ACT science practice test 20

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Soil salinity is the concentration of potentially harmful salts dissolved in the groundwater that fills soil pores. Salinity is determined by measuring a soil’s electrical conductivity (EC) and exchangeable sodium percentage (ESP). High EC indicates a high concentration of dissolved salt particles; ESP indicates the proportion of electrical conductivity that is due to dissolved sodium ions.

Soil samples were collected from five different distances west of a particular river. Figure 1 shows the electrical conductivity of the soil samples at four different depth ranges measured in milli-Siemens per centimeter (mS/cm).

Figure 1

Figure 2 shows the exchangeable sodium percentage of the five sites at different depths.

Figure 2

1. Figure 2 indicates that, compared with the soil tested in Sample 1, the soil tested in Sample 4 contains:

F. a higher percentage of sodium ions throughout.
G. a lower percentage of sodium ions throughout.
H. a higher percentage of sodium ions at shallower depths only.
J. a lower percentage of sodium ions at shallower depths only.

2. According to Figure 2, in the soil collected in Sample 3 at a depth of 30-60 cm, approximately what percent of the soil conductivity is due to sodium ions?

A. 14%
B. 17%
C. 24%
D. 44%

3. Based on Figures 1 and 2, the electrical conductivity due to sodium ions in the sample collected 40 m west of the river was:

F. greatest at a depth of 90-120 cm.
G. greatest at a depth of 0-30 cm.
H. least at a depth of 30-60 cm.
J. least at a depth of 0-30 cm.

4. Based on Figure 2, which of the following figures best represents the exchangeable sodium percentage for the five soil samples collected at a depth of 90-120 cm?

A.
B.
C.
D.

5. A student claimed that as soil moves away from a major water source, such as a river, the salinity of the soil increases. Is this claim supported by Figures 1 and 2?

F. No; the electrical conductivity and exchangeable sodium percentage both decreased from Sample 1 to Sample 5.
G. No; there was no consistent trend for electrical conductivity and exchangeable sodium percentage.
H. Yes; the electrical conductivity and exchangeable sodium percentage both increased from Sample 1 to Sample 5.
J. Yes; the electrical conductivity increased and exchangeable sodium percentage decreased from Sample 1 to Sample 5.

A group of researchers performed the following study in order to investigate declines in primarily carnivorous polar bear populations in the Arctic over a 10-year period.


Study

The researchers obtained previously collected data from several areas previously identified as polar bear habitats. From this data, the researchers selected sixty 5 km × 5 km blocks that do not overlap with one another. The blocks were selected to fall into six groups, each with a different set of conditions selected in order to conform to criteria for listing animals as threatened species. Previous research has indicated that Arctic sea ice and available food are among the factors which may affect polar bear populations.

Table 1 identifies each of the groups utilized in the study. Conditions other than the ones listed were considered to be normal.

Table 1
GroupConditions
1These areas had significantly decreased populations of marine mammals consumed by polar bears.
2These areas had significantly increased populations of seaweed commonly consumed by marine mammals.
3These areas had been subject to excess thawing of Arctic sea ice.
4These areas were subject to the same conditions as Groups 1 and 3.
5These areas were subject to the same conditions as Groups 2 and 3.
6Unaffected polar bear habitat.

Data for each of the plots was collected, and the population density of polar bears was calculated in terms of adult polar bears/km2. Table 2 shows the population density of the blocks in Group 6.

Table 2
Area LabelPopulation density of Group 6 areas (polar bears/km2)
A0.93
B2.10
C0.21
D0.72
E0.88
F0.72
G0.91
H0.53
I1.12
J0.74

The data collected was analyzed to find the average population density ratio for each group. The researchers defined the average population density ratio of a given group as being equal to the result of the following expression:

Figure 1 shows the average population density ratio of Groups 1?5.

Figure 1

6. Which of the following statements provides the best explanation for why the researchers collected data for Group 6 in their study?

A. Group 6 provided data indicating the types of predators which most threaten polar bears in their natural habitat.
B. Group 6 provided a standard by which the other groups could be compared in order to determine how each set of conditions affected polar bear populations.
C. Group 6 provided a means by which the researchers could carefully identify and select the conditions for the remaining five groups.
D. Group 6 provided a means of determining the greatest number of polar bears that would be likely to survive in an area of 25 km2.

7. Which one of the following is a question that most likely explains why Group 2 areas were included in the study?

F. Does an increase in the food source of their prey affect the population density of polar bears?
G. If additional masses of seaweed were to be introduced to the Arctic, would polar bears be increasingly omnivorous?
H. If additional masses of seaweed were to be introduced to the Arctic, would prey population density increase?
J. Does an increase in the number of prey animals living in the same area as polar bears affect the amount of Arctic ice?

8. Which of the following correctly ranks Groups 1-5 from the group where the conditions are most conducive to polar bear population density in the study to the group where the conditions are least conducive?

A. Group 1, Group 2, Group 3, Group 4, Group 5
B. Group 4, Group 3, Group 1, Group 5, Group 2
C. Group 2, Group 5, Group 1, Group 3, Group 4
D. Group 2, Group 1, Group 5, Group 3, Group 4

9. Which of the following is most likely an organism that the researchers identified as exhibiting a significantly decreased population when defining Group 1?

F. Snowy owl
G. Seal
H. Salmon
J. Polar bear

10. Synergy between two effects is said to exist when their combined effect is greater than the sum of each effect considered separately. The study appears to be designed such that the researchers can investigate possible synergy in which of the following two groups?

A. Groups 1 and 2
B. Groups 1 and 4
C. Groups 4 and 5
D. Groups 1 and 3

11. Before performing their analysis of the data, the researchers developed four different hypotheses. Each one of the four hypotheses below is supported by the results of the study EXCEPT:

F. Declining prey populations have had some effect on polar bear populations.
G. The melting of Arctic sea ice has a greater effect on polar bear populations than declining prey populations.
H. Declining prey populations have a greater effect on polar bear populations than the melting of Arctic sea ice.
J. The melting of Arctic sea ice has had some effect on polar bear populations.