ACT science practice test 9

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.


Vasoconstriction involves a narrowing of blood vessels that could lead to poor blood flow in the body if it persists over a long time. Ergotamine is a substance that can cause vasoconstriction. When ergotamine is injected into a normal blood vessel, vasoconstriction occurs quickly at the site of the injection (see Figure 1).

The diameter of the blood vessel at the site of vasoconstriction is less than the diameter of the normal blood vessel, so blood flow has a higher velocity through this narrow site. As a result, the blood pressure in the site of vasoconstriction is less than the blood pressure in the normal blood vessel. Moreover, the higher the velocity of the blood flow through the site of vasoconstriction, the lower the blood pressure at that site.

The percent change in blood pressure (%BP) can be defined as:

Blood vessel sections of similar diameters were isolated from laboratory rats and %BP was measured over three experiments. When the researchers needed to create a site of vasoconstriction for some of the experimental trials, they would inject ergotamine to induce vasoconstriction within the blood vessel section.

Experiment 1

An artificial heart, which mimics a human's heartbeat, is used to move a constant volume of 500 mL of blood with each beat through four blood vessel sections. These four blood vessel sections were injected with the same amount of ergotamine, leading to sites of vasoconstriction of the same diameter. The rate at which the blood is pumped was varied for the four different blood vessel sections, and the %BP values that resulted were measured.

Table 1
Rate of artificial heart beat (beats per minute)%BP
601.2
909.3
12022.3
15045.1

Experiment 2

The artificial heart used in Experiment 1 was then used to pump a constant volume of 500 mL of blood with each beat at a constant rate of 90 beats per minute through five other blood vessel sections. These blood vessel sections were injected with different amounts of ergotamine, resulting in sites of vasoconstriction with different diameters. The %BP values were then measured.

Table 2
Diameter of site of vasoconstriction (cm)%BP
0.440.3
0.618.6
0.89.3
1.04.6
1.22.5

Experiment 3

The artificial heart used in Experiment 1 was used to pump different volumes of blood at a constant rate of 90 beats per minute through five blood vessel sections with the same diameter at the site of vasoconstriction. The %BP values were then measured.

Table 3
Volume of blood pumped (mL)%BP
4008.4
4508.8
5009.3
5509.7
60010.2

1. Under the conditions described for Experiment 3, a %BP of 9.0 would most likely be obtained if the entering volume of blood equaled:

A. 350 mL.
B. 475 mL.
C. 550 mL.
D. 650 mL.

2. Based on the results of Experiment 1, if the rate of the artificial heart beat had been less than 60 beats per minute, then the %BP would most likely have been:

F. less than 1.2.
G. between 1.2 and 9.3.
H. between 9.3 and 22.3.
J. greater than 22.3.

3. Which of the following is the most likely explanation for the results of Experiment 1? As the rate of the artificial heart beat increases, %BP:

A. increases, because the velocity of blood through the site of vasoconstriction increases.
B. increases, because the velocity of blood through the site of vasoconstriction decreases.
C. decreases, because the velocity of blood flow through the site of vasoconstriction increases.
D. decreases, because the velocity of blood flow through the site of vasoconstriction decreases.

4. Consider blood flow through three regions of the same blood vessel, each of which has a different diameter. The velocity of blood flow is measured in milliliters per minute (mL/min) and the blood pressure is measured in millimeters of mercury (mmHg), and their values for each of the blood vessel regions are shown in the following table:

LocationVelocity of blood flow (mL/min)Blood pressure (mmHg)
A50031
B1,00029
C90030

Based on the information in the passage about blood flow, which of the following diagrams best represents the relative diameters of the three blood vessel regions?

F.
G.
H.
J.

5. Based on the results of Experiments 1 and 2, what was the diameter of the site of vasoconstriction in the blood vessel section used in Experiment 3?

A. 0.4 cm
B. 0.6 cm
C. 0.8 cm
D. 1.0 cm

6. For the blood vessel sections used in Experiment 2 that had sites of vasoconstriction with diameters of 0.4, 0.8, and 1.2 cm, which of the following graphs best displays the comparison between blood pressure at each site of vasoconstriction and blood pressure in the normal region of the blood vessel leading to the site of vasoconstriction?

F.
G.
H.
J.

As the pressure on a gas is increased, the volume of that gas is expected to decrease by an inversely proportional amount. For example, if pressure is doubled the volume is halved. Under certain conditions, the volume of the gas will change by an amount that deviates from an inverse proportion. Various 10.00 L samples of gas were subjected to increases in pressure. Table 1 shows the resulting volume changes at 300°C, while Tables 2 and 3 show the volume changes at 25°C and -200°C, respectively. All pressures are measured in atmospheres (atm).

7. Which of the following gases shown in Tables 1-3 was compressed by the same amount each time the pressure was changed, regardless of its initial pressure?

A. Helium
B. Carbon Dioxide
C. Neon
D. Oxygen

8. Which of the following is the best explanation for the change in volume seen in any one of the samples of carbon dioxide in Table 1? As pressure on one sample of carbon dioxide was increased, the volume of that sample:

F. increased as the molecules of carbon dioxide were forced closer together.
G. increased as the molecules of carbon dioxide were forced farther apart.
H. decreased as the molecules of carbon dioxide were forced closer together.
J. decreased as the molecules of carbon dioxide were forced farther apart.

9. Based on Table 2, if the sample of nitrogen at a pressure of 4 atm were returned to its initial pressure of 2 atm, the volume would most likely:

A. decrease by 5.00 L.
B. decrease by 8.00 L.
C. increase by 5.00 L.
D. increase by 8.00 L.

10. Based on Table 3, if the pressure on a 10.00 L sample of neon gas is increased from 8 atm to 16 atm at a temperature of -200°C, the change in volume will most likely be closest to which of the following?

F. -5.12 L
G. -5.06 L
H. -5.03 L
J. -5.02 L

11. A scientist concludes that whenever the pressure on helium is increased, its volume will decrease. Based on Tables 2 and 3, is this a valid conclusion?

A. Yes; in every trial that the pressure of helium was increased, the change in volume was negative.
B. No; in every trial that the pressure of helium was increased, the change in volume was positive.
C. Yes; when the pressure on helium was increased from 1 to 2 atm, its change in volume was positive at 25°C and negative at -200°C.
D. No; when the pressure on helium was increased from 1 to 2 atm, its change in volume was negative at 25°C and positive at -200°C.