube containing a piece of exposed camera film and all three enzyme solutions

C

In chloroplasts, ATP is synthesized from ADP plus inorganic phosphate (Pi) in a reaction catalyzed by ATP synthase molecules that are embedded in the thylakoid membrane.Which of the following statements provides evidence to support the claim that no ATP will be synthesized in the absence of a proton gradient across the thylakoid membrane? A) Blocking electron flow from one carrier to the next in the electron transport chains blocks formation of a proton gradient in the thylakoid. B) Increasing the proton concentration difference across the thylakoid membrane is not associated with a parallel increase in the rate of ATP synthesis. C) No ATP is synthesized when channel proteins that allow the free passage of protons are inserted into the thylakoid membrane. D) No ATP is synthesized while the Calvin cycle is synthesizing carbohydrates and using ATP and NADPH at a high rate.

C

One of the researchers proposes using oxygen gas production to measure reaction rates. Which of the following statements best justifies the use of the proposed modification as a way of creating an appropriate control for the investigation? A) The experiment can be repeated without hydrogen peroxide, which will help eliminate an uncontrolled variable. B) The experiment can be repeated without peroxidase, which will introduce a second independent variable. C) The experiment can be repeated without guaiacol, which will reveal the effect of guaiacol on the reaction rates. D) The experiment can be repeated without water, which will reveal whether the reaction can occur inside a living cell.

C

Protein digestion in humans is primarily carried out by three enzymes. Pepsin is found in the stomach (pH2), where it aids in the breakdown of large proteins into smaller peptides, while trypsin and chymotrypsin are found in the small intestine (pH8), where they aid in the further breakdown of the proteins into amino acids and dipeptides that can be absorbed into the bloodstream. Which of the following best predicts how the structure and function of pepsin will change as it enters the small intestine? A) Pepsin will not change in shape and will continue to break down proteins in the small intestine. B) Pepsin will not change in shape but may not work due to the basic environment of the small intestine. C) Pepsin will change in shape because of the basic environment of the small intestine; therefore, its enzymatic activity will decrease. D) Pepsin will change in shape because of the presence of trypsin and chymotrypsin in the small intestine, both of which act as competitive inhibitors.

C

Which of the following best predicts the immediate result of adding more substrate to the reaction mixture at the point indicated by the arrow in Figure 1? A) The amount of product will decrease until the reaction rate goes to zero. B) The amount of product will decrease until the reaction reaches its equilibrium point or until the enzyme is been used up by the reaction. C) The amount of product will increase until the reaction reaches its equilibrium point or until the substrate is used up by the reaction. D) The amount of product will increase without stopping because the enzyme will be unchanged by the reaction

C

Which of the following statements best helps explain the reaction specificity of an enzyme? A) The free energy of the reactants is greater than the free energy of the products. B) The equilibrium constant of the reaction is much greater than 1. C) The shape and charge of the substrates are compatible with the active site of the enzyme. D) The concentration of the enzyme inside living cells is greater than the concentration of substrate.

C

Which of the following statements best helps justify the inclusion of test tube 5 in the experiment? A) It will act as a control for test tube 4 by showing the effect of the presence or absence of the substrate. B) It will act as a control for test tube 4 by showing the effect of a change in environmental temperature. C) It will act as a control for test tube 6 by showing the effect of the presence or absence of the enzyme. D) It will act as a control for test tube 6 by showing the effect of a change in sodium chloride concentration.

C

A researcher claims that genetic variation provides organisms with the ability to survive and reproduce in different environments. To support the claim, the researcher makes the following observation: bacteria that contain plasmids (small DNADNA molecules) are resistant to a wider range of antibiotics than are bacteria that contain no plasmids. Which of the following statements best establishes a connection between the observation and the researcher's claim? A) Some antibiotics inhibit the synthesis of bacterial cell walls. B) Some antibiotics inhibit protein synthesis in bacteria cells. C) Some plasmids cannot exist in a bacterial cell with certain other plasmids. D) Some plasmids contain antibiotic resistance genes.

D

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? A) Atmospheric carbon dioxide is produced by the burning of fossil fuels, which are formed from the remains of living organisms such as plants. B) Atmospheric carbon dioxide is a byproduct of cellular respiration, which is a metabolic process that occurs in plants and other living organisms. C) Atmospheric carbon dioxide typically enters plant leaves through stomata, which plants rely on for regulating gas exchange with the atmosphere. D) Atmospheric carbon dioxide is the raw material for photosynthesis, which plants rely on for producing sugars and other organic compounds.

D

A researcher claims that the incorporation of carbon dioxide into organic molecules during photosynthesis does not violate the second law of thermodynamics. Which of the following statements best helps justify the researcher's claim? A) Organisms contain enzymes that lower the activation energies of specific chemical reactions. B) An ecosystem is formed by the interaction of a community of organisms with their surrounding environment. C) Photosynthetic organisms use the organic molecules produced during photosynthesis for growth and repair. D) The total system that includes photosynthetic organisms and the Sun becomes less ordered over time.

D

A researcher claims that the initial rise of oxygen in Earth's early atmosphere, which occurred approximately 2.3 billion years ago, resulted from the metabolic activity of prokaryotic organisms. The claim is based on an interpretation of the geochemical and fossil evidence. Which of the following types of evidence will best support the researcher's claim? A) Evidence that some of the earliest eukaryotes used oxygen to produce ATP by cellular respiration B) Evidence that the earliest plants produced oxygen as a by-product of photosynthesis C) Evidence that some of the earliest organisms carried out photosynthesis without producing oxygen D) Evidence that the cyanobacteria produced oxygen as a by-product of photosynthesis

D

A researcher proposes a model to explain how enzyme-substrate interactions determine enzyme specificity. The model is based on the idea that substrate molecules form favorable interactions with the amino acid side chains in an enzyme's active site. Based on the model, which of the following statements best explains an enzyme's specificity for a particular substrate molecule? A) A hydrophilic molecule interacts with nonpolar side chains in the enzyme's active site. B) A hydrophobic molecule interacts with polar side chains in the enzyme's active site. C) A molecule with positive charges interacts with positively charged side chains in the enzyme's active site. D) A molecule with negative charges interacts with positively charged side chains in the enzyme's active site.

D

Alcohol dehydrogenase (ADH) is an enzyme that aids in the decomposition of ethyl alcohol (C2H5OH) into nontoxic substances. Methyl alcohol acts as a competitive inhibitor of ethyl alcohol by competing for the same active site on ADH. When attached to ADH, methyl alcohol is converted to formaldehyde, which is toxic in the body. Which of the following statements best predicts the effect of increasing the concentration of substrate (ethyl alcohol), while keeping the concentration of the inhibitor (methyl alcohol) constant? A) There will be an increase in formaldehyde because ADH activity increases. B) Competitive inhibition will be terminated because ethyl alcohol will bind to methyl alcohol and decrease ADH activity. C) The peptide bonds in the active site of the enzyme will be denatured, inhibiting the enzyme. D) Competitive inhibition will decrease because the proportion of the active sites occupied by substrate will increase.

D

Figure 1. The effect of pHpH on peroxidase activity Which of the following actions will provide a negative control for the investigation? A) Repeating the experiment at 25°C B) Repeating the experiment using twice the amount of hydrogen peroxide C) Repeating the experiment using twice the amount of peroxidase D) Repeating the experiment using heat-denatured peroxidase

D

In addition to the pigments commonly associated with photosynthesis, a certain photosynthetic species contains two additional pigment types. Which of the following best supports the claim that this species is better adapted to environmental changes than other photosynthetic species are? A) The increased pigment concentration better facilitates energy production within the cells of the species. B) The pigment combination allows the organism to absorb heat as well as light, making better use of available energy. C) The additional pigments allow the species to outcompete other species for the wavelengths of light commonly used in photosynthesis. D) The additional pigments allow the species containing them to harvest energy from wavelengths of light that the other photosynthetic species cannot use.

D

Phycobiliproteins are a complex of accessory pigments and proteins found in cyanobacteria but not in green algae. A researcher claims that the phycobiliprotein pigments in cyanobacteria allow the cyanobacteria to survive in certain aquatic niches better than green algae can. Which of the following statements best justifies the researcher's claim? A) The additional pigments allow the cyanobacteria to store light energy so that it can be used at night to continue photosynthesis. B) The additional pigments block light and prevent it from reaching photosynthetic organisms at greater depths, so no photosynthetic organisms can live below the surface waters containing cyanobacteria. C) The additional pigments require energy and cellular resources to produce, so they can be used as an energy source during times of insufficient light. D) The additional pigments absorb light at wavelengths that green algae cannot absorb; this may allow cyanobacteria to capture more light energy for photosynthesis than green algae can in certain areas.

D

The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose. Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase's active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate. Which of the following statements best helps explain the reaction specificity of hexokinase? A) Both glucose and water are polar molecules that form favorable interactions with charged and polar amino acid side chains in hexokinase's active site. B) Both glucose and water have oxygen atoms that can form covalent bonds with the phosphorus atoms of phosphate groups. C) Glucose is an energy-rich organic molecule that can be broken down by glycolysis to produce ATP, whereas water is an inorganic molecule. D) Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

D