ACT Science Practice Test 31
Thời gian làm bài: 1 giờ
Đề thi nằm trong bộ sưu tập: Tuyển Tập Bộ Đề Thi Đại Học Hoa Kỳ (ACT) - Có Đáp Án Chi Tiết
Hãy bắt đầu chinh phục nào!
Xem trước nội dung:
Two investigations were conducted on a sample of green nickel sulfate (NiSO4) that was dissolved in water. The first investigation placed a sample of the nickel sulfate into a spectrometer. Most solutions absorb some wavelengths of light and allow other wavelengths to pass right through. The spectrometer changed the wavelength of light shining into the solution and recorded how much of the light was absorbed by the solution. An absorbance of 0.00 would indicate that all of the light shone into the solution passed through with no light being absorbed. Figure 11.4 shows the result of absorbance versus wavelength for a sample of NiSO4(aq).
Figure 11.4
The next experiment used five different solutions of NiSO4(aq) at different known concentrations (measured in molarity). Each solution was placed in a spectrometer set at 740 nm, and light was shone into each sample to determine the absorbance of each of the five solutions. Table 11.3 shows the results.
TABLE 11.3
Which wavelength of light was absorbed to the greatest degree in the first investigation?
380 nm
500 nm
740 nm
830 nm
The wavelength of 490 nm is green light. Why is the absorbance of NiSO4 low at 490 nm?
The spectrometer is not accurate at the wavelength of 490 nm.
The NiSO4(aq)
The NiSO4(aq)
The green light gets reflected back to the spectrometer when it contacts the green NiSO4(aq)
What conclusions can be drawn from the data collected in Table 11.3?
As the wavelength of light aimed at the sample increases, the absorbance increases.
Light with a wavelength of 740 nm is not absorbed to a great extent by NiSO4(aq)
Concentration of solution is inversely proportional to absorbance of light.
As the concentration of NiSO4(aq)
Which of the following statements accurately describes the trend found in Table 11.3?
Light with a wavelength of 740 nm increases absorbance by about 0.09.
Doubling the concentration of NiSO4(aq)
An increase of 0.08 mol/L causes an increase in the absorbance of about 0.90.
The absorbance of NiSO4(aq)
Which set of data would best represent the results if Investigation 2 were repeated with a wavelength of 490 nm instead of 740 nm?
Concentration
The process of spectrometry works well on colored solutions such as green nickel sulfate (NiSO4) and cupric sulfate (CuSO4). Why might spectrometry not work well on solutions such as table salt dissolved in water (NaCl(aq))?
Table salt is clear, so it will absorb all wavelengths of light.
Table salt is clear, so all colors of light will pass through the solution.
The researcher cannot vary the concentration of table salt.
Spectrometry is not appropriate for food-grade substances.
Experiment 2 was repeated with a sixth sample of NiSO4 solution with a concentration of 0.48 mol/L. However, the test tube had fingerprints on the glass where the light passed through. The fingerprints absorbed some light from the spectrometer. What would be an expected value for the absorbance?
0.451
0.522
0.542
0.622
What would be the results of Investigation 1 if a more concentrated solution of NiSO4(aq) were used to make the graph in the table?
Staphylococcus aureus (S. aureus) is a bacterium found on the skin of 25% of healthy individuals with no adverse effects. However, when transferred to food products, the toxins it can produce have been known to cause food-borne illness, particularly in cooked and cured meats. It is important to determine conditions that promote the growth of pathogenic species of bacteria and apply that knowledge in food preparation and handling. Two groups of students set out to determine the ideal growth conditions for S. aureus. In each group, bacteria were inoculated in a nutrient broth and allowed to grow over a period of time.
When analyzing the growth of bacteria in a liquid medium, an increase in turbidity corresponds to an increase in the bacteria growing in suspension. Because the bacterial cells scatter light, spectrophotometry can be used to determine bacterial growth. Changes in the logarithmic absorbance scale on the spectrophotometer correspond to changes in the number of cells, and a growth curve can be plotted by graphing the absorbance readings from the spectrophotometer versus time. The rate of growth can be determined by the slope of the lines, and the type of growth occurring at a given time can be determined by the shape of the curve.
Group 1
The students in Group 1 set out to determine whether temperature affected the growth rate of S. aureus in a nutrient-rich medium. They tested S. aureus by inoculating a flask of nutrient-rich broth with a pH of 6 at the following temperatures: 3°C, 20°C, 37°C, 45°C, and 60°C. The spectrophotometer absorbance readings are shown in Table 11.4.
TABLE 11.4
Group 2
Students in Group 2 planned to determine the effect of pH on the growth of S. aureus. They wanted to test growth at a range of values from highly acidic (low pH) to highly basic/alkaline (high pH). The cultures were grown at a temperature of 37°C, and the pH levels of each culture were as follows: 3, 5, 6, 7, and 9. Table 11.5 shows their data.
TABLE 11.5
(A) Which of the following is a valid assessment of the data from Group 1?
As temperature increases, the growth rate of aureus
As temperature decreases, so does the growth rate of aureus
The stationary phase of growth is entered as the nutrients in the medium begin to run out and the growth of bacteria changes the conditions in the flask. Cell division slows, and the turbidity ceases to increase because the overall population remains unchanged. When did the bacteria in Group 1/Trial 3 likely begin the stationary phase of growth?
97 minutes
148 minutes
600 minutes
1,470 minutes
Which of the following statements is most accurate?
pH factor does not have an effect on the growth of aureus
pH is a control for Group 1 and an experimental variable for Group 2.
Generation time is the amount of time it takes for the bacterial population to double. Some bacteria, such as E. coli, have a doubling time of 20 minutes under ideal conditions, while other bacteria may take days to double their population size. Which of these is most likely the approximate generation time for the bacteria in Group 1/Trial 3 during the first 100 minutes of the experiment?
6 minutes
29 minutes
75 minutes
100 minutes
Which of the following does NOT represent a controlled variable for both groups?
The nature of the nutrient media
The temperature of incubation
The strain of aureus
The wavelength of light set on the spectrophotometer
Which of the following is a valid assessment of the data in Table 11.5?
The data for Group 2/Trial 5 indicate that:
at this high level of acidity, aureus
at this high level of alkalinity, aureus
at this low level of alkalinity, aureus
at this high level of alkalinity, aureus
Which of the following trials were run under the same conditions for Groups 1 and 2?
Group 1/Trial 1 and Group 2/Trial 1
Group 1/Trial 2 and Group 2/Trial 4
Group 1/Trial 3 and Group 2/Trial 3
Group 1/Trial 5 and Group 2/Trial 5
If scientists wanted to do further testing on the growth of S. aureus to inform food processing and handling decisions, such as the effect of salinity, what conditions would be best as the controls for their test?
37°C and pH 6
37°C and pH 5
20°C and pH 6
45°C and pH 7
Which of the following graphs most closely resembles the shape of a graph that could be drawn for Group 1/Trial 3?
Figure 11.9
B.
Figure 11.10
C.
Figure 11.11
D.
Figure 11.12
Chemical inhibitors such as sodium benzoate are often used as food preservatives because of their ability to retard, although not completely inhibit, bacterial growth. If a study were done on the effects of sodium benzoate on the growth of S. aureus at 37°C, one would expect to see results similar to those of:
Group 2/Trial 1.
Group 1/Trial 5.
Group 2/Trial 2.
Group 1/Trial 3.
What is the independent variable for both Group 1 and Group 2?
Time
pH
Temperature
The type of bacteria being tested
Meat in a delicatessen tested positive for the presence of bacteria, and this bacteria was to be identified using spectrophotometry. Which of the following test results would most clearly indicate that the bacteria found was S. aureus?
The bacteria died at temperatures above 55°
The bacteria experienced rapid growth at temperatures below 20°
The bacterial generation time was determined to be approximately 30 minutes at 37°
The bacteria showed no increase in turbidity when incubated in an ice bath.
Which of the following statements is the best explanation for what occurred in Group 2/Trial 2 between 10 and 24 hours?
The bacterial population grew exponentially.
The birth and death rate of bacterial cells were relatively equal during this time.
The bacteria were dying more rapidly than new bacteria could be generated.
No new bacteria were generated or died during this time.
Xem thêm đề thi tương tự
12 câu hỏi 1 mã đề 1 giờ
214,128 lượt xem 115,283 lượt làm bài
24 câu hỏi 1 mã đề 1 giờ
219,431 lượt xem 118,132 lượt làm bài
26 câu hỏi 1 mã đề 1 giờ
219,200 lượt xem 118,020 lượt làm bài
22 câu hỏi 1 mã đề 1 giờ
219,715 lượt xem 118,293 lượt làm bài
12 câu hỏi 1 mã đề 1 giờ
218,852 lượt xem 117,831 lượt làm bài
24 câu hỏi 1 mã đề 1 giờ
219,338 lượt xem 118,090 lượt làm bài
24 câu hỏi 1 mã đề 1 giờ
218,445 lượt xem 117,614 lượt làm bài
22 câu hỏi 1 mã đề 1 giờ
208,273 lượt xem 112,133 lượt làm bài
29 câu hỏi 1 mã đề 1 giờ
215,740 lượt xem 116,158 lượt làm bài