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by [email protected] » Fri Jun 07, 2013 3:05 am
In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing
discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand
tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in
areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have signifi cant barnacle
populations, even though they seldom burrow.
Which of the following, if true, most helps to explain the surprising fi nding?
(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
(C) The strength of the tidal currents in a given location varies widely over the course of a day.
(D) A very large barnacle population can signifi cantly decrease the ability of a horseshoe crab to fi nd food.
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.

I could not understand the question. Can anybody explain? along with answer?
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by krishnapavan » Fri Jun 07, 2013 8:52 am
IMO B
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by vivekchandrams » Tue Jun 11, 2013 5:41 am
IMO E.

The question says - young crabs cannot hold on to barnacles when the tidal strength is high. This is because they can't withstand the tides and save themselves form getting flown away by burrowing in the sands. But, when they grow up they are not affected by the tides. Hence they can cling onto the barnacles and hence it is expected that barnacle populations will be high.
Then comes the paradox. It says - even in areas where tidal strength is less, the juvenile crabs don't have significant barnacle populations.

Now the options -

A - All it does it it rules out the possibility of tidal waves' influence the dislodging of barnacles. But, it does not explain the paradox given. Hence eliminate

B - It strengthens the 1st statement made in the question but does not get anywhere near solving the paradox

C - Tidal strengths might vary across the day, but in the question the 2nd statement it is mentioned that tidal strengths are low. So it weakens this statement but doesn't answer the paradox

D - Very large population might decrease the ability of crabs to get food. This might, at the most, result in lower crab populations (because of lack of food), but doesn't explain why the population of the barnacles is less.

E - This is the best of the lot. It says that juvenile crabs shed their shells while they grow. Hence whatever be the tidal strength, the barnacle population is not affected. The population will definitely be less because the young crabs continue to shed the barnacles. Hence the paradox is resolved.


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by apoorva86 » Tue Jun 11, 2013 9:51 am
IMO B should be the ans.
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by tarunjohri » Tue Jun 11, 2013 10:06 am
In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.

The question is about barnacles lodging onto the crab shells. Tidal currents do not dislodge only shows that there is some other mechanism but this point does not explain the paradox.

(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.

If barnacles do then we should see them on the shells but we do not see this effect. Hence this point again does not explain the paradox.

(C) The strength of the tidal currents in a given location varies widely over the course of a day.

Out of scope. Does not matter


(D) A very large barnacle population can signifi cantly decrease the ability of a horseshoe crab to
find food.

The paradox does not involve the ability of the crab to find food.

(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.

Hence left only with E. In this question rather than finding the correct one try eliminating the wrong ones. The one that is left makes sense. The barnacles do attach themselves but since the crabs keep shedding the shells off the barnacle population is bot seen in significant amount at any time.
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