ACT science practice test 13

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.


The Citric cycle is an essential process used to transform carbohydrates, lipids, and proteins into energy in aerobic organisms. If yeast is unable to produce succinate, it cannot survive. The Citric cycle steps leading to the creation of succinate in yeast are shown in Figure 1. Each step in this cycle is catalyzed by an enzyme, which is essential to overcome the energy barrier between reactant and product. In the first step, Enzyme 1 is the enzyme, citrate is the reactant, and isocitrate is the product.

Figure 1

Experiment

A scientist grew four strains of yeast on several different growth media. Each strain was unable to produce succinate because it lacked one of the enzymes required for the reaction pathway shown in Figure 1. Table 1 shows the results of the scientist's experiment: "Yes" indicates that the strain was able to grow in the basic nutrition solution (BNS) + the particular chemical. An undamaged strain of yeast would be able to grow in the basic nutrition solution without any additional chemical. If a strain was able to grow in a given growth medium, then it was able to produce succinate from the additional chemical added to the basic nutrition solution.

If certain genes are damaged, the essential enzymes cannot be produced, which means that the reactions that the enzyme catalyzes cannot go. Table 2 lists the genes responsible for the enzymes in the steps of the Citric cycle leading to succinate production in yeast. If an enzyme cannot be produced, then the product of the reaction that enzyme catalyzes cannot be synthesized and the reactant in that reaction will become highly concentrated. If a gene is damaged, then it is notated with a superscript negative sign, as in Cat3-; if a gene is not damaged it is notated with a superscript positive sign, as in Cat3+.

Table 2
GeneEnzyme
Cat1Enzyme 1
Cat2Enzyme 2
Cat3Enzyme 3
Cat4Enzyme 4

1. Based on the information presented, the highest concentration of isocitrate would most likely be found in which of the following yeasts?

A. Yeast that cannot produce Enzyme 1
B. Yeast that cannot produce Enzyme 2
C. Yeast that cannot produce Enzyme 3
D. Yeast that cannot produce Enzyme 4

2. According to the information in the passage and Table 2, a strain of yeast that is Cat1+ Cat2- Cat3- Cat4+ CANNOT produce:

F. Enzyme 1 and Enzyme 4.
G. Enzyme 3 and Enzyme 4.
H. Enzyme 2 and Enzyme 3.
J. Enzyme 1 and Enzyme 2.

3. Which of the following statements best describes the relationships between citrate, isocitrate, and α-ketoglutarate as shown in Figure 1?

A. Isocitrate is a product of a reaction of α-ketoglutarate, and α-ketoglutarate is a product of a reaction of citrate.
B. α-ketoglutarate is a product of a reaction of isocitrate, and isocitrate is a product of a reaction of citrate.
C. α-ketoglutarate is a product of a reaction of citrate, and citrate is a product of a reaction of isocitrate.
D. Citrate is a product of a reaction of isocitrate, and isocitrate is a product of a reaction of α-ketoglutarate.

4. Strain X yeast was most likely unable to synthesize:

F. isocitrate from citrate.
G. α-ketoglutarate from isocitrate.
H. succinyl-CoA from α-ketoglutarate.
J. succinate from succinyl-CoA.

5. One of the growth media shown in Table 1 was a control that the scientist used to demonstrate that all four strains of yeast had genetic damage that prevented the reactions shown in Figure 1, the reactions which are responsible for the synthesis of succinate. Which growth media was used as a control?

A. BNS
B. BNS + succinate
C. BNS + isocitrate
D. BNS + succinyl-CoA

6. For each of the four strains of yeast, W-Z, shown in Table 1, if a given strain was able to grow in BNS + succinyl-CoA, then it was also able to grow in:

F. BNS.
G. BNS + isocitrate.
H. BNS + α-ketoglutarate.
J. BNS + succinate.

Many viruses are known to persist more prevalently during certain times of the year. A study of four relatively unknown viruses was conducted to examine their annual rate of prevalence and mortality in a host population. A large survey was conducted of local populations for the presence of antigen markers indicative of viral exposures to the four virus types. Measurements were acquired monthly beginning in January of 2000 and concluding two years later. All monthly measurements were averaged for comparison.

Figure 1 shows the incidence (cases per 1,000 individuals studied) of viral infections attributed to each viral type over the duration of the study. Figure 2 shows the number of deaths (per 1,000 individuals studied) attributed to virus A and D infections.

Figure 1

Figure 2

7. According to Figure 1, the incidence of virus A is greatest during which season of the year?

A. Spring (Mar-May)
B. Summer (Jun-Aug)
C. Fall (Sep-Nov)
D. Winter (Dec-Feb)

8. According to Figure 1, during April 2001, which virus was least prevalent in the studied population?

F. Virus A
G. Virus B
H. Virus C
J. Virus D

9. In a previous study, a virologist claimed that the incidence of virus B has always exceeded the incidence of virus C. As shown in Figure 1, the data for which of the following months is inconsistent with the virologist's claims?

A. Jan-00
B. 1-Feb
C. 1-Aug
D. 1-Dec

10. According to Figure 1, the incidence of at least 3 of the viruses is most alike during which of the following months?

F. Apr-00
G. Sep-00
H. 1-Nov
J. Jan-02

11. During both years of the survey, in one month every year, 7 out of 1,000 individuals died as a result of infection with virus A and 2 out of 1,000 individuals died as a result of infection with virus D. According to Figure 2, these data most likely were obtained during which of the following months?

A. January
B. March
C. May
D. October