PSAT Reading Practice Test 47: Science: Caffeine

Questions 1-9 refer to the following information.

passage 1
All told, there exist just over sixty species of plant known to produce caffeine, among the
mostly widely cultivated of which are coffee from the berries of the Coffea arabica plant, tea
from the leaves of Camellia sinesis, and chocolate from the seeds of the Theobroma cacao tree.
Caffeine, curiously enough, is in its structure quite closely related to adenine and guanine,
05the two purine nitrogenous bases that comprise about half of our DNA. Moreover, it is precisely
this structural similarity between caffeine and nucleic acids that gives coffee, tea, and
chocolate their uniquely stimulating properties. While amphetamine, ephedrine, nicotine,
cocaine, and the vast majority of other common psychoactive stimulants work to modulate
the dopaminergic circuits of the central nervous system, the stimulation we feel from ingest-
10ing caffeine arises from a completely distinct neural pathway.
Within every metabolically active cell of the human body, a molecule called adenosine
triphosphate acts as a major reservoir of transferrable chemical energy. That is, in the thermodynamically
favorable liberation of phosphate groups from adenosine, free energy is released
that can be harnessed to drive forward a variety of the thermodynamically unfavorable chem-
15ical reactions required to sustain life. For our purposes, the main implications of this system
are fairly intuitive: cells with significant energy reserves will be those with a large amount of
adenosine triphosphate at their disposal, while those that have exhausted their reserves will
contain merely adenosine, and inorganic phosphate.
Throughout our evolution, the neurons that make up our brain and spinal cord have
20adapted to detect the presence of adenosine, and to react to it by increasing the secretion of
melatonin from the pineal gland, which in turn mediates feelings of "drowsiness" or somno-
lence. The purpose, one might reason, is simply to promote sleep; a state that is minimally
taxing to the metabolism of the central nervous system, and will allow its cells an opportunity
to replenish their energy stores.
25Adenosine itself is made up merely of an adenine nitrogenous base attached via a beta-
glycosidic bond to a pentose sugar. Thus, it is simply the approximate structural correspondence
between caffeine and adenosine that enables caffeine to interact with and antagonize
adenosine-sensing receptors without chemically activating them. The end result is a general
blunting of the brain's ability to perceive how much energy it has expended; though the effect,
30it should be mentioned, is self-limited. As the concentration of adenosine increases to critical
levels, adenosine displaces caffeine from its inhibitory position on the receptor in a phenomenon
known colloquially to some consumers of coffee and cola beverages as "the crash."
passage 2
Caffeine, admittedly, seldom kills. A toxic dose to an adult is roughly equivalent to the amount
contained in somewhere between eighty and one-hundred mid-sized cups of coffee. This is
35not to say, however, that caffeine is completely innocuous. By some estimates, more than
90% of the American adult population uses caffeine on a daily basis, and it is far and away the
most widely consumed psychostimulant worldwide. It is somewhat shocking, therefore, that
its distribution remains wholly unregulated by the Food and Drug Administration.
While the recreational use of caffeine is infrequently fatal, abuse of caffeinated supple-
40ments, medications, and beverages can precipitate a wide range of detrimental effects on the
body, particularly among individuals with underlying vulnerabilities. For instance, in those
already at risk for osteoporosis-such as post-menopausal women, and those suffering from
hyperparathyroidism-caffeine has been shown to significantly accelerate the rate of bone
loss, chiefly by increasing basal metabolic rate. Similarly, multiple studies have demonstrated
45a positive correlation between the agitating, stimulant-effects of caffeine use on the limbic
system and acute exacerbations of panic disorder and anxiety disorders. Caffeine increases
blood pressure. It promotes electrical dysrhythmias of the heart. It is anything but harmless,
and yet contrary to popular belief, the most commonly heard health complaint concerning
caffeine is something of a fallacy. That is to say, while chemical dependence, tolerance, and
50withdrawal from the stimulant are familiar entities to those who consume large quantities,
genuine pathological addiction to caffeine has not been documented in humans, and as such
is omitted from both the DSM-5, and the ICD-10 as well.

9 questions    11 minutesAll test questions


1. The respective purposes of Passage 1 and Passage 2 are best described as

2. Which of these gives the correct sequence of processes as described in the paragraphs in lines 11–24?

3. As used in lines 12–13, the phrase "thermodynamically favorable" most closely refers to a reaction in which

4. The process whereby caffeine works, according to Passage 1, is best paraphrased as

5. Which option gives the best evidence for the answer to the previous question?

6. As used in line 35, "innocuous" most closely means

7. Which of the following does the author of Passage 2 suggest is a way that caffeine does NOT present a danger to humans?

8. Which option gives the best evidence for the answer to the previous question?

9. When taken together, these two passages present a solid overview of caffeinated stimulation's

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