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AbdurRakib
Joined: 11 May 2014
Last visit: 08 Nov 2025
Posts: 465
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Status:I don't stop when I'm Tired,I stop when I'm done
Location: Bangladesh
Concentration: Finance, Leadership
Schools: Wharton '20 Yale '20 Tepper '20
GPA: 2.81
WE:Business Development (Real Estate)
Updated on: 03 Jun 2025, 09:43
Originally posted by AbdurRakib on 14 Jun 2017, 03:06.
Last edited by Bunuel on 03 Jun 2025, 09:43, edited 5 times in total.
Last edited by Bunuel on 03 Jun 2025, 09:43, edited 5 times in total.
Updated complete topic (54).
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Question 1
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
73% (03:19) correct
27%
(03:23) wrong
based on 5846
sessions
History
Date
Time
Result
Not Attempted Yet
Question 2
B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
75% (01:35) correct 25%
(01:51) wrong
based on 7140
sessions
History
Date
Time
Result
Not Attempted Yet
Question 3
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
55% (01:16) correct 45%
(01:31) wrong
based on 7073
sessions
History
Date
Time
Result
Not Attempted Yet
Line
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
(5)
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
(10)
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. Why have these cacti expanded their range of pollinators by remaining open and receptive in daylight?
(15)
This development at the northernmost range of columnar cacti may be due to a yearly variation in the abundance—and hence the reliability—of migratory nectar-feeding bats. Pollinators can be unreliable for several reasons. They can be dietary generalists
(20)
whose fidelity to a particular species depends on the availability of alternative food sources. Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species. Finally, they
(25)
may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.
Recent data reveals that during spring in the Sonoran Desert, the nectar-feeding bats are specialists feeding on cardon, saguaro, and
(30)
organpipe flowers. However, 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
(35)
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. While data suggest
(40)
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, cactus-flower density and bat population density appear to be much more evenly
(45)
balanced there: compared with the Sonoran Desert's cardon and saguaro, columnar cacti in southern Mexico produce far fewer flowers per night. Accordingly, despite their low population density, bats are able to pollinate nearly 100 percent of the available flowers.
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. 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. Why have these cacti expanded their range of pollinators by remaining open and receptive in daylight?
(15)
This development at the northernmost range of columnar cacti may be due to a yearly variation in the abundance—and hence the reliability—of migratory nectar-feeding bats. Pollinators can be unreliable for several reasons. They can be dietary generalists
whose fidelity to a particular species depends on the availability of alternative food sources. Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species. Finally, they
may be dietary specialists, but their abundance may be chronically low relative to the availability of flowers.
Recent data reveals that during spring in the Sonoran Desert, the nectar-feeding bats are specialists feeding on cardon, saguaro, and
organpipe flowers. However, 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. 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, cactus-flower density and bat population density appear to be much more evenly
balanced there: compared with the Sonoran Desert's cardon and saguaro, columnar cacti in southern Mexico produce far fewer flowers per night. Accordingly, despite their low population density, bats are able to pollinate nearly 100 percent of the available flowers.
(Book Question: 439)
1. 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
1. 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
(Book Question: 440)
2. 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
2. 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)
3. 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
3. 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
OG 2019 ID's
RC00633-01
RC00633-02
RC00633-06
14 Oct 2017, 08:00
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hoangphuc
A is incorrect because of one word only: sunset. The passage says the flowers remain open after SUNRISE (during the day) not after SUNSET (during the night).
E. The passage clears states that "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."
13 Dec 2018, 14:01
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Question 2
T1101
The passage does mention preference explicitly in lines 22-24:
- Or, they can be dietary specialists, but their abundance may vary widely from year to year, resulting in variable pollination of their preferred food species.
However, the role of preference is implied throughout the passage.
- The distinction between "generalist" and "specialist" begins with the premise that animals pollinate food species (in other words, animals pollinate what they feed on).
- Some pollinators (the generalists) pollinate whatever food species are available, while other pollinators (the specialists) do have a special preference, which can only be satisfied by a narrow range of food species.
So how we do we eliminate choice (C)? Well, here's the author says when describing reasons what could make a pollinator unreliable:
- Pollinators can be unreliable for several reasons. They can be dietary generalists whose fidelity to a particular species depends on the availability of alternative food sources.
According to the passage, a dietary generalist will be faithful to a particular food species if it's available. They don't have special food preferences. If they're feeding on a certain type of nectar, but an alternative food sources become available, then the generalists will begin pollinating that alternative food source instead. Is that what choice (C) says?
Quote:
Nope. (C) tells us that this flower is the most consistently available food for that generalist. If that's true, then we'd expect the generalist to be a reliable pollinator for this flower, because the generalist pollinates whatever is available.
But choice (C), as it's written, states that the generalist is likely to be an unreliable pollinator for this flower.
This contradicts the expected behavior of generalists -- so we must eliminate it.
I hope this helps!
