The energy an animal must expend to move uphill is proportional to its

The answer is C.

1) The argument above says that the energy an animal must expend to move uphill is proportional to its body weight and the animal’s energy output available to perform this task is proportional to its surface area.
2) Small animals can run up fast and the large animals slow down when moving up.

The second statement can only be true if we assume that the energy output of large animals is less than what is required and the energy output of small animals is more than what is required. From 1) it implies that surface area to body weight ratio is smaller in large animals than it is in small animals..

Hence option C.

"C" for sure!!
Explanations are provided next to the answer choices!!

let ratio for large animals = S/E
Ratio for small animals = s/e
option C: S/E < s/e.........when inverted looks like this:
E/S > e/s........ that is:
energy expended per unit space (for large animals) > that for small animals...
tallies with the stimulus

thats the kind of representation i was looking for , Got C in
3:00 min

(A) The amount of energy needed to move uphill is no greater for large animals that it is for small animals.
WRONG. Because the author agrees energies are different for different sizes.
(B) Small animals can move more rapidly than large animals can.
WRONG. This is the Premise so can't be the assumption.
(C) The ratio of surface area to body weight is smaller in large animals than it is in small animals.
CORRECT
(D) There is little variation in the ratio of energy output to body weight among animals.
WRONG. There is a lot of variation for larger animals ratio is higher and smaller animals ratio is smaller.
(E) The amount of energy needed to run at a given speed is proportional to the surface area of the running animal.
WRONG. Speeds are irrelevant to the argument. We are discussing only energies needed.

The energy an animal must expend to move uphill is proportional to its body weight, whereas the animal’s energy output available to perform this task is proportional to its surface area. This is the reason that small animals, like squirrel, can run up a tree trunk almost as fast as they can move on level ground, whereas large animals tend to slow down when they are moving uphill.

Which one of the following is an assumption on which the explanation above depends?

(A) The amount of energy needed to move uphill is no greater for large animals that it is for small animals. - Negating the information already provided in the Premise
(B) Small animals can move more rapidly than large animals can. - Provided in the premise already
(C) The ratio of surface area to body weight is smaller in large animals than it is in small animals. - This provides the most appropriate assumption - Correct
(D) There is little variation in the ratio of energy output to body weight among animals. - If this is assumed, then both large and small animals should be able to move fast. Does not justify to be an assumption.
(E) The amount of energy needed to run at a given speed is proportional to the surface area of the running animal. - Irrelevant information

Though my reply is a bit late, still I shall not suffice just by solving and not by sharing.
ENERGY EXPENDED~ WEIGHT OF THE ANIMAL
ENERGY OUTPUT ~ SURFACE AREA OF THE ANIMAL
CLEARLY SURFACE AREA ~ WEIGHT,
let surface area be denoted by A and weight be W.
The more is A/W, the more is the energy output/energy expended.
If an option states that the ratio of surface area to body weight is smaller in large animals than it is in small animals, then for sure the ratio of energy output/energy expended is much less than that of smaller animals.
Hence c is the clear winner.

I chose C.
It clearly answers the question: bigger body weight means more energy output is needed to move uhill. Lower surface area means lower energy output. So in combination, this means slower uphill movement.

A is wrong. IMO, it weakens the conclusion. Because if energy amount is the same, then larger animals should be faster due to bigger surface area.
B looks irrelevant to me
D looks again irrelevant since the ratio of energy output to BW is not discussed in the question stem
E provides additional information which does not contribute to the logic of the author.
and it also talks about running while we are interested about moving uphill

let us simplify what the question says -

Energy required = constant * body weight
Energy output = constant * surface area.

Now, (energy output) / (energy required) = constant * (surface area) / (body weight)

We are told that smaller mammals can run almost as fast as they can on ground, whereas large mammals tend to slow down.

this means that energy output is more than able to meet the energy required in smaller mammals (that is why they do not slow down).
Whereas it is less in larger mammals (they slow down because they are not able to meet energy requirements)

Hence, ratio > 1 (in larger mammals) and < 1 (in smaller mammals). If we compare the two ratios, we get -

(surface area)/ (body weight) [for small mammals] > (surface area)/ (body weight) [for large mammals]

Which option states this? Option C.

A - Incorrect.
Not true. We know that they require more energy as their body weight is more.

B - Incorrect.
We do not know whether they can actually run at higher speeds than larger mammals. All we know is that they do not slow when moving uphill but larger mammals do.
We do not have any idea about their actual speeds.
Moreover, we have data only when they move uphill. Other scenarios are not known.

D - Incorrect.
We know that (energy output/surface area) is constant. We don't have any idea about (energy output/ body weight).

E - Incorrect.
Energy required is proportional to the body weight. We cannot infer about surface area.

nightblade354 adkikani gmatexam439

Couldn't understand this question. Hence need your help. Below is my understanding

Premise : -
Energy that an animal must expend ~ Body weight of this animal
Energy output available to perform this task ~ To surface area of the animal

Conclusion : -
Small animals such as squirrel can run at the same speed as it can run on level ground. But large animals tend to slow down when they are moving uphill.

I couldn't proceed ahead as i was confused with the options. Can you help to eliminate the options?

Okay. Fist of all you have a look at the question in such a manner that you understand as to how the conclusion was derived. You identified the conclusion correctly, but understand how the author reached at it.

Energy Input to the body ~ Body Weight
Energy Output to the body ~ Surface Area

It's nature's law that the surface area of large animals will be greater than the surface area of small animals. Another law of nature is that while moving uphill a person has to put in more efforts because of the gravitational force. Thus, if the surface area/body weight is smaller in large animals then it means that the Output/Input is less. If the output is less than that would definitely mean that the smaller animals would be faster. Thus, "C" is correct.



Hope this helps!

Regards

Kaplan Official Explanation:

We’re looking for an assumption in an explanation, so your first task is to locate the explanation and the observation it is supposed to explain. The Keyword phrase “This is the reason that . . .” gives the structure away: The first sentence is meant to explain the observation discussed in the second sentence. Squirrels can run up steep inclines very quickly whereas large animals slow down while moving uphill. What is it about squirrels that gives them the edge? The explanation claims that the energy required to run uphill is proportional to body weight, but the energy available to run uphill is proportional to surface area. So the animals that have an easier time running uphill have relatively more surface area as compared to their body weight. How does this apply to the observation about squirrels? We know that squirrels weigh less than larger animals, and so they don’t need as much energy to run up hills, but we can also infer that squirrels have less surface area than larger animals, and so they have less energy available to do the job. So while squirrels have an advantage in one aspect (body weight), they have a disadvantage in another (surface area). So what else has to be true about squirrels?

As (C) puts it, squirrels must have a high surface area to weight ratio, which means that they have more surface area relative to their body weight. (C) fills in the gap by explaining why the squirrels’ disadvantage in surface area is more than compensated by their advantage in body weight. Squirrels may have a little less energy to do the job, but this is more than made up by the fact that larger animals are much, much heavier.

(A) Au-contraire: In the event that large animals weigh more than small animals (which is most likely the case), the first line of the stimulus supports the opposite of (A).

(B) The issue here is moving uphill. The explanation therefore need not rely on any comparison of the general speed of small and large animals. Moreover, (B) ignores the surface area issue and thus fails to tie together the theory and the phenomenon it’s meant to explain.

(D) and (E) both focus on ratios that are never mentioned in the stimulus (energy output is proportional to surface area; energy needed is proportional to weight), so there’s no way that either of these can be the assumption on which the explanation depends. Moreover, (E) has the same problem as (A)— “run” is simply too general because the stimulus focuses on moving uphill.

Given:
1. The energy an animal must expend to move uphill is proportional to its body weight
2. The animal’s energy output available to perform this task is proportional to its surface area.
This is the reason that small animals, like squirrel, can run up a tree trunk almost as fast as they can move on level ground, whereas large animals tend to slow down when they are moving uphill.

Asked: Which one of the following is an assumption on which the explanation above depends?

Energy consumed = K1 * Body Weight
Energy output = K2 * Surface Area

Energy Efficiency = Energy output / Energy consumed = K3 * (Surface area / Body Weight)

Since energy efficiency is less for larger animals as compared to smaller animals, small animals, like squirrel, can run up a tree trunk almost as fast as they can move on level ground, whereas large animals tend to slow down when they are moving uphill.

For the statement to be TRUE ratio of surface area to body weight should be smaller in larger animals than it is in small animals.

IMO C

If you are rookie enough to overlook that option A B E can be eliminated straight, then this may not be helpful to you.
If you have eliminated A B E, good!!
Now D talks about relation between OUTPUT ENERGY and BODY WEIGHT where as passage does not talk about this relation.
passage talks about relation between OUTPUT ENERGY and SURFACE AREA.
so option D eliminated.

Mark option C and move on.
kudos to me!!

Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.