British CouncilIELTS – Academic Practice Test 1 – Passage 1
Electro-reception
electroreception U the detection by an aquatic animal of electric fields
or currents.
murky adj (of a liquid) not clear; dark or dirty with mud or another substance
SYNONYM CLOUDY She gazed into the murky depths of the water.
murky adj (of air, light, etc.) dark and unpleasant because of smoke, fog, etc.
a murky night
bleary adj indistinct; unclear
The day begins with a bleary view of one's world.
garbled adj if words or messages are garbled, they are
not clear and are very difficult to understand, often giving
a false idea of the facts:
There was a strange garbled message on my voicemail.
comprehend (often used in negative sentences) (formal) to understand something
fully
He stood staring at the dead body, unable to comprehend.
comprehend something The infinite distances of space are too great
for the human mind to comprehend.
comprehend how/why, etc… She could not comprehend how someone
would risk people's lives in that way.
comprehend that… He simply could not comprehend that she could be
guilty.
stimulus
A Open your eyes in sea water and it is difficult to garbled see much
more than a murky, bleary green colour. Sounds, too, are and difficult to
comprehend. Without specialised equipment humans would be lost in these
deep sea habitats, so how do fish make it seem so easy? Much of this is
due to a biological phenomenon known as electroreception – the ability to
perceive and act upon electrical stimuli as part of the overall senses. This
ability is only found in aquatic or amphibious species because water is an
efficient conductor of electricity.
B Electroreception comes in two variants. While all animals (including
humans) generate electric signals, because they are emitted by the
nervous system, some animals have the ability – known as passive
electroreception – to receive and decode electric signals generated by
other animals in order to sense their location.
C Other creatures can go further still, however. Animals with active
electroreception possess bodily organs that generate special electric
signals on cue. These can be used for mating signals and territorial
displays as well as locating objects in the water. Active electroreceptors can
differentiate between the various resistances that their electrical currents
encounter. This can help them identify whether another creature is prey,
predator or something that is best left alone. Active electroreception has a
range of about one body length – usually just enough to give its host time
to get out of the way or go in for the kill.
D One fascinating use of active electroreception – known as the Jamming
Avoidance Response mechanism – has been observed between members
of some species known as the weakly electric fish. When two such electric
fish meet in the ocean using the same frequency, each fish will then shift
the frequency of its discharge so that they are transmitting on different
frequencies. Doing so prevents their electroreception faculties from
becoming jammed. Long before citizens’ band radio users first had to yell
“Get off my frequency!” at hapless novices cluttering the air waves, at least
one species had found a way to peacefully and quickly resolve this type of
dispute.
E Electroreception can also play an important role in animal defences.
Rays are one such example. Young ray embryos develop inside egg cases
that are attached to the sea bed. The embryos keep their tails in constant
motion so as to pump water and allow them to breathe through the egg’s
casing. If the embryo’s electroreceptors detect the presence of a predatory
fish in the vicinity, however, the embryo stops moving (and in so doing
ceases transmitting electric currents) until the fish has moved on. Because
marine life of various types is often travelling past, the embryo has evolved
only to react to signals that are characteristic of the respiratory movements
of potential predators such as sharks.
F Many people fear swimming in the ocean because of sharks. In some
respects, this concern is well grounded – humans are poorly equipped
when it comes to electroreceptive defence mechanisms. Sharks,
meanwhile, hunt with extraordinary precision. They initially lock onto their
prey through a keen sense of smell (two thirds of a shark’s brain is devoted
entirely to its olfactory organs). As the shark reaches proximity to its prey, it
tunes into electric signals that ensure a precise strike on its target; this
sense is so strong that the shark even attacks blind by letting its eyes
recede for protection.
G Normally, when humans are attacked it is purely by accident. Since
sharks cannot detect from electroreception whether or not something will
satisfy their tastes, they tend to “try before they buy”, taking one or two
bites and then assessing the results (our sinewy muscle does not compare
well with plumper, softer prey such as seals). Repeat attacks are highly
likely once a human is bleeding, however; the force of the electric field is
heightened by salt in the blood which creates the perfect setting for a
feeding frenzy. In areas where shark attacks on humans are likely to occur,
scientists are exploring ways to create artificial electroreceptors that would
disorient the sharks and repel them from swimming beaches.
H There is much that we do not yet know concerning how
electroreception functions. Although researchers have documented how
electroreception alters hunting, defence and communication systems
through observation, the exact neurological processes that encode and
decode this information are unclear. Scientists are also exploring the role
electroreception plays in navigation. Some have proposed that salt water
and magnetic fields from the Earth’s core may interact to form electrical
currents that sharks use for migratory purposes.
Questions 1–6
Reading Passage 1 has eight paragraphs, A–H.
Which paragraph contains the following information?
Write the correct letter, A–H, in boxes 1–6 on your answer sheet.
1 How electroreception can be used to help fish reproduce
2 A possible use for electroreception that will benefit humans
3 The term for the capacity which enables an animal to pick up but not
send out electrical signals
4 Why only creatures that live in or near water have electroreceptive
abilities
5 How electroreception might help creatures find their way over long
distances
6 A description of how some fish can avoid disrupting each other’s
electric signals
Questions 7–9
Label the diagram.
Choose NO MORE THAN TWO WORDS from the passage for each
answer.
Write your answers in boxes 7–9 on your answer sheet.
Shark’s 7 ………………… alert the young ray to its presence
Embryo moves its 8 ………………… in order to breathe
Embryo stops sending 9 ………………… when predator close by
Questions 10–13
Complete the summary below.
Choose NO MORE THAN THREE words from the passage for each
answer.
Write your answers in boxes 10–13 on your answer sheet.
Shark Attack
A shark is a very effective hunter. Firstly, it uses its 10 ……………….. to
smell its target. When the shark gets close, it uses 11 ……………….. to
guide it toward an accurate attack. Within the final few feet the shark rolls
its eyes back into its head. Humans are not popular food sources for most
sharks due to their 12 ………………… Nevertheless, once a shark has
bitten a human, a repeat attack is highly possible as salt from the blood
increases the intensity of the 13 …………………
ANSWERS:
1. C
2. G
3. B
4. A
5. H
6. D
7. respiratory movements/signals
8. tail
9. electric currents
10. olfactory organs
11. electric signals
12. sinewy muscle
13. electric field
