Insect-eating bats rely heavily on echolocation

[NMencia09]

Hi, This is from the RC part of a CAT exam:

Insect-eating bats rely heavily on echolocation, a method of sensory perception by which certain animals orient themselves to their surroundings, detect obstacles, communicate with others, and find food. While using echolocation, these bats emit a series of short, high-frequency sounds from their mouths or nostrils that bounce off objects and surfaces and then return to the animals’ ears. Since high-frequency waves do not diffract, or bend, extensively, these ultrasonic vibrations provide bats with accurate maps of their surroundings. The biosonar of some bats is so advanced that it allows them to fly in complete darkness, snatch moving insects out of the air, or hover just above water level to drink.
For years, scientists have been aware that bats emit slightly different frequencies in differing situations. Recent research has provided insight into how certain physical features help bats use this variability to differentiate among objects in their environments. Many species of bats have elaborate, intricately shaped flaps, or noseleaves, around their nostrils that are adorned with grooves and spikes. Three-dimensional computer simulations of these noseleaves revealed that furrows along the top of the noseleaves act as cavities that resonate strongly with certain frequencies of sound. As a result, the grooves cause different frequencies of sound to discharge in different directions. Lower frequency sounds are spread more vertically, while higher frequency sounds emit more horizontally. The complexity the noseleaves add to the bats’ ultrasound perception could help the bats perform difficult tasks, such as locating prey while avoiding obstacles.


Which of the following can properly be inferred from the passage?

The sound waves a bat emits during echolocation only travel parallel or perpendicular to the bat's motion.
The spikes found on bats’ noseleaves are rarely utilized during echolocation.
Many insect-eating bats do not possess a well-developed sense of sight.
Low-frequency sound waves diffract less extensively than high-frequency sound waves.
During echolocation, bats do not rely on low-frequency sound waves.

Im not sure why the answer is (E) vs (C). At the end, it says the bats use the low-frequencies to 'avoid obstacles'... and echolocation is the use of frequencies to locate ones surroundings.

I chose (C) over (E) because I thought that since bats 'rely heavily on echolocation' allowing them to 'orient themselves to their surroundings', this is akin to what sight is used for. So, if you say they rely heavily on that, can't you infer that they dont have a well developed sense of sight?

Hmm..?

[jnelson0612]

I feel your pain here! However, you are going just a bit too far by inferring that they cannot see well because of the information stated in the last lines. What if instead they are doing most of this in the dark? They may possess good vision but lack any light by which to see.

I would justify E by looking at the second line of the passage: "While using echolocation, these bats emit a series of short, high-frequency sounds from their mouths or nostrils that bounce off objects and surfaces and then return to the animals’ ears." Thus, they are using high-frequency rather than low-frequency sounds.

[kristen.li]

question from the question bank on RC, same passage as above, but for a different question

Which of the following, if true, would most weaken the conclusion concerning the purpose of bats’ noseleaves?
A The range of frequencies that bats hear is much smaller than the range of frequencies that bats emit.
B Many bats emit echolocation sounds through their mouths rather than through their noses.
C Dolphins rely on echolocation, and they do not have noseleaves.
D When their food sources are stationary, some bats rely on eyesight and smell rather than echolocation.
E The sound waves emitted during echolocation are limited to a range of fewer than one hundred feet.

The answer is A. But I thought the answer is B and I don't fully understand and agree with A despite reading the explanation. In my opinion, the purpose of echolocation is to help bats "perform difficult tasks" and A would be the right answer if the question was about purpose of echolocation. However, the question is directed at purpose of noseleaves. Noseleaves is a physical feature that allows bats to emit sounds of different frequencies and therefore achieve echolocation. The passage describes in detail how noseleaves is located near the nostrils and the furrow above noseleaves act as cavaties. Doesn't this imply that noseleaves wouldn't work if "bats emit echolocation sounds through their mouths rather than through their noses"?

Thank you!

[tim]

you left out perhaps the most important word in B: "many". this refers to some subset of bats - but not all of them! this is not a sufficiently strong statement to weaken the conclusion. and your disagreement with A based on the distinction between echolocation and noseleaves is irrelevant; the entire discussion of noseleaves describes how they are intricately tied to the process of echolocation..

[CristoforoF605]

I feel your pain here! However, you are going just a bit too far by inferring that they cannot see well because of the information stated in the last lines. What if instead they are doing most of this in the dark? They may possess good vision but lack any light by which to see.

I would justify E by looking at the second line of the passage: "While using echolocation, these bats emit a series of short, high-frequency sounds from their mouths or nostrils that bounce off objects and surfaces and then return to the animals’ ears." Thus, they are using high-frequency rather than low-frequency sounds.

Hi may you please explain why B is wrong? It says the spikes "adorn" the noseleaves. Why doesn't this suggest that they serve no real purpose when using echolocation?

[Sage Pearce-Higgins]

It looks like you're taking 'adorn' to mean 'has an aesthetic rather than a practical function'. This is one meaning of the word, although the word can simply mean 'covered' as well. If you look carefully at the line 'the grooves cause different frequencies of sound to discharge in different directions' you can see that the grooves do have a purpose in echolocation; it seems that here the word 'adorn' means 'covered'.

When you're dealing with nuances of meaning, make sure that you check out other parts of the text that might be relevant.