Unit 6: Enzyme Activity - Practice Quiz

1 Which enzyme in saliva helps digest starch?

2 What is the main substrate of salivary amylase?

3 Which reagent is commonly used to test for the presence of starch?

4 What color indicates the presence of starch after adding iodine?

5 What happens to the iodine color as salivary amylase digests starch?

6 Why is saliva diluted before testing its amylase activity?

7 Which condition is generally suitable for salivary amylase activity?

8 What is the purpose of incubating the starch and saliva mixture?

9 What does enzyme activity describe?

10 Which substance is produced when amylase breaks down starch?

11 Why is a control tube included in an amylase experiment?

12 What is the independent variable in a test comparing different saliva dilutions?

13 What is the dependent observation in an iodine-starch amylase test?

14 What is the effect of boiling saliva before the assay?

15 What is denaturation of an enzyme?

16 Why should the incubation time be kept constant for all tubes?

17 What generally happens to enzyme activity when temperature is increased moderately toward the optimum?

18 What may happen if salivary amylase is exposed to very high temperature?

19 Which measurement can be used to compare amylase activity in a timed assay?

20 What is the role of saliva in this experiment?

21 A saliva sample is diluted before testing amylase activity. What is the main purpose of this dilution?

22 Why is starch commonly used as the substrate in a salivary amylase assay?

23 In the iodine method, a decrease in the blue-black color of the reaction mixture indicates:

24 A control tube contains starch and buffer but no saliva. Its purpose is to determine whether:

25 Why should saliva and starch solutions be pre-equilibrated at the assay temperature before mixing?

26 If the reaction temperature is increased well above the optimum for salivary amylase, the measured activity will most likely:

27 Salivary amylase usually shows reduced activity in a strongly acidic mixture because:

28 A buffer is included in the salivary amylase assay primarily to:

29 Two assays use equal volumes of starch and saliva, but one is incubated twice as long. If the reaction remains linear, the longer assay should show:

30 Why is enzyme activity preferably calculated from the initial reaction rate?

31 If a saliva sample is accidentally heated to boiling before the assay, its amylase activity will most likely be:

32 A reaction mixture gives a lighter iodine color than the control after the same incubation time. This result suggests that the sample:

33 In a spectrophotometric assay, absorbance at the starch-iodine wavelength decreases over time. The decrease most directly represents:

34 If the saliva volume is doubled while substrate, temperature, and time remain suitable, the initial reaction rate is expected to:

35 A student starts timing several seconds after mixing saliva with starch. The calculated activity will most likely be:

36 Why should saliva be collected under similar conditions when comparing amylase activity among samples?

37 If all tubes are not mixed equally after saliva is added, the main effect on the assay is:

38 A student obtains absorbance values outside the standard calibration range. The best response is to:

39 A blank containing all reagents except saliva is used to correct for:

40 If substrate concentration is increased from a limiting level while enzyme concentration remains constant, the initial rate will usually:

41 A starch–iodine assay is calibrated so that the absorbance at 620 nm is 0.800 when 100% of the initial starch remains and 0.080 when no starch remains. A reaction mixture gives an absorbance of 0.350. What percentage of starch was hydrolyzed, assuming a linear relationship?

42 In a salivary amylase assay, the sample contains 0.20 mL saliva and the reaction volume is 2.00 mL. After 5 minutes, 0.30 μmol of reducing sugar is produced. What is the activity expressed as μmol min⁻¹ mL⁻¹ of saliva?

43 Two assays use identical substrate concentrations and incubation times. Assay A contains 0.10 mL saliva diluted 1:5 and produces 0.40 μmol reducing sugar. Assay B contains 0.20 mL saliva diluted 1:10 and produces 0.60 μmol. Which conclusion is justified?

44 A blank containing starch, buffer, and iodine has an absorbance of 0.920. The complete reaction has an absorbance of 0.410, while a reagent blank without starch has an absorbance of 0.070. Which corrected absorbance should be used to estimate starch hydrolysis?

45 A student doubles the saliva volume while keeping substrate, buffer, total volume, and incubation time unchanged. The reaction is already substrate-limited and shows a proportional increase in product formation. What is the most likely result?

46 The initial rate of starch hydrolysis is 0.80 μmol min⁻¹ during the first 4 minutes. Between 4 and 8 minutes, the average rate falls to 0.35 μmol min⁻¹. Which interpretation is most appropriate?

47 A saliva sample is diluted 1:20. A 0.10 mL aliquot of this dilution produces 2.4 μmol reducing sugar in 6 minutes. What is the activity of the original saliva?

48 A calibration curve for maltose is , where is in μg mL⁻¹. A test tube has absorbance 0.390 after subtraction of a reagent blank. Its final assay volume is 3.0 mL, and incubation lasted 5 minutes. What is the product formation rate?

49 An assay is incubated at 37 °C, but the enzyme and substrate are mixed at room temperature and the timer is started 90 seconds later. Why can this create a systematic error?

50 A saliva sample gives lower apparent amylase activity after vigorous exercise, although the subject's enzyme production is unchanged. Which preanalytical factor most plausibly explains the result?

51 The measured activity is 12.0 μmol min⁻¹ mL⁻¹. The assay used 0.25 mL saliva, but the saliva had been diluted 1:4 before use. What total activity was present in the original saliva volume used?

52 A student uses iodine color intensity as though it were directly proportional to maltose concentration. What is the principal conceptual error?

53 A reaction mixture is incubated at pH 6.8, but the buffer capacity is very low. Hydrolysis causes the pH to fall to 5.2. What is the strongest reason this can distort the calculated activity?

54 A 1.00 mL assay contains 0.20 mL saliva and produces 0.50 μmol product in 2 minutes. A second assay contains 0.10 mL saliva and produces 0.28 μmol in 2 minutes. Which result best indicates the second assay?

55 In a time-course experiment, absorbance values for residual starch are 0.80, 0.62, 0.45, and 0.31 at 0, 2, 4, and 6 minutes. Which interval is most suitable for estimating the initial rate?

56 A sample's absorbance lies above the highest standard in a starch–iodine calibration curve. Which action gives the most defensible quantitative result?

57 In an iodine endpoint method, the test color is still strongly blue after incubation, but a no-enzyme control is also blue. Which conclusion is most appropriate?

58 An assay contains 0.15 mL saliva and is diluted 1:3. It produces 1.8 μmol product in 4 minutes. If the original saliva volume represented is used for normalization, what activity is obtained?

59 A student compares two saliva samples using different starch concentrations: sample X is measured at 0.5% starch and sample Y at 2.0% starch. Why is a direct comparison of absorbance changes potentially invalid?

60 A reaction is stopped by adding acid before iodine is added. If the acid volume is not included in the final-volume calculation for a reducing-sugar assay, what type of error results?