## LR question help please PT 1, s3, q21

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flash21

Posts: 1536
Joined: Fri Apr 19, 2013 8:56 pm

### LR question help please PT 1, s3, q21

Surface area..

Looked this question up. explanations didn't help, I literally cannot comprehend this for some reason.. i think its because it resembles math and I've got a deep hate for math. Thanks in advance.

CardozoLaw09

Posts: 2183
Joined: Sat Aug 28, 2010 1:58 pm

### Re: LR question help please PT 1, s3, q21

This is a tough argument to digest without simplifying it, especially under a time crunch. Basically, in the first part of the stimulus we're told that the amount of energy needed to move uphill is proportional to an animal's body weight + the total energy an animal has (energy output available) is proportional to its surface area. In more simpler terms, the greater the body weight, the more energy you need to move uphill; and, the amount of energy available to the animal is proportional to the animal's surface area ie) the smaller the animal's surface area, the less energy available for this animal to move uphill. Then we're told squirrels can move as fast on ground as they can up a tree; whereas large animals move progressively slower uphill, and the reason for this is because of the relationships given to us in the first part of the stimulus.

For this argument to hold, we need to assume something about the body weight and surface area and how that plays a role in small/large animals moving uphill. Why? Because if a squirrel can move just as fast on ground as it can climbing a tree, then it must require less energy to do so (or have more energy than they need), which would mean either that smaller animals have greater surface area than they do body weight OR less body weight than they do surface area; ie) either they have a lot of energy to move uphill OR because of their body weight, they don't need to expend too much energy to move uphill.

Consequently, the ratio between surface area and body weight must be larger than that of large animals, otherwise a squirrel would not be able to move just as fast climbing a tree as it can moving the ground, while a large animal is slower moving up a tree. A large animal might have a 1:1 ratio between surface area and body weight - which would mean they need as much energy as they have available to perform their task of moving uphill hence why they tend to slow down as they move up -- as they climb further and further up, they lose more energy. Squirrel's don't have this problem, because they have more energy available to them (surface area) than is required to move uphill (body weight). If you have more energy to do something than you need, then you wouldn't slow down.

TL;DR; the more body weight you have the more energy you need to move uphill BUT that can be compensated for by the animal's surface area ie) if it has a lot of surface area then it has a lot of energy; maybe more so than is required.

flash21

Posts: 1536
Joined: Fri Apr 19, 2013 8:56 pm

### Re: LR question help please PT 1, s3, q21

thanks, this is actually the best exploitation I have heard yet. this was really a tough one - I think cambridge made it as a level 3?