Questions 796–802 are based on the following information.

Circadian rhythms drive human and animal behaviors, such as activity, sleep, metabolism, and
mating. A scientist hypothesizes that exposure to light and dark regulate these rhythms by
altering the production of a hormone called melatonin. To evaluate the importance of light and
dark in regulating circadian rhythms, the scientist conducts a set of experiments.
Experiment 1
Over the course of one week, the scientist encloses three mice and exposes them to 24-hour
periods of varying exposure to light and dark. During each 24-hour period, the mice receive 12
consecutive hours of artificial light and 12 consecutive hours of complete darkness. At 15-
minute intervals, the scientist notes the activity levels of the mice and records his findings.
Furthermore, every 15 minutes during Day 7, the scientist collects a small blood sample from the
mice to measure their level of melatonin.
At the end of one week, the scientist graphs the mice’s activity levels in Figure 1, with black
bars indicating the periods of continuous activity. The scientist then graphs the mice’s levels
of melatonin as shown in Figure 2.

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 Experiment 2
The scientist then conducts a similar experiment in which he studies the activity levels of mice
exposed only to darkness over the course of one week. Figure 3 graphs the mice’s resulting
activity levels, and Figure 2 records their melatonin levels on Day 7.

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© John Wiley & Sons, Inc.

796. Approximately how long were the mice active each day during Experiment 1?
(A) 10 hours
(B) 6 hours
(C) 18 hours
(D) 24 hours

797. What aspect of the study was varied between Experiments 1 and 2? Compared to Experiment
1, in Experiment 2
(A) the number of mice used was greater
(B) the amount of daily mouse activity decreased
(C) the mice experienced only darkness
(D) the mice experienced equal daily exposure to light and darkness

798. Based on the results of both experiments, which of these statements is a valid
conclusion the scientist could reach?
 (A) Mice are more active during the day than during the night.
(B) Peak melatonin levels in mice closely coincide with the onset of periods of inactivity.
(C) Mice produce more melatonin during the day than during the night.
(D) There is no clear relationship between melatonin production and activity levels in
mice.
799. The scientist conducts a third experiment during which the mice experience darkness from
hours 0 to 12 and light from hours 13 to 23. Based on the results of Experiments 1 and 2,
when would peak melatonin production most likely occur on Day 7?
(A) Hour 18
(B) Hour 5
(C) Hour 1
(D) Hour 0

800. The scientist wants to conduct another experiment to support to his hypothesis. Which of
the following experiments would best provide that additional support?
(A) Repeat the two experiments with two mice.
(B) Repeat Experiment 2 but with 24 hours of daily light exposure.
(C) Repeat Experiment 1 and measure oxygen levels in the blood instead of melatonin.
(D) Repeat Experiment 2 with 12 hours of daily light exposure and 12 hours of daily
darkness.

801. Melatonin pills have been approved for use in humans. Based on information in the
passage, when should a physician advise his patients to take melatonin pills if they wanted
to get a better night’s sleep?
(A) Before bedtime
(B) In the morning
(C) With meals
(D) Every 4 hours

802. If the scientist had collected melatonin levels over the course of Day 4 during
Experiment 2, what would most likely represent the graph for melatonin level?
(A)
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(B)

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(C)
© John Wiley & Sons, Inc.

(D)

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Questions 803–809 are based on the following information.
 The Krebs Cycle is a key part of metabolism that helps create energy for cells. To start the
cycle (shown in Figure 1), a 2-carbon molecule called Acetyl-CoA (created from Glucose) is
combined with a 4-carbon molecule (Oxaloacetate) to create a 6-carbon molecule (Citrate). Over
the course of the rest of the cycle, the energy stored in Citrate is used to create other
molecules (NADH, FADH2 and GTP), all of which go on to produce ATP, the primary energy source
of the cell, as documented in Table 1.

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TABLE 1

Molecule ATP created per 1/molecule

NADH 2.5

FADH2 1.5

GTP 1

A scientist, using an exact measuring system, applied different amounts of glucose to a cell and
measured the resulting outputs from the Krebs Cycle. The results are recorded in Table 2.

TABLE 2

Number of Glucose Number of Acetyl Number of Number of GTP Number of

Molecules Applied CoA Created NADH Created Created FADH2 Created

1 2 6 2 2

10 20 60 20 20

20 40 120 40 40

30 60 180 60 60
803. Based on the results of the experiment and information in the passage, how many NADH are
produced per one turn of the Krebs Cycle?
(A) 1
(B) 2
(C) 3
(D) 6
804. In the experiment described in the passage, what is the independent variable?
(A) Number of Glucose molecules applied
(B) Number of Oxaloacetate molecules created
(C) Number of Acetyl-CoA created
(D) Number of turns of Krebs Cycle

805. A certain cell needs 600 ATP to survive for a day. Based on information in the passage,
how many Glucose molecules will the cell need for the day?
(A) 1
(B) 10
(C) 20
(D) 30

806. The scientist has isolated the step in the Krebs Cycle that occurs between Citrate and
Oxaloacetate. She notes that in addition to NADH, FADH2, and GTP, the 1-carbon gas
is also created. How many molecules of this gas are likely created in this step?
(A) 1
(B) 2
(C) 3
(D) 4

807. The scientist finds that ATP inhibits the reaction between Oxaloacetate and Acetyl-CoA.
What effect does this reaction have on NADH production?
(A) It increases because more Citrate is produced.
(B) It decreases because more Acetyl-CoA is produced.
(C) It decreases because less Citrate is produced.
(D) It increases because more Glucose is used.

808. Removal of which molecule would have the most significant effect on cellular ATP
production?
(A) GTP
(B) NADH
(C) FADH2
(D) Acetyl-CoA

809. Which is the most appropriate graph of the relationship between number of glucose
molecules applied and number of FADH2 created during the experiment?
(A)
© John Wiley & Sons, Inc.

(B)
© John Wiley & Sons, Inc.

(C)
© John Wiley & Sons, Inc.

(D)
© John Wiley & Sons, Inc.
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