Which of the following statements best justifies the inclusion of test tube as a control in the experiment?

Question

Researchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C

. The results of the experiment are represented in Figure 1.

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

Answer/Explanation

Ans: D
A negative control is a group in which no response is expected. It is the opposite of the positive control, in which a known response is expected. Heat-denatured peroxidase will be inactive. Repeating the experiment using heat-denatured peroxidase will allow the researcher to measure reaction rates in the presence of inactive peroxidase.

Question

esearchers investigated the influence of environmental pH on the activity of peroxidase, an enzyme that catalyzes the conversion of hydrogen peroxide to water and oxygen gas. In an experiment, the researchers added a hydrogen peroxide solution containing guaiacol to several identical test tubes and adjusted the solution in each test tube to a different pH. The researchers included the guaiacol because it caused the solutions to change color as the reactions proceeded, which the researchers relied on for measuring reaction rates. Finally, the researchers added the same amount of peroxidase to each test tube and measured the rate of each reaction at 23°C

. The results of the experiment are represented in Figure 1.

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.

Answer/Explanation

Ans: C
In the original experiment, the researchers used guaiacol as a reaction indicator. By using oxygen gas production to measure reaction rates, the researchers no longer need the guaiacol and can repeat the experiment without it, which will reveal the effect of guaiacol on the reaction rates.

Question

Catalase is an enzyme found in yeast cells that facilitates the chemical breakdown of hydrogen peroxide to water and oxygen gas. An experiment was conducted to determine the effect of pH on catalase function. Five buffer solutions of varying pH (2, 4, 6, 8, and 10) were prepared and added to separate test tubes. Hydrogen peroxide (H2O2)

was added to each test tube. Yeast was added, and the reactions were timed. After 1 minute the amount of oxygen gas released was determined by measuring the foam layer produced in each test tube. Figure 1 illustrates the experimental setup.

A set of five additional test tubes were prepared and used as controls. Which of the following best describes the contents expected to be contained in one of the five control test tubes?

A. pH 4 buffer solution and hydrogen peroxide only

B. All five pH buffer solutions combined and hydrogen peroxide only

C. Water, hydrogen peroxide, and yeast

D. Water and yeast only

Answer/Explanation

Ans: A
Since the experiment is studying the effect of pH on catalase in yeast, the control set should determine what would happen without yeast present. Each test tube in the control set should contain hydrogen peroxide and one of the pH solutions.

Question

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

Ans: C
The test tubes that do not contain the enzyme are negative controls in the experiment. The negative controls help confirm that the results of the experiment are related to enzyme function and not some other factor.

Question

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.

Ans: A
The seedlings in group 1 will be treated with a solution that contains actively reproducing bacteria, which will be metabolically active. In contrast, the seedlings in group 2 will be treated with a solution that contains heat-killed bacteria, which will be metabolically inactive. The researcher will be able to compare the results for group 1 with those for group 2. The comparison will help the researcher determine whether the changes observed in group 1 depend on the metabolic activity of soil bacteria.

Question

Pectinase is a protein that catalyzes the breakdown of pectic polysaccharides in plant cell walls. A researcher designs an experiment to investigate the effect of salinity on the ability of pectinase to lower the activation energy of the reaction involved. The design of the experiment is presented in Table 1. For each test tube, the researcher will measure the amount of product formed over 20 minutes.

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.

Ans: C
Test tube 5 will act as a control for test tube 6. The solutions in test tubes 5 and 6 are nearly identical except that the researcher will add pectinase to test tube 6 but not to test tube 5. A comparison of the data for test tubes 5 and 6 will show the effect of the presence or absence of the enzyme.

Question

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 pHon amylase function. The design of the experiment is presented in Table 1.

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.

Ans: C
Test tube V will contain all the components of the reaction mixture, but the amylase protein will be inactive because it will have been denatured during the pretreatment. Test tube V is an appropriate control in the experiment because it will show the color change that occurs in the absence of amylase activity.

Question

A researcher claims that some bacteria contain factors that influence the function of a particular enzyme but other bacteria do not. To test the claim experimentally, the researcher will grow two different bacterial strains in separate liquid cultures and isolate the contents of the cells in each culture. The researcher will add different combinations of cellular contents, substrate, and enzyme to test tubes containing a buffer solution adjusted to the optimal pH of the enzyme and then measure the rate of product formation. The design of the researcher’s experiment is presented in Table 1.

A. They will show whether the isolated cellular contents have enzymatic activity.
B. They will show whether environmental pH 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.

Ans: A
The researcher will add cellular contents and the substrate but not the enzyme to test tubes 3 and 7. As such, test tubes 3 and 7 will show whether the cellular contents have enzymatic activity.

Question

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

Ans: A
Keeping the initial substrate concentration constant allows the researcher to compare the reaction rates under different environmental conditions. The reaction rates will provide the researcher with information about the enzyme’s function in different environments.

Question

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.

Figure 1. Diagram of experimental setup.
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

Ans: C
Having one test tube with only water and camera film will show that water is not the substance that causes the film to change color.

Question

A researcher claims that different enzymes exhibit maximal function over different pH ranges. To test the claim, the researcher carries out an experiment that includes three different enzymes: pepsin, salivary amylase, and arginase. The results of the experiment are represented in Figure 1.

Figure 1. The effect of pH on three different enzymes

Which of the following actions will provide the most appropriate negative control for the experiment?

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

Ans: C
Repeating the experiment with denatured enzymes will provide an appropriate negative control for the experiment. The negative control will show that the changes observed in the experiment result from changes in enzyme function

Question

A researcher claims that increasing the environmental temperature by 10°C will double the rate of an enzyme-catalyzed reaction. To test the claim, the researcher designs an experiment that uses a particular enzyme isolated from plants. The design of the experiment is presented in Table 1. For each test tube in the experiment, the researcher will measure the rate of product formation.

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.

Ans: B
The contents of test tube 5 will be pretreated by boiling. The pretreatment will denature the plant enzyme used in the experiment. As such, test tube 5 will provide a measurement of product formation in the presence of a denatured enzyme.

Question

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 pH on amylase function. The design of the experiment is presented in Table 1.

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.

Ans: C
Test tube V will contain all the components of the reaction mixture, but the amylase protein will be inactive because it will have been denatured during the pretreatment. Test tube V is an appropriate control in the experiment because it will show the color change that occurs in the absence of amylase activity.

Question

A researcher claims that some bacteria contain factors that influence the function of a particular enzyme but other bacteria do not. To test the claim experimentally, the researcher will grow two different bacterial strains in separate liquid cultures and isolate the contents of the cells in each culture. The researcher will add different combinations of cellular contents, substrate, and enzyme to test tubes containing a buffer solution adjusted to the optimal pH of the enzyme and then measure the rate of product formation. The design of the researcher’s experiment is presented in Table 1.

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 pH 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.

Ans: A
The researcher will add cellular contents and the substrate but not the enzyme to test tubes 3 and 7. As such, test tubes 3 and 7 will show whether the cellular contents have enzymatic activity.

Question

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

Ans: A
Keeping the initial substrate concentration constant allows the researcher to compare the reaction rates under different environmental conditions. The reaction rates will provide the researcher with information about the enzyme’s function in different environments.

Question

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.

Figure 1. Diagram of experimental setup.

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

Ans: C
Having one test tube with only water and camera film will show that water is not the substance that causes the film to change color.

Question

A researcher claims that different enzymes exhibit maximal function over different pH ranges. To test the claim, the researcher carries out an experiment that includes three different enzymes: pepsin, salivary amylase, and arginase. The results of the experiment are represented in Figure 1.

Figure 1. The effect of pH on three different enzymes

Which of the following actions will provide the most appropriate negative control for the experiment?

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

Ans: C
Repeating the experiment with denatured enzymes will provide an appropriate negative control for the experiment. The negative control will show that the changes observed in the experiment result from changes in enzyme function.

Question

A researcher claims that increasing the environmental temperature by 10°C will double the rate of an enzyme-catalyzed reaction. To test the claim, the researcher designs an experiment that uses a particular enzyme isolated from plants. The design of the experiment is presented in Table 1. For each test tube in the experiment, the researcher will measure the rate of product formation.

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.

Ans: B
The contents of test tube 5 will be pretreated by boiling. The pretreatment will denature the plant enzyme used in the experiment. As such, test tube 5 will provide a measurement of product formation in the presence of a denatured enzyme.

Which of the following statements best justifies the inclusion of test tubes 3 and 7 in the experiment responses?

Which of the following best justifies the use of tube 2 as a control?

Which of the following observations best helps justify the researcher's claim?

Which of the following can be used to determine the rate of enzyme