Bigger cities need more infrastructure than smaller ones-but how much

Explanation for Question 1

1. The primary purpose of the passage is to

We can bring the primary purpose of the passage into focus by considering the important points and structure of the passage.

The first paragraph presents a "scaling relationship" that holds for infrastructure in big cities.

Then, the second paragraph starts of with the important point "Interestingly, a similar scaling relationship occurs among organisms." Then, it outlines that similar scaling relationship, presents an example how that relationship appears in elephants and mice, and discusses Kleiber's law about that relationship.

Finally, the third paragraph discusses Geoffrey West's argument that a scaling relationship similar to those discussed in the first two paragraphs would likely exist in systems in a variety of three-dimensional bodies.

A. describe a series of stages in the development of knowledge about a certain type of pattern

The passage does discuss "a certain type of pattern," the "scaling relationship" that is involved in a variety of situations.

However, this choice is incorrect because the passage does not discuss "stages in the development of knowledge" about that relationship. Rather, it discusses different situations in which that relationship exists.

Eliminate.

B. make a general point about the significance of relative size in social organization

While the passage does discuss a relationship between size of cities and infrastructure needs, it does not make a point about the significance (importance) of relative size.

Also, it doesn't discuss only "social organization." Rather, it discusses how a type of scaling relationship can exist in a variety of types of situations, including not only cities but also animal bodies.

Eliminate.

C. make a case for the usefulness of mathematics in various scientific endeavors

While the passage does discuss a mathematical relationship, it does not "make a case for the usefulness of mathematics."

Eliminate.

D. describe and illustrate a pattern found in diverse phenomena

In our analysis of the main points of the passage we saw that it discusses a type of "scaling relationship" that exists in a variety of situations and presents examples of situations in which that relationship exists.

We can see that discussing and providing examples of a type of scaling relationship that exists in a variety of situations is basically the same as describing and illustrating a pattern found in diverse phenomena.

Keep.

E. suggest through examples that nature exhibits pervasive, mathematically describable regularities

The passage discusses one type of scaling relationship that exists in certain types of situations. It doesn't suggest that mathematical regularities are pervasive (found everywhere) in nature.

Eliminate.

The correct answer is (D).

Explanation for Question 2

2. The primary purpose of the passage's discussion of elephant cells and mouse cells is to

A. provide an example to indicate that there are exceptions to Kleiber's law

This choice is partly correct because the purpose of the passage's discussion of elephant and mouse cells is to provide an example related to Kleiber's law.

However, this choice goes wrong in that the discussion of elephant and mouse cells is an example in which Kleiber's law holds, not an exception.

Eliminate.

B. extend the application of an idea about the food-energy needs of human populations to the collective food-energy needs of groups of animals

The passage says nothing about "needs of human populations" or "needs of groups of animals."

Eliminate.

C. illustrate a general principle regarding the relationship between the functioning of organisms and their relative size

Rereading the part of the passage in which the discussion of elephant and mouse cells appears, we see the following:

But in the animal's body, the larger the animal, the smaller the cells' average at-rest energy needs. Thus an elephant's cells individually consume far less energy than a mouse's.

We see that the purpose of the discussion of elephant cells and mouse cells is to illustrate the "general principle" that "the larger the animal, the smaller the cells' average at-rest energy needs."

Keep.

D. clarify a point, made earlier in the passage, about the range of size differences among cities

The passage does not make any point about "the range" of size differences among cities.

Also, the passage does not use the discussion of elephant and mouse cells to make any point about cities.

Eliminate.

E. suggest the universal applicability of a method for measuring energy consumption in animals

This choice goes wrong in two ways.

One is that the discussion of elephant and mouse cells does not show that something is universally applicable. Rather, presents a pattern that exists in one comparison of two animals.

The second is that the passage does not discuss any "method for measuring" energy consumption. Rather, it discusses a pattern that is found when energy consumption is measured.

Eliminate.

The correct answer is (C).

Explanation for Question 3

3. Which of the following is most strongly supported by the information in the passage?

A. Body size is not the main determinant of a mammal's daily calorie needs.

This choice is a little tricky to eliminate, since passage says the following:

Kleiber's law, which describes mammals' at-rest energy needs, indicates that they increase at a significantly slower rate than body weight.

Notice, however, that the fact that mammals energy needs increase at a slower rate than body weight does not mean that they don't increase with body weight or that there is some "main determinant" of calorie needs other than body weight.

Eliminate.

B. The total daily calorie needs of a population of small mammals that together weigh as much as one large mammal are generally less than the larger mammal's total daily calorie needs.

This choice states the exact opposite of what the passage supports.

After all, the passage says the following:

the larger the animal, the smaller the cells' average at-rest energy needs

That means that all the cells of a larger animal together would have a smaller daily calorie need than all the cells of a population of smaller animals that together weigh as much as the larger animal.

Eliminate.

C. Kleiber's law does not characterize changes in mammals' energy needs as those needs change with increases in level of activity.

The passage says that Kleiber's law "describes mammals' at-rest energy needs."

At rest is just one level of activity. So, Kleiber's law does not indicate anything about how mammals' energy needs change when the are not at rest and increase their levels of activity.

Thus, we can see that what the passage says indicates that "Kleiber's law does not characterize changes in mammals' energy needs as those needs change with increases in level of activity."

Keep.

D. Small mammals' circulatory systems deliver energy and nutrients more slowly than do larger mammals' circulatory systems.

The passage says nothing about the rate at which small or large mammals' circulatory systems deliver energy and nutrients.

That said, if anything, the fact stated by the passage, that "in the animal's body, the larger the animal, the smaller the cells' average at-rest energy needs," indicates that, if anything, the circulatory system of a larger mammal, rather than a smaller mammal, would deliver energy more slowly since the larger mammals' cells have smaller energy needs.

Eliminate.

E. The larger an ecosystem is, the fewer animals per unit of area it can support.

The pattern, or "scaling relationship," discussed in the passage is such that the larger a system is, the less infrastructure it needs per unit of size.

That pattern does not mean that the larger a system is, the fewer animals per unit of area it can support. After all, what a system needs and what it can support are two different things.

Eliminate.

The correct answer is (C).