Monarch butterflies

This topic has expert replies
User avatar
Master | Next Rank: 500 Posts
Posts: 176
Joined: Sun Feb 21, 2010 6:00 am
Thanked: 2 times
GMAT Score:710

Monarch butterflies

by Pdgmat2010 » Thu Jun 24, 2010 4:30 am
Which of the following best completes the passage below?
Monarch butterflies, whose average life span is nine months, migrate from the midwestern United States to selected forests outside Mexico City. It takes at least three generations of monarchs to make the journey, so the great-great-grandchildren who finally arrive in the Mexican forests have never been there before. Yet they return to the same trees their forebears left. Scientists theorize that monarchs, like homing pigeons, map their routes according to the earth's electromagnetic fields. As a first step in testing this theory, lepidopterists plan to install a low-voltage transmitter inside one grove of "butterfly trees" in the Mexican forests. If the butterflies are either especially attracted to the grove with the transmitter or especially repelled by it, lepidopterists will have evidence that______
(A) monarch butterflies have brains, however minuscule
(B) monarch butterflies are sensitive to electricity
(C) low-voltage electricity can affect butterflies, whether positively or adversely
(D) monarchs map their routes according to the earth's electromagnetic fields
(E) monarchs communicate in intergenerationally via electromagnetic fields

Pls note: question already discussed and debated before with no convincing explanations one way or the other.
hence a repost.

OA B
Source: — Critical Reasoning |

User avatar
Legendary Member
Posts: 1460
Joined: Tue Dec 29, 2009 1:28 am
Thanked: 135 times
Followed by:7 members

by selango » Thu Jun 24, 2010 4:44 am
the last sentence deals with how butterflies are reacting to electricity.

Option B and C are close.

Option C tell us abt low voltage electricity but we dont know abt reaction with high voltage.

Now option B supports the argument.

User avatar
Master | Next Rank: 500 Posts
Posts: 392
Joined: Sun May 16, 2010 2:42 am
Location: Bangalore, India
Thanked: 116 times
Followed by:10 members
GMAT Score:770

by albatross86 » Thu Jun 24, 2010 4:45 am
Let's breakdown the passage.

The theory is that monarch butterflies are able to map their routes (despite requiring three generations of them to make the journey) using the earth's electromagnetic field. We are trying to test this theory with an experiment.

Method: Low-voltage transmitter in a grove of butterflies in the Mexican forest.
Expected observations: Either attracted to the grove with transmitter, or repelled.

You can therefore rephrase the question stem as, "What would these observations best point to?", or "which conclusion does this evidence best support?"


A. Brains? Out of scope and irrelevant to the motive of proving the relationship between route mapping and EM fields.

B. This works - if it is proved that the grove with the transmitter attracts or repels the butterflies, it can be reasonably inferred that they are able to detect electricity. Also remember it is a low-voltage transmitter, so this means that they are able to detect low voltage too and thus must be sensitive to electricity.

C. Positively or adversely, and whether they affect butterflies, is a bit too extreme and changes the intended motive. For example, when I smell popcorn, I know that someone is making popcorn in the kitchen. Does this mean popcorn affects me positively or adversely? Basically, what I mean is that butterflies could detect these fields without the fields actually affecting them, and thus the conclusion need not be true.

D. This is too big a leap for such a specific experiment. More data would be required to jump from the butterflies' ability to sense the electricity, to whether they use this sense to map their routes with the EM fields. Remember, this is "a first step" and thus cannot lead directly to the intended conclusion written in this choice.

E. Intergenerationally? This cannot be proven by one experiment on a group of butterflies, and is again not the intent of the experiment. Also, just because they can detect the electricity doesn't mean they can "communicate" via EM fields.


Pick B.

User avatar
Legendary Member
Posts: 1460
Joined: Tue Dec 29, 2009 1:28 am
Thanked: 135 times
Followed by:7 members

by selango » Thu Jun 24, 2010 4:48 am
albatross86,

ur explanations are excellent.

Tat too option C very nice.

User avatar
Master | Next Rank: 500 Posts
Posts: 392
Joined: Sun May 16, 2010 2:42 am
Location: Bangalore, India
Thanked: 116 times
Followed by:10 members
GMAT Score:770

by albatross86 » Thu Jun 24, 2010 4:53 am
selango wrote:albatross86,

ur explanations are excellent.

Tat too option C very nice.
Thanks selango, I do my best :)

Your approaches are the perfect way to go on test day, and I also notice you are quick with your answers.

I guess we may not have time for such long-winded explanations, but I also feel it really helps us develop a reasoning process which speeds up with practice!

Legendary Member
Posts: 995
Joined: Tue Apr 13, 2010 11:56 pm
Thanked: 31 times
Followed by:1 members

by paes » Thu Jun 24, 2010 5:59 pm
I selected C over B

B : B says that
'monarch butterflies are sensitive to electricity '

Iy doesn't mention that weak electricity or strong electricity.
It uses a general term 'electricity'

C : low-voltage electricity can affect butterflies, whether positively or adversely

every word is justified here

low voltage -> given in the paragraph
positively or adversely -> repel or attract , given in paragraph

User avatar
Master | Next Rank: 500 Posts
Posts: 214
Joined: Mon Mar 29, 2010 1:46 pm
Location: Houston, TX
Thanked: 37 times
GMAT Score:700

by sk818020 » Thu Jun 24, 2010 6:21 pm
Could you please confirm the source of this question. I'm just curious.

Thanks,

Jared

User avatar
Master | Next Rank: 500 Posts
Posts: 176
Joined: Sun Feb 21, 2010 6:00 am
Thanked: 2 times
GMAT Score:710

by Pdgmat2010 » Fri Jun 25, 2010 2:09 am
source : 1000 CR