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In order to withstand tidal currents, juvenile horseshoe [#permalink]
29 Jul 2010, 12:47
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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. (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 significantly decrease the ability of a horseshoe crab to find food. (E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.
This is an OG Question Q No: 59, OG12. We are apparently asked to resolve the paradox that although the tidal currents are weak and crabs don't burrow, the barnacle population is weak. A. this gives a reason y there is significant barnacles in crabs that do not burrow. We are not looking out for this answer. Rather we want an answer that explains why there is less barnacle population. B. This gives an additional premise for the argument and triggers more intrigues as to y there is less population of barnacles even though there are weak tidal currents. C. Out of scope. D. Out of scope. Nowhere in the argument, Food comes into picture. E. Correct answer. This explains why Juvenile crabs have less barnacle population. When they shed their shells regularly, they also shed the barnacles that cling to them regularly. Thus, this explains the surprising finding.
I picked E too because it explains why in areas of weak tidal currents there is lesser barnacle population. Because crabs shed their shells the barnacles are clinged on to the shedded shells and hence are not seen much clinged on to the carbs. (thus less population).
E The question statement first establishes a cause and effect relationship: burrowing causes lack of barnacles. The question then states an observation that non-burrowing crabs do not have barnacles. The observation is inconsistent with the cause and effect relationship that was previously stated. Thus, we must find a new cause for a crab's lack of barnacles in order to explain the surprising finding. Answer "E" establishes a new cause: frequent shell shedding.
i am still not able to stand why E is correct answer.the statement E have same effect whether horseshoe crabs stay in strong tide current region or weak tide current region.how it explain the low population of barnacle in weak tidal current area.
This is a Resolve the paradox Question.The Paradox is when the tides hit the Adult Crabs there will be barnacles attched to them But in weak tide (this is a decoy)areas even though the tides hit Juvenile crabs there are not more barnacles.The correct ans choice must allow both the facts to be true and explain the paradox.Only Option E tells how the Juveniles shed the shell and hence have no barnacles if Adults they wud have had clusters of Barnacles too