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

Question

Bigger cities need more infrastructure than smaller ones-but how much more? For instance, among cities in the economically most developed countries, the number of service stations varies, not in direct proportion to the population, but to a far smaller number, obtainable by a precise formula applied to the population. This implies that given a city's population, we can predict how many service stations the city needs. The bigger the city, the fewer gas stations needed per thousand people. The same scaling relationship holds for certain other aspects of infrastructure.

Interestingly, a similar scaling relationship occurs among organisms. Outside their host organisms, almost all mammal cells have similar rates of energy use. 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. Kleiber's law, which describes mammals' at-rest energy needs, indicates that they increase at a significantly slower rate than body weight. The relevant scaling relationship is described by a formula quite like the one applicable to city infrastructure.

Physicist Geoffrey West has argued that a scaling relationship somewhat like Kleiber's is theoretically likely in systems using a network of branching tubes to convey energy and nutrients efficiently throughout a three- dimensional body. Such a transport system could be the circulatory system's architecture, but also a city's systems of roads, cables, and pipes.   1 
﻿ 1. The primary purpose of the passage is to

A. describe a series of stages in the development of knowledge about a certain type of pattern
B. make a general point about the significance of relative size in social organization
C. make a case for the usefulness of mathematics in various scientific endeavors
D. describe and illustrate a pattern found in diverse phenomena
E. suggest through examples that nature exhibits pervasive, mathematically describable regularities

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
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
C. illustrate a general principle regarding the relationship between the functioning of organisms and their relative size
D. clarify a point, made earlier in the passage, about the range of size differences among cities
E. suggest the universal applicability of a method for measuring energy consumption in animals

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.
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.
C. Kleiber's law does not characterize changes in mammals' energy needs as those needs change with increases in level of activity.
D. Small mammals' circulatory systems deliver energy and nutrients more slowly than do larger mammals' circulatory systems.
E. The larger an ecosystem is, the fewer animals per unit of area it can support.

MartyMurray · Accepted Answer

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).

Raman109 · Answer

Passage analysis –  
 P1 -  
 S1 - Bigger cities need more infrastructure than smaller ones-but how much more?  
 
  What is said – Author asks a question, which normally is key for the primary purpose. He says, yes bigger cities need more infra, but how much more?  
  Who says it – Author.   
  Why it is said – It seems author may share additional insights to help answer this question.

S2 - For instance, among cities in the economically most developed countries, the number of service stations varies, not in direct proportion to the population, but to a far smaller number, obtainable by a precise formula applied to the population.  
 
  What is said – The author shares an example of cities in the economically most developed countries. Say a population in a city is 100 and the number of service stations is 10. But when the population increases to 200, the number of service stations just increases to 12, as against 20 that we would expect considering the linear relationship between population and service stations. Basically, the author says that the relationship is more nuanced. If you see the per-capita has decreased from 0.1 to 0.6. And there exists a formula.   
  Who says it – Author.   
  Why it is said – Take an example that may help answer the question.

S3 - This implies that given a city's population, we can predict how many service stations the city needs.  
 
  What is said – Leveraging the formula, we can predict the number or service stations using the city’s population. But of course, it’s not a linear positive correlation.   
  Who says it – Author.   
  Why it is said – Implication of S2   
 S4- The bigger the city, the fewer gas stations needed per thousand people.  
 
 = What is said – explains that there exists a negative correlation.   
 = Who says it – Author.   
 = Why it is said – Concludes the nuanced relationship between the service stations and population.

S5 - The same scaling relationship holds for certain other aspects of infrastructure. 
 
  What is said – Expands the scope of the relationship from service stations to other infra.   
  Who says it – Author.   
  Why it is said – Answer to the question in S1, that not much more or more precisely, the rate of increase per capita decreases, alluding to the fact that may be efficiencies kicks in.

Summary – The author asks the question acknowledging that yes, the bigger cities need more infra but asks a question as to how much more. Then the author drives home a point that not much more.

P2 -   
 S6 - Interestingly, a similar scaling relationship occurs among organisms.  
 
  What is said – Extends the scope of relationship amongst the organisms.   
  Who says it – Author.  
  Why it is said – To extend the scope and may be to substantiate the point that as the size increases the amount of resources required per unit decreases.

S7 - Outside their host organisms, almost all mammal cells have similar rates of energy use.  
 
  What is said – Says that outside the mammals, individual cells has same energy usage. Say each cell requires 1 unit of energy if it were outside the host organism.   
  Who says it – Author.   
  Why it is said – To elaborate on the application of the scaling relationship amongst organisms in S6.    
 S8 - But in the animal's body, the larger the animal, the smaller the cells' average at-rest energy needs.  
 
  What is said – Contrast introduced by “but.” Explains that as the animal size increases the usage of energy per cell decreases. Say from 1 unit per cell in goes to 0.6 unit per cell.   
  Who says it – Author.   
  Why it is said – To explain the application of scaling relationship amongst organisms.    
 S9 - Thus, an elephant's cells individually consume far less energy than a mouse's.  
 
  What is said – Concludes giving an example of elephant’s and mouse’s cells. The same scaling relationship that as the size increase the energy consumption per unit decreases.   
  Who says it – Author.   
  Why it is said – substantiates the application of scaling relationship in organisms.

S10 - Kleiber's law, which describes mammals' at-rest energy needs, indicates that they increase at a significantly slower rate than body weight.  
 
  What is said – Author introduces Keliber’s law that indicates that the energy needs of mammals decrease as the weight increases, alluding to decrease in metabolism.   
  Who says it – Author.   
  Why it is said – To substantiate the conclusion in S9.

S11 - The relevant scaling relationship is described by a formula quite like the one applicable to city infrastructure. 
 
 = What is said – Draws similarities between scaling relationship between organisms and infra. Negative correlation for the rate of increase.   
  Who says it – Author.   
  Why it is said – to draw similarities between the scaling relationship and drive home the point – how much more? Not much more.

Passage 2 summary – extends the scope to organisms and further substitutes the point – not much more.

P3 -
S12 - Physicist Geoffrey West has argued that a scaling relationship somewhat like Kleiber's is theoretically likely in systems using a network of branching tubes to convey energy and nutrients efficiently throughout a three- dimensional body.  
 
  What is said – Author introduces “Physicist Geoffrey West who says that similar relationship is likely applicable for systems using network or branching tubes.   
  Who says it - Physicist Geoffrey West  
  Why it is said – To extend “Kleiber's law” scope from energy needs to the systems using a network of branching tubes.

S 13 - Such a transport system could be the circulatory system's architecture, but also a city's systems of roads, cables, and pipes. 
 
  What is said – author extrapolates the scope of efficient systems and scaling relationship to organisms and city infra.   
  Who says it – Author.   
  Why it is said – To extend the scope and substantiate the reason for scaling relationship mentioned in P1 and P2.    
  P3 summary - The author introduced physicist Geoffrey West's argument and suggested that this architecture (network of branching) extends to organisms and infrastructure.

Raman109 · Answer

Q3. 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. - No other determinants other than weight were mentioned. Distortion. 
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. - opposite. 
C. Kleiber's law does not characterize changes in mammals' energy needs as those needs change with increases in level of activity. - Yes, energy needs with "increases in level of activity" are not mentioned. Ok. 
D. Small mammals' circulatory systems deliver energy and nutrients more slowly than do larger mammals' circulatory systems. - this comparison is out of scope. 
E. The larger an ecosystem is, the fewer animals per unit of area it can support. - Out of scope.

Raman109 · Answer

Q2. 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 - No. Kleiber's law is shared to substantiate the conclusion mentioned in the earlier sentence. 
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 - out of scope. 
C. illustrate a general principle regarding the relationship between the functioning of organisms and their relative size - ok
D. clarify a point, made earlier in the passage, about the range of size differences among cities - "range of size differences among cities" is out of scope. 
E. suggest the universal applicability of a method for measuring energy consumption in animals - Distortion.

Anshika.g · Answer

MartyMurray   KarishmaB 
Q2, option A -
As per the paragraph 2, elephant cells use lesser energy than rats' cells (implies energy and weight are inversly proportional.)
But K is saying that the relationship is: energy increases at a significat lower rate than weight (this would meen that it is directly proportionate, even though with a much smaller factor)
So ideally both of them are contradicting to each other. and hence, this should be correct.
Please share your thoughts.

glagad · Answer

MartyMurray   KarishmaB 
Q2, option A -
As per the paragraph 2, elephant cells use lesser energy than rats' cells (implies energy and weight are inversly proportional.)
But K is saying that the relationship is: energy increases at a significat lower rate than weight (this would meen that it is directly proportionate, even though with a much smaller factor)
So ideally both of them are contradicting to each other. and hence, this should be correct.
Please share your thoughts.

K = energy increases at a significant lower rate than weight => Energy increase is  lower than that of weight increase  => This means that there is energy increase but not as much as weight increase.

Thus K supports the ongoing theory that the energy required/cell at a higher weight is comparatively less (than what could have been had the increase been proportional to weight)

The example of Mice and elephant is given to prove the same point.

Side note: If you observe the paragraph, there are no words like - "But, however, despite" which shows contrast thus making you think that Kleiber is actually proposing something different from what the original author states. In fact, I dont see any contradiction in the overall tone pursued by the author.

And hence A is not correct.

Hope that helps.

EloiseDU19 · Answer

Q3 - Another way to eliminate choice  A.     Body size is not the main determinant of a mammal's daily calorie needs.

It seems that body size and body weight are  not necessarily the same thing scientifically . So, the relationship between body size and a mammal's daily calorie needs is not discussed in the passage.

Stanindaw · Answer

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

What i can infer from the above statement is that Kleiber's law describes mammals' at-rest energy needs. How can i infer that Kleiber's law does not describe mammals' energy needs when they are active.
Does "which describes mammals' energy needs" encompasses all about the Kleiber's law?

GMATNinja · Answer

Question 3 
 
The passage specifically states that those laws describe mammals'  at-rest  energy needs. The law explains how those at-rest energy needs relate to body weight, and that relationship is described by some scaling formula.

It's a stretch to assume that this same law, relationship, and formula all apply to an entirely different phenomenon: mammals' ACTIVE energy needs. If that were the case, the author would have said so -- something like "Kleiber's law, which describes mammals' at-rest energy needs...".

That's a bit like taking some formula for calculating the maximum load of a steel bridge and assuming that it works on wooden bridges too. If the formula is specifically for steel bridges, there's no reason to assume it works on ALL bridges. Maybe it does, but in that case, why specify steel in the first place?

More importantly, remember that the question asks: Which of the following is   most  strongly supported  by the information in the passage? We don't need to PROVE that (C) is true. Maybe those laws do apply to all types of energy needs and the author was just using intentionally confusing language to trick the readers. But based on the wording and context of the passage, it's a safe bet that those laws only apply to  at-rest  energy needs.

Besides, none of the other answer choices work, so (C) must be it.

himanshi1172 · Answer

Hey Marty! for question 3 option D - how can infer the likelihood of the larger animals' systems delivering energy and nutrients slowly as the animal requires less energy? - the passage talks about  each  cells' average energy being less than that of a smaller animal. The larger animal may have a larger number of cells and higher overall energy requirement.

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

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

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