ACT science practice test 3

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.

Comets originate from regions of our solar system that are very far from the sun. The comets are formed from debris thrown from objects in the solar system: they have a nucleus of ice surrounded by dust and frozen gases. When comets are pulled into the earth's atmosphere by gravitational forces and become visible, they are called meteors. Meteors become visible about 50 to 85 km above the surface of Earth as air friction causes them to glow. Most meteors vaporize completely before they come within 50 km of the surface of Earth.

The Small Comet debate centers on whether dark spots and streaks seen in images of the Earth's atmosphere are due to random technological noise or a constant rain of comets composed of ice. Recently, images were taken by two instruments, UVA and VIS, which are located in a satellite orbiting in Earth's magnetosphere. UVA and VIS take pictures of the aurora borealis phenomenon, which occurs in the magnetosphere. The UVA and VIS technologies provide images of energy, which cannot be seen by the human eye.

The pictures taken by VIS and UVA both show dark spots and streaks. Scientists debate whether these spots and streaks are due to a natural incident, such as small comets entering the atmosphere, or random technological noise. The layers of Earth's atmosphere are shown in Figure 1.

Figure 1

Two scientists debate whether there is a constant rain of comets burning up in Earth's magnetosphere.

Scientist 1

Small comets are pulled into Earth's atmosphere by gravitational effects and burn up in the magnetosphere. They are about 20 to 30 feet in diameter and burn up in the magnetosphere because they are much smaller than the comets that become meteors. Comets with larger radii will burn up in portions of the atmosphere much closer to Earth. About 30,000 small comets enter the Earth's magnetosphere every day. The dark spots and streaks on UVA and VIS images occur when the small comets begin to boil in the magnetosphere, releasing krypton and argon and creating gaseous H2O, which interacts with hydroxyl, OH-, radicals. Images taken by these instruments at different points in time show the same frequency of dark spots and streaks and give conclusive evidence in favor of the Small Comet theory. If the spots and streaks were due to random technological noise, then the frequency of their appearance would fluctuate.

Scientist 2

The dark spots and streaks in the UVA and VIS images are due to technological noise, not small comets. If the Small Comet Theory were true, and 20 small comets bombarded Earth's atmosphere per minute, there would be a visible bright object at least twice every five minutes. This is because, as objects enter the Earth's mesosphere, they burn up, creating large clouds of ice particles. As the ice particles vaporize, they have a brightness in the sky approximately equal to that of Venus. Because comets rarely enter Earth's atmosphere, such bright flashes are rare occurrences, far less than two times every five minutes, so the Small Comet theory cannot be correct. Further, since comets originate from regions of space beyond the orbit of the farthest planet, they contain argon and krypton. If the Small Comet theory were true and Earth were bombarded by 30,000 comets per day, there would be 500 times as much krypton in the atmosphere as there actually is.

1. According to Scientist 2, which of the following planets in our solar system is most likely the closest to the region of space where comets originate?

A. Jupiter
B. Venus
C. Neptune
D. Saturn

2. Based on Scientist 1’s viewpoint, a comet that burns up in the thermosphere would have a diameter of:

F. 5-10 ft.
G. 10-20 ft.
H. 20-30 ft.
J. greater than 30 ft.

3. Which of the following generalizations about small comets is most consistent with Scientist 1’s viewpoint?

A. No small comet ever becomes a meteor.
B. Some small comets become meteors.
C. Small comets become meteors twice every five minutes.
D. All small comets become meteors.

4. During the Perseids, an annual meteor shower, more than 1 object burning up in the atmosphere is visible per minute. According to the information provided, Scientist 2 would classify the Perseids as:

F. typical comet frequency in the magnetosphere.
G. unusual comet frequency in the magnetosphere.
H. typical meteor frequency in the mesosphere.
J. unusual meteor frequency in the mesosphere.

5. Given the information about Earth’s atmosphere and Scientist 1’s viewpoint, which of the following altitudes would most likely NOT be an altitude at which small comets burn up?

A. 750 km
B. 700 km
C. 650 km
D. 550 km

6. Suppose a study of the dark holes and streaks in the UVA and VIS images revealed krypton levels in the atmosphere 500 times greater than normal levels. How would the findings of this study most likely affect the scientists’ viewpoints, if at all?

F. It would strengthen Scientist 1’s viewpoint only.
G. It would strengthen Scientist 2’s viewpoint only.
H. It would weaken both Scientists’ viewpoints.
J. It would have no effect on either Scientist’s viewpoint.

7. Scientist 1 would most likely suggest enhanced imaging technology that can take pictures of objects in the atmosphere be used to look at what region of the atmosphere to search for small comets?

A. The region between 15 km above sea level and 50 km above sea level.
B. The region between 50 km above sea level and 85 km above sea level.
C. The region between 85 km above sea level and 600 km above sea level.
D. The region between above 600 km above sea level.

A cotton fiber is composed of one very long cell with two cell walls. During a 2-week period of cell life called elongation, cotton fibers grow 3 to 6 cm. The level of hydrogen peroxide in cotton fiber cells during elongation is very high. Scientists wanted to study whether the level of hydrogen peroxide affected the length of the cotton fiber.

The amount of hydrogen peroxide is controlled by an enzyme called superoxide dismutase (SOD). This enzyme turns superoxide into hydrogen peroxide. Four identical lines of cotton fiber plants were created. Each line was able to express only one of three types of superoxide dismutase. The gene for SOD1 was incorporated into L1, the gene for SOD2 was incorporated into L2, and the gene for SOD3 was incorporated into L3.


Five cotton plants of each line were grown in nutrient solution until cotton fibers completed the elongation period. The average length of cotton fibers and the average concentration of hydrogen peroxide were determined. This information is shown in Table 1.

Next, because the scientists had determined the average elongation period, they measured the amount of hydrogen peroxide and the length of the cotton fibers halfway through their elongation period. This information is shown in Table 2.

Finally, the scientists measured the amount of hydrogen peroxide and the length of cotton fibers on the first day of the elongation period. This information is shown in Table 3.

8. For L2, as the elongation period moved from the first day to the end, the amount of hydrogen peroxide:

F. increased only
G. decreased only
H. increased, then decreased
J. decreased, then increased

9. Which of the following is a dependent variable in the experiment?

A. The point in time during the elongation period
B. The type of superoxide dismutase the plant could express
C. The length of the cotton fiber
D. The type of cotton plant

10. A cotton fiber is one very long cell with two cell walls. A cotton fiber is a special kind of what type of cell?

F. Prokaryotic
G. Animal
H. Plant
J. Bacterial

11. One plant had an average cotton fiber length of 0.5 cm, and the average amount of hydrogen peroxide in its fibers was 5.9 μmol/mg. Which of the following most likely describes this plant?

A. It was from L1 and at the end of its elongation period.
B. It was from L1 and at the midpoint of its elongation period.
C. It was from L2 and at the beginning of its elongation period.
D. It was from L2 and at the end of its elongation period.

12. The scientists used one of the four lines of cotton plants as a control. Which line was most likely the control?

F. L1
G. L2
H. L3
J. L4

13. Suppose the data for all the plants were plotted on a graph with the time of the elongation period on the x-axis and the average length of the cotton fiber on the y-axis. Suppose also that the best-fit line for these data was determined. Which of the following would most likely characterize the slope of this line?

A. The line would have a positive slope.
B. The line would have a negative slope.
C. The line would have a slope equal to zero.
D. The line would have no slope, because the line would be vertical.