In the Sonoran Desert of northwestern Mexico and southern Arizona, t

Passage breakdown

In the first paragraph (P1), the author asks a question:

• Why have cacti in the Sonoran desert evolved to open their flowers during the day?

In the second paragraph (P2), the author provides one potential explanation for the question raised in P1:

• The cacti may have evolved because of annual variations in the reliability of pollinators.
• The author then lists three reasons why a pollinator may be unreliable.

In the third paragraph, the author provides data that supports the explanation given in P2

• Bats are unreliable, so the cacti have evolved to allow birds to pollinate them during the day

For more on this process, check out this article and our live RC videos.

Explanations for individual questions

• Question 2
  
  • Part 1
  • Part 2
• Question 3
  
  • Part 1
  • Part 2

Very good passage. All correct but took 8 minutes to solve

The primary purpose of the passage is to
A. compare the adaptive responses of several species of columnar cacti in the Sonoran Desert with those in the arid tropical regions of southern Mexico
B. discuss some of the possible causes of the relatively low abundance of migratory nectar-feeding bats in the Sonoran Desert
C. provide a possible explanation for a particular evolutionary change in certain species of columnar cacti in the Sonoran Desert
D. present recent findings that challenge a particular theory as to why several species of columnar cacti in the Sonoran Desert have expanded their range of pollinators
E. compare the effectiveness of nocturnal and diurnal pollination for several different species of columnar cacti in the Sonoran Desert

Straight forward C. End of first paragraph pitches it clearly and rest of the passage tries to answer the question.


(Book Question: 440)
According to the passage, which of the following types of nectar-feeding pollinators is likely to be an unreliable pollinator of a particular cactus flower?
A. A dietary specialist whose abundance is typically high in relation to that of the flower
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
C. A dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food
D. A dietary generalist for whom that flower’s nectar is slightly preferred to other available foods
E. A dietary generalist that evolved from a species of dietary specialists



(Book Question: 441)
According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti
A. have flowers that remain open after sunset
B. are pollinated primarily by dietary specialists
C. can be pollinated by nectar-feeding bats
D. have stigmas that are unreceptive to pollination at night
E. are sometimes pollinated by diurnal pollinators

P1 - some cacti evolved from night time to day time pollination.
P2 - reasons given for situation defined in p1.

The primary purpose of the passage is to
A. compare the adaptive responses of several species of columnar cacti in the Sonoran Desert with those in the arid tropical regions of southern Mexico - p2
B. discuss some of the possible causes of the relatively low abundance of migratory nectar-feeding bats in the Sonoran Desert - P2/2
C. provide a possible explanation for a particular evolutionary change in certain species of columnar cacti in the Sonoran Desert - Most accurate among all.
D. present recent findings that challenge a particular theory as to why several species of columnar cacti in the Sonoran Desert have expanded their range of pollinators - challenge a theory is not there, its a simple explanation.
E. compare the effectiveness of nocturnal and diurnal pollination for several different species of columnar cacti in the Sonoran Desert -- Passage is certainly not about this.
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(Book Question: 440)
According to the passage, which of the following types of nectar-feeding pollinators is likely to be an unreliable pollinator of a particular cactus flower?
Lines to read - cactus-flower abundance tends to be high during spring, bat population densities tend to be low except near maternity roosts.
B. A dietary specialist whose abundance is at times significantly lower than that of the flower - correct.

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(Book Question: 441)
According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti

E. are sometimes pollinated by diurnal pollinators - the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, allowing pollination by such diurnal visitors as bees and birds.

The passage tells us that a generalist can be an unreliable pollinator because its "fidelity to a particular species depends on the availability of alternative food sources."

This tells us that a generalist doesn't really have a preference for which plant it eats -- it just eats whatever is most readily available. Let's say that out of plants X, Y, and Z, only plant X is available. Generalists will just eat plant X and be happy to do so! Now say that plants Y and Z move into the area -- the generalist doesn't remain faithful to plant X, but eats whatever is most convenient. Plant X will not get as much attention from the generalist -- so from plant X's perspective, the generalist is an unreliable pollinator when other plants are available for it to feed on.

The main point is that the generalist doesn't choose what it eats based on preference -- it chooses based on availability.

Take another look at (C):

Based on the discussion above, we know that generalists decide what to eat based on availability. So, it will reliably eat (and therefore pollinate) "the most consistently available food." This is essentially the opposite of answer choice (C), so (C) is incorrect.

To understand why (B) is correct, take a look at the two reasons identified in the passage to explain why a specialist may be an unreliable pollinator:

• "their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species." OR
• " their abundance may be chronically low relative to the availability of flowers."

Now take a look at answer choice (B):

You are correct to point out that (B) doesn't align well with a case in which the specialist population is "chronically low." However, this answer choice does fit nicely with the other case, in which the specialists' "abundance may vary widely." Because (B) specifically tells us that the specialist's abundance is "at times significantly lower than that of the flower," we can say that it is not consistently available to pollinate all of the flowers. Therefore, this particular specialist is an unreliable pollinator, and (B) is correct.

I hope that helps!

Sorry for the delay!

Yes, the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, and that capability doesn't come and go. But just because the cacti can remain open after sunrise does not necessarily mean that those cacti are ALWAYS pollinated by diurnal pollinators. What if the diurnal pollinators are only around certain times of the year?

The passage only really tells us about the spring:

"... whereas cactus-flower abundance tends to be high during spring, bat population densities tend to be low except near maternity roosts. Moreover, in spring, diurnal cactus-pollinating birds are significantly more abundant in this region than are the nocturnal bats. Thus, with bats being unreliable cactus-flower pollinators, and daytime pollinators more abundant and therefore more reliable, selection favors the cactus flowers with traits that increase their range of pollinators."

We can certainly infer that the Sonoran Desert cacti are pollinated by diurnal pollinators in the spring, but we don't know what happens the rest of the year. That's why "sometimes" is appropriate in choice (E).

I hope that helps!

Look at a simpler example first:

Following are the reasons you shouldn't trust him to help you:
1. He may be a bad person.
2. He may be a good person but he may be busy with helping others.
3. He may be a good person but he may not know what to do.


On the same lines, the passage is listing the various reasons why pollinators can be unreliable.

1. They can be dietary generalists (they eat anything) whose fidelity to a particular species depends on the availability of alternative food sources. (so if they get some other food sources, they may not pollinate and hence that makes them unreliable)

2. They can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species.

This is in contrast to point 1 above. They could be dietary specialists (not generalists) such that they would eat the nectar of this cacti only so they would be reliable, but their numbers may vary from year to year so that would make them unreliable.

3. They may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.

Another reason could be that their number could be lower than what is required to pollinate all flowers. So this would make them unreliable.

According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti
A. have flowers that remain open after sunset
B. are pollinated primarily by dietary specialists
C. can be pollinated by nectar-feeding bats
D. have stigmas that are unreceptive to pollination at night
E. are sometimes pollinated by diurnal pollinators
[/quote]

i think that the reson for choice E is not from : Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, allowing pollination by such diurnal visitors as bees and birds.
but from: While data suggest that population densities of nectar-feeding bats are also low in tropical areas of southern Mexico, where bats are the exclusive pollinators of many species of columnar cacti
it means that in sounthern bats are exclusively pollinator and diurnal can not be pollinator. So Sonoran cacti can be pollinated by diurnal but their close relative in sounthern mexico cannot be.

jabhatta@umail.iu.edu - I have summarize few things here, See if its helpful ? Main point is read for change in information and not for information. I say you
1. Go through link, make your own notes, choose what ever source you want.
2. Practice 2-4 RC daily. when I say practice, you need to apply your notes on the passage. once done try to read some OE if you can arrange or good replies on forum.
3. try to time yourself while doing it. Dont worry this will improve with time. time urself for max 4 question passage. Beyond that no point to time yourself.
4. if you make a mistake, find why you made that mistake. Lets categories problems
a. reading problem ?
b. question understanding problem,
C. once done with question, finding right text problem. - if not able to do this, problem with mapping the text. map what is in which paragraph.
D. POE problem - eliminate extreme choices straight. then POE. start looking back to passage when you left with 2-3 choices. rem you need to find 4 wrong one.

https://gmatclub.com/forum/my-notes-rea ... 75525.html

Question: 440
According to the passage, which of the following types of nectar-feeding pollinators is likely to be an unreliable pollinator of a particular cactus flower?
A. A dietary specialist whose abundance is typically high in relation to that of the flower
Choice A- Says opposite to what is mentioned in second para of the passage.-", they can be dietary specialists, but their abundance may vary widely from year to year" So it does not say high abundance but says abundance vary.
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
Correct Choice B-Refer para II Line 25[/b][color=#00a651]
C.A dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food[color=#111111]
Choice C - Mix up word trap- uses words from passage but conveys different meaning than what is said in passage. ( Ref line 24) Here if we go by meaning it should be reliable pollinator since flower nectar is most consistently available food .Eliminate C
D. A dietary generalist for whom that flower’s nectar is slightly preferred to other available foods
Answer Choice D-If Flower nectar is preferred - it will be reliable pollinator. Question talks about unreliable pollinator.- Eliminate D
E. A dietary generalist that evolved from a species of dietary specialists
Choice E -Passage does not discuss about this, so Eliminate.

For detail question we need to find match from the passage.


Question: 441
According to the passage, present-day columnar cacti in the Sonoran Desert differ from their close relatives in southern Mexico in that the Sonoran cacti
A. have flowers that remain open after sunset
Choice A- Uses one word off trap- where just one word is incorrect and changes the meaning from what is given in the passage. Passage says that Line 11"Sonoran Desert cacti have evolved to remain open after sunrise" Here it says Sunset. Hence Eliminate
B. are pollinated primarily by dietary specialists
Ans Choice B-Both are pollinated by dietary specialist- nectar feeding bats. So that is not the difference but common factor. So Eliminate. Dont forget we are looking for difference.
C. can be pollinated by nectar-feeding bats
Again same as ans Choice B- So Eliminate as it is common factor between both Sonaran Dessert Cacti and their close relatives in southern Mexico.
D. have stigmas that are unreceptive to pollination at night
Both are pollinated at night time though Sonaran Dessert cacti have evolved to getting pollinated day time also, but basically both get pollinated at night so there stigmas are receptive. This answer choice Note convery reverse of what is given in the passage. Hence Eliminate
E. are sometimes pollinated by diurnal pollinators
Correct- Passage talks about how Sonaran Dessert cacti have evolve to get pollinated by diurnal pollinators. unlike its close relative in southern mexico.

Dream it! Achieve it

According to the passage, which of the following types of nectar-feeding pollinators is likely to be an unreliable pollinator of a particular cactus flower?
A. A dietary specialist whose abundance is typically high in relation to that of the flower
B. A dietary specialist whose abundance is at times significantly lower than that of the flower
C. A dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food
D. A dietary generalist for whom that flower’s nectar is slightly preferred to other available foods
E. A dietary generalist that evolved from a species of dietary specialists

Is the OA really B
in B: A dietary specialist whose abundance is at times significantly lower than that of the flower
Evidence: Finally, they may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.
At times and chronically are clearly different.

In my opinion, the answer is C for the following evidence
in C: dietary generalist for whom that flower’s nectar is not a preferred food but is the most consistently available food
evidence: they can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources

Please explain why main theme is C.
Because the last paragraph talks about comparing adaptations of Sonoran desert cacti species and southern Mexico cacti species
I think answer to theme question is A.

Sent from my MI MAX using GMAT Club Forum mobile app

The essence of the passage can be derived from this line:
"Why have these cacti expanded their range of pollinators by remaining open and receptive in daylight?"

Beyond this line, the passage is trying to answer this query. Read again and it will become clear.

And then read again option C : C. provide a possible explanation for a particular evolutionary change in certain species of columnar cacti in the Sonoran Desert

It is like matching 1:1. Does that help?

Thanks for sharing this. A few things. Wouldn't the term "generalist", which suggests that they can pollinate more than one flower, indicate that a generalist would pollinate according to preference, and not abundance? It would make more sense for a specialist to prioritize abundance, since they can only feed on a select few flowers, whereas a generalist has more choices and can therefore be more picky. This would make Answer C more correct.

In addition, Answer A specifically mentions "at times significantly lower", whereas the excerpt in the passage quotes "their abundance may be CHRONICALLY low relative to the availability of flowers". It seems to be the passage is suggesting the only chronically low abundance would be a reliability issue, but if it happens once in a while ("at times"), the effects are not significant enough to warrant the "unreliable" label.

Let me know if the above makes sense. Based on the logic above, I am still struggling to understand why B is correct and not C. Thank you!

Question 3

The first sentence of the passage should make this more clear:

"In the Sonoran Desert of northwestern Mexico and southern Arizona, the flowers of several species of columnar cacti—cardon, saguaro, and organ pipe—were once exclusively pollinated at night by nectar-feeding bats, as their close relatives in arid tropical regions of southern Mexico still are."

From this, we know that the columnar cacti in Southern Mexico are ONLY pollinated at night by nectar-feeding bats, and NEVER pollinated by any daytime creatures. Cacti in the Sonoran Desert, by contrast, have adapted to allow for diurnal pollinators.

So, we can compare the frequency of diurnal pollination -- the cacti in Southern Mexico are never pollinated in the day, while the cacti in the Sonoran Desert are sometimes pollinated in the day.

(E) is the correct answer to question 3.

I hope that helps!

Q1)
Passage: Sonoran Desert

Question: Primary Purpose

The Simple Story

In the Sonoran Desert, the flowers of several species of cacti have evolved to stay open during the day as well as at night, allowing daytime animals to pollinate the flowers. One potential explanation for this change is that the nighttime pollinators (bats) were unreliable. Pollinators may be unreliable for a particular plant for several different reasons (listed in the passage). In the Sonoran Desert, there are many cacti and relatively few bats in the spring, so this is likely why the plants evolved to attract other, daytime pollinators.

Sample Passage Map

Here is one way to map this passage. (Note: abbreviate as desired!)

P1: SD flowers open during day -> why?

P2: Maybe unreliable poll by bats?

– 3 poss reasons

P3: SD Probably b/c low pop of bats

Note: the passage lists several possible reasons why the bats might be unreliable pollinators. You can jot down each one or you can just note that three reasons exist—and now you know where to look in the passage if you are asked about one or more of those reasons.

Step 1: Identify the Question

The words primary purpose in the question stem indicate that this a Main Idea question.

Step 2: Find the Support

For main idea questions, review your overall understanding of the passage story.

Step 3: Predict an Answer

The passage poses a question (Why did the cacti evolve in a certain way?) and provides a potential explanation.

Step 4: Eliminate and Find a Match

(A) In the final paragraph, the passage discusses some detail about the cacti in southern Mexico but the purpose of this example is to forestall a possible objection to the proposed theory earlier in the passage; the passage asserts that the non-adaptation of southern Mexican cacti still fits with the theory because, in that region, there are enough bats to pollinate the cactus flowers. The main purpose of the passage is to put forth that overall theory.

(B) The low populations of bats is provided as a possible reason for the adaption of the cacti, but the passage does not provide any possible reasons why the bat population is low.

(C) CORRECT. The main purpose of the passage is to hypothesize about the reason behind the changes in the cacti in a particular region of the Sonoran Desert.

(D) The findings provided in the passage support the theory about the reason for the adaption of the cacti. A competing theory that the findings challenge is not provided in the passage.

(E) The passage suggests that, in certain circumstances, daytime pollination may be more effective. But the purpose of the passage is to explain the reason for the changes in the cacti; the discussion of daytime vs. nighttime pollination serves to support this point.

Q3
Passage: Sonoran Desert

Question: Sonoran Cacti

The Simple Story

In the Sonoran Desert, the flowers of several species of cacti have evolved to stay open during the day as well as at night, allowing daytime animals to pollinate the flowers. One potential explanation for this change is that the nighttime pollinators (bats) were unreliable. Pollinators may be unreliable for a particular plant for several different reasons (listed in the passage). In the Sonoran Desert, there are many cacti and relatively few bats in the spring, so this is likely why the plants evolved to attract other, daytime pollinators.

Sample Passage Map

Here is one way to map this passage. (Note: abbreviate as desired!)

P1: SD flowers open during day -> why?

P2: Maybe unreliable poll by bats?

– 3 poss reasons

P3: SD Probably b/c low pop of bats

Note: the passage lists several possible reasons why the bats might be unreliable pollinators. You can jot down each one or you can just note that three reasons exist—and now you know where to look in the passage if you are asked about one or more of those reasons.

Step 1: Identify the Question

The words According to the passage in the question stem indicate that this a Specific Detail question.

Step 2: Find the Support

The Sonoran cacti and cacti from southern Mexico are compared in the first paragraph.

“In the Sonoran Desert of northwestern Mexico and southern Arizona, the flowers of several species of columnar cacti … were once exclusively pollinated at night by nectar-feeding bats, as their close relatives in arid tropical regions of southern Mexico still are. In these tropical regions, diurnal (daytime) visitors to columnar cactus flowers are ineffective pollinators because, by sunrise, the flowers’ stigmas become unreceptive or the flowers close. Yet the flowers of the Sonoran Desert cacti have evolved to remain open after sunrise, allowing pollination by such diurnal visitors as bees and birds."

Step 3: Predict an Answer

Note the key difference: Sonoran cacti have flowers that stay open during the day and thus can get pollinated by daytime pollinators. In contrast, the cacti of southern Mexico are still exclusively pollinated at night.

Step 4: Eliminate and Find a Match

(A) Cacti in both regions have flowers that remain open at night (i.e., after sunset). The difference is whether the flowers are open during the day.

(B) This description applies to cacti in both regions. The nectar-feeding bats, which are dietary specialists, pollinate at least some of the Sonoran cacti and the cacti in southern Mexico.

(C) The nectar-feeding bats pollinate cacti in both regions.

(D) It is true that the Sonoran cacti were having difficulty getting pollinated at night, but the passage proposes that this was due to the unreliability of the nighttime pollinators (the bats), not a problem with the stigmas.

(E) CORRECT. The Sonoran cacti have flowers that stay open during the day and thus can be pollinated by daytime (diurnal) pollinators. The southern Mexican cacti are still exclusively pollinated at night.

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