Under certain circumstances, the human body must cope
with gases at greater-than-normal atmospheric pressure. For example, gas
pressures increase rapidly during a dive made with scuba gear because the
breathing equipment allows divers to stay
Line underwater longer and dive deeper. The
pressure exerted on the human body increases
(5) by 1
atmosphere for every 10 meters of depth in seawater, so that at 30 meters in
seawater a diver is exposed to a pressure of about 4 atmospheres. The pressure
of the gases being breathed must equal the external pressure applied to the
body ; otherwise breathing is very difficult. Therefore all of the gases in the
air breathed by a scuba diver at 40 meters are present at five times their
usual pressure. Nitrogen, which
(10) composes 80 percent of the air we breathe,
usually causes a balmy feeling of
well-being at this pressure. At a depth of 5 atmospheres,
nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen
narcosis. Nitrogen narcosis apparently results from a direct effect on the
brain of the large amounts of nitrogen dissolved in the blood. Deep dives are
less dangerous if helium is substituted for
(15) nitrogen,
because under these pressures helium does not exert a similar narcotic effect.
As a scuba diver descends, the pressure of nitrogen in the lungs increases. Nitrogen
then diffuses from the lungs to the blood, and from the blood to body tissues.
The reverse occurs when the diver surfaces ; the nitrogen pressure in the lungs
falls and the nitrogen diffuses from the tissues into the blood, and from the
blood into the lungs.
(20) If the
return to the surface is too rapid, nitrogen in the tissues and blood cannot
diffuse out rapidly enough and nitrogen bubbles are formed. They can cause
severe pains, particularly around the joints.
Another complication may result if the breath is held
during ascent. During ascent from a depth of 10 meters, the volume of air in
the lungs will double because the air
(25) pressure
at the surface is only half of what it was at 10 meters. This change in volume
may cause the lungs to distend and even rupture. This condition is called air
embolism.
To avoid this event, a diver must ascend slowly, never at
a rate exceeding the rise of the exhaled air bubbles, and must exhale during
ascent.
Questions
21. What does the passage mainly discuss?
(a) The equipment divers use
(b) The effects of pressure on gases in the human
body
(c) How to prepare for a deep dive
(d) The symptoms of nitrogen bubbles in the
bloodstream
(a) leaving
behind (b) prepared
for
(c) propelled
by (d) subjected to
23. The word "exert" in line 15 is
closest in meaning to
(a)
cause
(b) permit
(c)
need
(d) change
(a)
yields (b)
starts
(c) surfaces
(d) travels
25. What happens to nitrogen in body tissues if a
diver ascends too quickly?
(a) it forms bubbles.
(b) It goes directly to the brain
(c) It is reabsorbed by the lungs
(d) It has a narcotic effect
(a)
joints
(b)
pains
(c)
bubbles (d)
tissues
27. The word "rupture" in line 26 is
closest in meaning to
(a)
hurt
(b) shrink
(c)
burst
(d) stop
presents the greatest danger to a
diver?
(a) pressurized helium
(b) Nitrogen
diffusion
(c) Nitrogen bubbles
(d) An air embolism
29. What should a diver do when ascending?
(a) Rise slowly
(b) Breathe faster
(c) Relax completely
(d) Breathe helium
Please tally your answer with the below provided answers and
then comment here how much you got!
Answers
21.
B 22. D 23. A 24. D 25. A 26. C 27. C 28. D 29. A
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